Project Report.pdf

Mini Project Report On BRIDGE CONSTRUCTION FOR NEW BROAD GAUGE LINE A Dissertation submitted in partial fulfillment of the requirement for the award of degree of Bachelor of Technology In

CIVIL ENGINEERING By

LOHITH REDDY D

(09241A0174)

T.S. ANURAG

(09241A0156)

T. MAHESH

(0924A01B5)

PAVAN VARMA K.N.S (09241A0186)

DEPARTMENT OF CIVIL ENGINEERING

GOKARAJU RANGARAJU INSTITUTE OF ENGINEERING AND TECHNOLOGY (AFFILIATED TO JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY) NIZAMPET ROAD, HYDERABAD-500090

DEPARTMENT OF CIVIL ENGINEERING CERTIFICATE This is to certify that the project report entitled “BRIDGE CONSTRUCTION FOR NEW BROAD GAUGE LINE” being submitted by LOHITH REDDY D (09241A0174) in partial fulfillment for the award of the Degree of Bachelor of Technology to the Jawaharlal Nehru Technological University. This record is a bona fide work carried out by him under my guidance and supervision. The results embodied in this project report have not been submitted to any other University or Institute for the award of any Degree or Diploma

Dr. Mohammed Hussain Internal Guide

Dr. G.Venkata Ramana Head of the Department

External Examinar

DECLARATION: I hereby declare that the work presented in this project titled “Bridge construction for new broad gauge line” submitted towards completion of mini-project in sixth Semester of B.Tech (CIVIL ENGINEERING) at the Gokaraju Rangaraju Institute of Engineering and Technology affiliated to Jawaharlal Nehru Technological University, Hyderabad is authenticate work and had not been submitted to any University or Institute for any award.

Place:

Hyderabad

Date:

29/04/2013

D. LOHITH REDDY

(09241A0174)

T.S. ANURAG

(09241A0156)

T. MAHESH

(0924A01B5)

PAVAN VARMA K.N.S

(09241A0186)

ACKNOWLEDGEMENT I would like to express my gratitude to all the people behind the screen who helped us to transform an idea into real application. I would like to express my heart-felt gratitude to my parents with whom I would not have been privileged to achieve and full fill my dreams. I am grateful to our principal Mr.Jandyala.N.Murthi who most ably run the institute and has had the major hand in enabling me to do my project. I profoundly thank Dr.G.Venkata Ramana, Head of the Department, Civil Engineering, who has been an excellent guide and also great source of inspiration to my work. I would like to thank my internal guide Dr. Md.Hussain for his technical guidance, constant encouragement and support I carrying out my project work. I would like to thank Mr. Ajay who guided us at the site at the time of execution The satisfaction and euphoria that accompany the successful completion of task would be great but in complete with the mention of the people who made it possible with here constant guidance and encouragement crowns all the efforts with the success. In this context, I would like thank all the other staff members teaching and non-teaching, who have extended their timely help and eased my task.

Lohith Reddy D

09241A0174

ABSTRACT BRIDGE CONSTRUCTION FOR NEW BROAD GUAGE LINE

From the moment human started exploring he started to travel across the world after the world- war II due to the industrial revolution these became even intense to travel for overseas human used only ships but to travel in his own country he made only slow means of transport like bullock cart which not even safe. Then human started thinking about to decrease his travel time and increase his own safety then they invented railway service which much safe, time conserving due to the low in expenditure to travesl by trains many middle class and lower middle class people depended on it a lot and it even cheap to transfer the good for long distance at low price with lead to growth of importance of railway services. Construction of new railway is really a tough task which involve in consideration of several parameters and several unexpected conditions. When the track is properly aligned it is a very good means of source of revenue to government and also good means transportation for public. At both the execution of construction work and even the maintenance it provide huge opportunity of employment.

CODE AND REGULATIONS Admixtures: - IS-9103 1. For reduction of water cement ratio:- IS-456 2. Water cement ratio:- IS-10262 ,IS-10264 3. Bridge bed block:-

IS-1786-285

All the above specifications should be 2010 modifications and latest. 4. Maximum water cement ratio:- 0.40 5. Minimum cementicious material:-400kg/mt 6. Reinforcement high yield strength deformed bars: IRS-1786-1985 7. Abutments mix:-M25 8. Piers:-M30

CONTENTS S.No

TOPIC

Page

1. CHAPTER-1 INTRODUCTION 1.1 Introduction to bridges

1

2. CHAPTER-2 TOPOGRAPHICAL SURVEY 2.1 Topographical survey

2

2.2 Alternative Alignment

2

2.3 Obligatory points

3

3. CHAPTER-3 DISCHARGE THROUGH DRAINAGE AREA 3.1 Discharge through drainage

4

4. CHAPTER-4 TYPES OF BRIDGES 4.1 Arch bridges

6

4.2 Reinforced slab bridges

6

4.3 Beam and slab bridges

7

4.4 Integral bridges

7

5. CHAPTER-5 TYPES OF FOUNDATIONS 5.1 Open foundation

9

5.2 Box foundation

10

5.3 Well foundation

10

5.3.1 Cutting edge

10

5.3.2 Curb

10

5.3.3 Steining

10

5.3.4 Bottom plug

11

5.3.5 Sand filling

11

5.3.6 Intermediate plug

11

5.3.7 Top plug

12

5.3.8 Reinforcement

12

5.3.9 Well cap

12

5.4 Sinking of wells

13

6. CHAPTER-6 PIER CONSTRUCTION 6.1 Pier construction

15

7. CHAPTER-7 PRE-STRESSED CONCRETE SLAB 7.1 Bonded post tensioned concrete

20

8. CHAPTER-8 POST-TENSIONED SLAB 8.1 post-tensioned concrete

22

9. CHAPTER-9 LAUNCHING OF PRE-STRESSED SLAB 9.1 Pre-tensioned slab

23

10. CHAPTER-10 INFLUENCING OF BUILDING MATERIALS 10.1 Building materials

24

10.1.1 Natural stone

24

10.1.2 Artificial stone, bricks, clinker

25

10.1.3 Reinforced and pre-stressed concrete

25

10.1.4 Steel and aluminum

27

10.1.5 Timber

29

10.2 Bridge construction technology

29

11. CHAPTER-11 TYPES OF BRIDGE CONSTRUCTION MACHINERIES 11.1 Construction machineries

31

11.1.1 Bridge cranes

31

11.1.2 Gantry cranes

32

11.1.2.1 Gantry cranes size and marking

32

11.1.2.2 Types of Gantry cranes

32

11.1.2.3 Renting gantry cranes

32

11.1.3 Floating cranes

33

11.1.3.1 Floating crane working

33

11.1.3.2 Floating crane uses

34

12. CHAPTER-12 TOTAL STATION 12.1 Coordinate measurement

35

12.2 Angular measurement

35

12.3 Distance measurement

35

12.4 Data processing

35

12.5 Applications

36

12.6 Mining

36

12.7 Stone block

36

13. CHAPTER-13 SLEEPERS 13.1 Wooden sleepers

37

13.2 Concrete sleepers

38

13.3 Steel sleepers

39

14. REFERENCES 15. LIST OF FIGURES Figure 6.1 Parts of a pier Figure 6.2 Machine for drilling a pier Figure 6.3 Tay Bridge Figure 6.4 Erection of a pier Figure 7.1 Pre-stressed slab Figure 7.2 Pre-stressed post tensioned anchor Figure 11.1 Bridge crane Figure 11.2 Gantry crane Figure 11.3 Renting gantry crane Figure 11.4 Floating crane Figure 13.1 Wooden sleeper Figure 13.2 Concrete sleeper Figure 13.3 Steel sleeper

