intro

Study on precast segments of HMRL project

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INTRODUCTION


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1 INTRODUCTION Conventional construction process deals with the cast in-situ techniques. Such techniques will not suit for heavy projects. For major projects accuracy is very important .even a small error can cause a lot of trouble in construction process. Every step like batching mixing transporting placing compacting curing etc. should be carried out under controlled conditions. To achieve desired level of accuracy in every stage casting should be done in a controlled area prior to placing in the site. Such process of preparing structural members in a yard instead of site is termed as precasting

Precasting process provides solution for many site problems like improper batching, mixing, laying dimensions of the structure etc .now a days a wide range of precast members are being used to reduce the complications in the construction work along with accuracy. The metro rail project of Hyderabad being a prestigious project which is in progress demands precast ed members for its construction .the elevated metro rail bridge can be represented by a standard 31m long segmented deck standing on two piers .though there are varying lengths of spans ,31m span is considered as standard.

Image a long 31m span bridge member being casting at casting yard far away from site , transported and erected at site. how difficult it is and makes us feel impossible and so can be avoided by casting i,e., dividing the entire 31m long bridge girder into few each segment of certain length and casting them at yard, transporting and joining the respective segments at the site to act as a monolithic structure of 31m span. this method of casting all the segments of a span side by side at casting yard with a ease to separate from one another into single individual segment is called match casting.

1.1TERMINOLOGY

1.1.1 Precast Definition


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A precast concrete product is a factory-made piece manufactured with concrete and which, later, together with other pieces, will become part of a larger structure. Precast concrete elements are prepared, cast and hardened at specially equipped plants with a permanent location. Once a precast concrete product is produced and all the undertaken quality controls satisfactory, the unit is stored until delivery. It is then transported for use at another site.

1.1.2 Readymade Steel Plant (RMS) Readymade Steel plant is primarily in the business of providing ready to use steel for construction activities to the infrastructure industry. Readymade Steel is used in commercial and residential projects and infrastructure works, including metro/mono-rail, bridges, highways, power plants, airports, malls, hotels, buildings, factories. The plants products include: cut and bend, prefabricated cages, beam cages and welded mesh fabric. Cut and bent steel is used in columns, beams, foundations and slabs.

1.1.3 Ready Mix Concrete (RMC) Ready-mix concrete is concrete that is manufactured in a factory or batching plant according to the design mix, and then delivered to a work site, by truck mounted intransit mixers. This results in a precise mixture, allowing special concrete mixturesto be developed and implemented on construction sites.

Ready mix concrete is sometimes preferred over on-site concrete mixing because of the precision of the mixture and reduced work site confusion.

1.1.3.1 Standard Ready Mix Concrete Vs Site Mixed Concrete A centralized concrete batching plant can serve a wide area. Site-mix trucks can serve an

even larger area including remote locations that standard trucks cannot. The plants are located in areas zoned for industrial use, and yet the delivery trucks can

service residential districts or inner cities. Site-mix trucks have the same capabilities. Better quality concrete is produced. Site mix can produce higher compression strength

with less water than standard batching methods.

1.1.4 Match Casting


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This is the method used to cast pier and field segments. One face of the segment will have small concrete blocks protruding from the cross-sectional surface (Male Shear Key), while the face of the adjacent segment will have holes sunken into the surface (Female Shear Key). These two segments will be connected during construction with Male Shear Key fitting into the Female Shear Key.

The main purpose is to ensure that the precast segments can be perfectly joined together without any voids in between. This is very important for a post-tensioned bridge, if the contacting surfaces of the two segments are not perfectly matched, stress concentration may occur. This may lead to sudden failure of the structure.

The Match Casting starts with the production of the pier segment. After it has reached the required strength, it will be used as the end socket for the first field segment, so that the male/female Shear Key of the first field segment will perfectly match with the female/male Shear Key of the pier segment. Then, the first segment will be used as the end socket for the second field segment and so on.

1.1.5 Match Cast Mould Match cast mould is a specially built formwork to cast the segments at casting yard. Various parts of match cast mould are

1. soffit assembly 2. inner form

3. bulkheads 4. access staircase

5. outerform Match cast mould is like a master piece that makes the similar kind of impression and gives design for all the segments.

1.1.6 Debonding Agent Before concreting a debonding agent is applied over the inner side of the match cast mould in-order to resist adhesion between the mould and the casting segment. While de-shuttering there will not be any inconvenience caused by this adhesive force and the segment can easily be


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de-shuttered. The debonding agent here in L&T pre casting yard used is wonder wax 1008 or bee wax and coconut oil.

1.1.7 Post tensioning Post-tensioned concrete is a term heard more and more in the construction industry today. This method of reinforcing concrete enables a designer to take advantage of the considerable benefits provided by prestressed concrete while retaining the flexibility afforded by the cast-in-place method of building concrete structures. Post-tensioning is simply a method of producing prestressed concrete, masonry, and other structural elements. The term prestressing is used to describe the process of introducing internal forces (or stress) into a concrete or masonry element during the construction process in order to counteract the external loads applied when the structure is put into use (known as service loads). These internal forces are applied by tensioning high-strength steel, which can be done either before or after the concrete is placed. When the steel is tensioned before concrete placement, the process is called pretensioning. When the steel is tensioned after concrete placement, the process is called post-tensioning. Because pretensioning requires specially designed casting beds, it is used generally in the precast manufacturing process to make simple shapes that can be trucked to a jobsite. Post-tensioning is done onsite by installing post-tensioning tendons within the concrete form-work in a manner similar to installing rebar.

1.1.8 Grouting The definition of grouting is filling masonry joints or gaps with a coarse, thin cement or mortar mixture.

1.1.8.1 Purpose Of Grouting Grouting prevents debris and dirt from gathering in between tiles or rocks. It also provides additional structural support to the pieces so they remain stationary for a long time, even with regular use and exposure to heat, cold and moisture. Grout also adds visual appeal to projects and gives the laid materials a finished look.

1.1.9 Tendons


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The basic element of a post-tensioning system is called a tendon. A post-tensioning tendon is made up of one or more pieces of prestressing steel, coated with a protective coating, and housed inside a duct or sheathing. A tendon has anchors on each end to transmit the forces into the structure. Long tendons may have intermediate anchors along their length to allow for stressing at construction joints. The prestressing steel is manufactured to the requirements of ASTM A-416 and typical strand sizes are 0.50 and 0.60 inch diameters. The entire tendon assembly must meet the requirements of ACI 423, and should be manufactured and fabricated by a plant that is certified by a program such as the Post-Tensioning Institute's Plant Certification Program. To get an idea of the high strength of this type of steel, a typical steel strand used for post-tensioning will yield about 243,000 psi. In contrast, a typical piece of rebar will yield about 60,000 psi.

1.2L&T IN METRO

The prestigious task of developing this project of national importance has been awarded to Larsen & Toubro Limited (L&T) - the USD 9.8 billion engineering, technology, construction and manufacturing organization. L&T has an impressive track record of executing major metro projects in the country. This involved construction of elevated and underground metro rail corridors, monorails, composite railway construction works including station buildings and associated systems in this sector. Metro Network Consisting of three high density corridors, Hyderabad Metro network will cover a total distance of 71.16 km involving 66 ultra-modern station buildings with state-of-the-art depots and complete infrastructure.

Corridor - I Miyapur - LB Nagar (28.87 km - 27 stations) Corridor - II JBS Falaknuma (14.78 km - 16 stations) Corridor - III Nagole Shilparamam (27.51 km - 23 stations)Features of L&T metro rail

Advantages Of Hyderabad Metro

Elevated world-class station buildings at approximately every kilometre.

Connects major offices, retail and residential areas - The two tracks (up and down lines) pass through the arterial roads of the city


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Connects major bus stations at Miyapur, MGBS, Koti, Dilsukhnagar, Charminar and Jubilee Bus Station

Integration with existing rail terminals at Secunderabad, Begumpet and Nampally

Link to MMTS services at Bharatnagar, Begumpet, Khairatabad, Malakpet&Falaknuma

Feeder bus services to stations from different areas of the city is being planned by GoAP

1.3 OBJECTIVE OF THE PROJECT The main objective of the project is to explain the importance of match casting process in order in complete large projects like HMRL. The prestigious project of 71.16km long metro rail bridge along with 66 stations which is provided with a limited completion time of 56 months can be completed intime without compromising regarding the issues like quality ,durability, performance etc only by adopting modern techniques like match casting , post tensioning and several other methods. Match casting will enable to cast all typical segments side by side ,separate each other for the ease of transportation and handling and joing all together into a monolithic structure by post tensioning tendons


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REVIEW OF LITERATURE


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2.1 INTRODUCTION

The planning and implementation of the first phase of Hyderabad metro rail project in record time has drawn attention of many other metro cities within India as well as outside India to have their own Mass Rapid Transit System (MRTS). In fact, MRTS project in Mumbai, Chennai, Banglore are already in advanced stages of tendering, design and implementation etc.

