Department of Civil, Structural and Environmental
Engineering
Trinity College Dublin
The Schoharie Creek
Thruway bridge collapse
SS structures project
Group 18
Simon McCourt
Ronan Duffy
Michael Dowling
Paul Duignan
Paul
Submission Date: 24th October 2008
Introduction
The Schoharie Bridge located northwest of Albany in the Mohawk Valley was
constructed in the early 1950’s as part of a 900km superhighway which was proposed
to cross the entire State of New York. Officially opened in the winter of 1954 the
bridge operated as a pivotal piece of the 900km stretch of superhighway which
allowed New Yorker’s travel around the state with ease. That was until the morning
of the 5th of April 1987 when the bridge during high flood conditions suddenly and
catastrophically collapsed into the storm waters below and tragically claimed the lives
of 10 people.
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 supports and foundations 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.
Design and Construction
The Consulting Engineering company which was awarded the job of designing
the Schoharie Bridge was Madigan-Hyland Consulting Engineers. In the initial
designs stages of the bridge there were two specific designs which were being
considered, the main differences between these two structures was that of the length
of the superstructure. In the end the design which was chosen was that of a 165m long
structure with 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 shown below in figure 1.
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: Cross-Section of Pier and Superstructure
Figure 1 - Pier Section ( after "Collapse," 1987 )
The construction contract was won by B.Perini and Sons Inc. and the
construction of the bridge got underway in the Spring of 1953 and was completed in
the winter of 1954. Some important facts about the footing construction was that it
had been recommended that the temporary sheet piling which had been installed
during excavation should have been left in place and the ripraping which was
supposed to be placed inside the sheet piling was inadequate.
Shortly after construction several small jobs needed to be done on the structure
but these were all completed by autumn in 1957, this was the last time that any
maintenance work was to be carried out on the bridge.
The Collapse
The collapse of the Schoharie Creek Bridge occurred during the spring flood.
Rainfall totalling 150mm as well as snowmelt combined to produce an estimated 50
year flood.
The collapse was initiated by the toppling of pier 3. This caused spans 3 and 4
to also collapse and fall into the creek. A car and a tractor and trailer were on the
bridge when it collapsed. A further 3 cars also fell into the gap. This was possibly due
to the drivers being so close to the bridge at the time of collapse that they were
unable to stop in time. In total 10 people died but only 9 bodies were recovered. 90
minutes later pier 2 and span 2 collapsed. It has been suggested by the 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.
Causes Of Failure
Reports from teams investigating the cause of failure of the bridge concluded
that the collapse was due to extensive scour under pier 3. The vulnerability of
scouring under pier 3 was affected by some important
factors.

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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 riprap used was too light. Riprap weights of 1000-1500lb should have
been used instead of the riprap weights of 100-300lb.
Although the main cause of the bridge failure was scour, there were several other
items considered during the investigation of the collapse. These items include design
of the superstructure, inspection and maintenance of piers above streambed, and
inspections performed using the guidelines available at the time of inspections. These
items did not contribute to the collapse of the bridge.
Thornton-Tomasetti (investigating the collapse) found items that aggravated the
tendency for scour:
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A curve in the river upstream of the bridge directed a higher velocity flow
toward pier 3.
The flood was greater than that anticipated by the designers and followed
others (such as 1955) which disturbed the riprap.
Berms built in 1963 directed floodwaters under the bridge.
An embankment west of the creek channel increased flood velocities.
Drift material caught against the piers directed water downward at the base of
pier 3.
The severity of the collapse was also influenced by the following factors:



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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.
Scour
Palmer and Turkiyyah (1999) defines scour in the following manner:

Scour is the removal of sediment from a streambed caused by erosive
action of flowing water.
Scour was the principal action that resulted in the sudden collapse of the
Schoharie Bridge in 1987. There are many different mechanisms through which
scouring occurs, however for bridge construction there are some mechanisms that
have more adverse effects than others. The most applicable mechanism is that which
was summed up by Huber in 1991.
Huber wrote:

Local scour occurs when flow is obstructed by a pier or abutment
placed in the floodplain. Vortexes that form at the pier or abutment
remove stream bed material. (Figure 4)
Figure 4: Exaggerated Artist’s Rendition of Bridge Scour
Scour could only have been countered by riprap, by supporting piers on piles,
or by providing cofferdams around piers.
Lessons Learned
The collapse of the Schoharie Bridge, although unfortunate, provided vital
information on the design methods to resist scour and appropriate methods of bridge
scour inspection.
There were many suggested ways the disaster could have been prevented.
Firstly the bridge could have been supported on piles, which would have resisted
scour. If this could not have been accommodated, leaving the sheet piling in place and
using enough riprap could have helped protect the pier also. In addition, the use of
continuous spans could have helped to further avoid the failure. The continuous span
could have helped to redistribute the forces between the spans after the failure of pier
3.
Another important lesson learned is that appropriate and consistent inspections
be carried out on all aspects of the structure, including the underwater features of the
bridge.
References
http://timesunion.com/specialreports/tu150/stories/graphics/weather_thruway.jpg
http://en.wikipedia.org/wiki/Schoharie_Creek
http://www.eng.uab.edu/cee/faculty/ndelatte/case_studies_project/Schoharie.htm
Why buildings fall down - Levy and Salvadori, 2002 Norton
Fault Tree Analysis of Schoharie Creek Bridge Collapse:
J. Perf. Constr. Fac. Volume 21, Issue 4, pp. 320-326 (July/August 2007)