The Schoharie Creek Thruway
bridge collapse
4A6(1) Structural Design Project
By Group 18
David O’Brien
Karen McMorrow
Clare Whitely
Submitted October 23rd 2009
Introduction
The Schoharie Creek Bridge collapsed on April 5, 1987, just 30 years after it was
constructed. It was a New York State Thruway bridge over the Schoharie Creek near Fort
Hunter, in New York State. The bridge operated as a pivotal piece of the 900km stretch of
superhighway which allowed New Yorker’s travel around the state with ease. The collapse
was caused due to erosion of the foundations and the surrounding footing. Five vehicles fell
into the flooded river resulting in the death of 10 people.
Design and Construction
Construction of the Schoharie Creek Bridge began on February 11, 1953. The truss design
bridge was supported with pier frames along with abutments at each end. The pier frames
were constructed of two slightly tapered columns with tie beams. The columns were fixed in
place within a lightly reinforced plinth positioned on a shallow, reinforced spread footing.
The spread footing was to be protected with a dry layer of riprap (rock).
The superstructure consisted of two longitudinal main girders with transverse floor beams.
The skeleton of the bridge deck (200 millimeters thick) was made up of steel stringers.
The 165m long structure had 5 separate spans, each span measuring 30.5m, 33.5m, 36.6m,
33.5m, and 30.5m respectively, along with 4 concrete pier frames which would support the
bridges spans along with abutments at each end, 2 were to be erected in the creek with
shallow pad footings and two on the banks of the creek. A cross-section of a typical pier with
footing is as follows:
112.5'
27.75'
57'
27.75'
Symmetrical about
C
L
Deck
Stringer at
8'-6" o.c.
Floor Beam at
approx. 20' o.c.
Knee Brace
Main Girder
Cantilever Floor
Beam Ends
Bearing
7'-0" sq Column
5'-0" wide X10'-0" deep
Tie Beam
Column
Plinth Reinforcement
Plinth
Footing
Figure 1 - Pier Section ( after "Collapse," 1987 )
Collapse
In April 1987, the collapse of the Schoharie Creek Bridge occurred during the spring flood.
Rainfall totalling 150mm together with snowmelt produced an estimated 50 year flood.
The collapse was triggered by the toppling of pier 3. The main cause of the collapse was the
intense scouring of pier three. Scour is the removal of sediment from a streambed caused by
erosive action of flowing water. It created a scour hole approximately 3 metres deep and 9
metres of the pier was undermined. The pier fell suddenly into the hole, without any warning
signs. This led to spans 3 and 4 also collapsing and falling into the creek. When it collapsed,
a car and a tractor and trailer were on the bridge. An additional 3 cars also fell into the gap.
90 minutes later pier 2 and span 2 collapsed. It has been suggested by the National Transport
Safety Board (NTSB) that pier 2 collapsed due to a blockage caused by the debris from pier 3
and the 2 spans in the river. This caused the water to be redirected towards pier 2 and also
increased the stream velocity. In total 10 people died but only 9 bodies were recovered. The
body of the 10th victim was recovered in the Mohawk River in July 1989.
Other factors contributing to the failure of The Schoharie Bridge collapse are:

The shallow footings used, bearing on soil, could be undermined.

The foundation of pier 3 was bearing on erodible soil.

The as-built footing excavations and backfill could not resist scour.

Riprap protection, inspection and maintenance were inadequate.

Also sheet-piles which were used in early construction were removed – if they were
present scour may have been avoided.

The simple spans were not redundant.

Concrete piers did not have enough ductility to permit frame action.

Bridge bearings allowed the spans to lift or slide off of the concrete piers.

Plinth reinforcement stopped the hinge action of the plinth cracks.
Conclusion
The collapse of the Schoharie Bridge provided essential information on the design methods to
resist scour and appropriate methods of bridge scour inspection.
There are many ways in which the collapse could have been prevented. The bridge could
have been supported on piles, which would have resisted scour. If this was not possible the
sheet piling could have been left in place and along with using more riprap, could have
helped protect the pier also. Failure could have also have been avoided by using continuous
spans. This could have helped to redistribute the forces between the spans after the failure of
pier 3.
Another important lesson learned is that appropriate and frequent inspections be carried out
on all aspects of the structure, including the underwater features of the bridge.
The collapse of the Schoharie Bridge is a reminder to us that during bridge design it is not
only the dead and live loads we need to consider but also the hydraulic forces which the
foundations and supports are subject to. The Schoharie Bridge is also a reminder of why we
need regular inspection and maintenance of the bridges which cross our waterways.
References:

www.wikipedia.org/wiki/Schoharie_creek

Levy and Salvadori, “Why buildings fall down” 2002 Norton. ISBN 0-393-31152-X

http://mdl.csa.com/partners/viewrecord.php?requester=gs&collection=TRD&recid=A
20042202158CE&q=Schoharie+bridge+collapse%2Cscour&uid=788423659&setcoo
kie=yes

http://www.eng.uab.edu/cee/faculty/ndelatte/case_studies_project/Schoharie.htm