FOREWORD Road Engineering Association of Malaysia (REAM), through the cooperation and support of various road authorities and engineering institutioni in Muluys'ia, publishes a series of official documenrs on sTANDARDS, spgcm,tcATloNs, GUIDELINES, MANUAL and TECHNICAL NOTES which are related to road engineering. The aim of such pubiication is to achieve quality and consistency in road and highway construction, operation and maintenance. The cooperating bodies are:-
Public Works Deparrment Malaysia (pWD) Malaysian Highway Authority (MHA) Department of Irrigation & Drainage (DID) The Institution of Engineers Malaysia (IEM) The Institution of Highways & Transportation (IHT Malaysian Branch) The production of such documents is carried through several stages. At the Forum on Technology and Road Management organizeo uy rwuREAM in Novemb er 1997, Technical Committee 6 - Drainage was formed with the intention to review Arahan
Teknik (Jalan) 15/97
- INTERMEDIATE GUIDE To DMINAGE DESIGN oF ROADS' Members of the committee were drawn from various goue**"nt departments and agencies, and from the private sector including privitized road operators, engineering consultants and drainage products minufacturers and
contactors.
Technical Committee
6 was divided into three sub-committees to review Arahan Teknik (Jalan) l5l9l and subsequentry produced 'GUIDELINES FoR ROAD
DRAINAGE DESIGN' consisting of the folrowing vorumes: Volume 1 Volume 2 Volume 3 Volume 4 Volume 5 -
Hydrological Analysis Hydraulic Design of Culverts Hydraulic Considerations in Bridge Design Surface Drainase Subsoil Drainale
The drafts of all documents were presented at workshops during the Fourth and Fifth Malaysian Road Conferences held in 2000 and,2002 respectively. rfr" comments and suggestions received from the workshop participant, *"r" reviewed and incorporated in the finalized documents.
ROAD ENGINEERING ASSOCIATION OF MALAYSIA 46-A, Jalan Bola Tampar r3/r4, Section 13, 40100 Shah Alam, Selangor, Malaysia Tel: 603-5513 Fax: 5513 e-mail:
[email protected]
652r
6523
i i I
TABLE OF CONTENTS Page
3.' INTRODUCTION 3.2 PRELIMINARY INVESTIGATION 3.2.7 Site Selection ... 3.2.2 Reconnaissance Survey ..... 3.2.3 Data Collection . 3.3 3.4
SURVEY
3.3.1 3.3.2
DATA
Survey of Bridge Site and Hydraulic
Survey
Beyond
...3-7
........3-i "....3-1
......3-z ......3-3
...,..3-4 ......3-4 .....3-6
ESTIMATION OF DESIGN DISCHARGE AND WATER PROFII,E ...3-5 ........3-6 3.4.I Design Recurrence Interval
3.4.2 3.4.3
DesignDischarge Water Profile
3.s
BRTDGE WATERWAY
3.6
SCOUR AT BRIDGE CROSSING
3.6.1 3.6.2
.
...,.3-"1
...3-8
.
.........3-9
Scour Countermeasures
.
....3-9
.....3-9 .....3-11
PIERS
3.7
FORCES ON BRIDGE
3.8
DESIGN OF BRIDGE TO ALLOW FOR FUTURE RIVER IMPROVEMENT WORK
...3.1]
,....3-17
LIST OF FIGURES
3.1 3.2
Figure Figure Figure 3.3A Figure 3.38 Figure 3.3C Figure 3.3D Figure 3.3E Figure
3.4
.. . Riprap
Extent of Survey for Bridge Site ......3-5 .....3-10 Scour at a Bridge Site . ....3-I2 Typical Wire Enclosed Typical Interlocking Concrete Block and Cable Tied Block System ..3-73 .......3-I4 Typical Articulated Grout Filled Mat . "..3-15 Typical Cement/Grout Filled Bags at ....,.....3-16 Typical Cement/Grout Filled Bags at Pier ........3-19 Freeboard and Embedding Depth for
Design Abutment .. Footing
LIST OF TABLES Table
3'1
Recommended Average Recurrence Interval for Design Discharge...3-7
LIST OF REFERENCES APPENDIX
...,.....3-20
1
Reprint of Appendix D - Hydrauiic Design of Bridges, Urban Drainage Design Standards And Procedures For Peninsular Malaysia No. I (1g75).
