CYCLIC STRENGTH AND DUCTILITY OF RUSTED STEEL MEMBERS

After some recent earthquakes that demonstrated the potential seismic vulnerability of some types of steel bridges, many transportation agencies have initiated programs to evaluate the seismic resistance of their existing bridges. However in some regions, the problem will be more severe by the fact that steel bridges have frequently been exposed, for years, to an aggressive corrosive environment, particularly where road de-icing salts have been heavily used, seismic-resistant members frequently appear to be severely corroded. Similar problems occur to other steel structures. To determine whether such rusted members can reliably exhibit stable ductile behavior that is expected during an earthquake, a number of rusted pieces (having up to a 60% loss of cross-sectional area) taken from an old steel bridge, were subjected to some tension and cyclic bending tests. Non-cyclic tension stress-capacity and ductility did not change significantly due to corrosion. However, cyclic tests showed that, while stable hysteretic behavior comparable to that of unrusted specimen is possible, premature low-cycle fatigue, typically develops. Irregularities along the rusted surface apparently act as crack initiators and precipitate crack propagation throughout the section