Berthing Structures

Berthing Structures

Chapter 6

BERTHING STRUCTURES R. SUNDARAVADIVELU Professor Dept. of Ocean Engineering Indian Institute of Technology Chennai India

6.1

INTRODUCTION

The berthing structures are constructed for berthing and mooring of vessels to enable loading and unloading of cargo and for embarking and disembarking of passengers, vehicles. The design of berthing structures depends on various factors. However, the vessel characteristics govern the design of berthing structures. The various structures constructed along the coast can be classified as Port and Harbour Structures, Coastal Protection Structures, Sea water Intake Structures and Effluent discharge structures. Port and harbor structures are constructed along the coast to provide berthing facilities to ships for loading and unloading of cargo or for embarking and disembarking passengers. The different types of berthing structures are given in this section. 6.2

TYPES OF BERTHING STRUCTURES

Berthing structure is a facility where the vessel may be safely moored. The berthing arrangements can be classified as along side type, open dolphin type or ferry type as shown in Figure 6.1 (Gaythwaite (1990)). The berthing structure can also be classified as vertical face type or open type structure. Typical examples are shown in Figure 6.2 (Agerschou et al (1985). In vertical face R. Sundaravadivelu

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structures, sheet pile wall, block wall, caissons are used, while open type structures are represented by open piled construction.

ALONGSIDE TYPE

BREASTING DOLPHIN

TRESTLE TO SHORE

MOORING DOLPHIN LOADING PLATFORM

OPEN DOLPHIN TYPE

FINGER PIER OR DOLPHINS

TRANSFER BRIDGE

GUIDE DOLPHINS

FERRY (SLIP) TYPE

Fig 6.1 Types of Berthing Structures

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Berthing Structures

(a) CAISSON

(b) SHEET PILE WALL

(c) OPEN PILED STRUCTURES

Fig 6.2 Types of Vertical Face Berthing Structures R. Sundaravadivelu

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The berthing structures can also be classified depending on the type of cargo handled. The Madras Port outer harbour basin has oil berth, ore berth and container berth where oil, ore and containers are handled respectively. The berthing structures can also be classified as follows: (A) GRAVITY STRUCTURES (i)

Masonry wall

(ii)

Concrete block walls

(iii)

Concrete caissons

(B) FLEXIBLE STRUCTURES (i)

Steel sheet piles

- Tie back - Cantilever

(ii)

Diaphragm walls

- Cantilever - Tieback - Relieving platform

(iii)

Jetties

- consist Berthing & Mooring Dolphin, Jetty Head & Approach Jetty.

The minimum length of a berthing structure should be sufficient for mooring the longest ship expected to arrive. The minimum depth includes a bottom clearance equivalent to 10 % of the draught of the largest vessel using the terminal. The top surface of the berthing structure should be built above the highest high water level. The dimension of the berth as recommended by IS 4651 (Part V) - 1980 is given in Appendix 6.1 for various size of Passenger ships, Freighter, Tankers, Ore Carriers and Large Fishing Vessels. 6.2.1

Quay or Wharf

Quays are defined as one or more berths, continuously bordering on and it contact with a land or dock area. The inner harbour basin of Madras Port has North, South, East and West Quays where berthing facilities are provided for number of ships.

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Berthing Structures

The quays are constructed as sheet pile wall, diaphragm wall, open piled structure or gravity structure [Quinn (1972) and Bruun (1981)]. Quay is a continuous berth where fenders and bollards are provided at different points along the berth to facilitate berthing of ships. Wharf is the same as Quay, constructed as an open structure supported on piles. 6.2.2

Pier or Jetty

A pier or jetty is a structure projecting into water, in a harbour basin. They are also located in open water outside actual harbours. A finger jetty will have berths on two sides and abut land over their full width. A jetty consists of a number of structures such as berthing dolphin, mooring dolphin, loading platform, trestle to shore each of which has special type of functions. The mooring dolphins pick up the pull from the hawsers. Mooring dolphins for breast lines shall be located at bow and stern at a distance (about the beam of the ship) from the berth line, which will not make the moorings too steep. The berthing dolphins support fenders which absorb berthing impacts. The berthing dolphins should be placed as wide apart as possible. The distance should neither exceed the length of the straight side of the smallest vessel nor be less than approximately onethird of the maximum length of the largest vessel. The loading platforms support special loading or unloading equipment but normally no horizontal forces apart from wind loads will act on the loading Platforms. 6.2.3

Offshore Berthing Structures

Offshore berthing structures are used for liquid cargo (oil or gas) or for dry cargo, for iron ore, coal, sugar, phosphates or grains. The design for offshore berthing structures should consider the following : a) Single type of cargo b) Rapid loading and unloading (10,000 T of Iron ore per hour or 60,000 bbl (barrel) of oil per hour) c) Sufficient storage on shore d) Open sea and exposed to winds, waves and currents R. Sundaravadivelu

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e) Construction practicability f) DWT of the vessel in the range of 0.1 million T to 0.3 million T The type of ship loader generally governs the design of offshore berth. The three main types of ship loader are (1) Fixed type (2) travelling Gantry type and (3) Slewing telescopic boom loaders. The fixed loader is used in small ships. The travelling gantry loader is expensive, since the loader is to be supported by a berth which is continuous. The above three types of loaders are to be critically evaluated for dry bulk cargo terminals, whereas for liquid cargo, the loading system does not influence the offshore berthing structure. The approach jetty to the offshore berthing structure is the critical component and governs the total cost of the facility. The offshore terminal at CAPE Santa Clara in the Atlantic ocean consists of a principal berth to load 2,80,000 DWT ship, moored 7400 m from shore. The mooring and berthing force in the offshore berth is to be critically evaluated for the safe design of the offshore berthing structure. 6.3

LOADS ON BERTHING STRUCTURES

The berthing structures are designed for the following forces :

434

(i)

Berthing force

(ii)

Mooring force

(iii)

Dead load

(iv)

Live load

(v)

Active earth pressure if the berth retains the earth

(vii)

Environmental forces

(viii)

Seismic force

(ix)

Secondary stresses due to shrinkage, creep, temperature etc.

-

-

Rail Road Bulk unloaders Cranes etc. UDL due to cargo

Wind Wave Current Differential water pressure

Berthing Structures

6.3.1

Classification of Loads

The various loads acting on the berthing structures are classified as : i)

Loads from the sea side

ii)

Loads from the deck and

iii)

Loads from the land side

6.3.1.1 Loads from Seaside The loads from the sea side include the horizontal forces caused by waves, the forces caused by berthing and vessel’s pull from bollard. The forces caused by berthing of vessels are determined from the velocity and angle of approach of the vessels. For the vessels lying at the berth, the forces are determined due to wind, waves and currents on the vessel. The vertical forces from sea side are due to vessels hanging upon the fendering system, vertical component of the forces from bollards etc. 6.3.1.2 Loads from Deck The important loads from the deck are the vertical loads caused by self weight of the deck, superimposed loads from buildings and handling equipments. Horizontal loads are mostly due to wind forces on buildings and structures and also due to the breaking force of cranes. 6.3.1.3 Loads from Landside Horizontal loads are caused from landside due to the earth pressures and differential water pressure. Vertical loads are caused by the weight of filling and superimposed load on filling. 6.3.2

Live Loads

6.3.2.1 Vertical Live Loads Surcharges due to stored and stacked material such as general cargo, bulk cargo, containers and loads from vehicular traffic of all kinds including trucks, trailers, railway cranes, containers handling equipment and construction plant, constitute vertical live loads.

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6.3.2.2. Truck loading and Uniform loading The berths shall be generally designed for the truck loading and uniform loading as given in Table 6.1 (IS 4651 (Part III) - 1974). Table 6.1 Truck Loading and Uniform Loading Function of Berth Passenger berth Bulk unloading and loading berth Container berth Cargo berth Heavy cargo berth Small boat berth Fishing berth

Truck Loading (IRC class) B A

Uniform Vertical Live Loading (T/m2) 1.0 1 to 1.5

A or AA or 70 R A or AA or 70 R A or AA or 70 R B B

3 to 5 2.5 to 3.5 5 or more 0.5 1.0

6.3.2.3 Crane Loads Concentrated loads from crane wheels and other specialised mechanical handling equipment should be considered. An impact of 25 percent shall be added to wheel loads in the normal design of deck and stringers, 15 percent where two or more cranes act together and 15 percent in the design of pile caps and secondary framing members. 6.3.2.4 Railway Loads Concentrated wheel loads due to locomotive wheels and wagon wheels in accordance with the specification of the Indian Railways for the type of gauge and service at the locality in question. For impact due to trucks and railways one third of the impact factors specified in the relevant codes may be adopted. 6.3.2.5 Special Loads Special loads like pipeline loads or conveyor loads or exceptional loads such as surcharges due to ore stacks, transfer towers, heavy machinery or any other type of heavy lifts should be individually considered.

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Berthing Structures

6.3.3

Berthing Load

Berthing Energy : When an approaching vessel strikes a berth, horizontal force acts on the berth. The magnitude of this force depends on the kinetic energy that can be absorbed by the fendering system. The reaction force for which the berth is to be designed can be obtained and deflection-reaction diagrams of the fendering system chosen. These diagrams are obtainable from fender manufacturers. The kinetic energy, E, imparted to a fendering system, by a vessel moving with velocity V is given by 2

W xV C m x Ce x Cs E= D 2g

(6.1)

where E

=

Berthing energy in T- m

WD

=

Displacement tonnage in T

V

=

Berthing velocity in m/sec

Cm

=

Mass coefficient

Ce

=

Eccentricity coefficient

CS

=

Softness coefficient

g

=

Acceleration due to gravity in m/sec2

6.3.3.1 Mass Coefficient When a vessel approaches a berth and as its motion is suddenly checked, the force of impact which the vessel imparts comprises of the weight of the vessel and the effect of water moving along with the moving vessel. Such an effect, expressed in terms of weight of water moving with the vessel, is called the additional weight (W A) of the vessel or the hydrodynamic weight of the vessel. Thus the effective weight in berthing is the sum of displacement tonnage of a vessel and its additional weight, which is known as virtual weight (WV) of a vessel. a.

The mass coefficient (Cm) is calculated using the following equation

Cm = 1+

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2D B

(6.2)

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where D

=

Draught of the vessel in m,

B

=

Beam of the vessel in m.

b. Alternative to (a) in case of a vessel which has a length much greater than its beam or draught or generally for vessels with displacement tonnage greater than 20,000 the additional weight may be approximated to the weight of a cylindrical column of water of height equal to the length of vessel and diameter equal to the draught of vessel, then π D 2 Lw

C m =1 + 4

WD

(6.3)

where D

=

Draught of the vessel in m,

L

=

Length of the vessel in m

w

=

Unit weight of water (1.03 T/m2 for sea water)

WD

=

Displacement tonnage of the vessel in tonnes.

Wv = WD x C m 6.3.3.2 Eccentricity Coefficient A vessel generally approaches a berth at an angle, denoted by θ and touches it at a point either near the bow or stern of the vessel. In such eccentric cases the vessel imparts a rotational force at the moment of contact, and the kinetic energy of the vessel is partially expended in its rotational motion. a)

The eccentricity coefficient (Ce) may then be derived as follows: Ce =

1 +(l / r ) 2 Sin 2 θ 1 +(l / r ) 2

(6.4)

where l =

Distance from the centre of gravity of the vessel to the point of contact projected along the water line of the berth in m, and

r =

Radius of gyration of rotational radius on the plane of the vessel from its

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Berthing Structures

Center of gravity in m (Figure 6.3) b) The approach angle (θ) unless otherwise known with accuracy should be taken as 10°. For smaller vessels approaching wharf structures, the approach angle should be taken as 20° (Refer Figure 6.3).

θ= 10° UNLESS KNOWN ACCURATELY 20° FOR SMALLER VESSEL

G

θ

ECCENTRICITY COEFFICIENT (Ce)

1.0

0.8

0.6

0.4

0.2

0.0 0.1L

0.2L

1/4L

0.3L

0.4L

0.5L

BERTHING POINT OF THE VESSEL (l) For θ = 0

Fig 6.3 Approaching Angle of Vessel with a Berth R. Sundaravadivelu

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c)

The rotational radius of a vessel may be approximated to L/4 and in normal case the point of contact of the berthing vessel with the structure is at a point about L/4 from the bow or stern of the vessel which is known as a quarter point contact. If the approach angle θ is nearly 0° and r = 0.25 L, then Ce = 0.5.

6.3.3.3 Softness Coefficient This coefficient (Cs) indicates the relation between the rigidity of the vessel and that of the fender, and also the relation between the energy absorbed by the vessel and the fender. Since the ship is relatively rigid compared with the usually yielding fendering systems, a value of 0.9 is generally applied for this factor, or 0.95 if higher safety margin is thought desirable. Quinn (1961) has suggested a suitable formula for calculating the berthing energy assuming 50% of the total energy of the berthing vessel to be absorbed by fenders. E =

11   mv 2  22 

(6.5)

where m is the (mass + added mass) of the vessel and v is the berthing velocity. 6.3.4

Mooring Loads

The mooring loads are the lateral loads caused by the mooring lines when they pull the ship into or along the dock or hold it against the forces of winds or current. 6.3.4.1. Forces due to Wind The maximum mooring loads are due to the wind forces on exposed area on the broad side of the ship in light condition F = Cw Aw P

(6.6)

Where

440

F

= Force due to wind in kg

Cw

= Safe factor = 1.3 to 1.6

Aw

= Windage area in m2 and

P

= Wind pressure in kg/m2 to be taken in accordance with IS : 875-1964

Berthing Structures

The windage area (Aw) can be estimated as follows Aw = 1.175 Lν (DM - DL)

(6.7)

where Lν = Length between perpendicular in m DM = Moulded depth in m DL = Average light draft in m. When the ships are berthed on both sides of a pier, the total wind force acting on the pier, should be increased by 50 percent to allow for wind against the second ship. Gaythwaite (1990) has suggested the following formulas to calculate windforce in the longitudinal (Fwx) and lateral (Fwy) force components and a yawing moment (Myw). Fwx

=

0.0034 CDx V2w Ax

(6.8)

Fwy

=

0.0034 CDy V2w Ay

(6.9)

Myw

=

Fwy LOA Cym

(6.10)

Where Fwx and Fwy Myw CDxand CDy Vw Ax and Ay LOA

= Wind Force along x and y directions in pounds = Yawing Moment in pounds-ft = Drag Coefficients along x and y directions = Wind speed in Knots = End-on and Side projected areas of vessel (including the areas of masts, stacks, rigging, deck cargoes, etc.) = Overall Length of Ship in ft

The hydrodunamic coefficients are the functions of angle of wind approach(θ). The yaw moment is given in terms of the lateral force times the vessel’s length overall (LOA) and Cym. The total resultant force for wind from any direction (Fw(θ)) is found from this equation: Fw (θ)

=

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0.0034CD(θ) V2w (Ax cos2 θ + Ay sin2 θ)

(6.11)

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6.3.4.2 Forces due to Current Pressure due to current will be applied to the area of the vessel below the water line when fully loaded. It is approximately equal to w v2/2g per square metre of area, where v is the velocity in m/s and w is the unit weight of water in T/m3. The ship is generally berthed parallel to the current. With strong currents and where berth alignment materially deviates from the direction of the current, the likely force should be calculated by any recognised method and taken into account. Ship is aligned predominantly in head sea condition with current direction. Example problem 1: Calculate the berthing force, and Mooring force due to 30,000 DWT bulk carrier approaching the berth at Kandla Port with a berthing angle of 10°. The site condition is moderate wind and swells and the berthing condition is moderate. Use the following informations. (Design data) Length of the berth

=

240 m

Width of the berth

=

55 m

Top level

=

+ 9.74 m

Dredge level

=

- 11.10 m

Length of the vessel

=

205 m

Width of the vessel

=

26.5 m

Draught

=

10.70 m

Berthing force Site conditions

:

Moderate wind and swells

Berthing condition

:

Moderate

As per IS 4651 (Part III)-1974 for the above site condition and berthing condition Berthing velocity (v) E=

442

WD V 2 C m C e CS 2g

=

0.2 m/s

Berthing Structures DT = 1.32 as per Section 3.1.2 of IS 4651 (Part II)-1974 DWT

WD = 1.32 x 30,000 = 39,600 T Cm = 1 +

π 2 D LW 4

WD

where w

= Unit weight of sea water 1.025 t/m3

Cm

= 1+

Cm

= 1.48

Ce

=

π *10.7 2 *205*1.025 4

39,600

()

l 2 r

1+

1+

sin 2 θ

(1r )2

l = L/4 = 205/4 = 51.25 m r = 0.2 L = 0.2 x 205 = 41 m θ = 10° 1+

(5141.25 )2 sin 2 10 2 1 +(514.25 )

Ce

=

Ce

= 0.41

CS

= 0.95 (As per code)

E

E

=

39,600*(0.2) 2 *1.48*0.41*0.95 2*9.81

= 46.54 T – m

Ultimate energy = 1.4 x 46.54 = 65.2 T-m

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Fender details : fender type - cell (from fender manufacture catalogue)

Size of fender – 1600H x 2005D x 1800 P Berthing force = 100 T Mooring force Length between perpendicular (Lp )

= 0.9 L = 0.9 x 205 = 184.5 m

Moulded depth of the ship

(Dm )

= 14.3 m

Average light weight draft

(DL )

= 10.3 m

Due to Wind Aw

= 1.175 x 184.5 (14.3 - 10.3)

Aw

= 867.15 m2

P

= 0.06 Vz2 (As per IS 875-1987)

Vz

= Vb k1 k2 k3

Vz

= Design wind speed at any height

k1

= Probability factor (risk coefficient)

k2

= Terrain, height and structure size factor

k3

= Topography factor

Basic wind speed - 39 m/sec (at Kandla) Vb

= 1.15 x 39 (for offshore area) = 44.85 m/sec

K1

= 1.08, K2 = 1.05, K3 = 1

Vz

= 44.85 x 1.08 x 1.05 x 1 = 50.86 m/s

P

= 0.06 x (50.86)2 = 155 Kg/m2

Fw

= 1.4 x 867.15 x 155 (as per Equation (6.6)) = 188 T

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Berthing Structures

Due to Current where Fc =

wv 2 x projected area of ship 2g

w

= Unit weight of water in t/m3

v

= Current velocity 5 knots

g

= Acceleration due to gravity in m/s2

w

= 1.025 t/m3

g

= 9.81 m/s2

Fc

=

v = 0.5 x 0.505 = 2.525 m/s

1.025* 2.525 2 * 26.5*10.7 = 94.91 T 2 *9.81

Total force = sqrt(1882 + 952) = 210 T The total force can be assumed to be equally distributed to four bollards, if the ship is mored to eight bollards. Force on each bollard = 210/4 = 52.5 T The line pull as per Table 6.2 is 60 T for the 20000 DWT vessels and T for the 50000 DWT vessels. Table 6.2 : Bollard Pulls Displacement (Tonnes) 2,000 10,000 20,000 50,000 100,000 200,000 >200,000

Line Pull (Tonnes) 10 30 60 80 100 150 200

Hence the mooring pull for 30,000 DWT vessel is 67. However the mooring pull is assumed as 75 T.

