2023 179 E1

Seismic Force of Nonstructural Components in Based Isolated Buildings

By: Sepehr Shakeri

Department: Engineering 

Faculty Advisor: Dr. Jenna Wong

Chapter 13 of ASCE 7-22 was significantly updated and now includes floor accelerations and building periods in seismic design anchorage force calculations. One carryover from the previous edition of ASCE 7 is the factor ai (floor acceleration obtained from dynamic analysis). The ai factor is used in the seismic design force (Fp) equations to allow the designer to account for reduced floor accelerations from seismic isolation and/or increased damping of the structure. However, the upper and lower limits of Fp used for a fixed based structure still bound the calculation of Fp with the ai factor, even with the reduction of forces from isolation or damping. In this paper, a series of nonlinear dynamic analyses of a special steel moment frame structure are conducted for quantification and comparison between seismic anchorage resultant forces calculated for a fixed based building versus a seismically isolated building. The result of the analysis indicates that seismic resultant forces (Fp) calculated based on the story acceleration of seismically isolated buildings are much lower compared to ones calculated based on the acceleration of a fixed based building. As a result, the lower Fp limit required by ASCE 7-22 is much higher than the resultant force calculated for the seismically isolated building, which results in the overestimation of anchorage forces of components.