INSTRUMENTATION, PROOF-TESTING AND MONITORING OF THREE REINFORCED CONCRETE DECK-ON-STEEL GIRDER BRIDGES PRIOR TO, DURING, AND AFTER SUPERLOAD

A 352 ton (776 kip) weight cooling unit was scheduled to cross over three steel stringer bridges in Toledo. Permission was granted with the condition that compensation would be received for any resulting damage, providing that it was scientifically documented. Writers predicted the super-load responses using finite element analysis (FEA) and experimental test results, and then measured super-load responses to establish whether the event caused any damage. While the conservative FEA results predicted an over-bound of critical stresses, experimental results gave closer predictions of the measured response under super-load. During the super-load crossing, the maximum stress levels at the girders remained at about 6 ksi (41 MPa). Some of the cross-braces were stressed up to 10 ksi (69 MPa), exceeding the girder stresses. This study brought up questions about the real behavior versus design assumptions regarding cross-braces in steel stringer bridges. Cross-braces would be the weak links that would fail first, causing lateral instability and failure. The study revealed that it is possible to predict super-load responses and behavior quite reliably by a combination of diagnostic tests and FEA. These tools permit an optimum design of super-load axle configuration, crossing path and positions on bridges, and even possible options for effective bridge strengthening when needed.