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6.3.5

Differential Water Pressure

In the case of waterfront structures with backfill, the pressure caused by difference in water levels at the fillside and the waterside has to be taken into account in design. The magnitude of this hydrostatic pressure is influenced by the tidal range, free water fluctuations, the ground water influx, the permeability of the foundation soil and the structure as well as the efficiency of available backfill drainage. In the case of good and poor drainage conditions of the backfill the differential water pressure may be calculated on the guidelines given in Figure 6.4. The average of MLWS and LLW is assumed water level on the sea side for both poor and good drainage conditions. The average of MHW and MLW is assumed as ground water (GW) on the land side for poor drainage condition, while 0.3 m above MLW is assumed a ground water (GW) on the land side for good drainage condition

MHW a

ASSUMED GW

0.3m

MLWS b

MLWS LLW

b LLW

ELEVATION OF FLAP VALVE BOTTOM

ASSUMED GW

MLW

a

MLW

MHW FLAP VALVE

b

b

(a) POOR DRAINAGE CONDITION

(b) GOOD DRAINAGE CONDITION

MHW - MEAN HIGH WATER MLW - MEAN LOW WATER MLWS - MEAN LOW WATER SPRINGS LLW - LOWEST LOW WATER GW - GROUND WATER

Fig. 6.4 Differential Water Pressure

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Berthing Structures

6.3.6

Seismic Force

The horizontal force caused by earthquakes called seismic force can be calculated using the seismic coefficient method given in IS 1893-1984 (10). The horizontal seismic force(Fh) is given by the following equation Fh = αh Wm

(6.12)

where αh

= Design horizontal seismic coefficient

Wm

= Weight of mass under consideration ignoring reduction due to buoyancy of uplift and is equal to the total dead load plus one-half of the live load as per IS 1893 (Part III)-1984.

The design values of horizontal seismic coefficient, in the Seismic Coefficient method shall be computed as given by the following expression: αh = βIαo

(6.13)

where

β

=

A coefficient depending upon the soil-foundation system

I

=

A factor depending upon the importance of the structure

αo

=

Basic horizontal seismic coefficient based on the zone

β, I and αo can be obtained from IS 1893-1984, depending on type of soil foundation, importance of the structure and the zone in which the structure is located. 6.3.7

Wave Forces

As far as analysis and computation of forces exerted by waves on structures are concerned, there are three distinct types of waves, namely, 1.

Non-breaking waves

2.

Breaking waves and

3.

Broken waves

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6.3.7.1 Non-breaking Waves Generally, when the depth of water against the structure is greater than about 11 /2 times the maximum expected wave height, non-breaking wave conditions occur. Forces due to non-breaking waves are essentially hydrostatic. ‘Sainflou Method’ may be used for the determination of pressure due to non-breaking waves. 6.3.7.2 Breaking Waves Breaking waves cause both static and dynamic pressures. Determination of the design wave for breaking wave conditions may be based on depth of water about seven breaker heights (Hb) seaward of the structure, instead of the water depth at which the structure is located. The actual pressures caused by a breaking wave is obtained by following the method suggested by Minikin. 6.3.7.3 Broken Waves Locations of certain structures like protective structure will be such that waves will break before striking them. In such cases, no exact formulae have been developed so far to evaluate the forces due to broken waves, but only approximate methods based on certain simplifying assumptions are available. 6.3.7.4 Wave Force on Piles Wave forces on vertical cylindrical structures, such as piles exerted by non-breaking waves can be divided into two components; a. Force due to drag b. Force due to inertia A set of generalised graphs which are available in shore protection manual together with the following formulae may be used to compute these; FDM

= 1/2 CD ρg D H2 KDM

FIM

= CM ρg

FM

= φm ρg H2D

448

πD 2 H KIM 4

(6.14) (6.15) (6.16)

Berthing Structures

MDM

= SD FDM d

(6.17)

MIM

= SI FIM d

Mm

= αm ρg CD H D d

(6.19)

CM D C DH

(6.20)

(6.18) 2

W =

where FDM

= Total drag force on a vertical pile from the sea bottom to the surface crest elevation and this occurs at the crest positions in N

d

= Water depth in m

g

= Acceleration due to gravity

ρ

= Mass density of sea water = (w/g) = 1025.2 kg/m3

D

= Diameter of pile in m

H

= Wave height in m

KDM

= Drag force factor (Figure 6.5)

FIM

= Total inertial force on a vertical pile from the seabed to the free surface elevation in N

KIM

= Inertial force factor (Figure 6.6)

SDM

= Drag force moment arm (Figure 6.7)

SIM

= Inertia force moment arm (Figure 6.8)

αm,φm = Coefficients read from the Figures 6.9 to 6.16 CD,CM = Drag, Intertia coefficient (Figures 6.17 to 6.18) FM

= Maximum value of the combined drag and inertial force in N

MDM

= Moment on pile about bottom associated with maximum drag force in N-m

SD

= Effective lever arm for FDM from the bottom of pile in m

MIM

= Moment on pile about bottom associated with maximum inertial force in N-m

SD

= Effective lever arm for FIM from the bottom of pile in m

MM

= Maximum total moment in N-m

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Fig. 6.5 KDm versus Relative Depth (d / gT2)

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Fig. 6.6 KIM versus Relative Depth (d / gT2)

Berthing Structures

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Fig 6.7 SDM versus Relative Depth (d/gT2)

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Fig 6.8 SDM versus Relative Depth (d/gT2)

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Fig 6.9 Isolines of φ m versus H/gT2 and d/gT2 (w = 0.05)

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Fig 6.10 Isolines of φ m versus H/gT2 and d/gT2 (W= 0.1)

Berthing Structures

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Fig. 6.11 Isolines of φ m vs H/gT2 and d/gT2 (W = 0.5)

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Fig 6.12 Isolines ofφ m versus H/gT2 and d/gT2 (W = 1.0)

Berthing Structures

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Fig 6.13 Isolines of αm versus H/gT2 and d/gT2 (W = 0.05)

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Fig 6.14 Isolines of αm versus H/gT2 and d/gT2 (W = 0.1)

Berthing Structures

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Fig 6.15 Isolines of αm versus H/gT2 and d/gT2 (W = 0.5)

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Fig. 6.16 Isolines of αm versus H/gT2 and d/gT2 (W = 1.0)

Berthing Structures

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Fig 6.17 Interia and Drag Coefficient for a Fixed Vertical Cylinder

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Berthing Structures

Fig 6.18 Drag Coefficient for a Smooth Oscillating Cylinder R. Sundaravadivelu

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Harbour & Coastal Engineering (Indian Scenario) : Vol. I

Example Problem 2 : A design wave height of (H) 5.0 m and period (T) 10 secs acts on a vertical circular pile with a diameter (D) of 1 m and depth (d) 8 m. Assume Cm = 2.0 and P = 1025.2 kg/m3. Find the maximum total horizontal force and the maximum total moment on the pile. Solution Calculate d gT 2

=

8

=

(9.8)(10)2

8.16 x 10-3

From Figure 3.26 the breaking limit curve Hb gT 2

Hb

=

=

0.006

0.006 x 9.8 x 102 = 5.88 m

and H Hb

=

From Figures 6.5 and 6.6 using

5 5.88 d gT 2

=

0.85

= 8.16 x 10-3 and

H = 0.85 Hb, Interpolating between curves H = Hb and H = 3/4 Hb; find KDm = 0.620 Kim = 0.39 π 2 D HKim 4

Fim

=

Cmρ

Fim

=

(2)(1025.2)(9.8) π (1)2 x 5.0 x 0.39 = 30.77 kN 4 103

FDm

=

CD

464

1 ρg DH2 x KDm 2

Berthing Structures

= 0.7 x 1/2 x (1025.2) (9.8) (1) (5)2 x 0.62 = 54504.76 N, = 54.5 kN W

H gT 2 d gT 2

=

CM D CD H

=

(2.0) (1) (0.7 ) (5)

=

0.57

=

5 (9.8) (10)2

=

0.005

= 0.0082

using the Figures 6.11 and 6.12 find φm W

= 0.5

φm

= 0.34 (from Figure 6.11)

W

= 1.0

φm

= 0.44 (from Figure 6.12)

W

= 0.57

Interpolating the values of 0.5 and 1.0 we can get the values for W = 0.57. W

= 0.57

Fm

= φm ρg CDH2D

φm

= 0.354

= 0.3554 (10,047) (0.7) (5)2 (1) = 62241.2 N Fm

= 62.24 kN

From the Figure 6.8

Sim

= 0.8

From the Figure 6.7

SDM

= 0.996

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Harbour & Coastal Engineering (Indian Scenario) : Vol. I

Mim

= Fim d Sim = (30774) x 8 x 0.8 = 196953.6 N m = 196.9 kN m

MDM

= FDM d SDM = (545040.76) x (8) x (0.996) = 434287.8 N m 4343 kN m

To find αm, using the Figure 6.15 and 6.16 are used. W

= 0.5

αm

= 0.34 (from Figure 6.15)

W

= 1.0

αm

= 0.40 (from Figure 6.16)

Interpolating the values of 0.5 and 0.1, We can get the values of 0.57 W

= 0.57 Mm

αm

= 0.3484

= αm ρg CDH2 Dd = 0.3484 (10,047) (0.7) (5)2 (1) (8) = 490052.47 N m

Mm 6.3.8

= 490 kN m.

Combination of Loads

The combination of loadings for design is dead load, vertical live loads, plus either berthing load, or line pull or earthquake or wave pressure, for open type berthing structure. The worst combination should be taken for design. In addition to the above load earth pressure & differential water pressure shall be consider for vertical force typing structures.

466

Berthing Structures

The partial safety factors for different types of loads in limit state design is given in Table 6.3 and increase in permissible stress for different combination of loads are given in Table 6.4. 6.3.9

Expert System

The Knowledge Based Expert System for estimation of forces in berthing structures KNOWBEST have been developed at IIT Madras. (Sundaravadivelu & Ranga Rao (1996)). The user friendly menu driven expert system KNOWBEST not only helps the user to estimate various forces depending on the type of berthing structure (open type or closed type) but also recommends the appropriate values of coefficients to be used for estimating various forces. Table 6.3 Partial Safety Factors for Loads in Limit State Design Partial Safety Factor Loading Dead load Vertical Live Load Earth Pressure Hydrostatic and Hydrodynamic Forces Berthing and Mooring Forces Secondary Stresses Wind Forces Seismic Forces

R. Sundaravadivelu

Limit State Serviceability 1.0 1.0 1.0 1.0

1.5 1.5

1.2 (or 0.9) 1.2 (or 0.9)

1.2 (or 0.9) 1.2 (or 0.9)

1.2 (or 0.9) 1.2 (or 0.9)

1.0

1.0

1.0

1.0

1.0

1.0

1.0

1.0

1.0

1.2

1.0

1.0

-

1.0

1.5

-

-

-

1.0

-

-

-

-

-

-

-

-

-

1.5 -

1.5

Limit State of Collapse

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Harbour & Coastal Engineering (Indian Scenario) : Vol. I

Table 6.4 Increase in Permissible Stresses

Sl. No.

1

2

3

4 5 6 7

Increase in Permissible Stress

Combination of Loads

DL + LL + impact of breaking or traction or vehicles + centrifugal forces of vehicles DL + LL with impact, breaking or tractive and centrifugal forces + earth pressure, percent DL with/without LL including impact, breaking or tractive and centrifugal forces + earth pressure + hydrodynamic and hydrostatic forces + berthing and mooring forces, percent Wind forces on structures + load combination of (1) + (2) or (3) Seismic forces + load combination of (1), (2) or (3)percent Secondary stress + load combination of (1), percent Erection stage stresses with DL and appropriate LL + earth pressure + hydrodynamic forces + wind forces, percent

Increase in Allowable Bearing Pressure

Reinforced Concrete

Other Materials such as steel and Timber

Nil

Nil

Nil

15

15

15

25

33 1/3

25

15

15

15

15

33 1/3

25

6.4

ANALYSIS OF BERTHING STRUCTURES

6.4.1

Analysis of a Bulk Berth

The layout of a berth to receive 30,000 DWT bulk carrier is given in Figure 6.19. The dimension of 30,000 DWT bulk carrier as per IS 4651 (Part III)-1974 are as follows:

468

Overall length

=

205 m

Width

=

26.5 m

Height

=

14.3 m

Berthing Structures

Fully loaded draft

=

10.7 m

The total length of the berth should be 10% more than the length of the ship. Hence a length of 250 m is adopted. The total length of the berth of 250 m is divided into five blocks each of 50 m length with expansion joints in between them. IS 4651 (Part IV) section 10 recommends a length of 39 m between the expansion joints. A spacing of 60 m is recommended for better stiffness. However 250m long berth without any

20500

30000 DWT M1

M4

M2 B2

B1

M5

M3 F2

F1

B4

B3

B5

B6

3

16 50000

50000

50000

50000

50000

25000 M1 = STERN LINE M2 = AFT BREAST LINE M3 = AFT SPRING LINE M4 = FORD SPRING LINE M5 = FORD BREAST LINE M6 = BOW LINE F1 & F2 = FENDERS B1 & B2 = BOLLARDS

Fig. 6.19 Layout of Berth With 30000 Dwt Tanker expansion joints are also constructed. However for these structures the loads due to variation of temperature shall be considered in addition to other loads. The typical cross section of a berth is shown in Figure 6.20. It consists of a diaphragm wall tied back by a cross beam to four rows of vertical pile. The fully loaded draft is 10.7 m. Hence the dredge level is assumed as 10.7 + 10% of draft + 0.5 m for over dredge allowance. Hence dredge level should be greater than 12.27 m. The dredge level is assumed as 12.5 m. The tidal levels are HHWL

=

+ 3.25 m

LLWL

=

+ 0.40 m

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Harbour & Coastal Engineering (Indian Scenario) : Vol. I

2515

+5.00 HWL +3.25 MAIN BEAM

1000Ø PILE DREDGE LEVEL -12.50

1300Ø PILE

1300Ø PILE 1100 THK DIAPHRAGM WALL -20.00 -22.50

-23.00

(B) FINAL DESIGN

Fig.6.20Typical Cross Section of Fertilizer Berth Hence the top level of the jetty is assumed as (3.25 + H/2 + 1) m where, H is the expected wave height. The wave height inside the harbour during extreme weather condition is 1.2 m. Hence the top level is assumed as + 4.85 m. The third and fourth row of piles are provided below the conveyor columns, the second row of pile is provided below one of the rails of crane track. It is preferable to carry out three dimensional analysis for each block considering all the rows of piles especially for berthing and mooring force. However it is a common practice to carry out a two dimensional analysis for a typical pile bent for 1/3 of berthing force and 1/3 or mooring force assuming that the berthing force and mooring force will be distributed to 3 pile bents. 6.4.1.1 Preliminary Analysis of System A typical 4 m panel of 1100 mm thick diaphragm wall having 3.65 m deep beam supported by piles at 6 m, 12 m, 15.65 m and 22.45 m (Figure 6.21) is considered for the analysis. This depth of the beam is found to be very conservative. The economical depth is about

470

Berthing Structures

3950

6000

6800

+1.00 G.L BELOW DECK Y +3.0m TIE +1.0m 3

-1.0m

Y

X

1

X -3.0m

R4

R3 -5.0m V2

V4

V3

-7.0m -9.0m -11.0m K(T/M) -13.0m

920

V1

1197 -15.0m

7787 8319

-17.0m

7067 6942

-19.0m

6942

3650

4000

7100 -21.0m

9800 11575

-23.0m

5940 500 1100 SECTION - XX

SECTION -YY

Fig. 6.21 Idealization for Preliminary Analysis

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Harbour & Coastal Engineering (Indian Scenario) : Vol. I

1.65m. The preliminary analysis of the following three different systems (Raju et al. (1995)) has been carried out using the general purpose, Structural Analysis Program SAP IV developed by Bathe, K.J. (1973). (A)

Diaphragm wall with anchor rod and deadman diaphragm wall (Figure 6.22a).

