Issues in Superload Crossing of Three Steel Stringer Bridges in Toledo, Ohio

Abstract

A 371-ton (816.7-kip) cooling unit crossed over three steel stringer bridges in Toledo, Ohio. Any bridge damage was compensated if scientifically documented. Researchers predicted the superload responses by using finite element analysis and experimental test results, and then measured the superload responses to establish whether the event caused any damage. Although the conservative results of the finite element model predicted an overbound of critical stresses, experimental results gave closer predictions of the measured response under superload. During the superload crossing, the maximum stress levels at the girders remained at about 34.5 MPa (5 ksi). The cross braces were stressed up to 68.9 MPa (10 ksi), exceeding the girder stresses. The study included questions about the real behavior versus design assumptions regarding cross braces in steel stringer bridges. (Cross braces are the weak links that fail first, causing lateral instability and failure.) Research revealed the possibility of predicting superload responses and behavior quite reliably by using a combination of diagnostic tests and finite element analysis. These tools permit the best design for superload axle configuration, crossing paths and positions on bridges, and possible options for effective bridge strengthening when needed.