It is to be noted that the most important requirement for successful implementation of MRTS project is dependent on the appropriate selection of Rolling Stock (metro trains) based on the city i.e. commuter traffic, population, traffic demand, demography. However there is a serious lack of issue of lack of rolling stock expert availability in India and further, whatever limited manpower is unavailable from Indian Railways who were in deputation to HMRL and have either returned to their parent organization or are currently engaged in some other MRTS projects. Few of the experts have also moved to other overseas projects like Dubai metro, Singapore metro etc.in search of greener pasture. Hence, it is to be noted that there is a serious shortage of skilled manpower in Rolling Stock industry currently

2.2 BACK GROUND

The entire metro rail project is constructed using precast segments, station members and cast in-situ piers. As its name implies, a segmental bridge is a bridge built in short sections (called segments), i.e., one piece at a time, as opposed to traditional methods that build a bridge in very large sections. The bridge is made of concrete that is either cast-in-place (constructed fully in its final location) or precast concrete (built at another location and then transported to their final location for placement in the full structure).These bridges are very economical for long spans


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(over 100 meters), especially when access to the construction site is restricted. They are also chosen for their aesthetic appeal.

Taking stock of the urban transport scenario in Indian cities, this is the first full-length study of the metro rail system in India. In recent times the metro rail has come up as a favoured alternative of mass transport in urban spaces faced with growing population, heightened vehicular traffic, and increased pollution. Using data, analysis, and first-hand information, this book tells the story of metro rail as proposed and undertaken across India from Kolkata in the east and Mumbai in the west to Delhi and Jaipur in the north and Chennai, Bangalore, Hyderabad, and Kochi in the south. Focusing on the complexities of project planning and contrasting the Indian experience with those of its global counterparts, this volume distils important lessons for future infrastructure projects. While the metro rail system has considerably improved inter-city connectivity, the metro story in India is an ongoing one. This chapter discusses the development of the metro rail system in Hyderabad. It details the various phases of the project from proposal to implementation. The project demonstrates that is it only when the government takes firm steps to move the metro process forward will the city get its mass transit system. As far as project planning was concerned, the Hyderabad Metro project conformed to most of the requirements except for having clear-cut criteria of prioritization in implementation.

2.3 DIFFERENT TYPES OF PARAMETRES

According toParthaPratim Roy, General Manager (Technical), ADAPT International Pvt. Ltd. KolkataMost Modern Bridges are Built Segmentally. In such bridges, the components carry loading in a configuration other than thecompleted structure. Stress during construction exceeds that of the completed structure. Early-age loading of concrete results in large deformations. Bridge engineers must keep these aspects in mind while designing segmental bridges. Major design objectives are:

Geometry Control During Construction (Deflection and Camber) Crack Control During Construction (Stress Check) Structural Safety and Stability During Construction


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Control of Stresses in Completed Structure Control of Strength of Completed Structure

Evolution of Concrete Bridge Geometry

Simple Span & Support

Initially, the best and possible way was to opt for Simply Supported Span Bridges. That was easy to construct, but required huge sections. Still for certain cases and specific requirements, it is practical to go ahead with such combinations.Later the concept of Continuous Span Bridges came up, where more economic section utilization was possible. To save construction time Precast Prestressed concrete sections (PCPS) are cast and carried to job site from casting yard; erected over pier and finally spliced over supports. Needless to mention these sections are pretensioned. It helps to establish continuity for live load distribution to achieve longer spans (generally upto 40m). Compared to Single Span bridges, sudden change of slopes can be avoided which allows improved maintenance and quality of ride. However, potential possibilities of crack formation at the joints (non-prestressed) still exists.

To overcome the potential of crack formation, the concept of post-tensioning got introduced (PCPS with Post-Tensioning over the Supports only). It allows the engineer to achieve following advantages:

Continuity established for live load Better performance of joints due to presence of precompression at the joints Reduction of Dead Load Moment Thinner, and longer spans

Later engineers started using the advantages of PT (Post-Tension) over the entire legth of bridge frame. This time Post-Tensioning directly participates in resisting positive moment at mid-span. Deflections are also controlled more effectively. Longer spans (more than 60 meter) are achievable. This concept also provides added economy by reducing the number of piers.


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However, still at this stage Bridge geometry was restricted by non-technical parameters like limitation of transportation in length and width of members. Moreover, weight of sections were limited by the available crane capacity and lifting equipment. Hence the new concept got introduced when small pieces are casted and transported to job site; erected in place and hold with bracket to be spliced. Longer spans of 100 meter or more are achievable in this process and no of piers can be reduced to achieve economy.

About Segmental Construction

As its name implies, a segmental bridge is a bridge built in short sections (called segments), i.e. one piece at a time, as opposed to traditional methods that build a bridge in very large sections. The bridge is made of concrete that is either cast-in-place (constructed fully in its final location) or precast concrete (built at another location and then transported to their final location for placementin the full structure).These bridges are very economical for long spans (over 100 meters), especially when access to the construction site is restricted. They are also chosen for their aesthetic appeal.

Readymade Steel Limited, is one of the pioneers in introducing the concept of ready to use steel for the construction industry in the country . Established in 2006 , the company had an early mover advantage for the ever growing demand for factory fabricated steel reinforcement that is required by many contracting companies working on fast track infrastructure, residential and commercial projects coming up all over India.Traditionally steel reinforcement had been fabricated on the construction site which involved a large labor force and a huge amount of wastage of steel. Readymade Steel offers the contractor a fast and efficient service, delivering steel in phased requirements to the site. Through the factory process, Readymade Steel emphasises the use of the Green Building Concept which is rigorously monitored to ensure that we conserve natural resources and the processed steel also meets site requirements. All our processes are non polluting and keep the environment free from hazardous materials.

An ISO 9001:2008 certified company the product range of Readymade Steel includes not only factory fabricated reinforcement steel bars cut into various shapes and sizes like cranked bars, stirrups, verticals, column /beam cages etc. but also pre-fabricated cages and welded wire mesh


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fabric.

Readymade Steel within a period of six years has been associated with many prestigious structures such as Mumbai Mono Rail, Sahar Elevated Access Road,Nashik Elevated Corridor,Phoenix Mills Market City Kurla and Palais Royale, Mumbai , Hyderabad metro rail project

METHODOLOGY


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3. SEGMENT CASTING Segment can be explained as a unit of girder. In this particular project there are 4 types of segments for standard span of 31m namely S1, S2, S3, S4.all these segments are erected and connected together using post tensioning tendons. Every segment is provided with extra features in order to satisfy special functions required.

3.1 PARTS OF SEGMENT

a. Shear Keys

b. Blisters

c. Arrangement For Future Stressing

d. Guide Cones

e. Access Openings

f. Drainage Spouts


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Fig 1. Parts of segment

SHEAR KEYS One face of the segment will have small concrete blocks protruding from the cross-sectional surface (Male Shear Key), while the face of the adjacent segment will have holes sunken into the surface (Female Shear Key). These two segments will be connected during construction with Male Shear Key fitting into the Female Shear Key.

BLISTERS Blisters are provided in bottom slab for temporary stressing of segments. These shall be concreted after shifting the segments to stack yard for concreting of the blisters. A box made of structural steel of required dimensions shall be placed and concrete is poured. Temporary stressing is done during erection of spans

GUIDE CONES Guide cones are provided for pier head segment S1 to anchor the post tensioned strands.


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This will protect the surrounding concrete from stress induced due to post tensioned tendons.

SHEATHING The main purpose of sheathing is to provide access way to tendons to pass through all the segments according to the coordinates mentioned. HDPE pipes are inserted into segment reinforcement prior to concreting to leave space for tendons. Sheathing will act like a layer between precast concrete and filling grout.

DRAINAGE SPOUTS Drainage spouts will help in avoiding the accumulation of water on the deck which may cause interruption for trains. Prolonged exposure to water will result in reduction in durability of the structure

ACCESS OPENINGS Access openings are provided for regular inspection and repairs. These are exclusively provided for S3 segment. Each span has 2 openings.

ARRANGEMENTS FOR FUTURE STRESSING Arrangements are provided for any future requirement of stressing. This facility is available for few particular segments.

