IMPROVING STEEL BRIDGES AGAINST EARTHQUAKE THROUGH THE USE OF FLEXIBLE LATERAL DIAPHRAGMS

Abstract

In earthquake zones, bridges are designed in such a way that the entire earthquake energy and its subsequent damages are directed into substructure parts (such as pillars, piers and bearings). This causes a critical issue particularly for old steel bridges with non-flexible substructures. In order to take advantage of steel structure of a bridge, a periodic strengthening method is suggested. In this method, fundamental damages to the substructure can be prevented by substituting flexible diaphragms for steel diaphragms in bearings and piers. This paper presents a brief summary of flexible diaphragms design method for seismic strengthening of steel bridges (with steel main beam and concrete slab), describes the related concepts and also analyzes the test results for diaphragm samples. Some tests in which the flexible lateral diaphragms with SPS, EBFs and TADAS (systems of dissipation of earthquake energy) had been used were performed on full-scale samples from the end part of a steel bridge with the span of 40 meters. According to the results of the tests, high resilience and high resistance against dissipation of Hysteresis energy were quite obvious. Fracture of resisting plates through bending status or link beam base loss through buckling and fracture of wings were the main causes of damage for flexible diaphragms in large lateral drifts. Although lateral bearings had not been used in these samples, they showed high formability capacity.