40

CHAPTER-1 INTRODUCTION 1.1 Introduction to Railway bridges: Our mini project is totally concreted on railway bridge construction. In general rail way track is aligned in most economical way but sometimes railway line come across several obligatory points like holy places, schools, areas with high land value and even tributaries of river or streams in such cases bridges and designed and constructed. It is done by following methods. At first and foremost step followed align the railway line is topographical survey. In this part a topographical map is used to check the possibilities of alignment of track and from that the best possible path is finalized. Then the field test is carried out to get a clear idea about the site condition. Which consist of total station survey for central line alignment, leveling works which also results in finding the RL at different point and even useful to transfer them to required location to avoid obstruction in visibility, then followed by soil exploration works which involves in lab work. Once these work is done the next procedure of work continues i.e. land acquisition as a part of these the railway authority make contact with local revenue department officials for land purchase from the respective owners. Then it is followed by earth work where excavation work for different types of foundation, as we know different methods of foundations are followed based on the ground condition. When the main excavation work is done the bridge construction starts ex foundation, piers to get all the piers in exact alignment total station is used. Once the piers are done then the bed block marking is done over which precast girders are place. All these processes go into the sub tenders form. When the construction of bridges is done, sleepers are placed at the site for the next

process

i.e.

track

alignment

along

1

the

center

marked

line.

CHAPTER-2 TOPOGRAPHICAL SURVEY 2.1 Topographical survey A topographic map is a type of map characterized by large-scale detail and quantitative representation of relief, usually using contour lines in modern mapping, but historically using a variety of methods. Traditional definitions require a topographic map to show both natural and man-made features. A topographic map is typically published as a map series, made up of two or more map sheets that combine to form the whole map. A contour line is a combination of two line segments that connect but do not intersect; these represent elevation on a topographic map. The Canadian Centre for Topographic Information provides this definition “A topographic map is a detailed and accurate graphic representation of cultural and natural features on the ground.” Other authors define topographic maps by contrasting them with another type of map; they are distinguished from smaller-scale "chorographic maps" that cover large regions, "plan metric maps" that do not show elevations, and "thematic maps" that focus on specific topics. However, in the vernacular and day to day world, the representation of relief (contours) is popularly held to define the genre, such that even small-scale maps showing relief are commonly (and erroneously, in the technical sense) called "topographic". The study or discipline of topography, while interested in relief, is actually a much broader field of study which takes into account all natural and manmade features of terrain.

2.2 Alternative alignment As part of topographical survey all the possible alignment of railway line is examined.

2

2.3 Obligatory points As a part of topographical survey we come across several obstruction like, holy place, rivers streams, which leads to change the direction or bridge construction.

3

CHAPTER-3 DISCHARGE THROUGH DRINAGE AREA 3.1 Discharge through drainage area The catchment of a river above a certain location is determined by the surface area of all land which drains toward the river from above that point. The river's discharge at that location depends on the rainfall on the catchment or drainage area and the inflow or outflow of groundwater to or from the area, stream modifications such as dams and irrigation diversions, as well as evaporation and evapo-transpiration from the area's land and plant surfaces. In storm hydrology an important consideration is the stream's discharge hydrograph, a record of how the discharge varies over time after a precipitation event. The stream rises to a peak flow after each precipitation event, then falls in a slow recession. Because the peak flow also corresponds to the maximum water level reached during the event, it is of interest in flood studies. Analysis of the relationship between precipitation intensity and duration, and the response of the stream discharge is mm by the concept of the unit hydrograph which represents the response of stream discharge over time to the application of a hypothetical "unit" amount and duration of rain, for example 1 cm over the entire catchment for a period of one hour. This represents a certain volume of water (depending on the area of the catchment) which must subsequently flow out of the river. Using this method either actual historical rainfalls or hypothetical "design storms" can be modeled mathematically to confirm characteristics of historical floods, or to predict a stream's reaction to a predated storm. The relationship between the discharge in the stream at a given cross-section and the level of the stream is described by a rating curve. Average velocities and the cross-sectional area of the stream are measured for a given stream level. The velocity and the area give the discharge for that level. After measurements are made for several different levels, a rating table or rating curve may be developed. Once rated, the discharge in the stream may be determined by measuring the level, and determining the corresponding discharge from the rating curve. If a continuous level-recording device is located at a rated cross-section, the stream's discharge may be continuously determined.

4

This is done based on the records of last 10 years if fluctuation is more it can be made up to 20 years. Based on the analyses data for the discharge of drainage the bridges are finalized based on the acting on them due to discharge of water, All the forces acting on pier, additional that can be acted on bridges, span, reinforcement, amount of concrete is estimated at these stage.

5

CHAPTER-4 TYPES OF BRIDGES 4.1 Arch bridges Arch bridges derive their strength from the fact that vertical loads on the arch generate compressive forces in the arch ring, which is constructed of materials well able to withstand these forces. The compressive forces in the arch ring result in inclined thrusts at the abutments, and it is essential that arch abutments are well founded or buttressed to resist the vertical and horizontal components of these thrusts. If the supports spread apart the arch falls down. The Romans knew all about this. Traditionally, arch bridges were constructed of stone, brick or mass concrete since these materials are very strong in compression and the arch could be configured so that tensile stresses did not develop. Modern concrete arch bridges utilize prestressing or reinforcing to resist the tensile stresses which can develop in slender arch rings. The shape attracted the attention of many of the early pioneers of concrete construction. In 1930, Freyssinet was responsible for a spectacular arched bridge at Plougastel in France and three years later, Swiss engineer, Robert Maillart created the famously elegant Schwandbach bridge in which slender cross-walls tie the arch to the horizontally curved roadway. 4.2 Reinforced slab bridges For short spans, a solid reinforced concrete slab, generally cast in-situ rather than precast, is the simplest design. It is also cost-effective, since the flat, level soffit means that false work and formwork are also simple. Reinforcement, too, is uncomplicated. With larger spans, the reinforced slab has to be thicker to carry the extra stresses under load. This extra weight of the slab itself then becomes a problem, which can be solved in one of two ways. The first is to use pre-stressing techniques and the second is to reduce the deadweight of the slab by including 6

'voids', often expanded polystyrene cylinders. Up to about 25m span, such voided slabs are more economical than pre-stressed slabs. 4.3 Beam and slab bridges Beam and slab bridges are probably the most common form of concrete bridge in the India today, thanks to the success of standard precast pre-stressed concrete beams developed originally by the Pre-stressed Concrete Development Group (Cement & Concrete Association) supplemented later by alternative designs by others, culminating in the Y-beam introduced by the Pre-stressed Concrete Association in the late 1980s. They have the virtue of simplicity, economy, wide availability of the standard sections, and speed of erection. The precast beams are placed on the supporting piers or abutments, usually on rubber bearings which are maintenance free. An in-situ reinforced concrete deck slab is then cast on permanent shuttering which spans between the beams. The precast beams can be joined together at the supports to form continuous beams which are structurally more efficient. However, this is not normally done because the costs involved are not justified by the increased efficiency. Simply supported concrete beams and slab bridges are now giving way to integral bridges which offer the advantages of less cost and lower maintenance due to the elimination of expansion joints and bearings. 4.4 Internal bridges One of the difficulties in designing any structure is deciding where to put the joints. These are necessary to allow movement as the structure expands under the heat of the summer sun and contracts during the cold of winter. Expansion joints in bridges are notoriously prone to leakage. Water laden with road salts can then reach the tops of the piers and the abutments, and this can result in corrosion of all reinforcement. The expansive effects of rust can split concrete apart.