PIPES TO FILL BEARING GROUT After erection process is finished bearing grout is to be filled between the S1 segment and

LIFTING HOLES Lifting holes are provided for every segment to the top slab. For every segment four holes will be provided in order to make provision for insertion of crane hooks while transporting. These are useful to move segment to stack yard, to lift on to the truck before transporting to the site and also during erection to suspend from launching girder before post tensioning.

3.2 MATERIALS USED

Table 1.Materials used


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S. no.

Name Brand/source Conforms to remarks

1. Concrete M45

grade RMC India Nacharam and

captive batching plant

IRSCBC/Clause 1.5 of outline specifications for

viaduct works

2 Water Construction water from

bore well Clause 4.3 of IRSCBC

3 HDPE sheathing Rex polymers Confirming to clause

7.2.6.4.2.4, appendix B and B1 of IRS.CBC

4 Anchorage sets Approved supplier

5 Reinforcement

steel SAIL/TISCON/RINL/ISW Fe 500TMT IS 1786

6 Debonding agent Wonder wax 1008 or

Beewax and coconut oil

Technical specification and MTC

7 Mould releasing

agent

Wonder releasing comp 9999

Technical specification and MTC

8 Structural steel

for moulds Approved supplier Confirming to IS:2062

9 GI Binding

Wire(18 gauge) Locally available IS 280 & IS 4826

10 40mm threaded Bars 1030 grade

Macalloy or equivalent

11 Formwork L&T Depot


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12 Grouting material

Non shrink comentitious

ready mix grout GP2 Sika grout 214, BASF

master flow 918T.

13 Retarder Rheomix 288

14 Inhibitor Approved supplier

15 M.S. Round

20mm dia for earthing

Approved brand

16 Pierheadmoulds Both straight and

curve bed 12 nos.

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1HP pump with

accessories and hose for curing

6 nos.

3.3 MATCH CASTING

Pre-cast construction of bridge members has several advantages in comparision with cast-in-place bridge construction. The key advantage is that casting of the segments can be performed under controlled, plant-like conditions at the pre-cast yard. Figure 2 shows reinforcement for a typical pre-cast segment and Figure 3 shows the segment after completion. The industrialized process allows easy quality control of segments prior to placement in the superstructure and saves money through reuse of the pre-casting formwork. Further, surface finishing works, such

as texturing, sandblasting, painting, and coating can be performed on the ground level without scaffolding when the segments are still accessible from all sides prior to installation in the superstructure.


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Fig2. Reinforcement for segment

Figure3. Typical precast segment Another major advantage is that the complete casting of the superstructure can be removed from the critical path of the overall construction schedule, since superstructure segments can be precast during construction of the substructure. Assembly of the bridge superstructure takes


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much less time than cast-in-place construction, as precast segments have gained more strength and do not need to cure on site before being pre-stressed together . Match-casting is an important concept in the construction of precast segmental construction. This was developed by Jean Muller and it allows the transverse slicing of concrete box girders and the assembly of such slices the segments in the same order as they were produced, without any need for additional in situ concrete to complete the bridge deck. Match-casting using the short-line method is illustrated in Figure 3. This is done by ensuring that the segments are cast in the formwork between a bulkhead at one end and an already cast segment at the other . The segments are cast in the casting yard one at a time. The segments are cast against the previous one so that the end face of one segment will be an imprint of the neighbor segment, ensuring a perfect fit at the erection. One of the key elements to effective match-casting is accurate geometry control. Control of geometry is important as the tolerances are in the order of a fraction of a millimeter and any deviation in excess of this will result in misalignment of the bridge. The error becomes more critical when there are horizontal and vertical curves in the bridge alignment On a recent project it was found that the accurate calculation and correction of the errors in the match casting process s was tedious and caused delays in the casting process. While software for the geometry control is commercially available, its use is restricted to specialty consultants and expensive. Using some algorithms the errors and corrections required can be calculated rapidly and will not be a bottleneck for the match-casting process. A description of the match-casting process is given in the next section.

3.3.1 Short-line method


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Figure.4 Match casting using short line method Short-line match casting method can be adopted for building a deck with any geometry. The geometry of the bridge is solely controlled during the casting of the segments. It offers very little option to control the geometry of the bridge or the span during the erection process. The principles behind the match casting operation to obtain the above mentioned geometry are discussed in the following text.

3.3.2 Match Casting for a Straight Bridge When a straight bridge is desired, the match marking mate segment (n- 1) is moved from the casting position to the match-cast position along a straight line, and this usually verified by taking measurements on the punched plates embedded on the concrete during casting. A pure translation of each segment between the cast and match-cast positions therefore results in the construction of a perfectly straight bridge (both in elevation and plan view), within the accuracy of the measurements made at the site.

3.3.3 Match-casting for a vertical curve To obtain a bridge with a vertical curve, the match cast segment (n-1) must first be translated from its original position and then give a small rotation in the vertical plane with respect to the horizontal axis as shown in Figure 5. Usually the bulkhead is left in the fixed position, and all


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segments have in elevation projected shape of a rectangular trapezoid with the tapered face along the match-cast segment. It is therefore only necessary to adjust the soffit of the cast segment during the adjustment operations.

Figure .5 Match casting for a vertical curve

3.3.4 Match-casting for a horizontal curve To obtain a bridge with horizontal curve the match cast segment (n-1) is first moved to its position by pure translation and then the segment is rotated in plan with respect to the vertical axis .The adjustment is done at the soffit level. The new cast segment takes the trapezoidal shape in the plan due to the rotation of the match-cast segment.

3.3.5 Geometry Control Procedure Before starting the construction on site it is required to established a system of stations at North and South side of mould. For setting out, the polar method is used . The coordinates (match casting & conjugate segment coordinates) of the design points (6 points of each segment) are pre-calculated and recorded in the memory of the Total Station. Setting out works is done from the closest station (survey tower). The orientation is observed from minimum two stations, to avoid mistakes and to check the actual accuracy of the instrument.


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3.3.6 Survey The marking of both axis lines is done before starting of any activity on each mould. The surveyor fixes the bulkhead position (fixed and temporary) with the Total Station and confirms that the position and level of bulkhead are accurate. The surveyor also checked the soffit level as per pre-calculated level and accordingly if necessary soffit levels was adjusted. After checking the bulkhead and soffit, the surveyor marks the four corners coordinates of segments. Six insert plates are at 50mm from edge and 9.0 m from center of segment for punching coordinates after casting. The level of the insert plate is fixed as per theoretical level from a Survey Tower. After casting of segments, the surveyor directs the crew to punch the coordinates on the 6 insert plates as per theoretical casting coordinates. The levels of the 6 insert plates are checked. Elevation and centerline offset measurements are adjusted to an accuracy of .0.3 mm. After punching of coordinates that segment is placed in conjugate (n-1) segment position and in that position that segment is fixed as per theoretical match-cast coordinates. The levels of the segment are checked at insert plate locations as per theoretical level and accordingly if necessary the levels are adjusted using the bottom jack adjustment system. At the time of positioning of the segment the surveyor indicates the theoretical position of insert plates (which was already punched). Once the theoretical position reaches (X, Y), the segment is fixed in that position. The coordinates and levels at all insert plates locations are finally checked after fixing the conjugate segment (n-1). After completion of formwork and reinforcement the set up position of two adjacent segments are independently determined by two observers and difference between two observation should not be more than: for Elevation 0.6 mm on control points and For Horizontal: 0.6 mm on a segment center line offset. .

Correction for Geometric Deviation During casting of the segments There are possibilities of deviation of the segment geometry from the theoretical geometry. The deviation arises due to wrong alignment of the match-cast segment or due to some thermal stresses. If the deviation in the geometry is not accounted then there will be a serious error in the alignment of the whole bridge geometry. In order to avoid any significant deviation from the theoretical geometry, it is necessary to provide for corrections when casting the next segment. Similar corrections are done for the vertical alignment. It is essential to check the super elevation


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(given by the crosswise difference in level of the insert plates) varies regularly according to the theoretical geometry. Failure to do so will result in misalignment. The goal of the geometry control program will be to monitor the casting operations and establish as-cast curves step-by-step to verify that the actual superstructure geometry is in close agreement with the theoretical casting curves. After each segment is cast, the position of this

segment is established in the general plot of the structure. Comparing the location of the newly cast segment with the location assumed in the casting curve will allow for the determination of the adjustments required before the next pour.