VOI-UME 3 - HYDR.AULIC CONSIDER.ATIONS 3.1"
NN
BR.IDGE DESIGN
INTR.ODUCTION The design of a bridge over a waterway requires a comprehensive engineering approach that not only includes route location, traffic flow forecast and structural and foundation requirements, but also the assessment of the characteristics of the
river flowing beneath. For this, it is necessary to collect data, and to understand the factors that govern stream runoff and water surface levels, sediment discharge and deposition, scour and channel stability and hydrodynamic forces acting on the
bridge" Predictions about likely event under particular site conditions have to be made.
This volume does not describe in detail ali the factors that require to be considered in bridge designs, but merely identifies the hydraulic aspects that characterise a river and provides directions to relevant literature, which give indepth details on these aspects. For hydraulic design of bridges, the designer could
refer to Appendix 1 which is extracted from Jabatan Pengairan dan Saliran publication - Planning and Design Procedure No. 1: Urban Drainage Design Standards and Procedures for Peninsular Malaysia (1915). The designer is encouraged to refer to the other relevant literature listed in the References.
3.2.
PRELIMINARY INVESTIGATION
3.2. r
Site Selection
Ideally the cost of alternative river crossing locations should be considered when making the preliminary selection of a route. However, in built-up areas the site
for a bridge and the approach roads are usually fixed and dictated by the town layout plan.
In rural areas, the bridge crossing is restricted to certain reaches of the river owing
to
by
existing landuse, road alignment and the river meanders. The selection of sites has to be made within these reaches and should avoid costly river works and land acquisitions. constraints imposed
3-r
F
s F F
!.
Bridge site selection normally commences with a desk-top study of available topographic maps which detail the geomorphologic features of the surrounding land, landuse, river pattern, meanders, sand deposits and sometimes, bank levels. on these topographic maps several potential bridge sites may be identified. The choice of a crossing site will be governed primarily by the main channel width and the proportion of overbank flow to total flow. Logically, the first consideration should be given to those sites that have the narrowest main channeis and the smallest proportion of flood plain flow.
On wide flood plains where rivers tend to meander, first consideration should be given to crossing sites where the channel could be controlled with minimal river training works. Occasionally rock outcrop or inerodible bank material may be located to reduce the requirement of river trainins works.
Other possible sites are at crossover modal points in the river meander pattern where the channel is wider and shallower and at bends where the channel is normally narrower and deeper particularly at the outside of the bend. The optimum location should be decided by considering the channel geometry, bank stability, river training work and type of bridge construction.
The desktop study should also include a literature search and examination of records or reports on river improvement works completed or yet to be impiemented by Jabatan Saliran dan Pengairan (JPS) and other sovernment
agencies.
3.2.2
Reconnaissance Survey
Bridge sites desktop study will include reconnaissance survey with the objective to gain a general appreciation of the river behaviour by examining available records and by carrying out field inspections. Information on the following should be collected: (a)
river channel regime to determine whether the river has a wide flood plain. or whether it is incised with little or no flood piain.
(b)
river channel stability to determine whether the river
(c)
river channel flow pattern, if it is sinuous, determine whether the channel migration is active, J-L
is
stable or unstable.
.
(d)
range of water levels, particularly high-water levels and their frequency
of
occurrence, historical flood events could be indicated by riverine users or
local inhabitants.
(e)
range of discharges, particularly for floods and their frequency,
(f)
width of waterway, width of flood p1ain, meander length and width,
(g)
type and grading of river bed materials,
(h)
type of material composing the river banks,
(i)
iocation of any naturai outcrops of inerodibie rock which may restrict channel movement. and
C)
extent of any regional floods in the locality.
Some of the above information may be obtained from topographic maps, aerial photographs, JPS hydrological records, previous river basin or drainage study reports and existing and proposed future river improvement works. The preliminary study of the bridge sites should include an estimation of the river
flood flows by current acceptable hydroiogical procedures,
if
stream flow records
at the selected sites are not available.
3.2.3
Data Collection Other information could be obtained by field inspection such as:
(a) (b) (c) (d) (e) (f) (g) (h)
type and grading of river bed material, existence of shoals and their composition, the material forming the river bank, vegetation on the bank, steepness ofbanks and evidence
ofbank erosion,
erosion pockets in the bank, existence of inerodible rock, debris marks on shrubs, trees or banks which may indicate the water level
of recent floods.
3-3
:
I
'
(t
:
0)
watermarks on walls, jetties and piers and buildings which indicate recent high water levels and
conskiction to water flow.
