Investigation on deflection amplification factor for steel special moment resisting frames with soft story

One of the most common irregularities in structures is irregularities in height and of the lateral stiffness. Due to the commonness of the use of the irregular structures and also different seismic response of this type of structures, in comparison with regular structures, investigating the seismic response of irregular structures has always been the subject of several research studies. The structures designed for the reduced base shear, under the design earthquake have inelastic response. To calculate the real (inelastic) displacements of structures under the design earthquake, the displacements obtained from the reduced base shear, are amplified by deflection amplification factor (Cd). The seismic codes have dedicated a Cd for each structural system. But different studies show that the dedicated Cd by the codes cannot accurately estimate the real displacements. The main purpose of this research is to propose the Cd values more specifically for more accurately estimating maximum interstory drift ratio (MIDR) and maximum roof drift ratio (MRDR) in steel special moment resisting frames (SMRFs) with soft story. Number of stories and the location of the soft story are the variables considered in this research. The Results show that the use of Cd = 5.5, recommended by the 2800 standard and ASCE 7-16 for steel SMRFs, underestimates the real MIDR (in most of stories), and also MRDR. Thus, for more accurately estimating MIDR in the considered structures, under the design earthquake, Cd = 8.5 is proposed. Furthermore, for more accurately estimating MRDR, Cd roof = 8 is proposed.