Schoharie Creek Bridge Collapse - Case Study including the root causes of the failure and the lessons learned from the collapse. Moreover details of what actually happened on the day of collapse

1. Presented By
Things Simplified
( A New Perspective )

2. 
 Schoharie Creek Bridge was situated in New York State. Total Length of bridge
was around 165 metres.
 The design of bridge was approved in 1952 and the construction of the bridge
was completed in 1954.
 The bridge originally consisted of 5 simply supported spans varying from 30 to
36 metres in length supported on pier frames in the middle and abutments at
the end.
 The pier frames were constructed of two slightly tapered columns and tie
beams. The columns were fixed within a lightly reinforced plinth, which was
positioned on a shallow reinforced spread footing. The spread footing was
protected by a layer of dry riprap.
 The superstructure was made up of two longitudinal main girders with
transverse floor beams. The skeleton of the 200 mm (eight-inch) thick bridge
deck was comprised of steel stringers
Schoharie Creek Bridge

3. Longitudinal section of the bridge

4. 
Cross section of the bridge

5. 
 In the morning of April 5, 1987 – bridge finally collapsed after the failure of one
of the piers after a record rainfall of 150mm.
 The toppling or failure of the pier three was the initiation of the collapse which
resulted in the collapse of span three and four. Two spans of the bridge fell into
the flooded creek below. Five vehicles fell into the creek before the traffic
could be stopped and total of 10 people died.
 One and a half hours later after initiation of the collapse, pier two collapsed
leading to the failure and fall of span 2 of the bridge in the creek below. The
NTSB suggested that pier two collapsed because the wreckage of pier three
and the two spans partially blocked the river, redirecting the water to pier two
and increasing the stream velocity.
 Furthermore two hours later, large displacement and distortion was reported in
span one and pier one.
Collapse of the Bridge

6. 

7. 

8. 
 The collapse of failure of the bridge did not happen in a day. It was series of the
events which eventually led to the failure of the bridge.
 The root cause of failure of the bridge was the extensive scouring under the
pier three. The scouring under the pier began shortly after the construction of
bridge due to the floods in the creek. The foundation of the pier was bearing
on erodible soil, consisting of layers of gravel, sand and silt, inter-bedded with
folded and tilted till. This allowed high velocity flood waters to penetrate the
bearing stratum.
 The sheet piles used during the construction of the piers were to be left in the
place after the construction of the bridge as per the original design of the
bridge, but in detailed investigation it was found that the sheet piles were not
left in place after the construction.
Causes of Failure

9. 
 The as-built footing excavations and backfill could not resist scour. The area
left around the footing due to excavation was backfilled with erodible soil and
topped off with dry riprap, rather than being backfilled with riprap stone to the
entire depth of the excavation as per the original design.
 The shallow footings used, bearing on soil were susceptible to undermining.
Therefore the depth of which the footings was not enough to take them below
the probable limit of scour.
 The simply supported spans were not redundant in nature and hence did not
allow for alternate paths for load transfer.
 The plinth reinforcement stopped the hinge action of the plinth cracks.
Therefore, instead of dropping slowly into the scour hole, the plinth cracked
suddenly. The inspection and maintenance of the bridge were inadequate.
Causes of Failure
(Cont.)

10. 
 Proper inspection and maintenance of the bridge must be done at regular
intervals.
 There should be proper erosion protection around the pier foundation.
 The design of such an important structure must be done only after careful and
in-depth analysis considering all the forces which can be encountered by the
structure in its service lifetime.
Lessons Learned

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12. Thanks for your
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Have a Nice Day

13. 
 Schoharie Creek Bridge Collapse Causes
https://www.youtube.com/watch?v=nwm0seFZXvM
 Schoharie Creek Bridge Collapse
https://www.youtube.com/watch?v=rBaoRhtMWLE
Video References