When the assessment of the survey information has been compieted, acceptable site for a bridge crossing from the fluvial aspect may be chosen. The detailed field surveys of the site will then follow. 3.3.
SURVEY DATA
3.3.1
Survey of Bridge Site and Beyond
After the selection of suitable sites for the bridge crossing have been made, hydrographic and hydraulic surveys have to be carried out to obtain the data required to determine the width of the bridge opening, the depth of scour and
hydrodynamic forces on piers and the upstream backwater. I
t
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t:
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I
For large and deep rivers the hydrographic survey should be carried out by using recording echo sounder systems. The topographic features of the river and flood plain on both banks should also be surveyed by normal topographic survey procedures, to the extent required for hydraulic analysis.
I
The survey of the alignment and contour of the river and flood plains should extend not less than 30 channel widths upstream (300m minimum) and, 20 channel widths downstream (200 m minimum) of the proposed crossing, see Figure 3'1' The width of the survey corridor should not be less than 50m on either side of the riverbanks.
where required, the survey shall be extended beyond the bridge site to upstream high flood risk areas to obtain data for analysis of backwater and assessment of its effects" Survey should also include downstream water flow constriction areas where they may affect the hydraulics of the bridee. Spot levels within the survey corridor shall be taken at not more than 10 m interval and shall include the bank levels and the invert levels of the river at the bottom of the banks, centre and deepest points. The survey should also include taking of panoramic photographs of the bridge site and its immediate upstream and downstream reaches.
3-4
g F
i:
TO EXTEND SURVEY UP
TO
HIGH FLOOD RISK AREA
IF
REOUIRED BY APPROPRIATE AUTHORITIES.
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= u. F
o a o- o n
.W'CHANNEL TOP WIDTH
RIVER MAIN CHANNEL
RIVER TERRACE
TO EXTEND SURVEY DOWNSTREAM TO AREAS WHERE THERE ARE CONSTRICTIONS TO WATER FLOW. WHERE NECESSARY
FIGURI
3.1
:
tXTINT
OF
SURVIY
FOR
BRIDGI SITt
3-5 s
The hydrographic and topographic surveys should be plotted on the same plan to facilitate extraction of cross-sectional data for hydraulic analysis and all levels should be reduced to a common datum.
For scour analysis samples of the riverbed material should be taken for particle size analysis at the crossing and upstream locations. 3.3.2
Hydraulic Survey For large rivers the discharge passing through the proposed bridge site should be measured at a number of different stages of flow. Each discharge measurement should be related to the date of survey, time and water levei and be reciuced to a standard datum. A gauging station should be established near the site of the proposed crossing as soon as possible.
Velocities
of flow in both magnitude and direction (in tidal sites) should be
measured across the river channel, preferably, during high flows and could be part of the discharge measurement prograrnme.
The designer should check with JPS stream flow records whether the river in the vicinity of the proposed bridge site has been gauged. Any information available should be incorporated in the hydrological study.
ESTIMATION OF DESIGN DISCHARGE AND WATER PROFILE
3.4.
J.+.
I
Design Recurrence Interval Stream flows for the
2,5, r0,25,50
and 100 years average recurrence intervals
(ARI) should be derermined.
The ARI of the design discharge should be in accordance to Table 3.r. Nevertheless, factors such as possible loss of life and economic damages due to any failure, have to be set against the higher capital cost of a bridge designed for a longer ARI must be considered.
3-6
Table 3.1: Recommended Average Recurrence Interval for Design Discharge Averase Recurrence Interval in Years Type of Structure
U2IF(2
u3
and lower
R3-R4
u5 - u6l R5_R6
50
100
100**
25*
50x
100*
Bridge
-u4/
Note:*The above average recuffence intervals can be used by the designer
if
any of the following conditions applies:
a) b) c)
the structure is located in a flood plain the structure requires a high embankment
the soil condition is poor making high embankment construction uneconomical
Under the above conditions, the structure must be designed as a submersible structure. Special consideration, however, must be given against accumulation of debris o,
i*p^"t by floating logs etc.
** For major bridges, the probability of the design flood being
exceeded
should not be more than 57o tn the design life
3.4.2
Design Discharge
Design discharge at the proposed bridge site can be determined in accordance with the various flood flow estimation hydrological procedures published by JPS. Where stream flow records are available for a particular station in the river or
located near
to the proposed
crossing, then the more accurate method of
streamflow frequency analysis should be adopted.
In the estimation of the design discharge, an assessment of the extent of current and future landuse development in the catchment has to be made and corrective measures must to be included in the estimated discharge
if future landuse changes
are going to be significant.