7

In addition, expansion joints and bearings are an additional cost so more and more bridges are being built without either. Such structures, called 'integral bridges', can be constructed with all types of concrete deck. They are constructed with their decks connected directly to the supporting piers and abutments and with no provision in the form of bearings or expansion joints for thermal movement. Thermal movement of the deck is accommodated by flexure of the supporting piers and horizontal movements of the abutments, with elastic compression of the surrounding soil. Already used for lengths up to 60m, the integral bridge is becoming increasingly popular as engineers and designers find other ways of

8

CHAPTER-5 TYPES OF FOUNDATIONS 5.1 Open foundation An open caisson is similar to a box caisson, except that it does not have a bottom face. It is suitable for use in soft clays (e.g. in some river-beds), but not for where there may be large obstructions in the ground. An open caisson that is used in soft grounds or high water tables, where open trench excavations are impractical, can also be used to install deep manholes, pump stations and reception/launch pits for micro tunneling, pipe jacking and other operations. A caisson is sunk by self-weight, concrete or water ballast placed on top, or by hydraulic jacks. The leading edge (or cutting shoe) of the caisson is sloped out at a sharp angle to aid sinking in a vertical manner; it is usually made of steel. The shoe is generally wider than the caisson to reduce friction, and the leading edge may be supplied with pressurized bentonite slurry, which swells in water, stabilizing settlement by filling depressions and voids. An open caisson may fill with water during sinking. The material is excavated by clamshell excavator bucket on crane. The formation level subsoil may still not be suitable for excavation or bearing capacity. The water in the caisson (due to a high water table) balances the up thrust forces of the soft soils underneath. If dewatered, the base may "pipe" or "boil", causing the caisson to sink. To combat this problem, piles may be driven from the surface to act as: Load-bearing walls, in that they transmit loads to deeper soils. Anchors, in that they resist floatation because of the friction at the interface between their surfaces and the surrounding earth into which they have been driven. H-beam sections (typical column sections, due to resistance to bending in all axes) may be driven at angles "raked" to rock or other firmer soils; the H-beams are left extended above the base. A reinforced concrete plug may be placed under the water, a process known

9

as Tremie concrete placement. When the caisson is dewatered, this plug acts as a pile cap, resisting the upward forces of the subsoil. 5.2 Box foundation A box caisson is a prefabricated concrete box (it has sides and a bottom); it is set down on prepared bases. Once in place, it is filled with concrete to become part of the permanent works, such as the foundation for a bridge pier. Hollow concrete structures float (seeWWII concrete ships), so a box caisson must be ballasted or anchored to prevent this phenomenon until it can be filled with concrete (indeed, elaborate anchoring systems may be required in tidal zones); adjustable anchoring systems, combined with a GPS survey, allows engineers to position a box caisson with pinpoint accuracy. 5.3 Well foundation This work consists of construction of well foundation, taking it down to the founding level through all kinds of sub-strata, plugging the bottom, filling the inside of the well, plugging the top and providing a well cap in accordance with the details shown on the drawing. Well may have a circular, rectangular, or D-shape in plan and may consist of one, two or more compartments in plan. Well Components & their Function In brief the function of various elements is as follows: 5.3.1 Cutting edge The mild steel cutting edge shall be made from structural steel sections. The cutting edge shall weigh not less than 40 kg per meter length and be properly anchored into the well curb, as shown in the drawing. When there are two or more compartments in a well, the bottom end of the cutting edge of the inner walls of such wells shall be kept at about 300 mm above that of outer walls. 5.3.2 Curb The well curb may be precast or cast-in-situ. Steel formwork for well curb shall be fabricated strictly in conformity with the drawing. The outer face of the curb shall be vertical.

10

Steel reinforcements shall be assembled as shown on the drawings. The bottom ends of vertical bond rods of staining shall be fixed securely to the cutting edge with check nuts or by welds. The formwork on outer face of curb may be removed within 24 hours after concreting. The formwork on inner face shall be removed after 72 hours. It is made up of reinforced concrete using controlled concrete of grade M-35. 5.3.3 Steining The dimensions, shape, concrete strength and reinforcements of the well shall strictly conform to those shown on the drawings. The formwork shall preferably be of M.S. sheets shaped and stiffened suitably. In case timber forms are used, they shall be lined with plywood or M.S. sheets. The steining of the well shall be built in one straight line from bottom to top such that if the well is tilted, the next lift of steining will be aligned in the direction of the tilt. After reaching the founding level, the well steining shall be inspected to check for any damage or cracks 5.3.4 Bottom plug Its main function is to transfer load from the steining to the soil below. For bottom plug, the concrete mix shall be design (in dry condition) to attain the concrete strength as mentioned on the drawing and shall contained 10 per cent more cement than that required for the same mix placed dry. 5.3.5 Sand filling Sand filling shall commence after a period of 3 days of laying of bottom plug. Also, the height of the bottom plug shall be verified before starting sand filling. Sand shall be clean and free from earth, clay clods, roots, boulders, shingles, etc. and shall be compacted as directed. Sand filling shall be carried out up to the level shown on the drawing or as directed by the Engineer. 5.3.6 Intermediate plug The function of the plug is to keep the sand filling sandwiched & undisturbed. It also act as a base for the water fill, which is filled over it up to the bottom of the well cap.

11

5.3.7 Top plug After filling sand up to the required level a plug of concrete shall be provided over it as shown on the drawing, It at least serves as a shuttering for laying well cap. 5.3.8 Reinforcement It provides requisite strength to the structure during sinking and service. 5.3.9 Well cap It is needed to transfer the loads and moments from the pier to the well or wells below. A reinforced cement concrete well cap will be provided over the top of the steining in accordance with the drawing. Formwork will be prepared conforming to the shape of well cap. Concreting shall be carried out in dry condition. A properly designed false steining may be provided where possible to ensure that the well cap is laid in dry conditions After water filling, pre-cast RCC slabs shall be placed over the RCC beams as per the drawings, as non-recoverable bottom shuttering for well cap. Initially built false wall shall act as outer shuttering for well cap casting. In case, there is no false wall, then steel shuttering is to be put from outer side. For well Steining and well cap shuttering, permissible tolerances are as follows: Variation in dimension

:

+50 mm to –10mm

Misplacement from specified Position in Plan: Variation of levels at the top

15mm :

+/- 25mm

Depth of Well Foundation As per I.R.C. bridge code, the depth of well foundation is to be decided on the following considerations: The minimum depth of foundation below H.F.L should be 1.33D, where D is the anticipated max. Depth of scour below H.F.L depth should provide proper grip according to some rational formula. The maximum bearing pressure on the subsoil under the foundation resulting from any combination of the loads and forces except wind and seismic forces should not exceed the 12

safe bearing capacity of the subsoil, after taking into account the effect of scour. With wind and seismic forces in addition, the maximum bearing pressure should not exceed the safe bearing capacity of the subsoil by more than 25% While calculating maximum Bearing pressure on the foundation bearing layer resulting from the worst combination of direct forces and overturning moments. The effect of passive resistance of the earth on the sides of the foundation structure may be taken into account below the maximum Depth of the scour only. The effect of skin friction may be allowed on the portions below the maximum Depth of scour. Accordingly for deciding the depth of well foundation we require correct estimation of the following: Maximum Scour depth. Safe bearing capacity. Skin friction. Lateral earth support-below maximum scour level. It is always desirable to fix the level of a well foundation on a sandy strata bearing capacity. Whenever a thin stratum of clay occurring between two layers of sand is met with in that case well must be pierced through the clayey strata. If at all foundation has to be laid on a clayey layer it should be ensured that the clay is stiff. 5.4 Sinking of Wells In case of well sinking on dry grounds, an open excavation up to half a meter above subsoil water level is carried out and the well curb is laid. In case the wells are to be sunk in mid-stream, a suitable cofferdam is constructed around the site of the well and islands are made. The islands in shallow water are formed by an edging of sand bags forming an enclosure filled with sand or clay. When the water depth is of the order of 3 to 5 m. the site is surrounded by sheet piling and the enclosure so formed is filled with clay or sand. The centre point of well is accurately marked on the island and the cutting edge is placed in a level plain. The wooden sleepers are inserted below the cutting edge at regular intervals so as to distribute the load and avoid setting of the cutting edge unevenly during concreting. The inside shuttering of the curb is generally made of brick masonry and plastered. The outer shuttering is made of wood or steel. Initially the well steining should be built to a height of 2m. Only. Later steining should not allowed to be built more than 5m. at a time. For this bridge the subsequent lifts were of 2.5 m. each. The well is sunk by excavating material from inside under the curb. Great care should be taken during well sinking in the initial stages because the well is very unstable. Excavation of the soil inside the well can be done by sending down workers inside the wells. 13

