Research on Durability Estimation for Steel Buildings

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This study showed that stress-corrosion-cracking behaviors and yield and/or tension strength after corrosion environmental loading. Used steels were SUS304 austenitic stainless steel, SMA490B weather proof steel for welding structure and SN490B rolled steel for building structure. Corrosion conditions were 2 hours spray of acid-rain contain 5% salts, 4 hours dray with 60□ temperature, 20% humidity and 2 hours full-humidity using artificial environmental testing apparatus. Those conditions were loaded cyclically with 650 times for stress-corrosion-test and 200 times for statically tension test.The results of stress-corrosion-cracking-test were as follows,(1)For SUS304, stress-corrosion-crack did not occurred until 650 corrosion cycles, but Luders band grew in front of the crack tip and the Luders band propagated according to the corrosion cycles. Consider the Luders band to be the crack, stress-corrosion-cracking threshold for SUS304 was 25.3-26.2 MN/m^<3/2> for base metal, 24.2-25.0 MN/m^<3/2> for heat affected zone respectively.(2)For SMA490B, stress-corrosion-crack did not occurred until 85 corrosion cycles too, and for this steel, rust formative rate was faster than stress corrosion crack propagation rate. It was thought that the rust layer of steel surface prevented the stress corrosion crack propagation. So that, the stress corrosion cracks hardly occurred for weather proof steel.(3)The surface of steel plate had bumpy condition by the corrosion. The bumpy conditions of SN490B were more remarkably than that of SMA490B weather proof steel. So that yield and/or tension strength of steels after corrosion deteriorated very much on account of the stress concentration by bumpy conditions.