07. BRIDGE CONSTRUCTION METHODS Precast bridge construction

Precast bridge construction method. ...
Cast in-situ bridge construction method. ...
Balanced cantilever bridge construction method. ...
Incremental Launching bridge construction method. ...
Cable-stayed bridge construction method. ...
Arch bridge construction method. ...
Advanced shoring bridge construction method

1. METHOD OF
CONSTRUCTION OF
BRIDGES/FLYOVERS

2. TYPE OF CONSTRUCTION
1. CAST IN SITU OF ALL STRUCTURES
a) Pile/raft foundation
b) Pile cap
c) Pier
d) Pier cap
e) Bearing pedestal
d) Deck slab/Box girder
e) Crash barrier
f) Ramp with retaining wall

3. 2.COMBINED OF CAST IN SITU AND PRECAST OF
BRIDGES AND FLYOVERS
CAST IN SITU PRECAST
Pile/Raft foundation Pier
Pile cap Pier Cap
Diaphragm wall Pre stressed girder
Deck slab Segmental section
Crash barrier Reinforced earth works
3. COMPOSITE WITH STEEL AND CONCRETE

4. SEQUENCE OF ACTIVITIES AND CONSTRUCTION
METHODOLOGY
SURVEYING
a. Selection of site
b. Fixing of alignment
c. Fixing of Horizontal curves
d. Fixing of vertical curves
(i) Summit curves
(ii) Valley curves
e. Fixing of gradient
f. Fixing of super elevation

5. SOIL INVESTIGATION
At every pier location soil bore log is required to
ascertain type of soil/rock . Accordingly designer
choose type of foundation i.e. raft/pile, depth of pile
and dia. of pile.
FOUNDATION
a. Raft foundation
b. Pile foundation
c. Caisson foundation

6. PROCEDURE OF PILE FOUNDATION
a. Bored cast in situ pile with hydraulic rotary rig.
Before start of boring it is required to study the soil bore log of the particular
location so that one can know the requirement of casing depth, type of augur
and bentonite quantity.Bentonite must be soaked in water for at least 24 hours
and it should have the liquid limit of and specific gravity of 1.1
Bentonite plays a vital role in pile boring which prevents collapse of soil from
side wall of bore hole specially in sandy soil. Hence good quality of
bentonite is required for pile boring.
The pile centre point must be checked thoroughly before start of piling.
Augur of the hydraulic rig is placed at the centre point of the pile point and
boring is done up to 4m to 8m. To prevent collapse of soil from side wall
temporary steel casing of length 4m to 8m and 10-12mm thick is erected.
After erecting temporary casing boring is continued with pumping of
bentonite slurry into the bore till recommended depth i.e. founding level of
pile reaches. After termination of boring, hole should be cleaned with
cleaning bucket very well so that mud and debris should not retain at the
bottom of the pile.

7. Before lowering reinforcement cage into bore hole flushing with bentonite
slurry is required so as to remove the leftover mud and debris.
Prefabricated steel reinforcement cage of required depth is lowered with the
help of crane /rig.
After lowering of reinforcement tremie pipe of 200mm dia. is lowered to
place concrete into bore.Tremie pipe should be minimum 300mm above the
founding level so that concrete can flow freely.
It is important to note that after boring, concrete should be placed as earlier
as possible to avoid collapse of soil from side wall of pile. And also it should
be ensured that placing of concrete must be continuous. Delay in pouring or
interruption of concrete may lead to chocking of tremie pipe and even
rejection of pile.

8. While placing concrete it is ensured that tremie pipe should always immerse
in the concrete so that slush and mud may not mix with concrete. Hence
tremmie pipe should be removed one by one as concrete comes up. Open
Channel is made to flow bentonite slurry into sump pit during concrete.
After placing concrete, excess concrete above cut-off level should be removed
by means of scoop when the concrete is green.

16. VERTICAL PILE LOAD TEST
a . Initial test ------2.0 Times of design load
b. Routine test ------1.5 Times of design load
SAFE LOAD CRITERION
According to the Indian Standard, IS: 2911 (Part IV) 1985, the safe load on
Single pile is the least of the following:
Two -thirds of the final load at which the total displacement attains a value
of 12 mm or the specified value based on the nature and type of structure;
and
b) Fifty per cent of the final load at which the total displacement equals
to 10 per cent of the pile diameter in case of uniform diameter piles
and 7.5 per cent of bulb diameter in case of under reamed pile.
In the case under consideration, the relevant settlements according to
Stipulations (a) and (b) above are, 12 mm and 100 mm, respectively.

17. Procedure for pile load test
Pile head should be chipped off to even level and finished smoothly to have good
bearing over the pile.
Steel kentledge platform is made to a suitable height and concrete blocks are loaded
over the platform till final load is required.
Sufficient capacity of hydraulic jack is placed over the centre of the pile.Itso that load
reaction will transmit to centre of the pile.
Now load is applied in incremental basis i.e. 20% of final load. Pressure gauge and
dial gauge readings are noted. Time settlement observations are made at
commencement and completion of each increment till the final load is applied.
The pile is kept under sustained loading for 24 hours and readings are noted at
certain intervals. After 24 hours load is released in reverse increment and readings are
noted from dial gauge as well as from pressure gauge to find the rebound.