When the depth of the water inside the well becomes more than one meter, the excavation is then carried out by a Jham or a Dredger. The sump position at 8 equidistant locations along dredge hole sides & at well center are taken & recorded. The dredge water level is also recorded. Vertical reinforcement of steining shall be bent & tied properly to facilitate the grab movement during sinking operations. The position of the crane shall be such that the operation shall be able to see the signalman on the well top at all the times, & the muck is safely deposited away from the intermediate vicinity of the well. Grabbing process shall commence normally with the grabbing at the above designated sounding positions. If the well is not sinking after reasonable amount of grabbing is done, say after two rounds of grabbing, the sump position shall be checked accordingly, in combination with the tilt position, the grabbing pattern shall vary. The sump should not normally exceed 1.75m average. And thereafter, air jetting or water jetting shall be resorted to. The sinking operation shall be done in two shifts, day & night. In normal course, the sump and the dredge hole water levels shall be observed twice in each shift, and the cutting edge reduced level shall be checked by level at four positions at the end of the shift. As the well sinks deeper, the skin friction on the sides of the well progressively increases. To counteract the increased skin friction and the loss in weight of the well due to buoyancy, additional loading known as kentledge is applied on the well. The kentledge is comprised of iron rail, sand bags concrete blocks etc. Pumping out of water from the inside of the well is effective when the well has gone deep enough or has passed through a clayey stratum so that chances of tilts and shifts are minimized during this process. When the well has been sunk to about 10 m. depth, sinking thereafter should be done by grabbing, chiseling and applying kentledge. Only when these methods have failed dewatering may be allowed up to depressed water level of 5 m. and not more. In case of sandy strata frictional resistance developed on the outer periphery is reduced considerably by forcing jet of water on the outer face of the well all round.

14

CHAPTER-6 PEIR CONSTRUCTION 6.1 Pier construction The dimensions and detailed construction of the cast-iron piers are shown in. A single pier consisted of six columns of cast iron tied together by struts, bars and rods made from wrought iron. Each pier in the high girders section was built up by bolting together seven flanged cast-iron columns, giving seven tiers. The ends of the flanges were fastened together with eight 1.125 inch (1⅛) wrought iron bolts as shown in Figures 16 and 17, below.

(Figure 6.1 Parts of a pier)

15

Figure 6.2 machine for drilling a well

16

Figure 6.3 Tay Bridge

17

The four columns, forming a rectangle in plan view, had an outside diameter of 15 inches and a wall thickness of 1 inch. The two outside columns had a diameter of 18 inches as shown in. The bracing bars were secured to lugs cast as one with the column. The horizontal bars (referred to in this unit as struts) were made from channel section wrought iron and were secured at each end with two wrought iron bolts. The diagonal bars (referred to in this unit as tie bars) were made from iron flats with a cross-section of 4.5 × 0.5 inches. Each diagonal tie bar was held by a 1.125 inch bolt at one end and was jointed into two sling plates at the other. The sling plates were attached by another 1.125 inch bolt going through 1.25 inch (1¼) holes in the lugs. The tie bar could then be tensioned at the joint by two cotters (opposed wedges) hammered into a slot that also housed a gib (metal pad), as shown. As a pier was erected, the inside of each column was filled with Portland cement, apparently to protect it against corrosion. The total weight of a pier complete with cement filling, bars and top plinth was about 120 tons.

Figure 6.4 Erection of pier

18

CHAPTER-7 PRESTRESSED CONCRETE SLAB

Figure 7.1 Pre-stressed slab

Pre-stressed concrete is a method for overcoming concrete's natural weakness in tension. It can be used to produce beams, floors or bridges with a longer span than is practical with ordinary reinforced concrete. Pre-stressing tendons (generally of high tensile steel cable or rods) are used to provide a clamping load which produces a compressive stress that balances the tensile stress that the concrete compression member would otherwise experience due to a bending load. Traditional reinforced concrete is based on the use of steel reinforcement bars, rebars, inside poured concrete. Pre-tensioned concrete is cast around already tensioned tendons. This method produces a good bond between the tendon and concrete, which both protects the tendon from corrosion and allows for direct transfer of tension. The cured concrete adheres and bonds to the bars and when the tension is released it is transferred to the concrete as compression by static friction. However, it requires stout anchoring points between which the tendon is to be stretched and the tendons are usually in a straight line. Thus, most pre-tensioned concrete elements are pre-fabricated in a factory and must be transported to the construction site, which limits their size. Pre-tensioned elements may be balcony elements, lintels, floor slabs, beams or foundation piles. An innovative bridge construction method using pre-stressing is the stressed ribbon bridge design.

19

7.1 Bonded post-tensioned concrete

Fig (7.2) Pre-stressed post-tension anchor on display at Instituto Superior Técnico's civil engineering department Bonded post-tensioned concrete is the descriptive term for a method of applying compression after pouring concrete and the curing process (in situ). The concrete is cast around a plastic, steel or aluminum curved duct, to follow the area where otherwise tension would occur in the concrete element. A set of tendons are fished through the duct and the concrete is poured. Once the concrete has hardened, the tendons are tensioned by hydraulic jacks that react (push) against the concrete member itself. When the tendons have stretched sufficiently, according to the design specifications (see Hooke's law), they are wedged in position and maintain tension after the jacks are removed, transferring pressure to the concrete. The duct is then grouted to protect the tendons from corrosion. This method is commonly used to create monolithic slabs for house construction in locations where expansive soils (such as adobe clay) create problems for the typical perimeter foundation. All stresses from seasonal expansion and contraction of the underlying soil are taken into the entire tensioned slab, which supports the building without significant flexure. Post-tensioning is also used in the construction of various bridges, both after concrete is cured after support by false work and by the assembly of prefabricated sections, as in the segmental bridge. Among the advantages of this system over un-bonded post-tensioning are:





Large reduction in traditional reinforcement requirements as tendons cannot De-stress in accidents. Tendons can be easily "woven" allowing a more efficient design approach. Higher ultimate strength due to bond generated between

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CHAPTER-8 POST TENSIONED CONCRETE 8.1 Post tensioned concrete Un-bonded post-tensioned concrete differs from bonded post-tensioning by providing each individual cable permanent freedom of movement relative to the concrete. To achieve this, each individual tendon is coated with grease and covered by a plastic sheathing formed in an extrusion process. The transfer of tension to the concrete is achieved by the steel cable acting against steel anchors embedded in the perimeter of the slab. The main disadvantage over bonded post-tensioning is the fact that a cable can de-stress itself and burst out of the slab if damaged (such as during repair on the slab). The advantages of this system over bonded posttensioning are: 1.

The

ability

to

individually

adjust

cables

based

on

2.

The procedure of post-stress grouting is eliminated

3.

