rehabilitation of bridge at agarwada

8/12/2019 Rehabilitation of Bridge at Agarwada

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Rehabilitation of Bridge atAgarwada

Course on Repairs and Rehabilitation

Faculty: Prof R.J Shah


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THESITE

The bridge was constructed across river Mahi on SH-2 at Km 107, nearvillage Agarwada. It about 31 Km downstream side of Panam dam.

This bridge connects North Gujarat and adjoining states of Rajasthan and

Madhya Pradesh


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TheBridge

SUBSTRUCTURE:The sub-structure consist six 1.0 m diameter solid R.C.C. columns resting on

R.C.C. well cap of 10.77m height.

Spacing of columns in transverse direction was 2.63 m and in longitudinal

direction was 6.86 m c/c .

There was a tie beam of 0.76 x 0.3 m at a height of 6.33 m from the top of well

cap and three columns were connected in transverse direction.


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TheBridge

FOUNDATION:single circular R.C.C. well foundation of 7.93m external diameter.

The depth of well varies from well to well.


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SUPER STRUCTURE:

Precast - prestressed post tensioned three girder and stab system on

R.C.C. frame of 6 no.

1.0m diameter Column.

Spans are simply supported on cantilevered hammer head.

Loading was anticipated as two lane of class A' and single lane of class AA,

having 7.0 m width of carriageway.

Length of the bridge was 439 m, consist of 6 central spans of 56.4m and

end spans of 50.3m.

TheBridge


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Schematic diagram Showing The bridge in details


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The girders are spaced at 2.36m c/c with depth of 3.04m.

The bottom bulb was of 0.49m and the top flange was of 1.14m and the web

thickness varies from 0.49m to 0.61m.

Thickness of the web stab is 0.15m.

Thus the overall depth of super structure is 3.2m .

The 9 no. 0.23m thick diaphragms are provided at equidistant.

TheBridge


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BEARINGUnder each girder over the hammer head the elastomeric bearings are

provided on both the ends.

WEARING COURSE

The average thickness of 75mm, R.C.C. is provided as wearing course.

EXPANSION JOINT

The sliding plate type expansion joint is provided at each junction, it

consists of 50 x 50 x 6 mm angle and 100 x 6 mm plate.

RAILING

R.C.C. H type vertical members and top hand rails have been provided.

TheBridge


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River flow data:Catchment area: 11815 miles^2

Design discharge: 15,00,000 cusecs

Design HFL: RL 246.25 ft

Rock Level: RL 280.50 ft

TheBridge

Contractual details:

Commencement Date: 4th Aug. '73

Completion date: 29th Feb. '84

Construction cost: Rs. 1,55,00,000/-


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The bridge was distressed due to certain reasons but the major cause was

that, in 1990 there was a high flood in which the discharge was measured as

much as 8 lakh cusecs though it was not so high as compared to designed

discharge of 15 lakh cusecs.

With in the short span of one hour discharge was increased from 5 lakh to 8

lakh.

Due to this the distress observed in foundation/pier P6, link in super

structure of span 6 and span 7 due to shifting of well P6.

Distress noticed in concrete such as cracking, spalling, Leaching, honey

combing, exposed reinforcement, damage to railings, damage to bearings,

improper functioning of expansion joints and cracking of wearing coat.

As per the reports there was the abnormal scour observed around well.


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Photograph Showing The bridge in distress


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The distress observed in structure are:

1. Pier P6 was tilted / shifted on downstream side, which resulted in the

shifting of the column and hammer head was also shifted from actual

position in the same direction, resulting the shifting of centre tine by0.60m on the deck level and 0.36m at well cap level.

2. This dislocation of the members affected the sliding plate type expansion

joints between P6 and P7. The upstream side parapet on P6 was crushed

and separated the downstream side parapet apart by 0.11m.

The other expansion joints are also not functioning property.

3. As per the report of Department of Roads and Buildings there had been

considerable scour around all the wells due to tremendous increase in the

discharge and in some cases the scour had traveled below the cutting

edge of the well.


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4. There was heavy spalling, cracking and exposure of reinforcement in

steining walls.

5. There were vertical cracks in column, maximum width of 1.11 mm.

6. The tie between the column at P6 was cracked at the intermediate level.

7. From the report of department and the video photography, it been found

that P6 was not resting on the rock uniformly and the cavities shown were

about 53%, the same is been observed that other piers but tilting / shifting

was observed in P6 only.