3.4 WORK PROCEDURE FOR MATCH CASTING 3.4.1 Sequence of work Pier head / end diaphragm segment

Alignment of soffit and outer forms

Alignment of bulkheads on both sides

Survey

Application of formwork releasing agent

Cutting, bending & tying of reinforcement

Lifting and placing of rebar cage along with sheathing pipe.

Alignment of HDPE sheathing pipe.

Alignment & setting of internal shutter

Providing and fixing inserts for drainage spouts, lifting holes, temporary pre-shuttering provision, if required.

Final survey and rebar checking.

Laying, compacting and finishing of concrete.

Curing

Allow setting of concrete to gain 20 MPa strength for removal of formwork.

De molding of external shutter.

Removal of internal formwork.

Shifting of pier head segment from casting bed to stacking bed after gaining 25 MPa strength.


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Intermediate/ running segment Alignment of soffit and outer forms

Alignment of bulkheads on both sides

Survey

Application of formwork releasing agent

Cutting, bending & tying of reinforcement

Lifting and placing of rebar cage along with sheathing pipe.

Alignment of HDPE sheathing pipe.

Alignment & setting of internal shutter

Providing and fixing inserts for drainage spouts, lifting holes, temporary pre-shuttering provision, if required.

Final survey and rebar checking.

Laying, compacting and finishing of concrete.

Curing

Allow setting of concrete to gain 20 MPa strength for removal of formwork.

Lifting of match cast segment and shifting to stock yard after gaining 25 MPa strength.

Alignment of temporary bulk head and shuttering above said sequence shall continue till completion of span.

3.4.2 Work procedure For a typical 31m span, arrangement of segments is as follows

S1-01 S2-02 S3-03 S4-04 S4-05 S4-06 S4-07 S4-08 S3-09 S2-10 S1-11

S1-01 & s1-11 are the pier head segments and remaining all i.e s2-s 02 to s2-10 are the intermediate segments.

General arrangement of casting yard


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A well-equipped pre cast yard of length around 580m consisting of 3parallel casting and stacking beds(3 n0s. of bays)shall be built-up for casting the precast elements with proper ground control for reinforcement , shuttering , concreting and curing, stacking of segments, drainage facility etc. 9nos. long line moulds of 34m (2 straight bed +7 curved beds) and shall be prepared for setting of 9nos. long-line casting moulds for regular spans. At the same time there shall be 9nos. pier head/end diaphragm moulds for casting of the pier segment only. A part from these three nos. of long line moulds for station spans and 3nos.of pier head moulds for station spans shall be placed

4electrically operated 10MT gantries shall be erected for handling segments formworks, reinforcement cage and other miscellaneous works. Whereas 6 nos. electrically operated 75MT gantries shall be used for shifting cast segments from casting bed to stacking bed and from stacking bed to loading on trailer.

Stacking yard shall be equipped to stack 1080nos. of segments in 2-tier stacking. The first tier segments shall be placed on two concrete sleepers of 3.2m x 0.5m x 0.4m on the ground. The second tier segments shall be placed over the first tier by placing wooden sleepers in between the segments.

Type Long line mould Pier head mould

Curved viaduct spans 7 7

Straight viaduct spans 2 2

Station spans 3 3

Total 12 12


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Reinforcement yard is located adjacent to the casting yard, reinforcement fig shall be provided for the pre fabrication of reinforcement cages of running segments. Reinforcement cages shall be handled by 10MT gantry for pier head segments. These have suitable lifting arrangements. Adjacent to running segments, pier head segment fig shall be provided for pre fabrication of reinforcement cage for pier head segments. These cages shall be handled by the 10T gantry with suitable lifting arrangements. These cages are transferred from reinforcement yard to casting yard by side shifting trolley.

Reinforcement cutting and bending machines shall be provided for cutting and bending of segments. All reinforcement shall be stacked diameter wise on wooden/ concrete sleepers. The method of receipt, acceptance, stacking,cutting ,bending and tying.

3.4.3 PRECAST YARD MOULD There are 24 moulds proposed in the casting yard, which shall include 9pier head moulds for casting viaduct pier head segments,9long line moulds for casting the intermediate segments of viaduct spans(2 nos. for straight span/7 nos.for curve span),3nos.pier head moulds for station viaduct and 3 nos. station long line moulds. Each pier head mould consists of following A. Inner form assembly B. Soffit assembly C. External side shutter (outer form) assembly with supporting truss-left and right D. Bulk head panels (2nos.) E. Working platform and access staircase

Each long line mould consists the following A. Inner form assembly (1 for s2, 1 for s3 and 2 for s4) B. Soffit assembly including T-panels C. External side shutter (outer form) assembly with supporting truss-left and right-2sets D. Bulk head panels (2nos.) E. Working platform and access staircase

SOFFIT ASSEMBLY-curved span bed/straight span bed


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Soffit for curved span segment shall rest on structural steel form with 4 adjustable built in jacks for height adjustment. The soffit shall be swiveled in all directions i.e. forward and backward, sidewise and also up & down with the help of screw jacks which is positioned below the soffit assembly.Soffit for straight span segment shall rest on structural steel form rested on rigid slab.

OUTER SHUTTER ASSEMBLY For each long lined mould 2 outer form assemblies shall be placed on either side of the soffit i.e. LHS & RHS (2nos.) In order to support the outer web of the segment to be cast, outer form of structure of panel type fixed at the joint of soffit and side shutter, is supported by heavy duty turn buckles ,it has a frame at the top of the shutter and horizontal jacks fixed to it for adjustment in the horizontal direction. It is also held in position to the soffit by locking arrangements to prevent movement due to vibrations during concreting. For the straight span, outer form shall move on the track line and for the curved spans, it shall move on the swivel wheels directly on the casting bed RCC surface.

Figure 6.outer shutter assembly


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INNER FORM ASSEMBLY The central void in the segment is achieved with the help of inner forms. Alignment / adjustment & de-shuttering of panels shall be carried out with the help of turn buckles and hinges provided in panels to restrict concrete pressure load during concreting.

BULK HEAD PANELS ASSEMBLY For pier head segments, bulk head assembly shall be placed on both sides. These temporary bulk head shutters are supported by turn buckle positioned with the help of gantry crane. These panels contain shear keys and anchor cone fixing arrangements according to alignment geometry. For immediate segments, bulk head shall be placed only on one side and on the opposite side segment is match cast with adjacent segment, the bulk head shutters are supported by turn buckles and are positioned with the help of gantry.

WORKING PLATFORM AND ACCESS STAIRCASE For each mould there is access staircase at one end leading to outer form walk way there is working platform 100mm width with hand railing, provided along the entire length of mould on outer form. After placing the reinforcement in the mould, a movable walk way platform of 3.5m/0.75m shall be placed on the top supported on the bulk head and match catch segment for work on the segment thus avoiding workmen movement on the top of the reinforcement.

3.4.4 TYPICAL CASTING SEQUENCE/ METHODOLOGY For a typical 31m span, sequence of segments is as follows

S1-01 S2-02 S3-03 S4-04 S4-05 S4-06 S4-07 S4-08 S3-09 S2-10 S1-11

S1-01 & S1-11 are the pier head segments and remaining all are the intermediate segments. The following are the activity cycle that is to be followed for the various types of segments.


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3.4.4(a) Sequence Of Casting For Pier Head Segments-SEGMENT S1-01 /S1-11. 1. Leveling the form work free/ fixed end and support for bearing outstand. 2. Closing the external formwork of pier segment

3. Application of mould releasing agent 4. Cutting, bending and tying of reinforcement. 5. Lifting and placing of reinforcement cage. 6. Fixing of guide cones on bulk head. 7. Fixing of first bulk head in the pier head. 8. Fixing of second bulk head in the match cast side. 9. Profiling the sheathing pipe as per the coordinates. 10. Aligning and setting of internal shutters in position. 11. Jacking and fixing up of internal form work. 12. Installations of all inserts and lifting, temporary stressing arrangements etc.. 13. Laying, compacting and finishing of concrete of segment 14. Allow setting of concrete for removal of form work. Curing to be done during setting. 15. De-shuttering of internal formwork and bulk head. 16. Shifting of pier head segment from pier head casting bed to stacking bed after gaining

25MPa strength 17. Curing of segment for 14 days.

3.4.4(b) Sequence Of Casting For Intermediate Segment ( Long Line)- Straight Span The pier head segment shall be cast first on independent bed and same shall be brought to long line bed to form the match cast segment for casting the adjacent segment. The sequence of casting for intermediate segments in long line methods is as follows i. for Typ. Segment S2-02/S2-10 1. Aligning the soffit formwork for straight span.