The ability to de-stress the tendons before attempting repair work.

poor

field

conditions

Picture number 6.1 (below) shows rolls of post-tensioning (PT) cables with the holding end anchors displayed. The holding end anchors are fastened to rebar placed above and below the cable and buried in the concrete locking that end. Pictures numbered 6.2, 6.3 and 6.4 shows a series of black pulling end anchors from the rear along the floor edge form. Rebar is placed above and below the cable both in front and behind the face of the pulling end anchor. The above and below placement of the rebar can be seen in picture number three and the placement of the rebar in front and behind can be seen in picture number four. The blue cable seen in picture number four is electrical conduit. Picture number 6.5 shows the plastic sheathing stripped from the ends of the post-tensioning cables before placement through the pulling end anchors. Picture 6.6 shows the post-tensioning cables in place for concrete pouring. The plastic sheathing has been removed from the end of the cable and the cable has been pushed through the black pulling end anchor attached to the inside of the concrete floor side form. The greased cable can be seen protruding from the concrete floor side form. Pictures 6.7 and 6.8show the posttensioning cables protruding from the poured concrete floor. After the concrete floor has been poured and has set for about a week, the cable ends will be pulled with a hydraulic jack.

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CHAPTER-9 LAUNCHING OF PRE-TENSIONED SLAB 9.1 Pre-tensioned slab The technique of incremental launching has been well developed. It is used for constructing multi span bridges across valleys and where it is desirable to minimize interference with traffic. Typical span lengths are 20 to 40 m (65 to 130 ft), although span lengths up to 140 m (459 ft) have been used with steel girders. The launching of a steel box girder on a horizontal curve has been successfully completed. One example of an incrementally launched bridge is the Wupper Valley Bridge on Autobahn 1. This project involved expanding the existing expressway from four to six lanes, plus adding an emergency shoulder in each direction. The only solution was to build a second bridge parallel to the existing one. The new bridge is a seven-span structure with span lengths ranging from 44 to 72.8 m (144 to 239 ft) for a total length of 4,18.3 m (1,372 ft). The cross section of the bridge consists of a rectangular steel U-shaped box beam (shown in figure 21a) with deck cantilevers beyond the webs supported by inclined struts (shown in figure 21b). Partial-depth, precast concrete deck slabs were used to eliminate the need for false work. The slabs were placed on soft polymer strips to seal the joints. Shear studs from the steel beams projected into openings in the precast slabs. These openings were filled with high-strength concrete before placing a CIP concrete deck. The structure was incrementally launched using hydraulic jacks that pushed on the end of the steel box beam. The piers were equipped with sliding bearings to facilitate the launching. The nose at the front of the structure was equipped with a hydraulically controlled lifting device that was used to raise the front of the structure as it reached each pier. Before launching, the precast concrete slabs in the mid-span region were placed. The slabs over the supports were then placed from the other slabs. If the steel construction had been moved without the concrete slabs, the slabs would have had to be placed on the bridge from the side—resulting in additional impact on traffic. If all concrete slabs had been placed before launching the structure, the existing hydraulic equipment would not have had sufficient capacity. This structure was reported to be the first to use precast deck slabs of this size.

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CHAPTER-10 INFLUENCE OF BUILDING MATERIALS 10.1 Building materials The traditional building materials for bridges are stone, timber and steel, and more recently reinforced and pre-stressed concrete. For special elements aluminum and its alloys and some types of plastics are used. These materials have different qualities of strength, workability, durability and resistance against corrosion. They differ also in their structure, texture and color or in the possibilities of surface treatment with differing texture and color. For bridges one should use that material which results in the best bridge regarding shape, technical quality, economics and compatibility with the environment.

10.1.1 Natural stone:The great old bridges of the Etruscans, the Romans, the Fraters Pontific of the Middle Ages (since about 1100) and of later master builders were built with stone masonry. The arches and piers have lasted for thousands of years when hard stone was used and the foundations constructed on firm ground. With stone one can build bridges which are both beautiful, durable and of large span (up to 150 m). Unfortunately, stone bridges have become very expensive, if considered solely from the point of view of construction costs. Over a long period, however, stone bridges, which are well designed and well built, might perhaps turn out be the cheapest, because they are long-lasting and need almost no maintenance over centuries unless attacked by extreme air pollution. Stone is nowadays usually confined to the surfaces, the stones being preset or fixed as facing for abutments, piers or arches. Of course, sound weather-resisting stone must be chosen, and fundamental rock like granite, gneiss, porphyry, diabas or crystallized limestone are especially suitable. Caution is necessary with sandstones, as only siliceous sandstone is durable. In Western Germany basalt-lava from the Eifel Mountains is popular. In choosing the stone one should respect any local experience gained from old buildings and bridges. Stone is worked upon in different ways, depending upon the direction of the natural strata occurring in the quarry and on the requirements in the bridge Very different effects can be produced with stone by the choice of the type of masonry, the height of the courses, the proportion of the stones (length to height), the arrangement of the joints, the surface treatment etc., and especially the overall scale. The choice of colors of the stone is also relevant. Granite of a uniform grey color and sawn surface can look as dull as simple plain concrete. A harmonious mixture of different colors and slightly embossed surfaces can look very lively, even when the masonry areas are extensive. Surfaces can also be enlivened by bright or dark joint-filling. The sizes of the stone blocks and the roughness of their surfaces must be harmonized with the size of the structure, the abutments, the 23

piers etc. Coarse embossing does not suit a small pier only 1 m thick and 5 m high, but large sized ashlars masonry is suitable for large arch bridges such as the Saalebrucke Jena or the Lahntalbrucke Limburg. Granite masonry was preferred for piers of bridges across the River Rhine, because it resists erosion by sandy water much better than the hardest concrete.

10.1.2 Artificial stones, clinker and bricks:Amongst the artificial stones, clinker and hard-burned brick are used in bridges both as liners and for bearing vaults. They were often used in northern Germany, the Netherlands, Belgium and Denmark, because there is no suitable natural stone available. The warm colors of clinker or brick blend happily into the landscape. Also in an urban environment, they are preferable to plain concrete, if brick is the regional construction material. The sizes of these stones are standardized, and one can only choose between different types of joint arrangements. Small differences in color and a pleasing treatment of the joints can embellish the surfaces. Finally, one can also use split concrete blocks for facing. If the concrete is made with colorful aggregates, which break when being split, then masonry-work produced with these artificial blocks can also look good - similar to masonry of natural conglomerates, which are in fact nothing else but natural concrete.

10.1.3 Reinforced and pre-stressed concrete Concrete is an all-round construction material. Almost every building contains some concrete, but its questionable application in certain buildings-for example in its use in the style of brutalism - has brought it into discredit. Its dull grey color has contributed to the fact that the word concrete has become a synonym for ugly. In the field of bridges, concrete deserves a more favorable judgment. Not all concrete bridges have turned out to be beauties, but pleasing bridges can be built with concrete if one knows the art. Concrete is poured into forms as a stiff but workable mix, and it can be given any shape; this is an advantage and a danger. The construction of good durable concrete requires special know-how - which the bridge engineer is assumed to have. Good concrete attains high compressive strength and resistance against most natural attacks though not against de-icing saltwater, or CO2 and SO2 in polluted air. However, its tensile strength is low, and the use of concrete alone is therefore limited to structures which are only subject to compressive stresses. But tensile stresses also occur in abutments and piers due to earth pressure, wind, breaking forces and to internal temperature gradients. To resist these tensile forces, steel bars must be embedded in the concrete, the socalled reinforcing bars, and this has led to the development of reinforced concrete. The steel bars only really come into play after the concrete cracks under tensile stresses. If the reinforcing bars are correctly designed and placed, then these cracks remain as fine "hair cracks" and are harmless. A second method of resisting tensile forces in concrete structures is by pre-stressing.

