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Hundreds of Bridges�Thousands of Cracks

by John W. Fisher, Prof. of Civ. Engrg.; Fritz Engrg. Lab., Lehigh Univ. Bethlehem, Pa.,
Dennis R. Mertz, Bridge Design Engr.; Modjeski & Masters, Harrisburg, Pa.,


Serial Information: Civil Engineering—ASCE, 1985, Vol. 55, Issue 4, Pg. 64-67


Document Type: Feature article

Abstract:

In the past 10 years hundreds of welded steel bridges, most of them relatively new, have suffered thousands of cracks due to secondary stresses, that is, the cracks are caused by deflections in the structure that are caused by loads. No crack has led to collapse of a bridge, and in no case has a bridge had to be closed or load-limited. The cracks were found in steel-girder web gaps between vertical connection plates and the girder flanges where a gap was left between connector and the girder's flange. Causing the cracks were lateral or out-of-plane bending of the web, caused by transverse beams or lateral bracing. Any of three corrective measures has stopped the cracking in existing bridges: (1) A hole is drilled at each end of each cracks; (2) the unstiffened web gap is lengthened, reducing stress concentration, by cutting away a piece of the offending stiffener; or (3) the web gap is closed by bolting (not welding) the connection plate to the web. New bridges are being designed to prevent this type of cracking.

Subject Headings: Cracking | Steel bridges | Steel structures | Girders | Flanges | Connections (structural) | Bridges

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