Full-scale steel column tests under simulated horizontal and vertical earthquake loadings

Abstract

This paper presents an experimental study to evaluate the vertical ground motion effects on steel wide-flange section columns in lower stories of steel frames. Eight full-scale specimens were tested utilizing the Multiple Usage Structural Testing (MUST) equipment, which can properly apply loading in both horizontal and vertical directions. Three cyclic lateral loading tests under constant axial load of 15% to 25% of nominal axial yield capacity were conducted to investigate the basic hysteretic behaviors. Five specimens were tested by pseudo-dynamic hybrid simulation with both horizontal and vertical excitations and an initial gravity load of 15% or 25% axial capacity. The failure mode of specimens tested by cyclic loading was notably influenced by the section compactness. Columns with thinner elements failed due to significant local buckling near the column ends corresponding to a drift ratio of 6% or even larger, while columns with thicker elements suffered rupture in the welding heat affected zones near column ends corresponding to a drift ratio of 4%. During the pseudo-dynamic hybrid loading with ground motions using the records of Imperial Valley earthquake and Northridge earthquake records, no rupture was observed. Lateral hysteretic response fluctuation was clearly observed in the pseudo-dynamic hybrid tests due to the inputs of both horizontal and the vertical ground motions. The pulse-type seismic input caused large residual displacements of the full-scale column specimens. Vertical ground motion also led to significant variations in axial loads, indicating the importance to study the seismic behavior of steel columns under realistic ground motion inputs.