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The zones of concrete girders which are under tensile stress due to loads or other actions are first put under compression - are pre-compressed - so that the tensile forces must first reduce these compressive stresses before actual tensile stresses come into being. This precompression is obtained by tensioning high strength steel bars or wire bundles, which are in ducts inside the concrete girder. Tensioning elongates the steel bars and they are anchored in this state at the ends of the girder, transferring this tensioning force as a compressive force onto the girder. These girders, pre-stressed with 'active steel" (pre-stressing steel) are in addition reinforced with "passive steel" (non-stressed steel bars) for various reasons. Pre-stressed concrete revolutionized the design and construction of bridges in the fifties. With pre-stressed concrete, beams could be made more slender and span considerably greater distances than with reinforced concrete. Pre-stressed concrete - if correctly designed - also has a high fatigue strength under the heaviest traffic loads. Pre-stressed concrete bridges soon became much cheaper than steel bridges, and they need almost no maintenance - again assuming that they are well designed and constructed and not exposed to de-icing salt. So as from the fifties pre-stressed concrete came well to the fore in the design of bridges. All types of structures can be built with reinforced and pre-stressed concrete: columns, piers, walls, slabs, beams, arches, frames, even suspended structures and of course shells and folded plates. In bridge building, concrete beams and arches predominate. The shaping of concrete is usually governed by the wish to use formwork which is simple to make. Plain surfaces, parallel edges and constant thickness are preferred. This gives a stiff appearance to concrete bridges, and avoiding this is one task of good aesthetic design. The extra cost for one-way curved surfaces, for tapering piers, for varying depth of beams or arch ribs is as a rule comparatively small. Therefore one should not hesitate to choose such divergences from the most primitive and simple forms in order to improve appearance. There is one great disadvantage to concrete as it emerges from the forms: the inexpressive, dull grey color of the cement skin. The surfaces frequently show stains, irregular streaks from placing the concrete in varying layers, and pores or even cavities from deficient compaction, which ire then patched more or less successfully. These deficiencies have lead to a widespread aversion to concrete, As well as to efforts for improvement. Some of the methods used to achieve a good concrete finish in buildings, like profiles and patterns on the formwork, ribs or accentuated timber veins etc. are not generally suitable. The best effect is obtained by bush hammering as was usual between 1934 and 1945 for the bridges of the German autobahn system. The concrete coating of the reinforcement is increased by 10 to 15 mm, so that a thin layer together with the cement skin can be taken off by fine or coarse bush hammering. The aggregate is then exposed with its structure and color.

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The protection of the embedded steel is not damaged, because the exterior cement skin is in any case the worst part of concrete. It is very porous, because mixing water collects at the forms of vibrating the concrete, and it is the porosity of the cement skin which makes it so susceptible to collecting the dirt of polluted air. With bush hammering one can adapt the degree of roughness to the size of the surfaces. Piers of viaducts, for example, were chiseled very roughly, taking off pieces 20 to 30 mm in depth by oblique chisel work. The color can be favorably influenced by the choice of colored aggregates like red porphyry or yellow limestone. Such surfaces age as well as natural stone masonry, and they retain their texture over a long period of time. The cement skin can also be washed off by special means after the concrete has hardened - such "exposed aggregate" surfaces can look pleasing, depending on the color and size of the aggregates. Bush hammering was given up after about 1950 due to the high labour cost. At that time suitable machines were not yet available, but with modern machinery this treatment should now be taken up again to embellish concrete surfaces. Another possibility is coloring the concrete it has been well developed during the last decade. By the use of mineral color pigments natural warm tones can be attained - earthy colors with tones of ochre, reddish-brown sepia. Umber, greyish-green, slate-grey. Dark toned piers of a viaduct often look better in the landscape than with a light grey color. Bright colored concretewith white cement-can for example be chosen to emphasize a fascia beam. Fritz Leonhardt has often recommended the painting of bridges in the same way that steel bridges are painted for corrosion protection. At the same time the dreary grey of normal concrete is converted into a harmonious colorful statement. For painting, soft colors should again be chosen and not bright loud colors. Before painting, the porous cement skin must be removed, so that the paint will not peel off later. Mineral colors, especially those with flour- or siliceous compounds, can also give an additional protection to the concrete. The colour film must be hygroscopic, so that it does not prevent the change of moisture content in the concrete. If the choice of color and type of paint is based on the most up-to-date information, then these paints can last long and keep their color like the paintwork of many old houses and churches, particularly in the Alps, which is often more than 200 years old and still beautiful. Color painting of concrete bridges has already been used in several places. A most striking example is that of the long bridges along the riverbanks in Brisbane, Australia.

10.1.4 Steel and aluminum Amongst bridge materials, steel has the highest and most favorable strength qualities, and it is therefore suitable for the most daring bridges with the longest spans. Normal building steel has compressive and tensile strengths of 370 N/mm2, about ten times the compressive strength of a medium concrete and a hundred times its tensile strength. A special merit of steel is its ductility due to which it deforms considerably before it breaks, because it begins to yield above 26

a certain stress level. This yield strength is used as the first term in standard quality terms. For bridges high strength steel is often preferred. The higher the strength, the smaller the proportional difference between the yield strength and the tensile strength, and this means that high strength steels are not as ductile as those with normal strength. Nor does fatigue strength rise in proportion to the tensile strength. It is therefore necessary to have a profound knowledge of the behavior of these special steels before using them. For building purposes, steel is fabricated in the form of plates (6 to 80mm thick) by means of rolling when red hot. For bearings and some other items, cast steel is used. For members under tension only, like ropes or cables, there are special steels, processed in different ways which allow us to build bold suspension or cable-stayed bridges. The high strengths of steel allow small cross-sections of beams or girders and therefore a low dead load of the structure. It was thus possible to develop the light-weight "orthotropic plate" steel decks for roadways, which have now become common with an asphalt wearing course, 60 to 80 mm thick. The pioneers of this orthotropic plate construction called it by the less mysterious and less scientific name "stiffened steel slabs". Plain steel plate, stiffened by cells or ribs, forms the chord of both the transverse cross girders and the longitudinal main-girders. Simultaneously it acts as a wind girder. This bridge deck owes its successful application mainly to mechanized welding, which is now in general use and which has greatly influenced the design of steel bridges. So plate girder construction now prevails, in which large thin steel plates must be stiffened against buckling. Previously, vertical stiffeners were placed by preference on the outer faces; longitudinal stiffeners were then arranged on the inside. Today all stiffeners are placed on this inside so as to achieve a smooth outer surface allowing no accumulation of dust or dirt deposits that retain humidity and promote corrosion - the "Achilles heel" of steel structures. Modern steel girder bridges now hardly differ from prestressed concrete bridges in their external appearance - except perhaps in their color. This is perhaps regrettable, because stiffeners on the outside enliven the plate-faces, give scale and make the girder look less heavy. In addition to plate girders, trusses also take full advantage of the material properties of steel. Very delicate looking bridges can be built by joining slender steel sections together to form a truss. Again welding has improved the potential for good form, because hollow sections can be fabricated and joined without the use of big gusset plates. In this way smooth looking trusses arise without the "unrest" which occurs by joining two or four profiles of rolled section with lattice or plates. Steel must be protected against corrosion and this is usually done by applying a protective paint to the bare steel surface. Painting of normal steels is technically necessary and can be used for color design of the bridge.

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The choice of colors is an important feature for achieving good appearance. There are steels which do not corrode in a normal environment (the stainless steels V2A and V4A to DIN 17440), but are so expensive that they are used only for components that are either particularly susceptible to the attacks of corrosion or that are very inaccessible. From the USA came Tentor steel, alloyed with copper, its 'first corrosion layer being said to protect it against further corrosion. This protective rust has a warm sepia-toned color which looks fine in open country. This type of protection, however, does not last in polluted air and the corrosion continues. For steel bridges, good use should be made of the technical necessity of protecting the steel with paint to improve appearance and to achieve harmonious integration of the structure within the landscape. Aluminum was occasionally used for bridges and the same form was used as for steel girders. Aluminum profiles are fabricated by the extrusion process which allows many varied hollow shapes to be formed, so that aluminum structures can be more elegant than those of steel. Aluminum profiles are popular for bridge parapets because they need no protective paint.

