Estimations of seismic input energy and inelastic top displacement demand in moment resisting frame type structures

Abstract

Energy-based seismic design (EBSD) methodology has an edge over force-based seismic design (FBSD) and displacement-based seismic design (DBSD) methodologies in many ways. Unlike FBSD and DBSD used in the current seismic design codes, it accounts for the type (near-fault, far-fault, etc.), frequency content, and total duration of the EQ record. Also, it takes the cumulative damage potential of an earthquake excitation into account. A basis for the EBSD was created in the content of this thesis study by proposing a methodology to calculate the seismic demands of a moment resisting frame fast and with an acceptable level of accuracy. Firstly, mass-normalized input energy response spectrum is calculated for SDOF systems using the ground acceleration and velocity response of the structure. Input energies (EI) imparted into each story of a MDOF system are estimated using the suggested formula which uses mode shapes, modal participation factors, and EI/m spectra constructed for SDOF systems. After total EI per unit mass is estimated, maximum inelastic top displacement (δtop) of a MDOF system during a seismic excitation is predicted using the proposed relation between EI/m and δtop. Model frames and EQ records to be used in the application and verification of the methodology were selected and nonlinear time history analyses (NLTHA) were performed on the model frames using Perform 3D software. In order to make sure that the methodology can be applied on moment resisting frames using different materials and with different number of stories, three-story reinforced concrete Manoukas frame, three- and six-story steel Akbas frames, nine- and twenty-story steel SAC-LA frames were selected. For the selection of EQ records, energy-displacement capacity curves were calculated for the model frames using the force-displacement capacity curves that were obtained after running static push-over analyses.