(B)

Diaphragm wall with vertical and raker piles (Figure 6.22b1 & 6.22b2).

(C)

Diaphragm wall with vertical piles (Figure 6.22c1, 6.22c2 & 6.22c3).

For the purpose of analysis the deck, diaphragm wall and pile systems are replaced by twodimensional beams. The passive pressure on the diaphragm wall is idealised by spring elements. The piles are assumed to be rigid at top and bottom. The fixity depth for piles as per IS 2911 (Part 1/ Se. 2) -1979 for an nh of 0.5 kg/cm3 is 5 times d, where d is the dia of the piles. Since the first row of piles is partly in the active zone of diaphragm wall, its fixity depth is increased to 6 m + 5 d and fixity depth for 2nd , 3rd and 4th rows of piles are assumed as 5d. Since the lateral load governs the design of these structures, the analysis is carried out for lateral loads only. The active earth pressure on the diaphragm wall and 100 T pull are considered as two typical load cases for the analysis. The shear force in diaphragm wall and piles at the top, the wind force in the raker piles, anchor force in the tie rod and the horizontal deflections at the top of diagram wall are summarized in Table 6.5.

472

Berthing Structures

110

100

130

100

75

110

(a) VERTICAL PILES WITH ANCHOR

110

100

130

100

130

75

100

100

130

100

75

(C1) VERTICAL PILES

110

(b1) VERTICAL PILES WITH RAKER

110

100

100

130

100

75

(c2) VERTICAL PILES

75

75

110

100

(b2) VERTICAL PILES WITH RAKER

130

75

75

(c3) VERTICAL PILES

Fig.6.22 Alternate Schemes

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Harbour & Coastal Engineering (Indian Scenario) : Vol. I

Table 6.5

474

Berthing Structures

6.4.1.2 Results and Discussions System ‘a’ - Diaphragm wall with tie rod and deadman diaphragm wall (Ref. Figure 6.25 and Table 6.5). The active earth pressure in the diaphragm wall exerts a shear of 109 T at the top of diaphragm out of which only 38 T goes to the anchor rod; i.e., only 35% of the total shear. For a pull of 100 T, the anchor force is only 28 T i.e., 28%. The anchor is loaded only after substantial lateral loads are transferred to the piles through the deep beam. The construction of anchor with a deadman diaphragm wall of 750 mm thick is time consuming, expensive and is structurally inefficient in the present case in view of the 4 large vertical piles. Hence it is desirable to eliminate the anchor and suitably strengthen the 3rd and 4th row of piles to take care of the lateral load. The 3rd and 4th row of piles can be strengthened either by increasing the diameter or by introducing additional raker piles. Results of both the alternatives are discussed below. System ‘b’ - Diaphragm wall with Raker & Vertical Piles Two different combination of raker and vertical piles are analysed. In b1 the 750mm dia raker pile is in the 3rd row and in b2, the raker pile is in the fourth row. It can be concluded from the results that one 750 mm dia raker pile takes almost the same amount of lateral force as that of 3 numbers of 80 mm dia HTS anchor rods. Compared to system b2, system b1 performs better by taking more lateral load as axial force. The horizontal displacement at top of diaphragm wall for system b1 is also less than that of system b2 (Ref. Table 5). Compared to the cost of installing 3 tie rods, the cost of installation of one 750mm dia raker piles is found to be cheaper. System ‘c’ - Diaphragm wall with vertical piles Three different combination of vertical piles are analysed. System c1 is similar to that of system ‘a’ without anchor rod. In system ‘a’ pile 2,3 and 4 takes 32, 21 and 12% respectively of the total load while anchor takes about 28%. In system c1, the piles 2,3 and 4 take 44, 28 and 17% respectively of the total load. In other words, the 28% load taken by the anchor rod is distributed to the 2nd , 3rd and 4th row piles as 12, 7 and 5% and the remaining 4% is transmitted to the diaphragm wall and pile 1.

R. Sundaravadivelu

1

Harbour & Coastal Engineering (Indian Scenario) : Vol. I

The system c1 is found to be inadequate since the lateral load on pile 2 is more than 85 T for the combination of different loads. Hence, the 3rd and 4th row of pile diameter is increased to 1300 & 1000 mm for system c2 and all the 3rd and 4th row of piles are increased to 1300 mm diameter for system c3. The system c3 is finally chosen since it distributes lateral load equally to the 2nd, 3rd and 4th row of piles. The typical cross section of the final system as adopted is shown in Figure 6.23. 6.4.1.3 Detailed Analysis A rigorous analysis of the final system (Figure 6.23) has been carried out using SAP IV program, by idealising the soil support using springs for both the diaphragm wall and piles. The nodes are at 1 m intervals along the depth of the diaphragm wall and piles. The springs are also placed at 1 m intervals. The spring spacing shall be nearly equal to the thickness of diaphragm wall or the pile diameter for effective modeling of soil support in finite element analysis. The spring constants at each node is calculated as the reaction offered by the soil in region 0.5 m above the node and 0.5 m below the node. The soil profile is given in Figure 6.24. The active earth pressure is also calculated at 1 m intervals and is applied as nodal load on the diaphragm wall. The nodal loads are given in Figure 6.25. The bending moment diagram for active earth pressure and a bollard pull of 30 T are given in Figure 6.26 & 6.27 respectively.

476

Berthing Structures

+1.2m +1.2m

-3.2m

ACTIVE EARTH PRESSURE -8.0m

-13.0m

-23.0m DIAPHRAGM WALL 1100 mm THICK 600

PILE-I 1000 mm

PILE-III 1300 mm

PILE-II 1300 mm Ø

600

PILE -IV 1300 mm

Ø

395

Ø

680

Fig 6.23 Idealization for Rigorous Analysis R. Sundaravadivelu

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Harbour & Coastal Engineering (Indian Scenario) : Vol. I

LEVEL IN M

DESCRIPTION

Y (T/M ) 3

C (T/M ) 2

Ø

H (M)

N (SPT)

-0.78

YELLOW SAND

1.95

0.0

30°

1.63

10

-3.78

YELLOW SAND

1.95

0.0

33°

3.00

20

-4.98

BLACK CLAY

1.70

2.0

0°

1.20

03

-7.78

CRAY SAND

1.95

0.0

33°

2.80

20

-11.76

GREY SAND

1.95

0.0

31°

4.00

15

-13.78

BLACK CLAY

1.80

4.0

0°

2.00

10

-15.78

GREY SAND

1.95

0.0

36°

2.00

30

-19.78

YELLOW SAND

1.95

0.0

34°

4.00

25

-20.78

BROWNISH

1.95

0.0

38°

1.00

40

1.95

0.0

45°

3.20

60

BROWNISH

SAND

-24.00

BROWNISH SAND

Fig. 6.24 Soil Profile

478

Berthing Structures

EARTH PRESSURE (T/M2 ) NODAL LOADS 0

2

4

6

+3.0

8

1 0

(TONS)

0.8

+1.0

1.9

1.9

-1.0

2.2

2.5

LEVEL IN M

-3.0

4.08

-5.0

4.5

3.3

3.6 0

-7.0

4.0 0 4.6 0

-9.0

4.8

5.1

-11.0

11.1

0.0

-13.0

NOTE:

NODAL LOADS ARE FOR 1 metre WIDE PANEL

Fig. 6.25 Active Earth Pressure and Nodal Loads

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1

Harbour & Coastal Engineering (Indian Scenario) : Vol. I

+3.0m A

B

42

16

2

E

200 187

16

42

-1.0m

-5.0m

-9.0m

-13.0m

-15.0m

-21.0m

-23.0m DIAPHRAGM WALL

PILE I

PILE II

PILE III

PILE IV

Fig.6.26. B.M Due to Active Earth Pressure A

B

2

2

+3.0m

D

C 1

2

1

3

E

1

-1.0m

-5.0m

-9.0m

-13.0m

-15.0m

-21.0m

-23.0m DIAPHRAGM WALL

PILE I

PILE II

PILE III

PILE IV

Fig.6.27 B.M Due to Bollard Pull of 30 Tons

480

Berthing Structures

The soil reaction offered to the pile to resist lateral loads is nonlinear and hence, nonlinear soil structure interaction of berthing structures is necessary. Either an iterative procedure or an incremental procedure can be used to implement the nonlinear behaviour (Ranga Rao & Sundaravadivelu (1995)) of soil structure interaction in the finite element analysis of berthing structure. 6.4.2

Analysis of Jetty

A berthing structure with deck slab mounted on piles embedded into sea bed and which has free passage of water underneath the deck, is known as open type of jetty. The jetty projects outward nearly perpendicular to or at some skew angle with the shore line. The jetty (Figure 6.28) generally consists of two berthing dolphins, four mooring dolphins, jetty head and an approach jetty.

SHORE LINE

PILE APPROACH CUM PIPE BRIDGE

LIQUID ETHYLENE PIPELINE TO STORAGE TANK

10 m

8m

25m MOORING DOLPHIN 8m

75m

25m MOORING DOLPHIN 8m

75m JETTY HEAD

8m

20m 8m

8m

1.2m WIDE WALK WAY

10m

8m 1.2 m WIDE WALK WAY

15m BOW LINE

8 m

20 m

ETHYLENE TANKER

STERN LINE

Fig 6.28 Layout of Jetty

R. Sundaravadivelu

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Harbour & Coastal Engineering (Indian Scenario) : Vol. I

The increase in vessel size has necessitated construction of offshore jetty in deep water in open sea and exposed to winds, waves and currents. Hence offshore jetty is a kind of structure totally different from those in a harbour. The length of approach jetty varies from 1000 to 2500 m and an economical design of approach jetty can be made only after analysing different types of pile configuration for varying water depths. The approach jetty for a length of about 2500 m may have five to seven typical pile bents and each pile bent have to be analysed for different environment forces and soil strata. Anchor bents with rakar piles to take of the longitudinal seismic / pipe line surge forces shall also have to be provided and a three dimensional analysis is necessary for such situations. In addition the berthing and mooring dolphins have to be designed not only for operating wave condition but also for extreme wave condition, during cyclones. Hence a computer aided analysis and design is required for the offshore jetty. The layout of a mooring dolphin is given in Figure 6.29. The mooring dolphin consists of 16 piles of 760 mm dia. The four corner piles are kept vertical, whereas, the three piles in each face is kept inclined, 3 vertical to 1 horizontal. This configuration has been chosen based on the analysis of various configurations of piles (Ranga Rao & Sundaravadivelu (1994 A)). The mooring dolphin has 2440 mm thick deck slab. The dredge level is -14.00 m and founding level is -24.6 m. The piles are assumed to be fixed at 5D below dredge level i.e., fixity level = 14 + (5 x 0.76) = -17.8 m. The analysis is carried out using SAP IV idealising the piles by beam elements and the deck using master slave option. The deck can also be idealised using brick element. In this case master-slave option is used since it is simple and gives comparable results with the brick element idealisation of the deck. The analysis is carried out for the following load cases:

482

(i)

Dead load

(ii)

Live load of 1 T/m2

(iii)

200 T bollard pull at θ equal to (a)

45°

(b)

30°

(c)

15°

(d)

0°

Berthing Structures

1000 13

2000

12

9

11 10

BOLLARD

14

8

15

7

2000 10000 2000 16 2000

6

1

2

2000

2000 2000 2000

3

4 5

1000 1000

1000

10000 A LAYOUT 10000

+3.66m

+1.00m

3

3

1

1

DREDGE LEVEL -16.00m

FOUNDING LEVEL -21.60m

B SECTION 1-1

Fig.6.29 Mooring Dolphin Based on the results of the individual load cases (Table 6.6), the critical combination of the tensile and compressive forces on each pile is worked out.

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Harbour & Coastal Engineering (Indian Scenario) : Vol. I

Table 6.6 Analysis of Mooring Dolphin Pile No

Dead load

Live load (T/m2)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

-50 -45 -45 -45 -50 -45 -45 -45 -50 -45 -45 -45 -50 -45 -45 -45

-7 -6 -6 -6 -7 -6 -6 -6 -7 -6 -6 -6 -7 -6 -6 -6

6.4.3

Axial forces in piles (T) due to 45° 0 -96 -58 -31 +99 -31 -58 -96 0 96 58 31 -99 31 58 96

200 T bollard pull at Max forces 30° 15° 0° Tension Compression 26 -101 -72 -56 97 -6 -42 -85 -26 102 72 56 -87 6 42 85

50 -99 -80 -76 87 20 -22 -68 -50 99 80 76 -87 -20 22 68

71 -91 -83 -91 71 46 0 -46 -71 91 83 92 -71 -46 0 46

21 49 57 38 47 13 41

-57 -152 -134 -142 -57 -97 -109 -147 -128 -51 -51 -51 -156 -97 -51 -51

Analysis of Container Berth

The typical layout of the extension of a container berth is given in Figure 6.30. The proposed extension of 220m of the container berth is divided into 4 blocks, each of 55 m. The width of the container berth is 20 m. The span of the container crane is 30 m. It will be uneconomical to provide 30 m width for the container berth and hence one row of piles are provided behind the berth to support the near rail of the container crane. Two container cranes are considered for the analysis. Each container has four legs and each legs has 8 wheels. The center to center distance between two legs is 16.5 m and center to center distance between two wheel is 0.8 m. The deck system consists of 0.4 m thick RCC slab, 0.05 m thick wearing coat, eight main beams of size 0.8 x 2.45 m, twelve secondary beams, three facia beams of size 1.0 x 2.45 m (Figure 6.31). The depth of the webs of all the beams are inclusive of the slab thickness except for the secondary beam which is not integral with the slab.

484

19000

R. Sundaravadivelu 1000

4500

4000

1

4000

4500

1000

1650

9000

4900

5550

6000

10380

8380

16500

CL OF CRANE 1

18500

8380

6400

22 26 34

5 13 21

4 12 20 24 32

3 11 19 23 31

10 18 22 30

9 17 21 29 FENDER

14

33

30000

Fig. 6.30 . Layout of Container Berth

20000

1650

55000

6

55000

35A 55000 KEY PLAN

27

55000

23

PILE MUFF

15

5550

7

638 0

36

CRANE RAIL

900 0

4900

28

1300Ø PILE

10380

8380

20

MOORING

18500

8380

16

55000

CL OF CRANE 2 16500

8

6380

10380

8380

LAND SIDE

Berthing Structures

ALL DIMENSIONS ARE IN mm.

