Load-end shortening curve of stiffener elements with beam-column buckling considering steel grades based on empirical formulae of critical stress

The existing load-end shortening formulae with beam-column buckling in CSR-H were derived from the theoretical buckling formulae of stiffener elements considering the effective width of attached plate. However, due to different yielding stress and plastic flow ability, the critical stress of stiffener elements for elastic-plastic beam-column buckling may be relevant to steel grades. The critical stress of beam-column buckling was analysed by numerical method and compression test under supply supported constraints. Separate seven steel column samples from slender to sturdy were designed to be studied for various grades of steel mainly including 921A, S355 and Q235. After comparison, the empirical formulae of critical stress considering different yield stress were proposed in power exponent expression, and then employed to replace the theoretical buckling formulae in the load-end shortening curves in incremental-iterative method. This new load-end shortening expression of stiffener elements with beam-column buckling mode could more accurately evaluate the progressive collapse behaviours under longitudinal compression.