Seismic performance of steel columns interacting with embedded column bases while exhibiting inelastic deformations

Abstract

Observations from past earthquakes indicate that embedded column bases (ECBs) in steel moment resisting frames (MRFs) exhibited inelastic deformations while they were designed to be non-dissipative. Consequently, the amount of inelastic damage concentrated in the respective fixed-end steel MRF columns was somewhat eased. This nonlinear interaction is examined by means of mixed-dimension continuum finite element (CFE) parametric simulations validated to available full-scale experimental data. The examined parameters are the ECB’s peak flexural strength, its plastic deformation capacity, and its elastic stiffness. The influence of the loading conditions along with the steel column geometric characteristics are also investigated. The simulation results indicate that, when ECBs exhibit partial inelastic deformation through controlled cracking, they feature enhanced plastic deformation capacities, which are, on average, 30–50% greater than those in commonly used non-dissipative bases. Moreover, residual axial shortening of first story steel MRF columns is reduced by up to 50% at a reference lateral drift of 4% rads. These benefits are more pronounced for steel columns with slender, but seismically compact cross sections (i.e., h/tw>20), which are prone to local and/or member instabilities at modest lateral drift demands (e.g., 2% rads). The extent of the above effects is controlled by the peak flexural strength ratio between the steel column and the ECB, the plastic rotation of the ECB and the loading history (cyclic versus monotonic). Limitations are discussed.