21. PILE CAP
Excavation is done at the pile group and excess concrete above
cut off level is chipped off. From cut off level pile cap is formed
which connects no of pile in a group.
PIER
Starts from pile cap top and upto bottom of Pier cap. It
is always better to place concrete in a single pour to
avoid unwanted joints.
PIER CAP
Over the pier cap Bearing pedestal is made. It is
generally a balance cantilever structure.

27. BRIDGE BEARING
a. Elastomeric bearing
b. POT bearing
c. Roller and Rocker bearing

30. PRESTESSED CONCRETE GIRDER
It is a fast track method, adopting Pre cast concrete members in
bridge/flyover construction. Mainly to save time and space at
site, pre cast members are cast at a separate yard and
transported to working place.
The construction of super structure with PSC girders consists
of two major activities.
i) Pre cast of girders in casting yard.
ii) Transport and erect them at the appropriate location.
Normally at casting yard long line method is adopted i.e. casting
of two or more girders at a time which is economic and faster
also.

31. The construction sequence of PSC girders as below
1.Casting of bed and reaction column at stressing end and at
dead end.
2.Fabrication of formwork to the required shape and size of
PSC girder.
3.Cleaning and oiling of formwork.
4. Place the pre fabricated reinforcement cage over form work
with proper spacers.
5.Place the HT Strand (normally low relaxation HTS 15.2mmdia.
7 ply strand class 2 confirming to IS : 14268) as per profile given
in the drawing.
6.Stress the strand from one end and lock other end or stress
from both ends.
7. After stressing close the shutter and do concrete.

32. 8. Steam curing will help to achieve early strength of
concrete than conventional curing. So Curing is
important to gain strength of concrete.
9.After ensuring required strength of concrete i.e. 80%
of its compressive strength, girder can be lifted from
bed.
10.Lift girder by using Gantry Overhead Crane and
shift to stacking bed.
11.After attaining full strength i.e. after 28 days beam is
ready to transport and erect at the span.

43. SEGMENTAL SECTION BEING PLACED

44. DIAPHRAGM WALL
In between beams diaphragm wall is constructed to tie the
erected beams.
DECK SLAB
After constructing diaphragm wall deck slab formwork
arrangement is started. For this while casting beams
perforations are left to pass a tie rod to hold the bracket on either
side of the beam. In this system there is no requirement of
supporting staging from the bottom. This method is very
suitable where space constraint is there.
Form work is done over the beams and reinforcement is placed.
After checking of gradient and levels concrete is placed.

46. BOX GIRDER AT 30M SPAN (POST TENSIONING)
It is not feasible to transport and erect 30m long PSC girder.
Hence at such condition cast in situ box girder is constructed
mainly at Obligatory span.
It is constructed in three stages as below
1. Bottom Slab
2. Web
3. Deck slab
Trestles are normally provided to support the entire dead load of
the box girder. Over the trestle temporary steel girders are
erected and longitudinal channels are provided to make a
platform i.e. bottom of the slab.
Formwork is done over platform and steel reinforcement is
placed for bottom slab and for web.

47. Concrete is casted first for bottom slab and then web formwork
is carried out. At web portion like PSC girder before closing side
shutter HT strand is placed into sheathing as per drawing.
Care shall be taken to keep sheathing intact while doing
concrete. After web concreting, formwork is arranged for deck
slab. Steel reinforcement is placed for deck slab and then
concrete is done.
After gaining required strength HT strands are stressed from
both ends by using suitable capacity of hydraulic jacks.
As per drawing elongation is noted from both ends and slippage
is observed for 24 hours. If slippage is within the permissible
limit then HT strands are grouted. And Supports are removed
after attaining full strength.

50. CONSTRUCTION OF RAMP WITH REINFORCED EARTH
WORK
Conventional method of constructing retaining walls in the
embankment portion and in ramp takes much time and
sometimes uneconomical also.
It consists of the following
1.Pre cast panels
2.Reinforcement i.e.G.I.strips
3.Filling Material i.e. Gravels
REW requires systematic planning and pre determined panel
sizes. Pre casting of panels at central yard reduce much time
and cost.

51. PROCEDURE OF REWORKS
1.Excavation is to done to the required depth
2.PCC to be laid for level pad.
3.Place first layer of panel and align.
4.Connect the G.I. strips to lugs provided in the panels.
5.Spread first layer of gravel and compact with vibro roller.
6.Repeat second layer of panel fixing and connect G.I.strips.
7.Gravel filling layer should not exceed 300 mm.
8.After completion of Erection of panel and filling of gravel
temporary supports may be removed.
9.For high embankment pull out test of the G.I. strip is required
to confirm the frictional resistance as considered in the design.

56. CRASH BARRIER AND ROAD WORKS
After deck slab concrete crash barrier is constructed to
entire length of bridges/flyovers.
Mastic asphalt is laid over the concrete surface for
water proof.
Over that Bituminous concrete is laid.
At the ramp portion over sub grade WBM/WMM is
laid and over that bituminous concrete is laid.

58. THANK YOU