Displacement based seismic verification method for thin-walled circular steel columns subjected to bi-directional cyclic loading

The present work evaluates influence of bi-directional cyclic loading on Finite Element (FE) models of thin-walled circular steel columns, especially preferred for highway bridges in Japan. An in-house developed material constitutive law is used for the material properties of FE model to understand the behavior of steel under inelastic cyclic loading. The empirical formulas for strength and ductility are developed based on the observations. Attempts are also made to develop a bi-directional seismic verification method by using relation between ultimate ductility of uni- and bi-directional loading, and characteristics of displacement response of the column under two-directional earthquake motions. The comparison between occurrences of ultimate displacement and ultimate strain, in different cases studied, indicates that displacement based seismic verification approach gives slightly over design of the steel column.