Effects of Ground‐Motion Characteristics on Floor Acceleration Demands in Fixed‐Base and Base‐Isolated RC Building Frames

This study investigates the floor acceleration response of 4‐, 8‐, and 12‐storey reinforced‐concrete moment‐resisting frame buildings with and without friction pendulum (FP) base‐isolation systems. Time‐history analyses are conducted for elastic and inelastic structural responses under 184 ordinary and pulse‐type ground motions each, including pulse motions with periods close to and significantly different from the fundamental modal periods of the structures. The effectiveness of FP isolation in mitigating acceleration demands on secondary systems is evaluated using in‐structure amplification factors, floor response spectra, and Fourier amplitude spectra (FAS). The results demonstrate that FP isolation provides substantially greater reductions in in‐structure amplification under ordinary ground motions than under pulse‐type ground motions. Floor response spectra further indicate that secondary systems tuned to the fundamental mode of the supporting structure achieve higher isolation efficiency than systems tuned to higher modes, particularly under pulse‐type ground motions. FAS confirms that base‐isolation filters seismic energy and suppresses modal amplification. Overall, the findings highlight the strong dependence of FP isolation effectiveness on ground‐motion characteristics and secondary‐system frequency, with substantially reduced protection against pulse‐type ground motions and higher‐mode excitation.