Seismic performance of steel moment frames incorporating ductile column base connections

Abstract

A common practice in the design of industrial steel structures in Chile is to consider column bases as seismic fuses. Unlike the North American philosophy, where plasticity is expected to develop at the lower end of the first-story column during a severe earthquake, the Chilean practice for the design of moment resistant frames (MF) attempts to concentrate the plastic demands in anchor bolts with extended lengths that prevents eventual brittle failures, and also to allow inspection and eventual retightening after the earthquake. Although this design philosophy and construction practice has been spread for many years, there is no in-depth documentation regarding formal and/or standardized design methods, and there are no studies on the seismic behavior expected in structures that consider this solution. In accordance with recent advances in this topic, regarding the expected behavior of this anchoring system against standardized design protocols, the present study presents a performance analysis of an MF with ductile anchors designed for different forces levels. The results indicate that inclusion of ductile column bases reduces the level of damage in the first-story columns and increases the median collapse capacity even when design forces as low as 30% of the expected capacity of the columns are considered.