2. Application of de-bonding agent at the match cast side. 3. Close the external formwork.

4. Cleaning of shutter and application of mould releasing agent.


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5. Placing of rubber cone in the match cast segment sheathing pipe for sealing of joint at match cast face.

6. Cutting bending and tying of reinforcement. 7. Lifting and placing of reinforcement cage. 8. Placing and fixing of bulk head. 9. Installation and profiling of sheathing pipe as per the coordinates. 10. Placing of internal formwork 11. Installations of all inserts and lifting, temporary stressing arrangements etc.. 12. Final survey

13. Casting of segments (S2-02) 14. Allow setting of concrete for removal of form work. Curing to be done during setting. 15. De-shuttering of internal formwork and bulk head. 16. Curing of segment for 14 days. 17. Internal shutter move from S2-02 to S2-10 and wit above sequence casting of S2-10 to be carried out.

ii.ForTyp.Segment S3-03/S3-09 1. Shifting of internal shutters on S3-03 and cast against S2-02 and end stopper . 2. Placing of bulk head and alignment. 3. Placing of rubber cone match cast segment sheathing pipe for sealing of joint at match cast face.

4. Cutting bending and tying of reinforcement. 5. Lifting and placing of reinforcement cage. 6. Installation and profiling of sheathing pipe as per the coordinates. 7. Placing of internal formwork

8. Installations of all inserts and lifting , temporary stressing arrangements etc.. 9. Final survey 10. Casting of segments (S3-03) 11. Allow setting of concrete for removal of form work. Curing to be done during setting. 12. De-shuttering of internal formwork and bulk head. 13. Curing of segment for 14 days.


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14. Same sequence follows as parallel activity forecasting for casting S3-09 also

iii. For Typ. Segment S4-04 /S4-08, S4-05 / S4-07 Casting of above said segments shall be followed as sequence mentioned for segments S3-09

iv. For Typ.Segment S4-06 After completing S4-07 internal shutters shall move from S4-07 to S4-06 and concreting of S4-06 shall be carried out with above sequence.

3.4.4(c). Sequence Of Casting For Intermediate Segment (Long Line)- Curved Span: For curved span also pier head segment casted on pier head mould and same shall be brought to long line mould to form the match cast segment for casting the adjacent segment, the sequence of casting for intermediate segments in long line bed as follows:

i. For Typ. Segment S2-02 /S2-10 1. Aligning of soffit formwork to curve span of required radius of curvature. 2. Shifting of S1-01 / S1-11 segments to match cast location for casting S2-02/S2-10

3. Aligning of temporary bulk head. 4. Appling of de-bonding agent over match cast segment. 5. Cutting, bending and tying of reinforcement . 6. Closing of external formwork. 7. Placing of rubber cone in the match cast segment sheathing pipe for ceiling of joint at match cast face.

8. Lowering of rebar cage. 9. Installation of sheathing pipe. 10. Profiling of sheathing pipe as per coordinates. 11. Moving of internal formwork.

12. Jacking of internal formwork.

13. Installation of all inserts of lifting/temporary stressing arrangements.

14. Final survey.

15. Casting of segment (S2-02)


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16. Allow setting of concrete for removal of form work. Curing to be done during setting 17. De-shuttering of internal formwork after requisite strength.

18. Curing of segment for 14 days. 19. Internal form work shall move from S2-02 to S2-10 and casting of S2-10 shall be carried with respect to above sequence

ii. For Typ. Segments S3-03 / S3-09 1. Shifting of internal shutter on S3-03 and cast against S2-02 and end stopper. 2. Placing of bulk head and alignment. 3. Placing of rubber cone match cast segment sheathing pipe for sealing of joint at match cast face.

4. Cutting, bending and tying of reinforcement. 5. Lowering of rebar cage. 6. Instillation and profiling of sheathing pipe as per the coordinates. 7. Placing of internal formwork

8. Installations of all inserts and lifting, temporary stressing arrangements etc.. 9. Final survey 10. Casting of segments (S3-03) 11. Allow setting of concrete for removal of form work. Curing to be done during setting. 12. De-shuttering of internal formwork and bulk head. 13. Curing of segment for 14 days. 14. Same sequence follows as parallel activity forecasting for casting S3-09 also.

iii.For Typ. Segment S4-04/S4-08 , S4-05/S4-07 After completing S4-07 internal shutters shall move from S4-07 to S4-06 and concreting of S4-06 shall be carried out with above sequence


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3.4.5 Casting Cycle

Figure 7.match casting cycle

3.4.6 FABRICATION OF REINFORCEMENT CAGE i. Reinforcement

TMT Fe 500 steel bars of approved vendor shall be used

Reinforcement steel shall be supplied to steel bending yard directly from manufacturer.


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Reinforcement shall be stacked on sleepers/concrete blocks to avoid direct contact with local earth. The sleepers/concrete blocks shall be of 200mm height and placed at a distance of 3m.

Reinforcement shall be marked batch wise and tested as per inspection and test plan. Reinforcement which confirms to the requriments shall be used for cutting and bending. Approved BBS shall be used for cutting and bending. Reinforcement shall be protected from rusting, mortars, mills scale, grease oil or paints

by covering with tarpaulin sheets as per the requirements in site. Handling of reinforcement shall be in such a way so as to prevent damage or unwanted

bending. Bars bent during transport or handling shall be straightening by heating shall not be

permitted.

ii. Cutting And Bending Of Reinforcement Reinforcement steel shall conform to the dimensions and shapes given in the approved

bar bending schedules. Reinforcement steel shall be fabricated through automatically operated machines and

mandrels conforming to IS 1786: 2008. Quantity of reinforcement steel fabrication shall be as per the production schedule. Cut & bent reinforcement shall be stacked on sleepers and protected to prevent rusting by

covering with tarpaulin sheets.

Cut and bent reinforcement shall be transported to place of work on trucks / trailers

Unloading of reinforcement at site shall be done either manually or by crane and checking the material test certificates for the particular lot

Reinforcement shall be stacked on elevated blocks in clean and dry condition.

iii. Placing Of Reinforcement

Reinforcement tying shall be done in specially fabricated Reinforcement jigs. typical jig is shown in the below sketch.

Reinforcement shall be tied together at every intersection with GI binding wire (18gauge).


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lap length shall be as given in the GFC drawing shall be staggered Couplers may also be used. whenever used, couplers shall be staggered atleast by the

distance of lap length shown in drawings. Only cover block made of grout / concrete shall be placed at suitable locations to

maintain clear cover.

Space bars shall be provided at 2m intervals in between Reinforcement layers as equal to maximum diameter of steel.

Projecting reinforcement (or the dowels left) shall be coated with inhibitor solution and cement slurry for protection against rusting. inhibitor solution is a clear liquid of pH value 10-14and specific gravity of 1.04 min. this inhibitor soltion shall be stored in closed plastic containers.

Before starting the treatment arrangement such as tools and tackles such as buckets, brushers, weighing balance, etc shall be provided.

A slurry of inhibitor solution and cement (OPC) at a ratio of 0.5 - 0.6 shall be prepared and mixed thoroughly till the mix is of uniform consistency.

The Reinforcement shall be applied to the bars to cover the entire surface opf projected area

The coated steel bars are allowed to dry atleast for 6 to 12 hrs or tll it is touch dry. Apply second coat of application .the thickness of the coating after this shall be 200-300

micron.

This coated Reinforcement shall be used within 15days from the date of application of second coat

Reinforcement steel shall be tested & record shall be maintained as per inspection test plan (ITP). After completion of the cage fabrication the same shall be offered for inspection. The Respective Engineers will approve the fabricated cage buy checking for standard measurements. Once it is cleared ,it shall be lifted by the lifting frame & placed inside the mould.


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3.4.7 Sheathing And Guide Cone Fixing

Figure 8.guide cone used in S1

HDPE duct shall be procured from supplier and shall be got approved from engineer before usage.

Profiling (layout of HDPE) shall be carried out according to the co-ordinates given in the approved drawing.

i. Steps In Duct Profiling

Figure 9.duct profiling in segment reinforcement

HDPE duck shall be fixed as per the x, y, z co-ordinates given in the drawings.


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Cone boxes shall be fixed at requires locations as per the drawing. These cones boxes shall be permanently welded to end block shutters and shall be approved from engineer prior to use.

HDPE pipe shall be fixed over supports. At the end of the cable, HDPE duct shall be inserted in the guide collar provided to accommodate the HDPE duct and the joint sealed with tape to avoid ingress of slurry during the concrete.

Threads of guide bolts can be protected by M.S threaded sleeves / PVC sleeves.