1

Harbour & Coastal Engineering (Indian Scenario) : Vol. I

SB1 200

SB2 SB3

MB - Main Beam -800x2450 SB - Secondary Beam -400x1000

SB4 MB2

MB1

(Depth of the beam Exclusive of slab thickness)

SB5

MB3 CB - Crane beam - 700x1200

SB6 11 x 1480

FB - Fender beam - 1000x2450

SB7 All Dimensions are in mm

SB8

Only CL of the beams are shown SB9 SB10 SB11 SB12 152

CB

200 50

FB

0

165

838

490

Three berthing points are provided for each panel, one at the middle and others at 10.74 m from each end of the panel. The mooring points are provided at 18.5 m c/c with the extreme one at 9 m from the respective panel edge. The various levels are given below. Top level of deck

:

+ 4.00 m

Lowest mean water level

:

0.00 m

The actual dredge level

:

- 13.75 m

The design dredge level

:

- 14.00 m

Cut-off level of piles

:

+1.50 m

The following loads are considered for the analysis. a) Dead load b) Live load

486

= 5.5T/m2 on deck slab

Berthing Structures

c) Crane Loads :

Crane operating

= Each Wheel Load is 40 t with 20% Impact and 10% tractive force

Crane Idle

= Each Wheel Load is 33.33t

d) Berthing Force

= 250 t at left or central or right berthing points

e) Mooring force (M.F)

= 150 t at left, central or right mooring points

f) Seismic Force

= 2% of (D.L + 50% L.L) (As per IS 1893 for Zone II)

6.4.3.1 Load Combinations i) ii) iii) iv) v) vi) vii) viii)

a + b + c+ d a+d a+e b + c + 250 T berthing force across the berth and 82 T along the berth at any one berthing point a+f a+c a+b a+b+c

The increase in the permissible stresses for load combinations (i) to (v) as per IS-4651 (Part IV) is 25 % and the same is assumed in design. 6.4.3.2 Structural Analysis The berth is analysed as a three dimensional structure using SAP IV Program (Structural Analysis Program - IV an inbuilt computer program). The pile is assumed to be fixed at 5 ‘D’ below the dredge level. Based on the results of the analysis, the piles are divided into four major groups and the axial forces and bending moments for two critical combinations are given in Table 6.7. Since 25% overstress is allowed for these combinations, the forces are reduced by 25% and the piles are designed. 6.4.3.3 Structural Design of Piles Piles in Group I (23-26) are provided with 2.25% steel, Piles in Group 2 (11-14, 31-34) are provided with 0.8 % steel, Piles in Group 3 (2-7, 10, 15, 18, 19, 22, 29, 30, 35, 36) are provided with 3.0% steel and Piles in Group 4 (1,8, 9, 16, 17, 20, 21, 28) are provided with 2 % steel. Figure 6.32 and Table 6.8 gives the reinforcement details. Structural design of piles is done using the design charts for the circular piles given by Manohar, S.N. (1964). R. Sundaravadivelu

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Fig 6.32 Pile reinforcement details

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Berthing Structures

Table 6.7 Design Forces in Piles

Pile Group No

Critical Load Combinations 1

Pile Numbers

2

Axial Load (T)

Bending Moment (T-m)

Axial Load (T)

Bending Moment (T-m)

I

23, 24, 25,26

533

144

160

150

II

11, 12, 13, 14 31, 32, 33, 34

478

105

143

90

III

2 to 7, 10, 14, 10, 15, 18, 19 22, 27, 29 30, 35, 36

375

158

59

156

IV

1, 8, 9, 16, 17 20, 21, 28

197

155

112

143

Table 6.8 Reinforcement Details Pile Group No.

Percentage of Steel (p)

Area of Steel (m2)

No. Of 32 mm φ bars in Zone ‘m’

Zone ‘n’

Lateral ties

Provide Y10-300 throughout the length of pile

I

2.25

0.0299

38

26

II

0.80

0.0107

14

14

-Do-

III

3.00

0.0399

51

34

-Do-

IV

2.00

0.0266

34

24

-Do-

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6.4.3.4 Foundation Design of Piles The piles are designed based on the soil profile. The soil profile indicates silty sand from – 14.0 m to – 22.0 m ( SPT ‘N’ =30), cemented sand from -22.0m to -25.0m (SPT ‘N’ = 50) and rock (SPT ‘N’ >100) for depth below –25.0m. However rock level varies at certain locations. Though 1300mm dia piles founded at -23 m level are found adequate as a good engineering practice, founding depth is adopted with penetration ½ times diameter of pile in hard rock or 3 times diameter of pile in cemented sand strata whichever is earlier. The pile capacities are worked out based on SPT ‘N’ values and using Meyerhof’s correlations as given below. T/m2

Ultimate end bearing resistance in sand =

12 [ SPT ‘N’]

Ultimate skin friction in sand

[ SPT ‘N’] /10 T/m2

=

The capacity in rock is worked out as per Cole & Stroud as given below. qa = Nc Cb/F fa = αCs where

qa

=

allowable end bearing pressure

Nc

=

bearing capacity factor taken as 9.0

Cb

=

shear strength of the rock at pile base

F

=

factor of safety taken as 3.0

fa

=

allowable frictional resistance

Cs

=

average shear strength of rock along rock socket and

α

=

shaft adhesion factor taken as 0.3.

For silty sand [ SPT ‘N’ = 30] Ultimate end bearing

=

12 x 30 = 360 T/m2

Allowable end bearing

=

144 T/m2 (ultimate end bearing /2.5)

Ultimate skin friction

=

30/10 = 3 T/m2

Allowable skin friction

=

3/2.5 = 1.2 T/m2

490

Berthing Structures

For cemented sand [ SPT ‘N’ = 50] Ultimate end bearing

=

12 x 50 = 600 T/m2

Allowable end bearing

=

600/2.5 = 240 T/m2

Ultimate skin friction

=

50/10

= 5 T/m2

Allowable skin friction

=

5/2.5

= 2 T/m2

For Rock For N > 100, taking the shear strength of rock from chart given by Cole & Stroud as 90 T/m2 Allowable friction resistance

=

0.3 x 90 = 27 T/m2

Allowable end bearing

=

9 x 90/3 = 270 T/m2

Total load

=

427 T

End bearing in rock

=

1.3 2 π× ×270 = 358.37 = 358 T 4

Pile Group I

Total skin friction from silty sand and cemented sand layers 1.3 (1.2 x 8 + 2 x 3)

=

63.71

= 64 T

Required skin friction capacity from rock 427 - (358 + 64) = 5 T A penetration of 1 m into the rock is recommended. Hence, the founding depth of piles in Group I shall be -27.0 or 1 m penetration into hard rock which ever is earlier. Pile Group II Total load = 383 T End bearing from cemented sand layer =

π ×1.3 2 ×240 = 318.55 T 4

Skin friction from cemented sand layer & silty sand layer = 63.71 T R. Sundaravadivelu

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Total load = 318.55 + 63.71 = 382.26 T = 383 T Give a penetration of 1 m into the rock. Hence, the founding level of piles in Group II shall be - 26.0 m or 1 m penetration into rock, whichever is earlier. Pile Group III Total load = 300 T Hence, the total load required is less than the end bearing capacity of cemented sand layer. But from the minimum embedment depth criterion, an embedment depth of 5 times the diameter of the pile should be provided. 5 x 1.3 = 6.5 m. But, this falls in the silty sand layer. Hence, give a penetration of 1 m in the cemented sand layer. Hence the founding depth for the piles in Group III shall be - 23.0. Similarly the founding depth of piles in Group IV shall also be -23.0 m. As the spacing between the groups of piles (23,24,25,26) & (31,32,33,34) is only 4.9 m, the foundling level for both these groups is kept as 1 m penetration to the rock or -27.0 m whichever is earlier. For the same reason as stated above for the two groups of piles (11,12,13,14) & (3,4,5,6) the founding level is kept as 1 m penetration into the rock or -26 m, whichever is earlier. For the rest of the piles the founding level is -23.0 m. 6.5

DESIGN OF BERTHING STRUCTURES

Once the analysis of any structural system is completed, the next step would be the design of various elements in the structural system. Generally, the design process is iterative as the design variables chosen may not satisfy the allowable stress/strain parameters. This process should be repeated until a satisfactory solution is obtained. The design shall be carried out as per the guidelines specified in IS 456-1978. As per IS 4651 (Part IV) - 1989 the minimum grade of concrete to be used in berthing structures is specified as M 30. The minimum cement content of 0.4 T/m3 and maximum water cement ratio of 0.45 shall be maintained for all grades of concrete. The minimum thickness of cover for structures

492

Berthing Structures

immersed in sea water, in splash zone or exposed to marine atmosphere should be 25 mm more than the cover specified in 4.1 IS 456 (1978) Hence the cover shall be as follows Slab = 15+25 = 40 mm Beam =25+25 = 50 mm Pile = 40 + 25 + = 65 mm However the cover shall not be greater than 75 mm. There are two methods of design namely, Working Stress method and the Limit State method. In the working stress method the design is based on the linear stress strain relationship within the elastic limit. The structure shall be designed for the working loads and checked for the permissible stresses. The permissible stresses are the stresses obtained after applying a factor of safety to the yield strength of the materials. In the limit state method the design is based on Limit State concept. The structure shall be designed to withstand safely all the loads liable to act on it throughout its life. It shall also satisfy the serviceability requirements such as limitations on deflection and cracking. The acceptable limit for the safety and serviceability requirements before failure occurs is called a “Limit State”. The diaphragm wall and pile are the two important structural elements of a berthing structure and the detailed design method for the diaphragm wall and pile is given in this section. 6.5.1

Design of Diaphragm Wall

The diaphragm wall is to be designed using the design philosophy given in the following section. Requirements of reinforcement are given in Section 6.5.1.2. 6.5.1.1 Design Philosophy The basic assumption is that the maximum strain in concrete at the outermost compression is 0.0035, when the neutral axis lies within the section. The strain varies from 0.0035 at highly compressed edge to zero at the opposite edge when the neutral axis lies along one edge of the section. For purely axial compression, the strain is assumed to be uniformly equal to 0.002 across the section. The strain distribution lines for these two cases intersect each other at a depth of (3/7) D from the highly compressed edge. This point is assumed to

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act as a fulcrum for the strain distribution line when the neutral axis lies outside the section as shown in Figure 6.33.

b

HIGHLY COMPRESSED EDGE

yi

d'

d'

a CENTRODAL AXIS 0.0035

NEUTRAL AXIS WITHIN THE SECTION

X

0.0035

0.002

x

Fig 6.33 Strain Diagrams

Neutral Axis Lying Outside Section: When the neutral axis lies outside the section, the shape of the stress block will be as indicated in Figure 6.34. The stress is uniform for a distance of (3/7)D from highly compressed edge because the strain is more than 0.002 and thereafter the stress diagram is parabolic. Let xu = kD and let ‘g’ be the difference between the stress at the highly compressed edge and the stress at the least compressed edge. Considering the geometrical properties of a parabola,

494

Berthing Structures

b

D

STRAIN DIAGRAM

STRESS DIAGRAM

Fig. 6.34 Stress Block when the Neutral Axis lies Outside Section  4  g = 0.446 f ck    7k − 3 

2

(6.21)

Area of the stress block 

= 0.446 f ck D 1 − 

4  4  21  7k − 3 

2

 

(6.22)

The centroid of the stress block will be found by taking moments about the highly compressed edge.

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Moment about the highly compressed edge = 0.446 f ck

D2 8 − gD 2 2 49

(6.23)

The position of the centroid is obtained by dividing the moment by area. While designing the diaphragm wall, the neutral axis at regular intervals is assumed. For each position of neutral axis, the strain distribution across the section and the stress block parameters are determined as explained earlier. The stresses in the reinforcement are also calculated from the strains. Thereafter the resultant axial force and the moment about the centroid of the section are calculated as follows: Pu = C1 f ck b D +

n

∑ i =1

pibD (f si − f ci ) 100

(6.24)

where C1

= Coefficient for the area of stress block

Pi fsi

= (Asi/bD) where Asi is the area of reinforcement in the ith row = Stress in the ith row of reinforcement, compression being positive and tension being negative

fci

= Stress in concrete at the level of ith row of reinforcement

n

= Number of rows of reinforcement

Taking moment of forces about the centroid of the section, D  M u = C1 f ck b D  − C 2 D  + 2 

n

∑ i =1

pibD (f si − f ci ) yi 100

(6.25)

where C2 D

= the distance of the centroid of the concrete stress block, measured from the highly compressed edge

yi

= the distance from the centroid of the section to the ith row of the reinforcement, positive towards the highly compressed edge and negative towards the least compressed edge.

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Berthing Structures

Neutral Axis Lies Within Section: In this case, the stress block parameters are simpler and they can be directly incorporated into the expressions which are otherwise same as for the earlier case. Thus the following expressions are obtained P = 0.36 f ck bk D +

n

∑ i =1

pibD (f si −f ci ) 100

M = 0.36 f ck bkD 2 (0.5−0.416k )+

n

∑ i =1

(6.26)

pibD (f si −f ci ) yi 100

(6.27)

6.5.1.2 Requirements of Reinforcement The minimum reinforcement of 0.4% and the maximum reinforcement of 4% are incorporated for the design of diaphragm wall. The shear reinforcement shall be provided to carry a shear equal to Vs = V-τc.bd. The spacing of the vertical stirrups, sv is given by Sv =

0.87 f y A sv d VS

(6.28)

where V

= Shear force due to design loads

Vs

= Strength of shear reinforcement

Asv

= Total cross sectional area of stirrup legs

sv

= Spacing of the stirrups along the length of the member

τc

= Design shear strength of the concrete

fy

= Characteristic strength of the stirrup, which shall not be greater than 415 N/mm2

6.5.2

Design of Pile

Circular piles are widely used as foundations for coastal and offshore structures like berths, jetties, dolphins etc. Circular piles are preferred in these structures because they can be easily installed with a liner. As these sections have uniform c/s about any diametrical axis, R. Sundaravadivelu

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these sections are best suited to resist multi-directional wave loads (Srinivas & Sundaravadivelu (1987)). Piles are designed by working stress method to limit crack width. 6.5.2.1 Design Philosophy The design of compression members can be carried out in two distinct stages. 1. Design based on uncracked section, i.e. there is no tension anywhere in the section or the resultant tensile stress is less than the permissible tensile stress of concrete. 2. Design based on cracked section, i.e. the resultant tensile stress is more than the permissible tensile stress in concrete. Design of Uncracked Sections: In general, for an assumed percentage of reinforcement and neutral axis depth the stresses under given loading are checked against permissible stresses. The various steps involved in the design are as follows: 1. Check by interaction formula :

The interaction formula as given below has to be satisfied.

f cc f + cbc ≤ 1 σ cc σ cbc

fcc

= Calculated direct compressive stress in concrete

σcc

= Permissible axial compressible stress in concrete

fcbc

= Calculated bending compressive stress in concrete

σcbc

= Permissible bending compressive stress in concrete

(6.29)

For more exact calculations, the maximum permissible stress in a reinforced column or part there of having a ratio of effective column length to least radius of gyration above 40 shall not exceed those which result from multiplication of the appropriate maximum permissible stresses by the reduction coefficient, Cr given by the following formula Cr = 1.25 - (lef)/(160 )imin imin

498

= Least radius of gyration

(6.30)

Berthing Structures

lef

= Effective length of column (pile)

If the assumed section satisfies interaction formula, then it has to be checked for cracking. 2. Check for cracking : If fcc is greater than fcbc, there is no tension in the concrete and hence the section is considered as uncracked. Even if fcc is less than fcbc, the section is considered to be uncracked if the resultant stress given by ft = fcbc -fcc is less than (i) 0.75 times the modulus of rupture of given grade of concrete at seven days; (ii) 0.25 times the maximum resultant compressive stress given by (fcc + fcbc). If ft is greater than either (i) or (ii), then the section is considered to be cracked. Design of Cracked Section: In case of cracked section design, the tensile stress of concrete is ignored. The design of cracked section is carried out using two equilibrium equations. P = Cc + C s - T

(Force equilibrium)

M = Cc Xc + Cs Xsc + TXst

(Moment equilibrium)

(6.31) (6.32)

Where Cc = Compression in concrete segment. =

2fcbc R 2  sin 3 β β cos β cos βsin 2β  − +   (1 − cos β)  3 2 4 

(6.33)

Cs = Compression in steel reinforcement. =

fcbc R 2 p (1.5 m - 1) (1-d/R) (sin α - α α) 100(1 − cos β)

(6.34)

T = Tension in steel reinforcement. =

f cbcR 2 mp (1-d/R) (sin α + (π - α) cos α) 100(1 − cos β)

(6.35)

Cc Xc = Moment of compression in concrete about the center line.

