Restoring Force Model of Blind-Bolted T-Stub Joints in Steel Chinese Traditional-Style Buildings

Steel Chinese traditional-style buildings (SCTBs) retain the architectural features of ancient Chinese buildings and reflect traditional cultural and regional characteristics. However, their beam–column joints have complex configurations, and conventional welded connections face construction constraints in projects involving archaeological site protection. Blind-bolted T-stub connections provide a prefabricated connection solution for SCTBs. Previous studies have mainly focused on blind-bolted connections in conventional steel structures, while research on such joints in SCTBs remains limited, particularly regarding their restoring force models. To address this gap, low-cycle reversed loading tests were conducted on four blind-bolted T-stub beam–column joint specimens for SCTBs, including two double-beam joints and two single-beam joints. The experimental data were analyzed to evaluate the failure modes, hysteretic responses, skeleton curves, and stiffness degradation characteristics. The results showed that damage was mainly concentrated in the T-stub connection region. With increasing loading amplitude, bolt slip, gap opening, and bending deformation of the T-stub flanges progressively developed, followed by crack initiation and fracture at the T-stub flange–web junction, while no obvious damage was observed in the beams, columns, or joint core regions. The specimens exhibited stable spindle-shaped hysteretic loops, and the double-beam joints showed fuller hysteretic responses and higher moment resistance than the single-beam joints. The absolute ultimate moments ranged from 113.17 to 207.82 kN·m, and the ductility coefficients ranged from 2.27 to 3.96. Based on the experimental results, a restoring force model was developed using a normalized trilinear backbone curve, stiffness degradation relationships, and hysteretic path rules. The model reasonably reproduced the overall cyclic response and positive–negative asymmetry observed in the tests. The proposed model extends the restoring force modeling of T-stub connections to the irregular joint configurations of SCTBs and provides a basis for their nonlinear seismic response analysis. The modeling approach may also serve as a reference for similar blind-bolted T-stub joints in other regions.