Experimental investigation of the inelastic cyclic behavior of concrete filled double skin tubular beam-columns with corrugated inner skins and ultra-high-strength corner tubes

This paper presents the experimental results from nine full-scale concrete-filled double-skin tubular (CFDST) beam-columns. The test specimens exploited two fabrication strategies featuring either hollow steel inner skins with corrugated geometry or ultra-high-strength steel corner tubes to enhance the seismic performance of non-compact CFDST beam-columns for potential use in low-to-moderate seismicity regions. The effects of loading sequence, axial load ratio and cross-sectional geometry were investigated. The experimental results suggest that the current AISC specification may be used to predict the axial strength of the composite members with a relatively good accuracy. In the post-buckling range, conventional CFDST beam-columns and those with corrugated inner skins are prone to fracture at the corner welds of the built-up cross section. However, the latter exhibit up to two times larger drift capacities than their conventional CFDST counterparts prior to losing their axial load carrying capacity. Non-compact beam-columns retrofitted with ultra-high-strength steel corner tubes exhibit a 4% lateral drift demand without experiencing more than 25% flexural strength loss. The presence of ultra-high-strength steel increases the plastic hinge length of CFDST beam-columns by up to four times relative to that of CFDST beam-columns with corrugated inner skin, regardless of the employed loading history.