8. The elastomeric bearing was damaged under spans 6 and 7.

9. The wearing coat had been cracked and damaged.

10.Some water spouts were missing due to which, the concrete was badly

affected.

There was some vegetation is grown in some places an debris were

accumulated in expansion joints and spouts.


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Schematic diagram Showing Locations of Rebound

hammer testing points.


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TESTS CONDUCTED FOR CONDITION SURVEY

The consultant for condition survey of the bridge conducted the test and

visual inspection.

They accessed the position with help of trolley, for inspection of main girders,diaphragms, soffit of deck slab, bearings, expansion joints and sub structure

elements.

To arrive at the conclusion they have conducted the tests tike:

1) Rebound Hammer test for assessment of strength of concrete.

2) Ultrasonic test for assessment of cracks and quality of concrete.

3) Cover test for checking of quality and adequacy of cover concrete.

4) Corrosion test for checking of depth and the intensity of corrosion.


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SYSTEMATIC APPROACH TO REHABILITATION OF PROJECT

SURVEY OF PROBLEM

From the documented data available related to the problem from the authorities

and the condition survey report of the present status about problem, the

survey was conducted.

LOCATING THE DAMAGES / DEFECTS /DISTRESS

The deterioration of a structure often appears in visible signs of damages.

A detailed inspection provides information about the damages.

An assessment of the structure may become necessary as a result.

Various tests may be conducted to complement the results of the visual

inspection.

Testing techniques and equipment to be determined relative to the extent and

type of the deterioration and the importance of structure.

To the extent possible, nondestructive methods are preferable.


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VISUAL INSPECTION

It is the primary survey that was been conducted, for each component of the

bridge an for at) the spans.

For convenience of identification, the spans were numbered from Thana Swali

side to Agarwada side.

Numbering of pier was also done on the same lines as for the spans.

And the inspection report was prepared, from which the testing positions and

alternatives were decided. TESTING

The tests are conducted for judging proper condition of elements as given insection.


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ANALYSIS OF CAUSES OF DAMAGES / DEFECTS /DisTRESS

The purpose of evaluating the structure-damage was not only to determine

the effect of damage to its remaining service-life/toad carrying capacity, butalso determination of causes of defects, so as to enable an intelligent

determination of an effective retrofit.

Before a repair-plan is implemented, either the causes of the damages have to

be removed or else the repair-measure have to be so designed as to

accommodate the causes, and build-in protection against them for future.

SELECTION OF METHOD

The evaluation will be as to whether or not an economical and technically

effective repair plan, can limit or contain the damage and thus enhance the

effective life of structure, in this case the degree of urgency required toimplement a repair-plan because of the advance stage of damage. This

preparation includes for structural and non structural elements.


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APPLICATION OF REHAB SCHEME

As per the selected method the specification was prepared, according to that

the work is under execution.


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ALTERNATIVES PROPOSED FOR REHABILITATION

ALTERNATIVE PROPOSAL NO. 1 The existing well will be cover by new R.C.C. steining from out side

and cast a new well cap.

Encase the existing column and hammerhead with R.C.C, to extend it.

Shift the dislocated spans to the proper alignment.

Not suitable because there is no provision for jacking and shifting of

spans.


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ALTERNATIVE PROPOSAL NO. 1


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ALTERNATIVES PROPOSED FOR REHABILITATION ALTERNATIVE PROPOSAL NO. 2

Dismantle the deck stab and the diaphragms between all the girders ofspans 6 & 7, and shift the girders to the adjoining spans.

Dismantle the hammer head, columns, and well cap.

Empty the dredge hole and provide new reinforcement cage with rockanchors up to 5m in the rock, and cast new steining.

Reconstruct the well cap, column, and hammerhead.

Replace the shifted girder to the proper position.

Not suitable because it is costlier proposal.


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Support the spans 6 & 7 on the boulder crated boulder steelcolumns

Proceed same as alt. No. 2 for tackling the old well.

Most suitable solution because it is economical and lessrework involved in it which will reduce the time.


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Erect supporting frames on hammer head of P6 and holds thespans 6 & 7, with the help of it.

Follow the sequence of alt no. 1.

Not suitable because, erection of frame on the distressedfoundation of P6 may cause more distress.


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Support the super structure as alt. No. 3;


Cast a cluster of piles on both, upstream and downstreamsides of existing bridge and cast new pile cap, column, hammerhead.

Lower the suspended spans to the proper position.


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Dismantle the superstructure of span 6 & 7, substructure of P6.

Construct two new wells in the same alignment and cast thethree spans instead of two.

Not suitable because it is costlier proposal.


