The Schoharie Creek Thruway bridge collapse Department of Civil, Structural and Environmental Engineering Trinity College Dublin The Schoharie Creek Thruway bridge collapse SS structures project, group 18 Cormac Carroll Patrick Heck Laura Dowdall David Steinboim

Summary Introduction Structural history Mode of failure Reasons for failure Conclusions

Introduction I 90 New York-Buffalo Thruway 4 pier (2 in water), 5 span beam bridge. Total length 165 m, span width 34.3 m Piers founded on pad footings on alluvial soil.

Plinth reinforcement

Structural history Constructed 1954 1955: 100 year flood 1957: extensive repairs 5 April 1987: 50 year flood, pier 3 collapsed suddenly Result: 10 people died

Aerial view of collapsed bridge

Mode of failure Pier 3 suffered from « scour » phenomenon Pier was undermined by 9 m Hole 3 m deep Pier 3 suddenly fell into the hole Spans 3 and 4 failed immediately 90 minutes later: failure of pier 2

Scour failure illustrated

Reasons for failure « As built » not same as on paper Riprap used too light and not replaced No underwater foundation inspections Lack of redundancy in structure Later modification of course of river Added stiffness due to plinth reinforcement

Conclusions Need for clear design objectives Scrupulous attention to construction Appropriate maintenance of structures Implementation of legislation Knock-on effect of later structures Redundancy to avoid sudden failure