Co-ordinates shall be checked once again since there is chance of disturbances due to shifting of pre-fabricated cage to the casting yard.

For proper matching of center line of duct for previously cast segment to be cast and to avoid ingress of slurry during concreting, a rubber cone shall be inserted inside the HDPE pipe of match cast segment. Joints shall be sealed by glass putty.

Layout of the duct shall be marked on the pre-fabricated cage as per the drawing of respective segment.

For Y-ordinate a 10mm diameter for steel bar shall be tied to the supporting arrangement at the required heights measured from top of the shutter to the top of the duct.

Z-ordinate shall be taken from the center of segment to the center of pipe. The pipe shall be tied securely over the support bar, so that it shall not be displaced during concreting.

The duct for pre-stressing shall be fully checked for correct profile and is ready for concreting.

A. Detailed Procedure Of Surveying For Box Geometry Control At Precast Yard

I. Specialized equipment Advanced total station capable upto 1sec accuracy & auto level capable to read upto 1mm shall be used for geometry control surveying. The tolerance of survey control points will be aimed at the minimum values attainable with these instruments.

II. Survey tower Two survey towers will be constructed at both ends of each bay to control alignment of segments. 1 bay consists of 4 nos. long-line beds & 4 nos. pier mould beds.

III. Setting out with total station


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Before starting the construction at site, the survey department has already established a system of station (on each survey tower / target tower at both sidea of mould). The co-ordinates (for 1st cast and match cast segment ) of the design point are pre calculated and recorded in the memory of total station. Setting out works shall be done from the closest station, (survey tower) unless for any reason (eg. obstruction) the orientation shall be observed from minimum two stations.

IV. Survey checking before casting of segments The marking of both axis lines shall be given before starting of any activity on each mould. The surveyor from survey tower / target tower will check with the total station and the target into the bulk head position and level of bulkhead are in right position. Surveyor will also check the soffit position and level as per pre-calculated level and co-ordinates and accordingly if necessary soffit levels and position will be adjusted. After checking the bulk head and soffit, surveyor will mark the four corners coordinate of segments. Total six numbers of insert plates will be fixed at 150mm from edge and 4.25m from center of segment for checking level after casting. Level of the insert plates will be fixed as per the theoretical level from survey tower.

V. Survey checking after casting of segments (for starter/1st cast segment) After casting of segments the surveyor from survey tower with his instrument and prism will check the bulkhead position at center and subsequently, he will check the level at 4.25m on both sides of the centre line. After recording all the data, surveyor will punch the co-ordinates insert plates(2 nos. at center of size 50*50 and 4 nos. at sides of size 50*50) as per theoretical coordinates, after completion of punching those coordinates, all coordinates and level will be finally checked, confirmed, and recorded by the surveyor. The whole set of data taken for 1st cast segment(for starter segment only) will be given input into the worksheet to calculate the twist error and alignment data for next match cast segment to get the corrected casting coordinates.

VI. Survey checking after casting of segments (for match cast segment) The surveyor from survey tower with total station and prism will check the fixed or temporary bulkhead position at center and the level at 4.25m from both side of center line. After recording the entire data surveyor will punch the coordinates, after completion of punching those all coordinates and level will be finally checked by two surveyor, both


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surveyor will also check and record the final position at center level at four insert plates of match cast segment. All data taken wet cast for segment will be given input into the software to calculate the twist error and alignment data for next match cast segment

3.4.8 Casting of Segments Once alignment is over, survey checking shall be carried out as per survey checking

procedure .after alignment of all mouldparts ,all minor gaps shall be filled up by putty to prevent leakage of slurry. Debonding agent shall be applied to the matchcast surface. All joints /gaps shall be covered by rubber plugs, marking tape so that no slurry or concrete enter inside the shuttering .on completion of all activities at mould through cleaning shall be done by compressed air. Finally the segment shall be offered for checking to engineers representatives supervision team. Upon clearance casting shall be done.

Survey inserts of 50*50*5 thick plates shall be placed for survey setting out as per the sketch and tack welded to the reinforcement.

Bottom slab & top slab concrete shall be finished by aluminum box ruler, the top surface shall be smooth finished.

Blisters are provided in bottom slab for temporary stressing of segments. These shall be concreted after shifting the segments to stack yard for concreting of the blisters. A box made of structural steel of required dimensions shall be placed and concrete is poured. Temporary stressing is done during erection of spans. The temporary blisters drawing is attached.

Wherever construction joint is required on the surface of the fresh finished concrete surface retarder shall be sprayed within 30min.of finishing. The rate of application shall be 100-120ml per sqm. The retardation depth is upto 8mm. the sprayed surface shall be left as it is till the final setting of concrete not less than 18hrs.

Construction joint shall be prepared by cleaning an air-water jet or wire brooming on the concrete which is still soft enough that can be removed but hard enough to prevent aggregate from loosening if the concrete for some reason is set before the construction joint preparation, then in such situation the joint shall be prepared using a wet sand blast or ultra-high pressure water jet.


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Curing shall be done for 14 days from the date of casting. For identification of the segment dateof casting shall be written along with the segment ID.

Before de-moulding of segments, the top surfaces shall be covering with hessian cloth and dampening by regular sprinkling of water.

The segment shall de-moulded after attaining a strength of 20Mpa span when curing shall be done by sprinkling water by sprinklers or water jets kept moist.

After matchcasting of the next segment and attaining a strength of 25Mpa , the segment shall be lifted and placed in the curing bay for a period of 14days from the date of casting and continuously cured by dedicated curing workmen with water sprinklers or pump fitted with flexible pipes in each curing bay.

Segment ID shall be marked with golden yellow or any other suitable paint on inner face at both ends i.e. bulk head face & match cast face

3.4.9 NUMBERING After outer shutter removed & before segment lifting , numbering shall be done as

follows

Sample: Segment ID: C3NU-P12P13-S2-10

Date of casting: DDMMYY

Span : C3NUP12C3NUP1

Type of segment : S2

Segment no : 10(fixed end being 01 segment)

3.4.10 STACKING & READY FOR DISPATCH While transporting the segment from the bay to the casting bay and then to stacking

bay, two riggers shall be moving along with the gantry rail by using guide rope for safe movement.

Before lifting of every segment , care shall be taken such that the segment is attached required strength as per the drawing (require strength is 25Mpa). For segment lifting purpose , suitable lifting beam shall be used as per the approved drawing and testing


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as shown below. The lifting beam shall be fixed to the segment by means of threaded bars ( macalloy ) . For bolting the bars a secure ladder & stool shall be used. The lifting beam drawing , general arrangement drawing for fixing of beam to segment is attached in annexure c. the threaded bars shall be new along with the MTCS, the bars are bolted to the segment at four locations in equal lengths. For lifting at the PC yard, the nuts shall be tightened without stressing , maintaining flatness in the nut.

Complete Segment Tolerance For Segment Ox Girder Bridge Construction The Cast Segment Shall Confirm To The Following Tolerances

Length of match cast segment _+10 mm/m, +_ 25mm max

Length of cast-in place segment +_12mm

Length of one span +_50mm

Web thickness +_10mm

Depth of top and bottom slab +_10mm

Overall top slab width +_5mm/m, +_25mm max

Diaphragm thickness +_12mm

Grade of form edge and soffit +_1mm/m

Tendon hole location +_3mm

Position of shear keys +_6mm

Horizontal position of the pier segment +_15mm of the alignment

Vertical position of the pier segment +_15mm of the alignment


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3.5 SAND BLASTING 3.5.1 SCOPE The objective of this construction work procedure is t prepare the surface of match segment with sand blasting at the casting yard in order to remove the debonding agent ,debris and laitance.

The sand blasting is required for preparation of the surface to receive the Epoxy glue during erection of segments.

3.5.2 SEQUENCE OF WORK *The segment should be covered with Tarpaulins / GI sheets. *The match cast face shall be cleaned of any chanks of debris. *Sand blasting equipment shall be connected to the compressor and required pressure shall be applied . *The sand blasting operator shall hold the nozzle and spray on the match cast face and green cutting portion.

