Experimental Study on Seismic Fatigue Capacity of High- and Mild-Strength Structural Steels with and without Corrosion

Abstract

The test results on hourglass specimens of steel under repetitive sine loads provide graphs that indicate the stress range in terms of the number of cycles to failure and are known as S-N curves. Using this curve, it is determined that if the applied stress is less than a certain level, failure will not occur as the number of load cycles increases. The S-N curve can be affected by several factors such as yield stress, temperature, surface properties, and corrosion. In this research, the S-N curve has been investigated for two types of high-strength steels, S690 and S460, as well as two types of mild-strength steels, S235 and S355, at 25°C, and S355 with corrosion. The numbers of samples used for S235 and S460 steels were 45 each while S355 and S690 steels were 36 each and for S355 with corrosion was 15 with the high cycle fatigue curve obtained for them. To investigate the effect of plate thickness on the high cycle fatigue of the samples, four sets of 24-piece S235 steel samples, being 96 samples in total, were made of plates with different thicknesses of 8, 12, 15, and 20 mm and tested. Finally, a four-story three-span steel moment frame was designed, and under the Northridge earthquake record, the high cycle fatigue was investigated. It was observed that the high cycle fatigue was not effective for the mentioned structure under the Northridge earthquake record, but in the corroded structure, damage from high cycle fatigue occurs under this record.