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=

2f cbc R 3  β cos βsin 3 β sin 4β  −  −  (1 − cos β)  8 3 32 

(6.36)

Cs Xsc = Moment of compression of steel about the center line. =

f cbc R 3 p  α sin 2α  (1.5m−1) (1 − d ' / R ) 2  − 100(1 − cosβ) 4  2

(6.37)

TXst = Moment of tension in steel about the center line. =

f cbc R 3 mp  π − α sin 2α  (1 − d ' / R ) 2  + 100(1 − cosβ) 4   2

(6.38)

Equations (6.11) and (6.12) have to be solved for fcbc and either α or β. Usually trial and error method is used to solve these equations. Once these two equations are solved the stress in steel can be determined by using the following equations. f st =

mf cbc (2 R − n − d' ) n

(6.39)

where n = depth of neutral axis = R (1 - cos α)

(6.40)

= (R - r cosβ)

(6.41)

Knowing the stress in steel, cover to the reinforcement and modulus of elasticity of concrete, crack width can be calculated using appropriate crack width formula. 6.5.2.2 Requirements of Reinforcement The reinforcement shall not be less than 0.4% as per IS 2911 (part I)-1979. In general maximum reinforcement of 4% is considered in the design due to the difficulty in placing more than 4% reinforcement. The diameter of the reinforcement bar shall not be less than 12 mm. The diameter of the lateral ties shall be not less than one-fourth of the diameter of the largest longitudinal bar, and in no case less than 5 mm. The spacing of the transverse reinforcement shall not be more than the least of the following distances: 500

Berthing Structures

i) The least lateral dimension of the compression member ii) Sixteen times the smallest diameter of the longitudinal reinforcement bar to be tied iii) Forty-eight times the diameter of the transverse reinforcement 6.5.3

Calculation of Crack Width

Concrete is weak in tension and cracks when the tensile strain is of the order of 0.0002 to 0.0005. With the advent of high tensile steel, the strain in the concrete surrounding such reinforcement will be of the order of 0.001 even under service loads. In fact, the reinforcement becomes effective only when the surrounding concrete cracks. However, large scale cracking is not acceptable because of its ugliness and the resultant ingress of moisture and eventual corrosion. A dense concrete with adequate cover to the reinforcement can protect it during the entire useful life of the structural component. But cracking permits the ingress of carbon dioxide, chlorides, etc. thus initiating corrosion. Direct and indirect financial losses due to corrosion runs to several millions of rupees in India and hence the limit state of clacking is included as one of the important design limit states. Concrete cracks even when there is no external load applied on a structure, mainly due to shrinkage and temperature effects. Tension members of reinforced concrete have cracks penetrating right through the cross section and steel reinforcement is the only connecting link between the various parts. Such cracks are called as separation cracks. On the other hand, the reinforced concrete member subjected to pure flexure has cracks in the tensile zone only and they penetrate the cross section of the member up to the neutral axis. These flexural cracks are of primary concern to the designers. For purposes of crack control, it is essential to define the admissible crack width. As per IS 4651 (Part IV)- 1989 the crack width should be less than 0.004 times the cover provided. Many research organizations and codes like CEB/FIP, ACI Code, Russian Code, DIN Code, British Code, IRC Code etc., have recommended various formulae for the calculation of crack width. Many of these formulae are arrived at conducting experiments on rectangular beams subjected to bending moment only. Consequently the expressions derived have included the width of the section as a parameter. Only IRC formula appears to be applicable for circular piles because it involves only stress in steel and effective cover concrete.

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The formulae given by CEB/FIP, IRC and SP24 are given below. 6.5.3.1 CEB/FIP Formula CEB/FIP recommends the following formula to calculate the crack width (Cw), Cw = (1.5 C + 16φ/Pf) (σs - 3000/Pf) x 10-6

(6.42)

Where C

= Effective cover

φ

= Diameter of the reinforcing bar

σs

= Stress in tensile steel

Pf

= (100 Ast )/(0.25 bh)

Ast

= Area of tensile steel

b

= Breadth of the section

h

= Depth of the section

6.5.3.2 IRC Formula The IRC formula is given for bridge like structures to calculate the crack width. As berthing structures are also subjected to truck loads such as class AA etc., the formula given by IRC has been used to calculate the crack width. The formula given by IRC to calculate crack width, Cw is as follows: Cw = (3.3 fst dc)/(m Ec) where fst

= Stress in steel

dc

= Effective cover

m

= Modular ratio

Ec

= Modulus of elasticity of concrete

502

(6.43)

Berthing Structures

6.5.3.3 IS code (SP 24) Formula As per SP 24, the crack width, Cw is calculated as follows:

Cw =

1+

3a cr ε m 2( a cr − C min )

(6.44)

D−x

where acr

= Distance from the point considered to the surface of the nearest longitudinal bar

Cmin

= Minimum cover to the longitudinal bar

εm

= Average strain at the level considered

D

= Overall depth of the member

x

= Depth of neutral axis

The average strain at the level at which cracking is being considering is given by ε m = ε1 −

0.7 b t D(a '− x ) x10 −3 A st (d − x )f s

(6.45)

Where ε1

= The strain at the level considered ignoring the concrete in the tension zone

bt

= The width of the section at the centroid of the tension steel

a’

= The distance from the compression face to the point of the crack

Ast

= The area of tension steel

fs

= Service stress in tension reinforcement which may be taken as = 0.58f y ×

Ast required Ast provided

(6.46)

The above formulae can be used provided the strain in tension reinforcement does not exceed 0.8 fy/Es. The negative value of εm indicates that the section is uncracked. In assessing the strains, the modulus of elasticity of concrete shall be taken as 280/3 σcbc as given in elastic theory to account for creep.

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6.5.4

Computer Aided Design

Since the design of berthing structures involves analysis of various configurations considering nonlinear behaviour of soil, and, codal provisions for crack width calculations, computer aided design of berthing structures has become necessary (Ranga Rao & Sundaravadivelu (1994). 6.6

MARINE FENDERING SYSTEMS

6.6.1

General

The purpose of the marine fendering system is to prevent damage to both the vessel and berth, during the berthing process and while the vessel is moored. As the vessel approaches a berth it possess kinetic energy by virtue of its displacement and motion. As the vessel contacts the berth and is brought to stop this kinetic energy must be dissipated. Fendering systems that is being berthed are provided to absorb or dissipate the kinetic energy of the ship. 6.6.2

Types of Fendering Systems

The different types of fendering systems are as follows: 1. Standard pile fenders 2. Rubber fenders 3. Pneumatic fenders 4. Gravity type fenders 6.6.2.1 Standard Pile Fenders This system is generally used for low energy absorption. The piles made of timber, steel. RCC and PSC are driven in front of the berthing structure to absorb the energy from the ship by direct compression and flexure. The energy capacity depends on the size, shape and length of the pile. Wooden piles does not have long life while the RCC piles have low energy absorption. Steel piles and PSC piles with rubber buffers are used for larger depths.

504

Berthing Structures

6.6.2.2 Rubber Fenders The few types of rubber fenders are shear, compression and buckling. The shear and compression fenders, have a linear P - ∆ relation, i.e. for energies smaller than the rated energy, the fender will be relatively soft. The buckling fenders, have swift increase in loads in the initial stages, but as the fenders are further deflected the loads are more or less maintained until the rated deflection is reached. A low ratio of load over energy (P/E) is reached for buckling fenders. 6.6.2.3 Pneumatic Fenders Pneumatic fenders are originally developed for ship to ship transfer but now-a-days are used for jetties and berths also because of its good performance. The pneumatic fender is an inflated rubber bag and dimensions vary from 0.5m to 4.5 m in dia and 1m to 12 m in length. The fender bag is protected by wire or chain net with tyres or rubber sleeves. The energy absorption does not decline at inclined compression for these fenders. 6.6.2.4 Gravity Type Fenders These are generally made of concrete blocks suspended from a heavily constructed wharf work. the Impact energy is absorbed by moving and lifting the heavy concrete block. 6.6.3

Selection Criteria of Fendering Systems

The selection of a optimum fender for a given service depends on the following factors : 1. The type, size, draft and allowable hull pressure of a vessel. 2. Berthing velocity and angle. 3. Distance between the berthing point and the vessels gravity centre measured along the face of the pier. 4. Water level, tidal range, wind velocity, direction of wind, direction and velocity of currents. 5. Behaviour and installation pitches of Dock fender 6. Structure and strength of Berthing facilities 7. Certain human factors involved in berthing.

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6.6.4

Berthing Energy of a Vessel

The design of fenders depends very much on the energy to be absorbed by the fenders during berthing. When a ship strikes the fender, it transfers some part of the kinetic energy to the fender and the other part gets dissipated to the motion of ship in water. Some part of the energy absorbed by the fender is transferred back to the ship, after the ship has come to rest, by the fender trying to recoil back to its normal shape. This process of exchange of energies between fender, ship and the loss of energy in water motion continues till the whole of the kinetic energy of ship is dissipated in water motion. The different methods that are used in determining the maximum amount of energy to be absorbed by the fender is given below : 6.6.4.1 Quinn Method In this method fifty percent of the energy of the ship calculated on the basis of the velocity of the ship normal to berthing structure is assumed as the energy absorbed by the fender. WV E =  G 4

2

(6.47)

6.6.4.2 Woodruff Method In this method the following empirical equation is used to calculate the berthing energy. E = W(0.004 - W x 10-8

(6.48)

Where W is in tons and E is in ton feet. 6.6.4.3 Vasco Costa Method Vasco Costa has given the following analytical solution, for a ship moving with translatory velocity u and angular velocity w, having no slip along the berth. E = (WV2/2g) (1 + 2D/B) (K2 + r2 Cos2r / K2 + r2 )

(6.49)

Where v Distance P= u + aw The value of k can be taken as 0.2 L to 0.29 L. The following three coefficients are to be considered along with equation.

506

Berthing Structures

1.

Geometric coefficient (Cg)

0.85 for convex surface contact of the ship 1.00 for broad side berthing 1.25 for concave surface contact of the ship.

2.

Deformation coefficient (Cd)

0.5 for resilient fender and 1.0 for stiff fender

3.

Berth configuration Coefficient (Cc)

0.8 for closed warf and 0.9 for closed berth and 1.0 for open type berth

6.6.4.4

IS: 4651 (Part III) - 1974

As per the Indian standard code of practice, the berthing energy is calculated as follows E =

WD x V 2 C m x Ce x C m 2g

(6.50)

where WD

=

Displacement tonnage (DT) of the vessel, in tonnes,

V

=

Velocity of vessel in m/s, normal to the berth

g

=

Acceleration due to gravity in m/s2

Cm

=

Mass coefficient

Ce Cs

= =

Eccentricity coefficient and Softness coefficient.

The approach velocity varies from 0.1 m/s to 0.75 m/s depending on the size of the vessel, site condition and berthing condition. The above equation depends on the angle of approach and l/r ratio where l is the distance from the centre of gravity of the vessel to the point of contact projected along the water line of the berth in metre and r is the radius of gyration of rotational radius on the plane of the vessel from its centre of gravity in metre. The l/r ratio is in the range of 1 to 1.25. The angle of approach varies from 0 to 20 degrees. The softness coefficient indicates the relation between the rigidity of the vessel and that of the fender. The value of 0.9 is generally used for this factor.

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Harbour & Coastal Engineering (Indian Scenario) : Vol. I

6.6.5

Fender Reaction

The fender reaction depends on the approximate energy to be absorbed and the characteristics of the fender. If the fender reactions are transmitted to the backfill immediately behind the quay wall there will be no problem in absorbing the reaction. If the structure, like open piers and jetties are to be designed for these reaction forces, the forces are critical since they control the design of these structures. If P/E ratio varies from 2 to 7 depending on the type of fender where P is the berthing force in T and E is the energy absorption at 50 % of defletion in T. m, in such cases it is preferable to have fenders with low reaction per absorbed unity of energy (P/E). It is also important to consider the fender performance beyond the rated energy capacity, since the fender reaction increases swiftly. 6.7

SINGLE BUOY MOORING SYSTEM

6.7.1

General

The art of implanting floating structures in the ocean is as old as man’s history. Marker buoys, mooring buoys and navigational buoys have long been familiar sights in the harbours and waterways and along the sea shores. The recent past has seen many large and sophisticated buoy mooring systems deployed in deep waters for a variety of purposes. A buoy mooring system consists of a buoy or buoys, connected by cables and anchored to the seabed. Being a compliant structure, the system is responsive to external effects and the movements are controlled by the mooring system. Buoy mooring systems are flexible and provide a progressive elastic response to environmental forces absorbing and dissipating energy from the ocean environment. To understand the effect of these constrained or freely drifting buoyant structures often require advanced Engineering knowledge from many disciplines are often required. A buoy can be considered as a major positively buoyant component in the system. Buoys may be classified, based on their position into three general groups, as (i) surface buoy system where the buoy floats on the surface (ii) subsurface buoy system where the buoy is below the sea surface and (iii) two part buoy system where it is a combination of the above two systems. Surface buoys can be surface following type with shapes such as spherical, cylindrical, disks etc. or surface decoupled such as spars. Surface following buoys have the advantage of having a large buoyancy to drag ratio whereas the spar buoys have small buoyancy to

508

Berthing Structures

drag ratio and they are not effective in providing the buoyancy required to support long mooring lines. Surface buoys are used at the air sea interface in the upper part of the water column. These are further classified as single leg surface buoy systems and multi-leg surface buoy systems. In the single leg surface buoy system, there is only one anchoring point. The ratio of mooring cable length to water depth is called the scope of the mooring line. A small scope indicates a taut moor and a large scope indicates a slack moor. The advantages of a taut moor are smaller buoy-watch-circle, reduced sensor motion and ease of deployment. The disadvantages of the taut mooring system are high dynamic loading due to wave action and high static tension under severe current conditions. These are reduced when the scope of the mooring line is increased. The motion of the float and of the sensors a slack moored system will become considerable, thus introducing an undesirable error in the measurements of velocity fields and other ocean variables. Subsurface buoy systems are also classified as single leg and multi-leg subsurface buoy systems. The great majority of oceanographic subsurface buoy systems have a single anchoring point. Cost efficiency and ease of deployment result from their simple configuration. As the buoy would be much below water surface, the wave force and the motion of the buoy due to waves would be less. Two part buoy systems are used when the need arises to provide motion stability for underwater sensors and at the same time to provide a surface expression for telemetry of data or for relocation of the main buoy system. The motion stability is provided by using a subsurface supported buoy system. A typical deep water buoy system may involve multiple lines with lengths varying from a few tens of metres to thousands of metres. When these are considered in conjunction with the equipment deployed from or associated with the moored buoys, the losses resulting from a mooring failure can be significant. Consequently there is much interest in design and analysis methods applicable to the buoy mooring systems. In general, based on the use of the buoy mooring system it can be grouped as (i) buoys used for monitoring or measuring the parameters of importance to oceanographers and naval scientists and (ii) buoys used for engineering purposes such as mooring oil tankers.

R. Sundaravadivelu

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Harbour & Coastal Engineering (Indian Scenario) : Vol. I

6.7.2

Oceanographic Buoy Systems

An oceanographic buoy system can be defined as a floating structure deployed in the ocean for the purpose of measuring environmental data (Berteaux, 1976). Because of their inherent capacity of efficiently providing long term series measurements of meteorological and oceanographic parameters, a relatively large number of buoy systems are deployed each year in world’s oceans. Buoy systems are used in the ocean environment for monitoring weather, oceanographic and defence related data acquisition, and also as vehicles for electronic navigational systems. An array of hydrophones used in conjunction with a subsurface moored buoy and a telemetry system can be used as a passive sonar to detect and transmit sounds in the sea either due to surface or subsurface ships. Standard navigation systems can be installed aboard floats, provided with power and moored offshore to extend the range of precision navigation. In the Ocean Acoustic Tomographic System (OATS), the use of buoy cable system would help to get very valuable oceanographic and scientific data. 6.7.3

Offshore Floating Storage Systems

Since many large oil fields are in remote places where harbours are non-existent, a need is felt to have artificial berths to moor the tankers during their loading operation. Many configurations of offshore tanker terminals are attempted. The single point mooring system (SPM) has emerged as the most rapidly deployed, economical and safest to operate. SPM enables economic transport of crude oil where use of pipelines is not technically or economically feasible because of rough seabed, topography or long distances from shore. Single point mooring terminals are, as the name implies, facilities of small horizontal dimensions, to which large vessels are moored by means of a bow hawser or by any other means which allows the vessel to rotate 360° around the mooring point. Generally, single point mooring terminal can have two functions. Primarily, it affords a safe mooring to the vessels. Secondly, it can form a link in the transport of oil. The single point mooring terminal can assume many forms. Of the more than 300 SPMs now in use around the world (Maari, 1985) approximately 80 percent are of the type single buoy catenary anchor leg mooring (CALM). CALMs have been employed as loading terminals since 1961. The CALM (Figure 6.35) basically consists of a cylindrical buoy type float anchored to the seabed by a number of radial catenary chain legs (up to eight chains) while the vessel is moored to the buoy by one or more elastic synthetic (usually nylon) lines. This system employs the properties of the catenary to supply the

510

Fig. 6.36 Catenary Anchor Leg Mooring (CALM) Terminal

Berthing Structures

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elasticity required when holding large tankers in open seas. The buoy is cylindrical and can have an outside diameter between six and twenty metres and a height between four and eight metres. Single buoy, multi-leg mooring systems are the most commonly used offshore loading facility which has grown in significance in the recent years through the use of single point mooring systems for the exploitation of marginal fields and in the development of moorings for deep water production facilities. One of the principle tasks of the designer of catenary moorings is to ensure that the system characteristics are such that the movement of the floating unit under extreme environmental conditions remains within acceptable limits. Scrutiny of the calculation of catenaries show that chains with their high weight per unit length often have high energy absorption capacity. Whilst chain has this very desirable property of being a good energy absorbing catenary, it unfortunately suffers from that well known failing character, being only as strong as its weakest link. This constitutes the second major design criteria i.e., the tensile loads under extreme wave conditions should be less than the proof loads. The typical examples of different types of offshore loading systems are given below: (a) Rotating manifold CALM system installed at Buchan, United Kingdom (Figure 6.36a ) (b) Soft yoke CALM system installed at Palanca, Angola (Figure 6.36b.) (c) Rigid yoke CALM system installed at Cadlao, Philippines (Figure 6.36c) Water depth can vary to a practical maximum of about 130 metres. Normal operating sea states with the tanker moored are the significant wave heights in the range of about four metres. High waves at a CALM terminal can generate prohibitive forces in the anchoring chains. This is especially the case where the ratio of maximum wave height to water depth is very high. CALMs have been installed in hostile areas such as North Sea with a maximum survival wave height up to 28 metres (Montrose Field) and the Enchora Field in Brazil with a maximum wave of 21 metres. Current velocity can be a limiting factor for the submarine hose system but CALM terminals have been installed and are operating successfully in currents of up to 2 m/s (four knots). Wind is not a significant factor because it only affects the SPM indirectly through forces applied on the tanker. Normal operating (with ship moored to the CALM) wind velocities are about 40 knots and design wind speeds are up to 70 knots.

