RESTORATION OF EXISTING MAJOR BRIDGE ACROSS RIVER BHADAR ON NATIONAL HIGHWAY N0. 8E BETWEEN PORBANDAR AND SOMNATH- CASE STUDY Date : 21/09/2015 S. R. SHAH J. N. PRAJAPATI Assistant Engineer Assistant Engineer Design Circle (R & B) Design Circle (R & B) P. C. GANDHI S. K. PATEL Executive Engineer
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RESTORATION OF EXISTING MAJOR BRIDGE ACROSS RIVER BHADAR ON NATIONAL HIGHWAY N0. 8E BETWEEN PORBANDAR AND SOMNATH- CASE STUDY
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RESTORATION OF EXISTING MAJOR BRIDGE ACROSS RIVER BHADAR ON
NATIONAL HIGHWAY N0. 8E BETWEEN PORBANDAR AND SOMNATH- CASE STUDY
Date : 21/09/2015
S. R. SHAH J. N. PRAJAPATI Assistant Engineer Assistant EngineerDesign Circle (R & B) Design Circle (R & B)
P. C. GANDHI S. K. PATEL Executive Engineer Superintending Engineer Design Circle (R & B) Design Circle (R & B)
General Information of Bridge :
Bridge location
The bridge situated across river Bhadar on National Highway No. 8E,
between Porbandar and Somnath National Highway No. 8E, previously
known as coastal highway ,runs along the Arabian sea coast.
The transportation of heavy vehicle becomes frequent due to proximity
of the port near by the bridge location and the bridge is only option of
connectivity .
The overweight vehicles from mines also passes frequently over the
bridge structure in this coastal region.
Location of bridge adjoining to Arabian Sea creates the adverse saline
environmental condition.
EXISTING BRIDGE
BRIDGE AFTER CONSTRUCTION IN THE YEAR 1985.
Details of Bridge Structure: The river bridge is of 480m length having 12 spans of 40m.
The bridge has square crossing i.e. bridge is having zero degree skew
The bridge has Post-tensioned Pre-stressed type superstructure & it
was constructed in the year 1985.
Post tensioned prestressed type superstructure has three girder
systems with centre to centre spacing of girder at 2.5m.
Main girder, intermediate cross girders,end cross girders & Deck slab
are provided with concrete grade M 35.
It has total 18 nos. 12T13 cables for prestressing.
Four stage Prestressing was done.
The total depth of super structure was 2.92 M.
The super structure rests on Elastomeric bearings.
RCC pier cap with cut & ease type shape.
The wall type mass concrete pier.
Well foundation having 8.0 m diameter is provided.
The bridge was designed for load combination under IRC loadings
of Class AA Tracked vehicle single lane or Class A vehicle 2 lane or
70 R vehicle single lane.
It has been under use for over 25 years without any problem of
super structure.
Span no. 9 collapsed from centre of span on Dated 7/04/2015.
.
Distressing of Bridge & Failure of Span 9
Failure of Span 9
Overweight vehicle produce large bending moment in the middle
portion of the span, which eventually results in flexural cracking.
This cracks leads to corrosion of strands
Under saline environment, these flexure crack allows more
penetration of chloride ions. Therefore, severe corrosion and spalling
of concrete is observed in the bottom portion of the girder at mid
span.
The cracks may not harm in short term period but in long term it leads
to failure of structure.
In severe exposed condition, Load causing Tension crack of width
0.2mm(IRC SP37-2010)is permitted.
As per provisions of IRC:SP37-2010, over weight movement should
be infrequent, but in the present case, due to large scale mining
activities, movement of over weight vehicles become frequent, which
has resulted in severe distressing of prestressed girders.
Result of Chloride test of concrete supports severe corrosion of steel.
Investigations & Tests After collapsed of span no 9 ,visual inspection was carried by the
committee members.
During visual inspection, sever distressing is observed at bottom
middle portion of the prestressed girders of the span no. 7 and 8.
Minor distressing is observed on other spans, also.
Span 8 GIRDER BOTTOM
Span 8 GIRDER BOTTOM
SPAN NO 8
SPAN 7 BOTTOM GIRDER
SPAN 7 GIRDER
Visual observation
The NDT test
Rebound Hammer test
Core test
Carbonations, PH and Chloride content test were carried out
Concrete Quality of existing girders were evaluated from N.D.T test.
Probable Cube strength of concrete worked out by consultant on basis
of N.D.T & rebound hammer test.
TYPE OF TESTS PERFORMED:
Result of NDT Test:Location Evaluation of Concrete
Quality of Girders as per NDT Test
Probable Cube compressive strength based on UPV/RH in
N/mm2
Span No. 1 Good 52 + 25 %Span No. 2 Good 54 + 25 %Span No. 3 Good 54 + 25 %Span No. 4 Good 46 + 25 %Span No. 5 Good 54 + 25 %Span No. 6 Good 42 + 25 %Span No. 7 Good, Medium to Good at