Reliability-based safety factor calibration of semi-rigid aluminum alloy reticulated shells

Reticulated shells are widely used as primary load-bearing systems in large-span buildings, but their global stability can be strongly affected by semi-rigid joint stiffness and spatially correlated initial imperfections. Current design provisions for aluminum alloy spatial grid structures still rely mainly on deterministic stability checks, and a probabilistic basis for safety factor calibration remains limited. This study investigates a Kiewitt-6 single-layer spherical aluminum alloy reticulated shell under dead-load- and snow-load-dominated conditions represented by the Harbin snow-load environment. A finite element model was established by incorporating material and geometric nonlinearities, the moment-rotation behavior of semi-rigid gusset joints, and Karhunen-Loève random-field imperfections. Based on this model, a stability reliability framework with 20 random variables was developed, and an active-learning Kriging method enhanced by hybrid importance sampling and subset simulation, denoted as AK-HIS-SuS, was proposed for efficient failure-probability evaluation under high-dimensional and small-failure-probability conditions. Parametric analyses were conducted for 18 cases with different rise-to-span ratios, load ratios, and ring numbers. The results show that the reliability index is sensitive to all three parameters. Smaller rise-to-span ratios and larger load ratios lead to lower reliability, whereas increasing the ring number generally improves stability reliability for most parameter combinations. For representative case S10, the reliability indices obtained from Bootstrap-MCS, AK-MCS, and AK-HIS-SuS are 2.77, 2.83, and 2.81, respectively, while AK-HIS-SuS requires only 80 finite element calls compared with 4000 for Bootstrap-MCS. With load partial factors fixed at γ_G = 1.3 and γ_Q = 1.5, the stability correction factor K_opt was calibrated against the target reliability index β_T = 3.7. Taking γ_R= 1.20 according to the Chinese code for aluminum alloy structures, the calibrated K_opt values range from 1.20 to 1.35, and the corresponding equivalent global stability factor K_eq ranges from 1.980 to 2.268. These values remain lower than the safety factor of 2.4 specified in T/CECS 634–2019, indicating conservative coverage for the studied cases.