AbstractThis 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 ultrahigh-strength steel corner tubes to enhance the seismic performance of noncompact 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 suggested that the current AISC specification may be used to predict the axial strength of composite members with a relatively good accuracy. In the postbuckling 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 exhibited up to two times larger drift capacities than conventional CFDST counterparts prior to losing axial load carrying capacity. Noncompact beam-columns retrofitted with ultrahigh-strength steel corner tubes exhibited a 4% lateral drift demand without experiencing more than 25% flexural strength loss. The presence of ultrahigh-strength steel increases the plastic hinge length of CFDST beam-columns by up to four times relative to CFDST beam-columns with corrugated inner skin, regardless of the employed loading history.

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