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Berthing Structures

(a) Rotating manifold type CALM system

(b) Soft yoke calm System

(c) Rigid yoke calm systems

Fig 6.36 CALM Systems R. Sundaravadivelu

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Harbour & Coastal Engineering (Indian Scenario) : Vol. I

Continuous motion of the buoy due to wave action results in wear and tear of the chains. The static tension in the chain is of the order of 50 to 100 kN. The static tension is a function of surface angle the chain makes with the buoy, submerged unit weight of the chain and water depth. Increasing the static tension reduces the movements of the buoy and consequently the wear of the chains but model tests have indicated that at this level of static tension (50 to 100 kN) the mooring forces are kept to a minimum. For rough sea condition, however, survival of the CALM terminal may be of greater importance than the effect of keeping mooring forces to a minimum. In such cases, an optimum must be determined between static tension, centre of gravity of buoy and wave spectra to minimise linear and rotational movements of the buoy and consequently minimise possible damage to the oil cargo hose. 6.7.4

Importance in Indian Context

India’s coastline extends over 6000 km, which is the seventh largest coastline in the world. It has an exclusive economic zone of 2.02 million sq. kms, which is also the seventh largest in the world. The prevailing environmental conditions viz., wave and wind climate, currents, air and sea surface temperature, salinity etc., at a specific location and their yearly variations are the most important inputs in the planning, design, construction and operation of offshore structures, coastal defence works, ports, ship routing and several other applied ocean research activities. Such data would also be vital for development of predictive models for forecasting of wave and wind climate of the ocean, ocean circulation, monsoon prediction, ship routing etc. Moored ocean buoys are considered the most appropriate system for measuring such data. India has launched a comprehensive programme for exploration of crude oil from offshore resources. Offshore activity is getting extended from west coast to east coast (Krishna, Godavari and Cauvery basins) where production wells have to be located at about 25 km from the shore. Offshore loading systems are particularly attractive and economical for small offshore oil fields. As the offshore marine environment imposes severe demands upon men, machinery and money, the research and development of buoy mooring systems is an immediate necessity for the country. 6.7.5

Movement of Moored Tankers at Berth

Transportation of crude oil or refined products is the most important maritime traffic in thw world. Crude oil is transported in generally high capacity tankers. The movements of tankers at berth are an important design consideration for berthing structures. Model studies are used to predict the motion of ship and the forces on the mooring line for ships

514

Berthing Structures

berthed at an offshore jetty. (Sundaravadivelu & Natarajan (1996 a & 1996 b) The details of tankers, the types of mooring lines and the permissible movements of tankers are given below: 6.7.5.1 Details of Tankers The refined products are usually transported in smaller tankers less than 100,000 DWT. The main dimensions of tankers corresponding to the dead weight capacity and the distribution of the tankers as on 1991 is given in Appendix 6.1 (PIANC working group 24 Feb 1991). 6.7.5.2 Mooring Outfit The mooring lines are handled by capstans, which are used to pull the lines and to tighten the lines when the ship is moored. The different types of mooring line are a) Steel wire b) Polypropylene or nylon c) Mixed rope i.e. a steel wire line connected to a short nylon lines(10 to 15m long) The number, size and length of the mooring lines depend on the size of the ships. The mooring equipment on board is also given in Appendix 6.1. 6.7.5.3 Ship Motions From the available data given in the literature, it is difficult to select precise figures on what could be the allowable movements of the ship. The values given below recommended by PIANC (1971) is a good basis for safe mooring conditions. Surge :

± 1.00 m

Rolling

:

± 2.5 deg

Sway

± 0.75 m

Pitching

:

± 1 deg

± 0.5 m

Yawing

:

± 1.5 deg

Heave: 6.8

:

MONITORING OF INTEGRITY OF BERTHING STRUCTURES

In this section the Integrity Monitoring of the following berthing structures has been presented.

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6.8.1

(i)

Mooring Dolphin

(ii)

Failure of piles in a bulk berth

(iii)

Forces measurement in tie rods

Mooring Dolphin

6.8.1.1 Condition of Dolphin Consequent on the direct hit of a ship of 60,000 DWT fully loaded, the dolphin has deflected. It is observed that there is a level difference of the rigid 2.44 m thick pile cap by 20 cm. In addition the central line of the front vertical pile had a displacement of 68.7 cm in one direction and 35.6 cm in the direction perpendicular to it. It is also reported that there is a twist of about 3° in bottom the axis on pile cap. In pile No.1 (Vertical pile) just below the pile cap there is buckling of the steel casing of the pile. This failure appears to be due to excessive bending. The buckling is observed over a height of 15 mm and for a perimeter of 300 mm length. The maximum projection of buckling is 10 mm. It is very clear that there is a rotation/displacement of the pile group. The pile cap can be readily repaired and the original conditions can be reestablished. On the other hand, it is extremely difficult to assess the damages, if any, that might have occurred below the sea bed level. According to analysis, under a horizontal force the point of maximum bending are at the top of the pile. On the other hand, vertical piles are subjected to maximum bending and there is a damage to the vertical piles at the top. Furthermore, steel casings for the vertical piles have not been provided upto full length. 6.8.1.2

Provision of Additional Piles

It is proposed that 4 vertical piles are provided at the 4 corners of the Mooring Dolphin as shown in Figure . These vertical piles shall go to the same founding level as the earlier vertical piles. Further, it is necessary that these piles have the steel liner full up to the bottom as in the case of rakers. 6.8.1.3 Remedial Measures for Damage The deck slab has spalling and cracking dolphin. There is also a consequential tilt of the surface of the deck slab. Hence remedial measures suggested for the following 4 categories of damage are :

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Berthing Structures

1. Opening of the joint between the concrete pile and the deck slab: The workmen should thoroughly inspect the joint and the corresponding opening. Hence it is sufficient to pack the gap between the top of the pile and deck slab with Epoxy concrete mortar with the maximum size of the aggregate not exceeding 12 mm. The area around this pile junction where surface concrete has spalled off can be covered with Epoxy mortar from below the deck slab. 2. Treatment of corner pile exhibiting compression bulge: The damaged concrete can be removed and the pile shall be repacked with M 30 concrete. The casing can be covered again with a steel plate of same thickness as the original casing. 3. Spalling and cracking of concrete in the corners of the deck slab: The concrete exhibiting spalling and cracking should be completely chipped off removing all loosened debris and the reinforcement shall be exposed. The exposed surface should be cleaned of all loose dust etc. and the deck slab should be refinished with M 30 concrete. It is desirable to use a shrinkage compensating additive in the fresh concrete. 4. Levelling of the top surface of the tilted deck (if required/desired): The concrete surface is to be made very rough and the surface levelled again with a fresh concrete of M 30 quality. For good bonding with the old concrete unless steel bars of old cap are extended into the new concrete whose thickness at places are 150 to 200 mm, is necessary to provide a thick weld mesh or HYSD bar 2-way reinforcing mesh in this new concrete and weld this on to the old reinforcement cage at a number of places. 6.8.1.4

Load tests for Adequacy of Mooring Dolphin

It is recommended to carry out horizontal load tests on the dolphin by means of wire ropes, pulleys and a turn buckle. Further they will strain-gauge the turn-buckly for measuring the pull as an additional check. Measurements to be carried out on the Dolphin are : (a) Tilts/rotations of the Mooring Dolphin.

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Harbour & Coastal Engineering (Indian Scenario) : Vol. I

(b)

The displacements, in the horizontal plane of the Mooring Dolphin have to be monitored with the help of theodolite.

6.8.1.5 Estimation of Relative Stiffness of the Damaged Mooring Dolphin Natural frequencies of vibration of two identical mooring dolphins, one of them hit by a cargo ship, were determined in order to estimate the extent of damage in comparison with the other. 4 accelerometers were fixed on the top of the bollard at the centre of the dolphin. Accelerometers 1 and 3 were connected to an on line signal analyser and 2 and 4 to recorders. Though the level of vibration at the maximum sensitivity of the accelerometer was sufficient to record the resulting vibration patter, for greater accuracy the dolphins were set to free vibration with the help of a tug. The auto spectral analysis of the vibration signals were done by the signal analyser and the results were displayed on the screen. The frequencies corresponding to the peaks in the auto power spectrum for the two dolphins are presented in the following table. Table 6.9 Frequency in Auto Power Specturm Frequency in Hz Mooring Dolphin 1 2.24 2.64

Damaged Undamaged

X Trial 2 3 2.28 2.24 2.68 2.64

Ave 2.25 2.65

1 2.24 2.52

Y Trial 2 3 2.24 2.28 2.52 2.52

Ave 2.25 2.52

Measurements were taken 3 times on both the dolphins and the average is given in table. For a structure simplified as a single degree of freedom system the natural frequency is given by fn =

1 K/m 2π

(6.51)

where K is the stiffness and m is the mass. Or the frequency is directly proportional to the square root of stiffness.

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Berthing Structures

Since both the dolphins are identical in all respects, the mass can be taken to be same and therefore their stiffness will be in the ratio of 7.023

:

5.063

- in the X-direction and

6.35

:

5.063

- in the Y-direction

The dolphin struck by the vessel has a reduced stiffness of 72 percent in the X-direction and 80 percent in the Y direction compared to the undamaged one. 6.8.1.6 Summary and Conclusions Mooring dolphin (supported by 12 raker and 4 vertical piles) has been accidentally hit by a fully loaded ship of 60,000 DWT and consequently dolphin has tilted. To restore the mooring dolphin to its original capacity of 200 T horizontal force, the following measures are recommended. 1. Repairing damages at the pile cap and pile interface. 2. Provide 4 additional vertical piles and make them integral with the existing mooring dolphin by suitably extending the pile cap. 3. Carry out load tests by pulling the Mooring Dolphin against each other upto 200 T and monitoring the performance, as a final confirmation of the restoration to its rated capacity 6.8.2 Failure of Piles in a Bulk Berth Investigation on the possible causes of failure of pile of a bulk berth is disumed in the chapter. The causes of failure, its impact on the behaviour of the overall structure and remedial measures required are investigated. 6.8.2.1 Brief Description of Failure of Pile The following weather conditions occurred nearer to the pile on that day of failure. Wind

- Mainly westerly 18 to 22 knots

Weather

- Fair

Sea

- Moderate to rough

Swell height

- 1.8 to 2.2 metres

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Harbour & Coastal Engineering (Indian Scenario) : Vol. I

In Pile P1 and 11 steel liners have fallen and 9 liners are inclined. The pile P2 has also titled. The concrete pile P1 was broken at 40 cm below the bottom of steel liner with a shape of sphere. 3 number of main reinforcement bars out of 14 in total were observed snapped at broken concrete face and the balance 11 bars were slipped out of concrete (Figure 6.42 ). The detailed of studies were carried out on the following aspects. 1.

Estimation of wave and current forces

2.

Estimation of foundation capacity of piles

3.

Estimation of structural capacity of piles

4.

Measurement of frequency response on freshly concreted and set piles.

During the construction of the piles, initially the steel casing of pile and subsequently the piles themselves are free cantlevers (as they are not braced at top) subjected to wave and current forces. Fixity to the cantilever initially comes from the soil surrounding the casing pipe and later from the soil layers around the casing and the pile below. In the case of pile P1 and P2, the clay layer thickness is only about 3.5 m and 2.6 m respectively as against an average thickness of 4.5 m at other locations. As the casing stops at the top of the rock layer, the ultimate moment resistance of soil is about 15.5 T.m only. This moment can be caused by 0.84 T of lateral force at +3.0 m level. This force can be caused by a current of 3 knots. In reality, waves and currents can act in unison and therefore even under medium weather conditions the moment on the casing pipe will exceed the moment resistance of the soil. This is also confirmed by the reported failing or tilting of several steel liners. After the pile is concreted, with external moment greater than the resistance from soft clay, bending stresses will be transferred below the bottom of the casing i.e., to fresh concrete. This is particularly true in case of pile P1 and P2. The natural frequency of freshly concreted pile is only about 1/3 of well set piles and will be nearer to the wave frequency resulting in dynamic amplification of the forces. Under such circumstances even if the pile may not fail (the external moments within ultimate limit) the concrete will not gain its full strength, in particular bond between the reinforcement and concrete at bottom will be affected. The ultimate structural capacity of the pile based on the bond stress that can be mobilised after 1, 7, 14 and 28 days are 15.3, 34.8, 44.8 and 50.0 T.m respectively. This means that even during the process of concrete gaining strength, the same is continuously

520

Berthing Structures

being subjected to stresses due to waves and currents. These stresses could be well beyond permissible stresses resulting in partial bond failure. The partial bond failure has happened in case of piles P1 and P2, particularly in view of the bending stresses transferred below the bottom of the casing i.e. to fresh concrete due to inadequate ultimate soil capacity around the casing. In other words even after the 28 days of setting, they were substantially weaker as compared to a full strength pile. Therefore, somewhat higher waves than normal, combined with effects of wave reflection and currents, has resulted in failure. The weakened piles will also have higher period compared to an integral pile. In such a case, the dynamic amplification factor of wave forces will much higher, resulting in failure of the pile. 6.8.2.2 Simplification to Safety of Structure In the light of the above discussions it cannot be ruled out that other piles in the region during the process of concreting and subsequently have been weakened at the bottom.. This has the following simplifications: The piles will not have full fixity at the bottom and in the extreme case behave as a hinge. This will in turn affect the structural behaviour of berthing structure. (a)

Under horizontal forces.

(b)

Buckling behaviour of the pile under axial loads.

This means that for the design of berth under consideration, if the piles are assumed as hinged at bottom, there may not be much of a consequence. 6.8.2.3 Recommendations arising out of Study for Future Construction Whenever piles of this type are installed using this technique, the following is to be adopted (Sundaravadivelu et al. (1993)). 1. The steel liner for the pile should have sufficient embedment into the soil strata such that the soil surrounding the casing will offer adequate resistance. 2. The casing should be braced at top against a firm support (and not another casing pipe or a freshly concreted pile).

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Harbour & Coastal Engineering (Indian Scenario) : Vol. I

3. The braces must be above high water level to avoid current and wave forces on the braces, otherwise the whole system has to be designed for the wave current forces on the braces as well. 6.8.3

Force Measurements in Tie Rods

6.8.3.1 Brief Description of Berth The typical cross section of the berth is given in Figure 6.37. The structural arrangement of the system consists of 1100 mm thick main diaphragm wall connected by 80 mm dia anchor rods at approximately 1500 mm c/c. In addition, the 1100 mm thick diaphragm wall is connected to two 1000 mm dia vertical piles by a rigid deck consisting of 3850 mm deep cross beam. Considering the rigidity of the deck system and capacity of 1000 mm dia piles to resist lateral load and the flexibility of the 80 mm dia tie rod, most of the lateral load will be transferred to the 1000 mm dia vertical piles. In order to verify the above , it is recommend to measure load transferred to the tie rod after dredging is completed i.e. when the tie rod is meant to transfer the horizontal force due to active earth pressure on front diaphragm wall to the deadman diaphragm wall. The details of the tie rod force measurements are given in Sundaravadivelu et al. (1990) and a brief description of force measurement is given below.