3.5.3 WORK PROCEDURE Sand blasting is a common element of concrete construction and routine building maintenance.it is most efficient way of removing debonding agent and other unwanted laitance It shall be done to remove the debonding agent loose particles in order to prepare the match cast face to receive the Epoxy glue during erection before dispatch of the segment. It requires two primary ingredients i.e; sand and compressed air .The sand should be coarse sand complying to zone 2 requirements of IS 383 and free of any debris .The sand shall be preferably uniform shape and size .The air compressor shall have a steady air pressure of at least 70 PSI to blast the sand fast enough, upto 100PSI is preferred .The area shall be covered with tarpaulin /GI sheets to recapture as much of the sand as possible. This makes it easier to clean up ,and the sand can be reused once the debonding agent and other debris have been shifted out. The nozzle of the sand blasting machine shall be held at a distance of 8 to 12 inches from the blasting surface .holding the nozzle closer than this shall narrow the impact area ,and shall tear through the surface material at a higher speed. This results in the sand being distributed across a wider area ,requiring more passes to remove the surface layer. It is also important to keep the


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sand blaster moving in a motion at all times .holding the blasting machine steady on a fixed point can create a hole in the segment .

Fig.10 . Sand used in sand blasting. Fig.11 gun used for sand blasting

Fig.12 Air Compressor used to pump sand with required pressure

3.5.4 MANDATORY SAFETY REQUIREMENTS * Every workman should be engaged after screening, safety induction &medical test with a valid ID card. * Appropriate PPE should be used at all times. * Work shall be executed in competent and continuous supervision . * Any unauthorized activity shall be strictly prohibited.


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* There should be proper coordination and communication between teams/workmen at all times. * Proper housekeeping shall be maintained. * Required inspections shall be carried out prior to start work. * Proper illumination shall be maintained during night work. * Permit system shall be followed for activities such as height work ,night work and hot work. * TBT shall be conducted before starting the work.

3.6 CURING Curing concrete is the term used for stopping freshly poured concrete from drying out too quickly. This is done because concrete, if left to dry out of its own accord, will not develop the full bond between all of its ingredients. It will be weaker and tend to crack more. The surface won't be as hard as it could be. There are different methods of curing which are to be selected according to the site . a. Leave the form work used to create the concrete formation. The form work itself, if left in

place, or on the underneath of a suspended slab, or around a concrete column will stop the concrete drying out too quickly, and so can be said to be a curing agent.

b. Use ponding, which as illustrated in the photo above, is done by forming a dam wall of sand around the concrete formation and then flooding with water. This method has the following disadvantages:

It takes a fair bit of work to do, and then quite often a breach occurs and the water runs off the slab.

Usually this can only be done for a few days as it inhibits other work and the pressure is usually on to get the walls up.

A possible drawback of this method, especially if soil or clay is used, is the chance of staining the concrete

c. Spray water onto the formation. A simpler way is to just keep water sprayed onto the slab with garden sprinklers or hand held hose pipes. Following are some disadvantages that you need to consider if you intend to use this method:

This method is very wasteful of water

Again, it can only be done for a short period usually. If you hand water, it should be wet all the time, that is you should not let it dry out at all, almost impossible to do.


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d. Use some sort of cover that holds and retains sprayed on water, like a sand layer or hessian. The sand cover or hessian has to be kept wet and if they do dry out they actually aid in sucking moisture out of the concrete.

e. Use a plastic shield, which basically is a plastic sheet laid on top of the slab to stop the evaporation process. This is one of the most efficient methods of curing concrete. Usually a spray from a hose pipe is used to wet the surface and the plastic is laid on, with generous laps at the joints. Use timber or cement blocks to keep the plastic in position, rather than taping the joints. To a certain extent the plastic can be used a few times. A major benefit of plastic is that it does not stop other work, like building the walls, and so it can be left in position for weeks if need be.

The photo shows concrete columns that have had the form work stripped (for further use) and then wrapped in a clear plastic film. The evaporation from the concrete condenses on the inside of the plastic and the surface of the column remains moist.

f. Use concrete curing oils or curing compounds. These compounds and oils are now coming in a variety of types. the water soluble waxy emulsions are used which can be sprayed onto the fresh concrete with a hand pump type spray. They are milky white when used but dry into a clear waxy film. They have the advantage that that they can be sprayed onto footpaths and the like even before the concrete is set enough to walk upon. Another major use is on concrete walls. They remain on the surface for weeks and finally break down in sunlight. Be hesitant to use concrete curing oils on internal floors, on the off chance that any residue would stop the full adhesion of ceramic tile glues etc.

Other types of concrete curing compounds are PVA based, chlorinated-rubber or resin based. They can also be obtained in coloured versions that fade over time on the surface for weeks and finally break down in sunlight.

3.6.1 SCOPE For the purpose of curing of concrete of concrete in segments instead of water curing film forming curing compounds is an alternative material which assists in the retention of water evaporation from exposed surface of concrete during hydration .Application of curing compound shall be as per methods specified.


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3.6.2SEQUENCE OF ACTIVITIES * Approval of curing compound. * Acceptance criteria of the curing compound. * Storage and identification. * Transportation to casting yard . * Arrangement for pump operation and spraying. * Application of curing compound. * Protection of the area.

3.6.3 WORK PROCEDURE APPROVAL OF CURING COMPOUND Source approval of curing compound shall be obtained on the basis of the third party test results complying with ASTM C309 supplied by the manufacturers test certificates.

ACCEPTANCE CRITERIA OF THE CURINNG COMPOUND Curing compound shall be received in original containers bearing name of manufacturer and the brand name. It shall be accepted on the basis of manufacturers test certificates and third party test certificates from the manufacturer. The material shall be issued to the site only after joint sampling is done by LTC &LTMRHL and on the basis of third party test reports received from approved laboratories.

STORAGE AND IDENTIFICATION The compound shall be stored in a manner to prevent damage to the containers. The material shall be stored separately in the store stockyard on leveled ground and covered with tarpaulin sheets. Proper tagging shall be done for the identification of the materials. Display boards shall be fixed for each and every batch .Every batch of curing compound shall be stored separately for easy identification and traceability. The display boards shall include batch numbers, testing status and date of receiving the material at storing location.

TRANSPORTATION TO SITE The material shall be transported to casting yard for application in containers .

ARRANGEMENT OF PUMP FOR SPRAYING CURING COMPOUND A pressure spray machine such as Gracotexspary 7900 HD Premium or equivalent shall be used for spraying curing compound on the segment .The container of the curing compound shall be


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mixed thoroughly with wooden batten for proper mixing of the material. then it shall be poured in to the bucket. Therefore the suction unit of the pump shall be dipped into the bucket containing the curing compound. The pressure shall be maintained in between 500 1500 psi. A hose pipe 100 ft long is further attached to the pump which in turn attached to pole gun(3ft or 6ft).

APPLICATION OF CURING COMPOUND Curing compound shall be applied immediately after removal of shutters from the segment. The motor is started and the required pressure is maintained for spraying. The material from the bucket is sucked through the suction unit and filled in the hose pipe . The suction unit is the one way suction unit. The material is pumped under high pressure through the supply line . Then in is further forced at high pressure through a small opening at the front of the valve called the spray tip and sprayed on the pier. The distance of the spray tip from the surface of the pier shall be at least 300 mm. The material shall be sprayed horizontally and uniform coverage of adequate thickness shall be maintained .50% overlap shall be ensured while spraying. The various stages of application are mentioned below:

(1) Pier head segment: Stage -1

After late finishing of the segment concreting, curing compound shall be applied on the top surface.

Stage-2

Upon the concreting attaining 20MPA strength, the bulkhead shall be removed and curing compound shall be applied to the inner void and bulkhead face.

(2) Running segment : Stage-1

After late finishing of the segment concreting, curing compound shall be applied on the top surface.

Stage-2 Upon the concreting attaining 20MPA strength, the bulkhead shall be removed and curing compound shall be applied to the inner void and bulkhead face.


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Stage-3 The outer wing form shall be removed to match cast position and curing compound applied to the outer face. Stage-4

After concreting of the match cast segment / upon attainment of 25MPA strength whichever is later ,the segment shall be lifted and curing compound shall be applied on the bottom portion before placing in the stack yard.

After 14 days from the date of concreting and before transportation for erection ,the segment match cast face and green cutting portion shall be sand blasted to remove the curing compound layer .The is necessary to receive the epoxy during erection on the match cast face and further concreting on the green cut areas.

3.6.4WEATHER LIMITATIONS Table 4.weather limitations for curing.

SEASON RISK ANALYSIS PREVENTIVE MEASURES

Rainy

Rain may washout the wet

film of curing compound before drying

Application of curing

compound shall be avoided during rain.

3.6.5 MANDATORY SAFETY REQUIREMENTS * Every worker shall only be engaged after screening , safety induction and medical test and shall be permitted only after photo identity card. * Every workmen shall only be allowed to work with personal protective equipment (safety shoes, safety helmet ,full body harness, reflective jackets, hand gloves, nose mask, ear plug, safety goggles). * Illumination level shall be not less than 55 lux at the place of work. * Tagline will be provided to prevent the cage from hitting the pier and to avoid undesired swing. * It shall be ensured that the workman does not enter the man basket without wearing safety harness.


