Experimental and numerical study on seismic performance of beam-column rigid joints with embedded transition columns in steel archaized buildings

Steel archaized buildings (SABs) commonly use transition columns connecting upper square and lower circular steel tubes. The abrupt sectional change can cause stress concentration and stiffness discontinuity along the column height, yet the influence of embedment in these all-steel transitions remains insufficiently quantified. Two full-scale beam-column joint specimens with embedded depths of 0 and 300 mm were tested under quasi-static cyclic loading. The non-embedded specimen developed damage in the cover-plate base metal near the transition welds and at the beam ends. Compared with the non-embedded specimen, the embedded specimen exhibited increases of 63.1% and 80.4% in ultimate lateral load capacity and initial stiffness, respectively, with failure confined to the beam ends and no damage observed in the transition region. A refined three-dimensional finite element model was developed, and its predictions were compared with the experimental failure modes, hysteretic response, and energy dissipation. Parametric analyses examined the effects of axial load ratio, embedded depth, beam-to-column flexural rigidity ratio, and cover-plate thickness. Increasing the embedded depth from 0 to 50 mm produced most of the performance gains, whereas high axial load ratios markedly reduced strength and ductility through second-order effects. Within the investigated parameter ranges, an axial load ratio not exceeding 0.3 and an embedded depth of 50–100 mm are suggested. These findings quantify the influence of embedment on all-steel square-to-circular tubular transition joints and provide preliminary guidance for their seismic design.