522

Fig. 6.37 Typical Cross Section of a Berth

Berthing Structures

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Harbour & Coastal Engineering (Indian Scenario) : Vol. I

6.8.3.2

Installation and Measurement of Forces in Tie Rods

Load Cell: Three locations were selected for installation of strain gauge type load cells. The strain gauge type load cells were selected considering various factors like - Economy - Time available for installation - Ease of measurement technique to be adopted at site etc. Pretension of Tie Rod: As a part of the construction scheme a pretensioning of all the tie rods was done as follows. Two hydraulic jacks were used to give a pretension of about 3 to 3.5 T. The tightening nut introduced before pretensioning was then first hand tightened. Then a pipe wrench of length 1 m was used to tighten the nut further. After this a check nut was introduced and tightened. Installation of the Load Cells: The same procedure as adopted for pretensioning the tie rod was used here also after placing the load cell, between the outer face of Deadman diaphragm wall and the nut. Measurement of Pretension: The two cables of the load cell were connected to strain measuring unit DMD 29 (HBM, West Germany) and the reading corresponding to no load condition was measured. The readings after pretensioning the tie rod was also measured. The results obtained are tabulated below in Table 6.10. Table 6.10 Measured Strain before and after Pre-tensioning of Tie Rod Location A Reading corresponding to No load Reading after pretension Difference in reading

524

Strain (Units of DMD Display) Bridge 1 Bridge 2 1427 641 1764 1090 337 449

Berthing Structures

Corresponding Loads Average Load

8.408 T 9.452 T

10.496 T

Though only a 3.5 T pretension was given using a jack, the tightening of the nut with the help of a wrench introduced an additional load of about 6 Ton in the rod. The measured load was once again verified by releasing the load on the cell with the help of hydraulic jacks. It was found that the pressure gauge of the jack showed a load of 9.57.T The same procedure was adopted for installation of the remaining two load cells. But the pretension was not measured for these two tie rods. 6.8.3.3

Measurement of Tie Rod Forces after Dredging

Though it was originally considered to measure the load at different stages of dredging, because of some practical difficulties, only one reading was taken after dredging to the required depth of -11m. Initially, all the strain gauge bridges were checked for its functioning. It was found that of the 6 bridges for which cables were available outside, only one bridge of cell 1 installed at location 85 was not functioning as some water has gone inside the cable. Measurements were taken for the remaining 5 bridges and the bridge for which the cable was terminated on the outer cover of the cell was left undistributed because any attempt to open it would cause water entering the cell (During measurement there was atleast 2 feet of water above the cell and continuous pumping of water was required to do the measurements). Mechanical jacks were introduced to release the load from the cells and readings of the bridges were taken one after the other for loaded and unloaded conditions. 6.8.3.4 Summary of Results From the preliminary measurements, it has been found that a pretension of 9.5 t is given to anchor rods instead of what was thought to be around 3.5 t. This however, do not in any way affect the behaviour of the soil-structural system. In fact, a higher pretension is better to keep the anchor rod tact. Result of the final load measurement shows that after dredging to a level of -11m, load in the anchor rod has increased only marginally by about 3 to 3.5 tons in locations A and B. R. Sundaravadivelu

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Harbour & Coastal Engineering (Indian Scenario) : Vol. I

The load measured in location C shows a marginal reduction, taking for granted that the pretension here was also of the order of 9.5 T. This, however, cannot be ascertained because pretension at this location was not measured during installation. (It may be pointed out here that the pretension was only a factor of the strength of the people who applied the tension using the wrench). The small difference in measured load by the two different bridges of same load cell is due to the eccentricity in loading which is characteristic of load transfer through screws. Small eccentricities are unavoidable in field situations, in spite of provision of spherical seating in the load cells. 6.8.3.5 Conclusion 1) It has been possible to monitor the forces in the rod using load cells as adopted. All the cells performed well 6 months after installation in spite of severe environmental conditions like full submergence in sea water. 2) The total tie rod forces even after dredging to -11.0 m level are between 7 to 13 T, as against an estimated permissible value of about 65 T from structural consideration for tie rod. This includes pretension force upto 9 T. Without this pretension the tie rod forces would have been even less. 6.9

SELECTION OF TYPE OF BERTHING STRUCTURE

A Berthing structure is usually constructed to serve a definite use. The purpose of it is to handle passengers or general cargo or a combination of both or it may be required to handle a specific type of cargo, particularly bulk cargo such as oil, ore, cement, and grains or to handle containers. The type of berthing structure depends upon the purpose of the berth, size of ships that use the berthing structure, the direction of the wave, wind and subsurface soil conditions, in particular the depth of the bed rock or firm bearing material and the water depth. The selection of type of berthing structure also depends on the magnitude and nature of loading, hydraulic conditions such as wave action and currents. Fire hazard and safety requirements, damage susceptibility and ease of repairs, environmental and regularity concerns over water circulation and habitat loss always favour open type construction. Closed type construction generally offers greater horizontal and vertical load capacity and impact resistance than the open piled construction. The vertical face of a closed type of construction reflects wave energy, if the structure face is exposed to significant wave action. The possible scouring at the face of the closed type structure due to current action

526

Berthing Structures

influences the choice of the type. If all factors considered for selection of the type of berthing structure remain the same the long-term maintenance govern the type of berthing structure. When a berthing structure has to be constructed in shallow water or on existing land in connection with the dredging of a harbour basin, a vertical face type structure such as the diaphragm wall is very competitive. The presence of bedrock or hard strata below the design depth of water favours the vertical type. The vertical face type structures will be preferred when tension piles fail to penetrate to sufficient depth due to hard layers. When the existing water depth is close to the desired dredge depth then this type of structure is suitable. When dredging is expensive and when weak and soft sediments endanger the overall stability, then open type structures are adopted. As a general rule vertical face construction such as diaphragm wall is favoured where water depths are shallow to moderate. Anchored bulkheads require some minimum embedment depth and these bulkheads are practical and economical to wall heights upto about 10 m. At deep water locations with soft soils extending relatively deep below the mud line then pile foundations are provided. Even though open pile supported construction is used at shallow rock locations, the cost to anchor the piles to the bed rock and to provide adequate horizontal stability usually exceeds that of a suitable vertical face type structure. Relieving platforms, which are a combination of open type and fill type construction, may be used to provide uplift resistance thereby improving the lateral load resistance of the piles. A relieving platform also reduces the required bulk head wall height thus extending the water depth capability of the system. When the slope of the bottom is so steep that a jetty or a pier cannot be projected out from the shore without having the outshore end in water so deep, then foundations are either impractical or very expensive. In such conditions a wharf or quay is suitable and economical. For bulk cargo berth, open type constructions with approach trestle is preferable. Oil docks and some forms of bulk-handling cargo docks are of lighter construction than general cargo-handling docks, as they do not require warehouses, nor do they have to support rail, road tracks or extensive cargo-handling equipment. Since the main products handled over oil docks are usually unloaded at fixed points and transported by pipelines, R. Sundaravadivelu

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Harbour & Coastal Engineering (Indian Scenario) : Vol. I

the required area of solid deck is very much reduced, as are width and length of the dock, if supplemented by dolphins to take the bow and stern mooring lines. For this reason, a full-length pier or wharf is not economical or essential, and the use of larger and deeper draft tankers has resulted in the adoption of the fixed mooring berth. This type of construction is economical because the large mooring forces imposed on the dock by the large ships shall be concentrated at single points. The pull of the mooring lines can be taken by dolphins off the bow and stern of the vessel and by breasting dolphins on both sides of the fixed platform. The breasting dolphins also keep the ship away from the platform and take the impact of the ship while docking. In some locations, it is impossible or uneconomical to provide a pier, wharf or fixed mooring depth owing to site conditions or the deep draft of some of the recently constructed supertankers and ore carriers. In such cases an offshore mooring may be provided and the cargo transferred to the shore either by lighters, long conveyors, ropeways or by submarine pipeline, if the product is a liquid such as oil, gasoline and molasses. Direction of waves and wind may have a bearing on the type of dock selected. In general, the dock should not be broadside to the prevailing wave front. If the terminal is in exposed location, and the wave front is parallel to the shore, a wharf type of dock may have to be ruled out. Also, all things being equal, it is better to have the ship anchored parallel to the direction of prevailing winds or if this cannot be accomplished, the ship shall be anchored in such a way that the wind is holding the ship off the dock. Soil conditions will have an important bearing on the type of dock selected. The bottom may be more favourable in the region close to the shore, thereby favouring a wharf or bulkhead installation. However, rock may be encountered which would make it very costly to obtain the required depth of water along the dock. In such a case, a pier with an approach trestle or mole may be the solution to eliminate the need for costly excavation. 6.10

DESIGN OF DIAPHRAGM WALL

6.10.1 General Remarks The definition of various structures such as dock, wharf, quay, jetty, etc. are given below: A dock is the most general designation for a structure or place at which a vessel can be moored. A wharf is a dock structure built nearly parallel to the coast and continuous with the shoreline, so that it also performs as a soil retaining structure. It is also called quay when it is of solid fill vertical wall construction and is long and continuous. Wharves and

528

Berthing Structures

quays are backed by warehouses, marshalling and storage areas, industrial areas, roads, rails, etc., which are often created by extensive fill operations. A pier or jetty is a dock structure, which projects out into the sea. Because of its geometry, it can be used for berthing of vessels on three sides. It does not necessarily run perpendicular to the shore line or wharf line but may project under any angle. It may also be connected to the shore or wharf line by a trestle and thus become T or L shaped jetty or pier. Moles or trestles are primarily pier or platform access structures, used for vehicular, pipeline, conveyor and sidewalk. Moles are of solid fill construction and trestles are of free standing pile bents or pile groups with bridging structure spanning them. Dolphins are isolated structures used mainly to absorb the impact of berthing ships referred to as breasting or berthing dolphins and to serve as a point for securing a vessel’s mooring lines, referred to as mooring dolphins. A fixed mooring berth is a marine structure consisting of dolphins for tying up the vessel and a platform for supporting the cargo handling equipment. A sheet pile wall comprises of a row of piles interlocking with one another so as to form a continuous wall to be used as earth retaining structure. Diaphragm wall is a vertical wall structure classified as a cantilever or tie back system. The tie back system can be a tie rod with a deadman or a combination of vertical and raker piles or only vertical piles. A relieving platform consists of a low level pile supported deck that is filled over in order to gain stability and relieve pressures behind the wall in weak soil conditions. Gravity wall consists of cut stone blocks or concrete blocks placed on top of each other and capped with a massive concrete wall or a concrete caisson monolith. Gravity walls gain stability against sliding and overturning by means of its weight, proportions and soil friction. 6.10.2 Example A cantilever type diaphragm wall of 5.0 m panel length is proposed for the fishing jetty. The reduced level of the ground varies between +1.60 m and 2.40 m. The cut-off level of the diaphragm wall is +1.0 m and the top level of the deck is +2.25 m.

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The diaphragm wall is proposed for the quay wall at +2.25 m and founding level is assumed at -8.0 m. Dredge level is -2.20 m. The total height of wall is 10.25 m. The passive pressure and active pressure acting on the wall is calculated based on the soil properties from the boreholes. Above the dredge level(i.e. above -2.20 m) the properties of the soil considered are N = 10, φ = 300, δ = 200 and ka = 0.297. Below the dredge level, the properties considered are N = 20, φ = 330 , δ = 220, ka = 0.264 and kp = 8.08. The surcharge of 10 kN/m2 is also assumed on the landside of the wall. The quay wall is analysed as a two-dimensional structure using SAP90 (Structural Analysis Programme 90). The discretization showing node numbers and element numbers of diaphragm wall is shown in Figure (6.38) For analysis, 1 m width of diaphragm wall is considered. The load acting at each node is shown in Figure (6.39). Below the dredge level, sea side springs are provided at each node and the values are shown in Figure (6.40) The first iteration indicates that the force coming on the springs at the node numbers 10, 11&12 is more than the passive resistance. Hence these springs are replaced with actual passive resistance at that location and the second iterative analysis is carried out. The iteration is continued till the forces on each spring is less than the passive resistance. The bending moment diagram and shear force diagram are shown in Figure 6.41(a) and Figure 6.41(b) respectively. The reinforcement details of diaphragm wall is shown in Figure 6.42. 6.10.3 Design of Quay Wall Limit state method is used for the design of quay wall. Grade of concrete : M30 Steel reinforcement

: Fe415

Thickness of quay wall

: 500 mm

Clear cover provided

: 75 mm

Section AA (From -2.5 m to -5.5 m) Maximum Bending moment

: 432.42 kN/m

Load factor as per IS 4651 for earth pressure : 1.0 Effective depth

: 500 - (75+ 28/2) using Y - 28 bars : 411 mm

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Berthing Structures

Fig.6.38 Discretisation Showing Node Numbers And Element Numbers

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Fig. 6.39 Load Acting At Each Node

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Berthing Structures

kN/m

Fig.6.40 Loads on Land Side and Springs on Sea Side R. Sundaravadivelu

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534

Fig. 6.41 (b) Shear Force Diagram

Fig. 6.41 (a) Bending Moment Diagram

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Berthing Structures

Fig.6.42 Reinforcement Details of Diaphragm Wall R. Sundaravadivelu

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Harbour & Coastal Engineering (Indian Scenario) : Vol. I

Mu bd 2

=

432.42X106 1000X 4112

(Considering one metre width)

From SP 16,

= 2.55

Pt

= 0.794

Ast

= 0.794 x 5000 x 411 (for 5 wide panel) = 16317 mm2

Provide 21 nos Y - 28 + 21 nos Y - 20 on earth side for 5 m wide panel π π x 282) + (21 x x 202) 4 4

Ast provided

= (21 x

Ast min

= 19,509 mm2 (0.78%) = 0.2/100 x 5000 x 411 = 4110 mm2

Provide 21 nos Y-16 on the seaside Ast provided

= 4221 mm2

Section BB (From + 2.25 m to -2.5 m and from -5.5 m to -8.0 m) Maximum bending moment Mu bd 2

From SP 16,

= 267.32 kN/m =

267.32x106 1000x 4112

(for one metre)

= 1.58

Pt

= 0.475

Ast

= 0.475 x 5000 x 411 (for 5 m wide panel) = 9761 mm2

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Berthing Structures

However provide 21 nos Y-28 (12931 mm2 ) on T-16 on seaside for 5 m wide panel Design for shear reinforcement: Maximum shear force

= 187.82 kN

Nominal shear stress, τ γ

=

187.82x1000 1000x 411

= 0.46 N/mm2 Permissible shear stress τ c

= 0.59 N/mm2 (for 0.78%steel)

τγ < τc Therefore provide nominal reinforcement only Provide 6 legged Y - 10 stirrups at 150 mm c/c as nominal shear reinforcement and Y - 10 stirrups at 300 c/c (Fig. 6.49)

Asv bxS v

6.11

π x102 4 = 1000x150 6x

0.4 fy

= 9.6 x 10 −4

Asv 0 .4 > bxS v fy

Hence O.K.