10.1.5Timber:Timber has favorable qualities of strength for resisting compression, tension and bending. Rough tree trunks or sawn timber beams have been used since primitive times for beam bridges; raking frames and arches soon allowed larger spans. The Swiss carpenters, the brothers Grubennann reached a 100 m span with the timber bridge across the River Rhine near Schaffhausen. Timber should be protected against rain and therefore covered bridges with a roof and sidewalls with windows evolved, and many of these are rightly preserved in the Alpine countries, testifying to the high standard of their craftsmanship. Many now only serve pedestrians. Recently timber bridges have been given a new impetus by glue technology which allows larger cross-sections and larger lengths of beams to be made than grow naturally. Moreover timber can now be better protected against weather and insect attack. So new possibilities have arisen or the choice of structure, for its shaping and for the size. Large timber trusses and even folded space trusses have been built using steel gusset plates for jointing the members. Timber bridges, however, have limits of span and carrying capacity, confining them mainly to bridges for pedestrians or for secondary roads.

10.2 Bridge construction technology Bridge construction technology has evolved over the years. In this age of advanced science, technology and machines, bridges have undergone various changes and different types of bridges are being constructed in major countries of the world. Construction techniques like slurry walls, post-tensioning, soil freezing, reinforced earth walls, suspension, folding etc. are being used. Bridge construction is changing. New construction techniques and new materials are

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emerging and accordingly the construction machinery industry has played a pivotal role.

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CHAPTER-11 TYPES OF BRIDGE CONSTRUCTION MACHINERIES 11.1 Construction machineries The various machineries for constructing bridges are: Bridge Crane Gantry Crane Floating Crane

11.1.1 Bridge cranes:-

Figure 11.1 Bridge crane Bridge crane is a heavy machinery that is designed to build or fix a bridge. It operates on two tracks and has four way horizontal movement. Bridge cranes cover rectangular area and can be floor supported or hung from the ceiling. The main components of bridge cranes are bridge, trolley, hoist drum, hoist cable, hoist block, hook bumpers, pendant and limit switches. On-off switch is on control pendant for taking emergency steps, in the event of failure of any of the control-panels. Bridge cranes are either double girder or single girder. Double girder bridge crane can be utilized at any capacity where extremely high hook lift is required because the hook can be pulled up between the girders. For high speeds and heavy services too, double girder bridge cranes are very useful. In bridge crane rigid box girder construction and durable trolley design are well suited for heavy service applications.

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11.1.2 Gantry cranes

Figure 11.2 Gantry crane

Gantry cranes are those cranes which are generally used for moving heavy loads. They are a common type of portable material handling equipment used in job station or secondary task areas. Gantry cranes are quite similar to overhead cranes except that the bridge which carries trolley is rigidly supported on two or more legs running.

11.1.2.1 Gantry crane sizes and marking:Though gantry cranes are known for its huge models but, there happen to be smaller cranes as well that are found in small industries and warehouses etc. The cranes are available in both, adjustable as well as fixed height. Its making too is either of steel or aluminum, depending upon the application of the crane. Each gantry crane is designed with two upright beams and a cross beam. It has an A-frame shaped set of two legs with wheels beneath to render maximum mobility and portability.

11.1.2.2 Types of gantry cranes:Gantry cranes can be of different range like single girder, double girder, double leg, single leg, and cantilever styles for indoor or outdoor service. It is also available in fixed height steel and adjustable steel. Gantry crane is an economical device for lifting materials anywhere in a facility. Gantry cranes are also supplied with four roller-bearing steel wheels for easy maneuverability.

Uses of gantry cranes:Gantry cranes or bridge cranes are useful machinery which find its application in constructing bridges. Lifting heavy industrial devices, lifting containers in seaports, and are ideal for use in air craft, automotive, and marine repair shops.

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11.1.2.4 Renting Gantry Crane For companies that cannot afford to buy a whole new gantry crane, it would be most cost effective to get a gantry crane on rent. Getting used gantry cranes have many advantages, the best being that one does not have to shell out a big amount upfront to get the required equipment.

A floating crane refers to a type of sea vessel which has a crane mounted on it. In earlier days, floating crane designs were nothing more than old ships transformed to include a huge crane mounted over the deck. Eventually, catamaran, semi-submersible designs changed the face of floating cranes. Read on to know more about these cranes.

Figure11.3Renting gravity crane

11.1.3 Floating Cranes Floating cranes are those heavy-duty cranes which are frequently used for building bridges, and constructing ports. Fleeting applications in ports etc. They also have great utility in loading and unloading of heavy weights on and off ships. The floating cranes are generally selfpropelled. They have the powerful diesel generators to work the crane winches, which can be switched to propel the craft.

11.1.3.1 Floating Cranes Working Floating cranes can be mounted on a swing base installed on the deck of a pontoon and can swing in a circular motion both in a clockwise and anticlockwise direction. Apart from pontoon mounted cranes, some floating cranes barges with a lifting capacity exceeding 10,000 tones and are used to transport entire bridge sections.

11.1.3.2 Floating Cranes Uses There are various uses of a floating crane. These vessels are able to lift and maneuver huge and heavy sub-assemblies into position. Floating cranes also felicitate the assembly of massive projects out of numerous smaller assemblies in most weather conditions. 32

Apart from drilling and construction purposes, floating cranes are used for sunken ship retrieval purposes also.

Used Floating Crane Since these are one of the most expensive types of construction cranes, the trend of hiring used floating cranes for a given time period is quite popular among builders and construction workers. One can find a number of floating crane suppliers online to set hiring or purchasing deals.

Figure 11.4 Floating crane For building bridges launching girder is an important machinery. With sophisticated equipment, launching girder itself is a normal structure. With different launching capacities and heights, launching girders are used for making different kinds of bridges. Launching girder itself is a steel structure which moves forward on the bridge piers span by span. As launching girder can handle cast-in place concrete, as well as prefabricated elements, it is highly adaptable for a wide range of spans and types of superstructure

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CHAPTER-12 TOTAL STATION 12.1 Coordinate measurement Coordinates of an unknown point relative to a known coordinate can be determined using the total station as long as a direct line of sight can be established between the two points. Angles and distances are measured from the total station to points under survey, and the coordinates (X, Y, and Z or northing, easting and elevation) of surveyed points relative to the total station position are calculated using trigonometry and triangulation. To determine an absolute location a Total Station requires line of sight observations and must be set up over a known point or with line of sight to 2 or more points with known location. For this reason, some total stations also have a Global Navigation Satellite System Interface which does not require a direct line of sight to determine coordinates. However, GNSS measurements may require longer occupation periods and offer relatively poor accuracy in the vertical axis.

12.2 Angle measurement Most modern total station instruments measure angles by means of electro-optical scanning of extremely precise digital bar-codes etched on rotating glass cylinders or discs within the instrument. The best quality total stations are capable of measuring angles to 0.5 arc-second. Inexpensive "construction grade" total stations can generally measure angles to 5 or 10 arcseconds.

12.3 Distance measurement Measurement of distance is accomplished with modulated microwave or infrared carrier signal, generated by a small solid-state emitter within the instrument's optical path, and reflected by a prism reflector or the object under survey. The modulation pattern in the returning signal is read and interpreted by the computer in the total station. The distance is determined by emitting and receiving multiple frequencies, and determining the integer number of wavelengths to the target for each frequency. Most total stations use purpose-built glass corner cube prism reflectors for the EDM signal. A typical total station can measure distances with an accuracy of about 1.5 millimeters (0.0049 ft) + 2 parts per million over a distance of up to 1,500 meters (4,900 ft). Reflector less total stations can measure distances to any object that is reasonably light in color, up to a few hundred meters.