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Same as proposal no. 3, but instead of temporary supportstructure, support the spans on two floating pontoon throughsteel column structure.

Not suitable because, the water !eve! of the Mahi River is not sosteady, so load heavy bearing pontoon may not stay in requiredposition though the anchors may tie it in bed.

ALTERNATIVE PROPOSAL NO 7


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ALTERNATIVE PROPOSAL NO. 6ALTERNATIVE PROPOSAL NO. 7


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STEPS INVOLVED IN REHABILITATION AT P6

. REMOVAL OP SAND

The sand in the working area has to be removed anyhow to concrete the

base and placing of steel sections in the position. For which there are manymethod had been tried to arrive the desired optimization, balance between cost

and time. The methods employed were: Demanding pump

For this method the diver has go inside of the water up to the bed level and

put the pipe to suck the sand from bed.

Air lifting pump

Modified sludge pump

Dragger


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. FILLING CAVITY

As stated in distress there are large cavities around the shifted and tilted

well, was filled with concrete of M20. using tremie pipes and funnel from top

of the deck. The concrete was mixed on deck itself with mixer of tilting, 10/7type.

The divers were used to pour the concrete to the exact location.

. DRIVING OF CASING

The casing was driven in side of the bed by grabing and hammering up to the

hard rock, then after it was taken to the 1.2 m below the hard rock. Temporary

support was given to it to keep it in alignment.

FOUNDING Of COLUMN SECTION


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. FOUNDING Of COLUMN SECTION

The fabricated column sections was towered in side the casing with the help

of crane, from the deck.

The casing was cast in M20 concrete from the same casing and the casingwas retrieved.

. FABRICATION Of TEMPORARY SUPPORT STRUCTURE

The bracing, under water with bolts, will brace at the founded column

sections by divers.

LIFTING ARRANGEMENT FOR SPANS 6 & 7


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. LIFTING ARRANGEMENT FOR SPANS 6 & 7

The total dead toad of each span is @ 285 T on each end.

Which is equally shared by 3 longitudinal girders.

Thus the total load on each girder is @ 95T.

So it is proposed to provide flat jacks of caring capacity of 1.25 times the

load, which comes out to be 420 mm diameter, and 170t rated capacity.

With assumption of 80 % efficiency, can take load of 136T.

These jacks are proposed to place under longitudinal girders at distance

from the end.

They will be supported on the steel plates placed over steel joist of isMB

450. After lifting of these spans it will be rested on the packing boxes with

Teflon stainless steel interface.

Than the girders will be side shifted on this least friction surface to therequired alignment by the jacks. After recasting the distressed elements,

and gaining have designed strength spans will be again lifted by same

jacks and place it over new hammer head on the correct position

DISMANTLING OF DISTRESSED STRUCTURAL PARTS


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. DISMANTLING OF DISTRESSED STRUCTURAL PARTS

Dismantle the deck stab and the diaphragms between all the girders of spans

6 & 7, and shift the girders to the adjoining spans.


. CASTINGOF NEW WELL FOUNDATION

Empty the dredge hole by clearing of inter/top plug and sand fitting, provide

new reinforcement cage with 80 no. 32 diameter rock anchors up to 5m in the

rock through bottom plug. and cast new steining. Tie them by 12 diameter torbar at 300mm c/c.


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. CASTING OF NEW STRUCTURE

To prevent the up liftment of the well it will be anchored in ground by 3m

with ground anchors through bottom plug.

There will be the new layer of R.C.C. of grade M25 in the dredge hole, which

is designed for taking the whole toad of the structure above. New well cap,

column and hammer head will be cast in proper alignment by concrete

grade M40.

The suspended spans will be towered, and shifted to the position afterproving new elastomeric bearings.


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. DISMANTLE SUPPORTING STRUCTURE

After shifting the load of suspended spans to the new hammer head the

erected supporting structure will be dismantled.

The precaution will be taken, not to disturb the existing structure, It will be

retrieved by the same method as of erection, with the help of crane and winch.

. WELL PROTECTION

To restrict scour around the well, the boulders fitted in a weir crate will be

placed all-round the rectified well steining in three layers.

The dimension of crate will be 2000 x 100 x 600 mm. It will be placed at the

depth of RL 63.7m in height of 1800mm and 15500mm beyond outer edge of

steining.


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THANKS

Ernest thanks to Prof. R J Shah for

providing guidance, Slides and

Photographs.

R and B Design circle Gandhinagar forproviding information and details

rehabilitation of bridge at agarwada

Documents