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3.7 Deck Construction Using Match Cast Segments The bridge deck is comprised of a pair of balanced cantilevers incrementally constructed on either side of the pier and parallel to each other. The length of the segments is nominally 2.8m and there are generally 12 segments per cantilever spine on either side of a pier. Each span is comprised of two parallel spines of 24 segments each giving a total of 48 segments per completed span. 1. The segments are transferred from the storage yard to the erection site by low loader. A crane lifts the segment from the low loader and suspends it off the ground while it is set to the correct angle of inclination. This procedure ensures that the segment is aligned correctly with the previously installed segment. A special lifting jig has a three-legged sling attached - one leg is fixed while the two other legs are hydraulically adjustable. These adjustable legs may be lengthened or shortened remotely using hydraulic rams to align the segment at any angle. During the later part of the project, it is planned to use an erection truss to hoist and position the segments. The truss is required to cater for the increased height of piers and for poor ground conditions. Significant costly ground improvements would be required to cater for very large capacity cranes.

2. Epoxy paste is to be liberally applied (3mm thick) by gloved hand ensuring that the whole face of the segment is covered. 3. The segment is then lifted into position and aligned with the segment against which it had been match cast. Inside each segment we have cast concrete blisters (anchor blocks) for the specific purpose of temporarily tying the segments together. A pair of two bar blisters at ceiling level while at floor level is a single three bar blister are casted. A total of nine bars tie the new segment to the previously erected segment. The bars are tensioned with a hydraulic jack and the nuts are tightened manually. The application of epoxy and tightening must be performed within approximately 45 minutes. Excess epoxy exuding from the joint on the inside and top surface of the segment is trowelled smooth. The remaining external jointed surfaces are dressed smooth during the final cleanup of the finished span. 4. After a pair of segments are installed to form a balanced cantilever, four conduits on top of the segment are utilised for longitudinal post tensioning. (As the cantilever advances the number of tensioned conduits is reduced to three.) These incrementally tensioned conduits are generally


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symmetrical about the segment webs At this stage of construction, post tensioning is only required at the top of the segments as the spans are acting as cantilevers. To facilitate the threading of stressing strand from one duct to another, a tensioning platform with a threading jig is mounted on each end of the cantilever tip. Four blue coloured threading jigs may be seen in. The pushing and tensioning of the strand is performed from only one cantilever end. The strand is threaded through the bent tubes where it is manually directed into the appropriate ducts. Once a strand is installed, it is cut to length and the next strand pushed through. The post-tensioning ducts are grouted within six weeks of tendons being placed and tensioned. 5. Following this post tensioning operation, the temporary tensioning bars in the upper part of the segment are removed. The bars at floor level of the segments are progressively removed as the cantilever develops. 6. During the erection process, the finished positions of the erected segments are surveyed to ensure correct alignment. If realignment is necessary, small shims are placed in the match cast joint between the segments to allow incremental fine tuning of the cantilever tips. On continuous spans (no halving joint), the erection process is continued until each balanced cantilever meets at the mid-point. 7. Every four to five spans an expansion joint is installed. The expansion joint span consists of two sections. The longer section forms part of a continuous beam with a simple support at the expansion joint; the other section is a short cantilever with a concentrated end load at the expansion joint. This supporting cantilever is relatively short as it is located on the fourth segment from the pier head. 8. Once the center span closure joint is cast, the completed span is fully post-tensioned and grouted to form a continuous beam. The majority of tensioning in the top of the segments has already occurred during construction to support the cantilever and finally to provide bending strength over the piers. The tendons in the bottom of the segments provide for the bending stresses in the bottom flange after continuity is achieved. 9. The remaining major operation is to stitch the two inner wing tips together to form one continuous deck. This remaining 900mm longitudinal gap is formed and stitch cast together. 10. A preformed groove at each segment joint is filled with epoxy paste to ensure a seal is formed to prevent moisture entry from the deck.


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11. The remaining operations are the installation of parapets, railing, lighting and finally the deck wearing surface is applied. A primary strip of high quality water proof membrane is applied to each of the segments epoxy joints and at the stitch joints. The total deck is then covered with a standard waterproof membrane prior to the laying of the final deck wearing course.

3.8 POST TENSIONING Post-tensioning is a method of reinforcing (strengthening) concrete or other materials with high-strength steel strands or bars, typically referred to as tendons. Post-tensioning applications include office and apartment buildings, parking structures, slabs-on-ground, bridges, sports stadiums, rock and soil anchors, and water-tanks. In many cases, post tensioning allows construction that would otherwise be impossible due to either site constraints or architectural requirements. Although post-tensioning systems require specialized knowledge and expertise to fabricate, assemble and install ,the concept is easy to explain. Imagine a series of wooden blocks with holes drilled through them, into which a rubber band is threaded. If one holds the ends of the rubber band ,the blocks will sag. Post-tensioning can be demonstrated by placing wing nuts on either end of the rubber band and winding the rubber band so that the blocks are pushed tightly together. If one holds the wing nuts after winding, the blocks will remain straight. The tightened rubber band is comparable to a post-tensioning tendon that has been stretched by hydraulic jacks and is held in place by wedge-type anchoring devices.

BENEFITS To fully appreciate the benefits of post-tensioning, it is helpful to know a little bit about concrete. Concrete is very strong in compression but weak in tension, i.e. it will crack when forces act to pull it apart. In conventional concrete construction, if a load such as the cars in a parking garage is applied to a slab or beam, the beam will tend to deflect or sag. This deflection will cause the bottom of the beam to elongate slightly. Even a slight elongation is usually enough to cause cracking. Steel reinforcing bars (rebar) are typically embedded in the concrete as tensile reinforcement to limit the crack widths. Rebar is what is called passive reinforcement however;

it does not carry any force until the concrete has already deflected enough to crack. Post-tensioning tendons, on the other hand, are considered active reinforcing. Because it is pre


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stressed, the steel is effective as reinforcement even though the concrete may not be cracked. Post-tensioned structures can be designed to have minimal deflection and cracking, even under full load.

ADVANTAGES/APPLICATIONS There are post-tensioning applications in almost all facets of construction. In building construction, post-tensioning allows longer clear spans, thinner slabs, fewer beams and more slender, dramatic elements. Thinner slabs mean less concrete is required. In addition, it means a lower overall building height for the same floor-to-floor height. Post tensioning g can thus allow a significant reduction in building weight versus a conventional concrete building with the same number of floors. This reduces the foundation load and can be a major advantage in seismic areas. A lower building height can also translate to considerable savings in mechanical systems and faade costs. Another advantage of post-tensioning is that beams and slabs can be continuous ,i.e. a single beam can run continuously from one end of the building to the other. Structurally, this is much more efficient than having a beam that just goes from one column to the next. Post-tensioning is the system of choice for parking structures since it allows a high

degree of flexibility in the column lay out , span lengths and ramp configurations. Post-tensioned parking garages can be either stand-alone structures or one or more floors in an office or residential building. In areas where there are expansive clays or soils with low bearing capacity, post-tensioned slabs-on-ground and mat foundations reduce problems with cracking and differential settlements. Post-tensioning allows bridges to be built to very demanding geometry requirements, including complex curves, variable super elevation and significant grade changes. Post-tensioning also allows extremely long span bridges to be constructed without the use of temporary intermediate supports. This minimizes the impact on the environment and avoids disruption to water or road traffic below. In stadiums, post-tensioning allows long clear spans and very creative architecture. Post-tensioned rock and soil anchors are used in tunneling and slope stabilization and as tie-backs for excavations. Post-tensioning can also be used to produce virtually crack-free concrete for water-tanks.


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TERMINOLOGY A post-tensioning "tendon" is defined as a complete assembly consisting of the anchorages, the pre stressing strand or bar, the sheathing or duct and any grout or corrosion-inhibiting coating (grease) surrounding the pre stressing steel. There are two main types of post tensioning: un bonded and bonded (grouted). An un bonded tendon is one in which the pre stressing steel is not actually bonded to the concrete that surrounds it except at the anchorages. The most common un bonded systems are mono strand (single strand) tendons, which are used in slabs and beams for buildings, parking structures and slabs-on-ground. A mono strand tendon consists of a seven-wire strand that is coated with a corrosion-inhibiting grease and encased in an extruded plastic protecti

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