12.4 Data processing Some models include internal electronic data storage to record distance, horizontal angle, and vertical angle measured, while other models are equipped to write these measurements to an external data collector, such as a hand-held computer. When data is downloaded from a total station onto a computer, application software can be used to compute results and generate a map of the surveyed area. The new generation of 34

total stations (e.g. Hilti POS 15/18) can also show the map on the touch-screen of the instrument right after measuring the points.

12.5 Applications:Total stations are mainly used by land surveyors and Civil Engineers, either to record features as in Topographic Surveying or to set out features (such as roads, houses or boundaries). They are also used by archaeologists to record excavations and by police, crime scene investigators, private accident re-constructionists and insurance companies to take measurements of senesce

12.6 Mining Total stations are the primary survey instrument used in mining surveying. A total station is used to record the absolute location of the tunnel walls (stopes), ceilings (backs), and floors as the drifts of an underground mine are driven. The recorded data are then downloaded into a CAD program, and compared to the designed layout of the tunnel. The survey party installs control stations at regular intervals. These are small steel plugs installed in pairs in holes drilled into walls or the back. For wall stations, two plugs are installed in opposite walls, forming a line perpendicular to the drift. For back stations, two plugs are installed in the back, forming a line parallel to the drift. A set of plugs can be used to locate the total station set up in a drift or tunnel by processing measurements to the plugs by intersection and resection

12.7 Stone block The type of sleeper used on the predecessors of the first true railway (Liverpool and Manchester Railway) consisted of a pair of stone blocks laid into the ground, with the chairs holding the rails fixed to those blocks. One advantage of this method of construction was that it allowed horses to tread the middle path without the risk of tripping. In railway use with ever heavier locomotives, it was found that it was hard to maintain the correct gauge. The stone blocks were in any case unsuitable on soft ground, where timber sleepers had to be used.

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CHAPTER-13 SLEEPERS 13.1 Wooden sleepers

Figure 13.1 Wooden sleeper

A variant fastening of rails to wooden ties

.

A variety of softwood and hardwoods timbers are used as ties, oak, jarrah and karri being popular hardwoods, although increasingly difficult to obtain, especially from sustainable sources. Some lines use softwoods, including Douglas fir; while they have the advantage of accepting treatment more readily, they are more susceptible to wear but are cheaper, lighter (and therefore easier to handle) and more readily available. Softwood is treated, historically using creosote, but nowadays with other less-toxic preservatives to improve resistance to insect infestation and rot. New boron-based wood preserving technology is being employed by major US railroads in a dual treatment process in order to extend the life of wood ties in wet areas. Some timbers (such as sal, mora, jarrah or azobé) are durable enough that they can be used untreated. Problems with wood ties include rot, splitting, insect infestation, plate-cutting (known as chair shuffle in the UK), (abrasive damage to the tie caused by lateral motion of the tie plate) and spike-pull (where the spike is gradually loosened from the tie). For more information on wood ties the Railway Tie Association maintains a comprehensive website devoted to wood tie research and statistics.

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13.2 Concrete sleepers

Figure 13.2 Concrete sleeper

In concrete railroad ties increased after World War II following advances in the design, quality and production of pre-stressed concrete. Concrete ties were cheaper and easier to obtain than timber and better able to carry higher axle-weights and sustain higher speeds. Their greater weight ensures improved retention of track geometry especially when installed with continuouswelded rail. Concrete sleepers have a longer service life and require less maintenance than timber due to their greater weight which helps them remain in the correct position longer. Concrete sleepers need to be installed on a well-prepared sub grade with an adequate depth on free-draining ballast to perform well. In 1877, M. Monnier, a French gardener, suggested that concrete could be used for making ties for railway track. Monnier designed a tie and obtained a patent for it, but it was not successful. Designs were further developed and the railways of Austria and Italy used the first concrete ties around the turn of the 20th century. This was closely followed by other European railways. Major progress was not achieved until World War II, when the timbers used for ties were scarce due competition from other uses, such as mines. Following research carried out on French and other European railways, the modern pre-stressed concrete tie was developed. Heavier rail sections and long welded rails were also being installed, requiring higher-quality ties. These conditions spurred the development of concrete ties in France, Germany and Britain, where the technology was perfected. On the highest categories of line in the UK (those with the highest speeds and tonnages) pre-stressed concrete sleepers are the only ones permitted by Network Rail standards. Most European railways also now use concrete bearers in switches and crossing layouts due to the longer life and lower cost of concrete bearers compared to timber, which is increasingly difficult and expensive to source in sufficient quantities and quality. On November 8, 2011, the US Federal Railroad Administration (FRA) put into effect new regulations on concrete ties, with notices published by the FRA in the April 1 and September 9, 2011 U. S. Federal Register. The FRA notices say that the need for the new rules was shown by the derailment of an Amtrak train near Home Valley, Washington on April 3, 2005, which according to the U.S. National Transportation Safety Board was caused in part by 37

excessive concrete tie abrasion. To be counted as a good tie under FRA regulation 213.109(d)(4), a concrete ties shall not be deteriorated or abraded under the rail to a depth of one-half inch or more. Limits on other types of concrete tie deterioration are also given.

13.3 Steel sleepers

Figure 13.3 Steel sleeper

Steel sleepers are formed from pressed steel and are trough-shaped in section. The ends of the sleeper are shaped to form a "spade" which increases the lateral resistance of the sleeper. Housings to accommodate the fastening system are welded to the upper surface of the sleeper. Steel sleepers are now in widespread use on secondary or lower-speed lines in the UK where they have been found to be economical to install due their ability to be installed on the existing ballast bed. Steel sleepers are lighter in weight than concrete and able to stack in compact bundles unlike timber. Steel sleepers can be installed onto the existing ballast, unlike concrete sleepers which require a full depth of new ballast. Steel ties are 100% recyclable and require up to 60% less ballast than concrete ties and up to 45% less than wood ties. Historically, steel ties (sleepers) have suffered from poor design and increased traffic loads over their normally long service life. These aged and often obsolete designs limited load and speed capacity but can still be found in many locations globally and performing adequately despite decades of service. There are great numbers of steel ties with over 50 years of service and in some cases they can and have been rehabilitated and continue to perform well. Steel ties were also used in specialty situations, such as the Hejaz Railway in the Arabian Peninsula, which had an ongoing problem with Bedouins who would steal wooden ties for campfires. Modern steel ties handle heavy loads, have a proven record of performance in signalized track, and handle adverse track conditions. Of high importance to railroad companies is the fact that steel ties are more economical to install in new construction than creosote-treated wood ties and concrete ties. Steel ties are utilized in nearly all sectors of the worldwide railroad systems including heavy-haul, class 1’s, regional, short lines, mining, electrified passenger lines (OHLE) and all manner of industries.

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Notably, steel ties (bearers) have proven themselves over the last few decades to be advantageous in turnouts (switches) and provide the solution to the ever-growing problem of long timber ties for such use.

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19. Jones, J. A. A. (1976). "Soil piping and stream channel initiation". Water Resources Research 7 (3): 602–610. Bibcode:1971WRR.....7..602J. doi:10.1029/WR007i003p00602. 20. Terzaghi, K., Peck, R.B., and Mesri, G. 1996. Soil Mechanics in Engineering Practice. Third Edition, John Wiley & Sons, Inc. Article 18, page 135. 21. Terzaghi, K., 1943, Theoretical Soil Mechanics, John Wiley and Sons, New York

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