A simplified procedure to estimate peak drift demands for mid-rise steel and R/C frames under narrow-band motions in terms of the spectral-shape-based intensity measure INp

In this study, a simplified procedure to predict the maximum inter-story drift demands of mid-rise framed buildings in terms of a spectral-shape-based ground motion intensity measure is proposed. For this aim, the maximum inter-story drift of steel and reinforced concrete (R/C) frames with 4, 6, 8 and 10 stories subjected to several narrow-band ground motions is estimated as a function of the spectral acceleration at first mode of vibration of the structure Sa(T1), which is commonly used in earthquake engineering and seismology, and with the recently developed parameter related to the structural response known as INp. It is observed that the spectral-shape-based intensity measure INp is the parameter best related with the structural response of the selected frames under narrow-band motions. Therefore, a new approach is used to propose equations to compute maximum inter-story drift demands and seismic uncertainty of mid-rise frames as a function of INp. The equations can be used for the rapid seismic assessment and to obtain structural fragility curves of the steel and R/C frame models. The fragility curves obtained with the simplified approach are compared to those obtained with traditional procedure to compute structural fragility. It is observed that the proposed equations provide good accuracy to calculate fragility curves of steel and R/C structures under narrow-band earthquake ground motions in terms of the spectral-shape-based intensity measure INp.