It would be useful to indicate
on bridge drawings the estimated discharge and
water levels of the river for various recuffence intervals. This information can be used as a guide in the planning and design of temporary works at the bridge site.
3-7 E
Water Profile
3.4.3
Where water level records are available at the crossing site, a frequency analysis should be carried out, otherwise, the water level corresponding to the design discharge can be calculated by a suitable flow equation, such as Manning formula. Where river stage discharge charts are available, water levels for various flows may be read off the charts.
For wide rivers, it is usually uneconomical to construct a bridge with a single span' More often multiple piers wiil be provided within the flood flow channel and earth embankments will encroach into the flood plain. These will constrict the flow and cause upstream water levels to rise above the original free flow level. The amount by which the water level rises above the free fiow level, may be calculated by the method described in the sub-section on Computation
of
Backwater in Appendix
1.
Should there be numerous river cross-sections and design flood flow scenarios then the manual calculation method cited in the foregoing will become time consuming. Many affordable water profile analysis software are now available to the designer to perform the task, such as:
o o o
- Water Surface profiles WSPRO (HY-7) - Bridge Waterway Analysis HEC 2
Model
HEC-RAS : River Analysis Svstem
The above are obtainable from Hydrological Engineering center, uS Army corps of Engineers and are very versatiie and capable of handring: o o
eccentric location of main channel within the flood plain skewed orientation of bridge crossing
o
various pier shapes and spacing
o
o
discharge through partially submerged bridges discharge over submerged road embankments and
o
scour at pier and abutment.
3-8
7
?{
BRIDGE WATER.WAY The bridge waterlvay area to be provided should be sufficient to ensure the design
I
flood can safely pass through without undue afflux or excessive increase in upstream flood levels, and at a velocity, which will not increase scour to such an extent, as to endanger the stability of the bridge structure.
Sufficient clearance of bridge deck above flood levels should be provided to allow the largest floating debris to pass through without clogging up the waterway. The minimum amount of freeboard is 1.0m above the design high
I
water level. Where the river is navigable by watercrafts attention should be given
to the headroom clearance required by the controlling authorities. When it is necessary to restrict the width of the waterway to such an extent that the scour would be severe, protection against damage shouid be made by providing deep foundations and adopting appropriate scour counter-measures. Where there is existing drainage or irrigation dikes aiong the banks of the rivet,
the soffit of the bridge deck and beams should be placed a minimum of 0.5m above the top of these dikes. The freeboard between the high water level and the top of the dike is usually 0.5m to 1.5m depending on the design discharge of the river, however this needs to be checked with the appropriate river authorities, mainly JPS. 3.6
SCOUR AT BRIDGE CROSSING
3.6.1
Scour
Scour can be very insidious whereby soil around a bridge foundation is removed
flood. The most common form of flood damage to bridges arises from the scouring of abutments and piers, which can and re-deposited elsewhere during a
underinine the structure, resulting in collapse of spans and possible loss of life. Four different types of scour must be considered, as follows: a)
General Scour
to which the riverbed at the bridge site is below the natural bed ievel. This normally occurs due to the
General scour is the depth scoured
constriction of flood flows through the bridge opening between abutments or embankments (see Figure 3.2).
3-9
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Local scour is the lowering of the riverbed immediately adjacent to bridge piers or abutments (see Figure 3.2).
c)
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Natural scour occurs in alluvial or tidal channels and is associated with variations in flow conditions, channel shifting or river bed migration at the bridge site.
d)
Progress Scour
Progressive scour which is progressive river bed lowering or river profile
degradation due to geological or man made processes
-
e.g. damming,
reservoir regulation, gravel mining, etc. The first three categories above can be estimated with reasonable accuracy but the
fourth is extremely difficult to predict.
3.6.2
Countermeasures
Upon assessment of the potential scour problem, countermeasures to control scour need to be provided. The countermeasures could include the following:
o
soil cement for sloping abutment,
o
wire enclosed riprap for sloping abutment (see Figure 3.3A),
o
interlocking concrete block system for abutment (see Figure 3.3B).
o
articulated grout filled mat for abutment and river bed (see Figure 3.3C) and
o
cement/grout filled bags
for pier and abutment (see Figures 3.3D
and
3.3E).
For design guidance and selection of countermeasures the designer should refer to:
o
FHWA Hydraulic Engineering Circular No. 23 -Bridge Scour and Stream Instability Countermeasures.
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