DESIGN OF DOLPHIN

6.11.1 Layout of Berthing Dolphin A typical plan and cross section of berthing dolphin are given in Fig.6.50. The dolphin consists of a deck slab of size 12 m x 21 m and 1500mm thick and supported over 15 numbers of vertical concrete piles each of 1500 mm diameter. Piles are braced at +2.0 m . The beam is of size 1500 x 1500 mm in longitudinal as well as transverse direction. A fender beam is provided from bottom of the deck to +0.5 m level. The thickness of the R. Sundaravadivelu

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Harbour & Coastal Engineering (Indian Scenario) : Vol. I

beam at deck level is 1000 mm and is reduced to 500 mm at +0.5 m level. The dredge level of dolphin is kept at -16.50 m and piles have been taken upto -30 m below the seabed. 6.11.2 Loads The loads and load combinations considered in the design of berthing dolphin are as follows: 6.11.2.1 Dead Load (DL) Self-weight of the structure plus superimposed loads of a permanent nature. 6.11.2.2 Live Load (LL) Dolphins are designed for a UDL of 10 kN/m2 6.11.2.3 Force on Berth (BF) The berthing force of 2785 kN per fender is considered for the 45000 DWT vessel with SVC 2000 H (RS) type fender. 6.11.2.4 Mooring Force (MF) The bollard pull of 1000 kN per bollard is considered and is applied at above deck level. Bollard forces are considered to act in any direction with in 1800 around the bollard in the horizontal plane. 6.11.2.5 Wave Force (WF) Wave load due to 1.8 m wave height is considered on piles with marine growth of 50 mm on the radius of piles. 6.11.2.6 Current Force (CF) Current load due to a maximum current of 0.5 m/sec is considered. 6.11.2.7 Seismic Force (SF) The horizontal earthquake force shall be calculated for Dead Load + 50% of live load. The importance factor of 1.5 are considered. 538

Berthing Structures

6.11.2.8 Load Combinations The following load combination is considered in the analysis. 1. DL + LL +BF + WF + CF 2. DL + LL +MF + WF + CF 3. 1.5DL + 1.5LL +1.5BF + 1.0WF + 1.0CF 4. 1.5DL + 1.5LL +1.5MF + 1.0WF + 1.0CF 5. 1.2DL + 1.2LL +WF + CF + 1.5 SF 6. 0.9DL + 0.9LL +WF + CF + 1.5 SF 6.11.3 Analysis Analysis is carried out using SAP 90 by idealizing dolphin deck using shell element and piles by beam elements. 6.11.4 Design The deck slab is designed as flat slab. The design of piles have been carried out using limit state method. M30 grade concrete and Fe415 grade of steel are considered in the analysis and design. The design is also checked against limit state of serviceability. The clear cover considered in the design are as following: Piles

: 75 mm

Beams

: 50 mm

Deck Slab

: 40 mm

6.12

DESIGN OF PILES

Grade of concrete to be used

: M30

Grade of steel

: Fe415

Diameter of pile D

: 1500 mm

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Harbour & Coastal Engineering (Indian Scenario) : Vol. I

Unsupported length of pile

: 28.25 m

Effective length

: 1.2 x 28.25 l eff

: 33.90 m

l eff /D

: 33.90/1.5 : 33.90>1.5

Therefore design as a slender member Eccentricity e min

=

1 D + 500 30

=

28.25x1000 1500 + 30 500

= 106.50 mm From SP 16 (Table 1), For l eff /D

= 33.9.6 e/D = 0.26

Therefore

e = 0.26 x 1500 mm = 390 mm

Maximum factored moment

= 7510.76 kN/m(Member 60)

Corresponding factored axial force P u , = 1644.91 kN (Compression) Moment due to eccentricity

= 1644.91 x 0.39 = 641.52 kNm

Total moment, M u ,

= 8152.27 kNm

Providing a clear cover of 75 mm,

540

d' D

= 0.05

Berthing Structures 1644.91x103 Pu = 2 fck D 30 x15002

= 0.024 8152x106 Mu = 30 x15003 fck D3

From chart 55 of SP 16 P/f ck

=

0.08

P

= =

0.08 x 30 2.4

A st

=

2.4 π 2 x x 1500 100 4

=

43,430 mm2 (2.5%)

provide = Ties:

54 432 mm2

Provide Y - 10 rings at 250 mm c/c

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REFERENCES

Agerschou, H., Lundgren, H., Sorensen, T., Ernst, T., Korsgaard, J., Schmidt, L.R. and Chi, W.K., (1983). “Planning and Design of Ports and Marine Terminals”, A WileyInterscience Publication, 220-225. Bathe, K.J., Wilson, E.L and Peterson, F.E. (1978). “SAPIV: A structural analysis Program for static and dynamic response of 4651 linear system”, Report EERC 73-11Univ. of California, Ber Kely. Berteaux, H.O., (1976). “Buoy Engineering”, John Wiley & Sons, New York. Bruun, P., (1981). “Port Engineering”, Gulf publishing company book division, Hudson, Texas. Faltinsen, O.M., Kjaerland, O Liapis N and Walderhaug H. (1979). “Hydrodynamic Analysis of Tankers at Single Point Mooring Systems”, Proceedings of Second International Conference on Behaviour of Offshore Structures, London, PP.177-206. Gaythwaite, John. (1990). “Design of Marine Facilities for Berthing”, mooring and repair of vessels, Van Nostrand Reinhold, New York. IS 2911 Part IV (1979). “Indian Standard Code of Practice” for design and construction of pile foundation. IS 456 (1978). “Indian Standard Code of Practice” for Plain and Reinforced concrete. IS 875-1984. “Indian Standard Code of Practice for structural safety of Buildings”, Wind Load Constructions, BIS, New Delhi. IS-4651 Indian standard Code of practice for planning and design of ports and harbour, Bureau of Indian Standards, New Delhi. Part 3 (1974) - Loading Part 4 (1989) - General Design considerations Part 5 (1980) - Layout and Functional requirements Langeveld, J.M. (1974). “Design criteria for single point mooring systems”, Journal of Waterways, Manohar, S.N., (1964). “Charts for the Design of Eccentrically Loaded Circular Columns”, Indian Concrete Journal. Maari, R., (1985). “Single Point Moorings”, SBM Inc. Publications, Monaco.

542

Berthing Structures

Nakajima, T., Motora, S and Fujino M. (1982). “On the Dynamic Analysis of Multimooring Lines”, Proceedings kof Fourteenth Annual Offshore Technology Conference, OTC 2212, Texas, pp.679-702. Per brun (1983). “Port Engineering” Gulf Publishing Co. PIANC (1991). “Movements of Moored Ships” and berthing Pianc working groups 24. Pinkster, J.A and Remery, G.F.M. (1975). “Role of Model Tests in The Design of Single Point Mooring Terminals”, Proceedings of Seventh Annual Offshore Technology Conference, OTC 2212, Texas, pp.679-702. Quinn, A.D. (1961). “Design & Construction of Ports and Marine Structures” McGraw Hill Book Co., Raju, V.S., and Sundaravadivelu, R and Gandhi S.R., "Analysis of alternative systems for a berthing structure", First National Conference in Docks and Harbour Engineering, IIT, Bombay, Vol. I, December 1985, pp B195- B206. Ranga Rao, A.V and Sundaravadivelu, R. (1992). "Non-linear Soil Structure Interaction of berthing Structures", National Seminar on Offshore Structures, Docks and Harbours, Roorkee, October 16-17. Ranga Rao, A.V and Sundaravadivelu, R. (1994 A). "Effect of Configuration of piles in Dolphin", National Seminar on Design of Pile Group and Pile Cap, Indian Geotechnical Society, Madras. Ranga Rao, A.V and Sundaravadivelu, R. (1994 A). "Computer Aided Design of Berthing Structures", INCHOE - 94, Pune, Vol I, pp B87-B96. SP: 16 (S&T) (1980). “Design Aids To Reinforced Concrete” IS: 456-1978. Srinivasan, R and Rangwala, R.S.C. (1991). “Harbour, Dock” and Tunnel Engineering. Sundaravadivelu, R., Idichandy, V.G., Gandhi, S.R. and Raju, V.S. (1990). "Tie rod force measurements in a Cargo Berth", Journal of Waterways, Port, Coastal and Ocean Engineering, ASCE, Vol.116, No.1, pp 43-56. Sundaravadivelu, R., Raju, V.S. and Idichandy, V.G. (1993). "Failure of Offshore Concrete Piles During Construction", Third International Conference On Case Histories in Geotechnical Engineering, St. Louis, Missouri. Sundaravadivelu, R., and Ranga Rao, A.V. (1996). "Expert System for Estimation of Forces on Berthing Structures", International Conference in Ocean Engineering, ICOE'96, pp 393-397.

R. Sundaravadivelu

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Harbour & Coastal Engineering (Indian Scenario) : Vol. I

Sundaravadivelu, R., and Natarajan, R. (1996). "Model Studies on Moorings of A LPG Tanker Berthed At An Offshore Jetty", The fourth Pacific/Asia Offshore Mechanics Symposium., Korea, Oct. 31- Nov.2. Sundaravadivelu, R, and Natarajan, R, (1996). "Experimental Investigation on Open Sea Berthign of a LPG Tanker", First Asia - Pacific Conference on Offshore Systems: Mobile and Floating Structures, Malaysia, 10-11. Supplement to Bulletin N 45 (1984). “Report of the International Commission for Improving The Design Of Fender Systems”, Permanent International Association of Navigation Congresses. Webster, R.L. (1980). “On The Static Analysis of Structures with Strong Geometric Nonlinearity”, Computers and Structures, Vol. 11, pp.137-145. Wichers, J.E.W. (1979). “Slowly Oscillating Mooring Forces in Single Point Mooring Systems”, Proceedings of Second International Conference on Behaviour of Offshore Structures, London, pp.661-692. Woodruff, G.B. (1963). “Berthing & Mooring force”, Tr. ASCE, Vol. 128, Part IV.

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Berthing Structures

NOTATIONS a’

-

acr Ast Ast Asv Aw Ax1 Ay b bt B C C1 C2 D

-

Cb Cc Cc CcXc CcXsc Cd CD,CM CDx, C Dy Ce Cg Cm Cmin CS Cs Cs Cw Cw Cym d dc D

-

R. Sundaravadivelu

The Distance from the Compression Face to the Point of the Crack Distance from the Point Considered to the Surface of the Nearest Area of Tensile Steel The Area of Tension Steel Total Cross Sectional Area of Stirrup Legs Windage Area (m2) End on Projected area of Vessel Side Projected Areas of Vessel Breadth of the Section The Width of the Section at the Centroid of the Tension Steel Beam of the Vessel in (m) Effective Cover Coefficient for the Area of Stress Block Distance of the Centroid of the Concrete Stress Block, Measured from the Highly Compressed Edge Shear Strength of the Rock at Pile Base Compression in Concrete Segment Berthing Configuration Coefficient Moment of Compression in Concrete Moment of Compression of Steel About the Center Line Deformation Co-efficient Drag, Intertia Coefficient (Figures 6.19 to 6.21) Drag Coefficients Along x, y Directions Eccentricity Coefficient Geometric Coefficient Mass Coefficient Minimum Cover to the Longitudinal Bar Softness Coefficient Average Shear Strength of Rock Along Rock Socker Compression in Steel Reinforcement Shape Factor = 1.3 to 1.6 Crack Width Yaw Moment Coefficient Water Depth (m) Effective Cover Diameter of Pile (m) 1

Harbour & Coastal Engineering (Indian Scenario) : Vol. I

D DL DM E Ec fa fcbc fcc fci fn fs fsi

-

fst fy F F FDM

-

FIM

-

FM Fn Fwx Fwy g h H imin I K KDM KIM L Lν l

-

lef leff LOA

-

546

Overall Depth of the Member Average Light Draft (m) Moulded Depth (m) Berthing Energy in (T- m) Modulus of Elasticity of Concrete Allowable Frictional Resistance Calculated Bending Compressive Stress in Concrete Calculated Direct Compressive Stress in Concrete Stress in Concrete at the Level of ith row of Reinforcement Natural Frequency Service Stress in Tension Reinforcement Which may be Taken as Stress in the ith Row Of Reinforcement, Compression Being Positive and Tension being Negative Stress in Steel Characteristic Strength of the Stirrup Force Due to Wind (kg) Factor of Safety Taken as 3.0 Total Drag Force on A Vertical Pile From the Sea Bottom to the Surface Crest Elevation (N) Total Inertial Force on a Vertical Pile from the Seabed to the Free Surface Elevation (N) Maximum Value of the Combined Drag and Inertial Force, (N) Horizontal Series Force Longitudinal Wind Force Lateral Wind Force Acceleration Due To Gravity in (m/sec2) Depth of the Section Wave Height (m) Least Radius of Gyration A factor Depending Upon the Importance of the Structure Stiffness Drag Force Factor Inertial Force Factor Length of the Vessel in (m) Length Between Perpendicular (m) Distance from the Centre of Gravity of the Vessel of the Point of Contact Projected Along the Water Line of the Berth In (M) Effective Length of Column (pile) Effective Length Overall Length of Vessel

Berthing Structures

m m m MDM

-

MIM

-

MM Myw n Nc P Pi qa r

-

sv SD SDM SIM TXst T u v w x yi V V V Vs W WD Wm α αm,φm αn αo β

-

R. Sundaravadivelu

Virtual (mass + added mass) Mass of Vessel Modular Ratio Mass Moment on Pile About Bottom Associated with Maximum Drag Force, (N, m) Moment on Pile About Bottom Associated with Maximum Inertial Force (N, m) Maximum Total Moment (N, m) Yawing Moment Number of Rows of Reinforcement Bearing Capacity Factor Taken As 9.0 Wind Pressure (kg/m2) (Asi/bD) where Asi is the Area of Reinforcement in the ith row Allowable End Bearing Pressure Radius of Gyration of Rotational Radius on the Plane of the Vessel (m) Reinforcement Spacing of the Stirrups Along The Length of the Member Effective Lever Arm for FDM from the Bottom of Pile, (m) Drag Force Moment Arm Inertio Force Moment Arm Moment of Tension Insteel About The Center Line. Tension is Steel Reinforcement Translatory Velocity of Ship Berthing Velocity (m/s) Unit Weight of Sea Water Depth of Neutral Axis Distance From The Centroid of the Section to the ith row of the Berthing Velocity in m/sec Shear Force Due to Design Loads Velocity of Vessel (m/s), Normal to the Berth Strength of Shear Reinforcement Unit Weight of Water (1.03 tonnes/m2 for sea water) Displacement Tonnage of the Vessel (in tones). Weight of Mass Under Consideration. Shaft Adhesion Factor Taken as 0.3. Coefficient Read from the Figures 6.10 to 6.17 Design Horizontal Seismic coefficient Basic Horizontal Seismic Coefficient Based on the Zone A Coefficient Depending Upon the Soil-Foundation System 1

Harbour & Coastal Engineering (Indian Scenario) : Vol. I

θ ρ φ ω ε1

-

τc σcbc σcc εm τr σs

-

548

Wind Direction or Angle of Attack Mass Density of Sea Water = (w/g) = 1025.2 kg/m3 Diameter of the Reinforcing Bar Angular Velocity of Ship The Strain at the Level Considered Ignoring the Concrete in the Tension Zone Design Shear Strength of the Concrete Permissible Bending Compressive Stress in Concrete Permissible Axial Compressible Stress in Concrete Average Strain at the Level Considered Nominal Sheer Stress Stress in Tensile Steel

Berthing Structures APPENDIX 6.1

SIZES OF PASSENGER SHIPS, FREIGHTER, TANKERS, ORE CARRIERS AND FISHING AND FISHING VESSELS A.6.1.1 BULK CARRIERS Dead Weight Tonnage (Tons) 4000 6000 8000 10000 12000 15000 20000 25000 30000 40000 50000 60000 80000 100000

Overall Length (m) 100.0 118.0 130.0 140.0 150.0 163.0 180.0 194.0 205.0 223.0 235.0 245.0 259.0 268.0

Width (m)

Height (m)

15.4 16.6 17.6 18.5 19.4 20.7 22.8 24.7 26.5 29.7 32.5 35.0 39.2 42.5

7.0 8.3 9.5 10.5 11.2 12.0 13.0 13.8 14.3 15.4 16.2 17.1 18.8 20.4

Fully Laden Draught (m) 6.3 6.9 7.4 7.9 8.5 9.0 9.7 10.3 10.7 11.1 11.3 12.0 12.6 13.0

A.6.1.2 COMBINATION BULK/ORE CARRIERS (100,000 DWT NOMINAL) Dead Weight Tonnage (Tons) 119190 112900 113180 102824 118000 104330 111120 98720 113180

Overall Length (m) 270 261 261 259 261 259.7 261 255 261

R. Sundaravadivelu

Breadth (Moulded)

Depth (Moulded)

Draught (Loaded)

42.00 40.20 40.60 41.30 42.00 38.00 40.60 40.20 40.60

21.20 21.40 24.00 20.40 22.80 21.30 23.00 23.90 23.00

15.60 15.50 16.00 14.20 16.13 15.52 16.00 14.63 16.00

Draught (Ballast) m (max) 8.4 10.62 (Max) 10.69 ” 8.29 ” 9.0 ” 9.37 ” 9.36 ” 9.00 ” 9.74 ” 1

Harbour & Coastal Engineering (Indian Scenario) : Vol. I

A.6.1.3 CLASSIFICATION OF CONTAINER VESSEL

Container Vessel 1st generation 2nd generation 3rd generation 4th generation Panamax-plus Conbulk

TEU DWT (ave) capacity 750 - 1100 14,000 1500 - 1800 30,000 2400 - 3000 45,000 4000 - 4500 57,000 4300 - 4600 54,000 mostly Panamax-size bulk carriers

L m 180 - 200 225 - 240 270 - 300 290 - 310 270 -300

D m

B m

9.0 11.5 12.5 11.5-12.5 11 - 12

27.0 30.0 32.0 32.3 38 - 40

A.6.1.4 TANKER DIMENSIONS Ship size (1,000 DWT) 20 50 70 100 150 200 250 300 550

550

Draft (m)

Beam (m)

Length (m)

9 12 13 15 16,5 19 21 23 28,5

22 31 35 41 46 50 52 55 63

180 235 260 270 300 330 340 350 415

Berthing Structures

A.6.1.5 DISTRIBUTION OF WORLD FLEET OF TANKERS Ship size (1000 DWT) 30 to 80 80 to 130 130 to 180 180 to 230 230 to 280 280 to 330 330 to 380 380 to 430 430 to 480 480 to 530 530 to 565

Number of ships 347 357 274 49 294 66 25 21 5 4 2

A.6.1.6 MOORING EQUIPMENT FOR DIFFERENT SHIP SIZES Ship size (DWT) 25,000 75,000 140,000 250,000 550,000

R. Sundaravadivelu

Mooring equipment 14 polypropylene dia 60 mm 20 polypropylene dia 72 mm 20 polypropylene dia 80 mm 24 polypropylene dia 88 mm 20 steel dia 42 mm + 2 polypropylene dia 80 mm

1

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