DOI: 10.17603/ds2-jnf5-e909
title: Validation of Seismic Design Provisions for Diaphragms and Assessment of Higher-Mode Responses on Earthquake-Resistant Buildings

description: This research assesses the design provisions for floor diaphragms per ASCE/SEI 7-22 Section 12.10.1 and the alternative design provisions for floor diaphragms per ASCE/SEI 7-22 Section 12.10.3. Emphasis is given to how these provisions account for the effects of the higher-mode responses on the peak floor accelerations (higher-mode effects) of earthquake-resistant buildings. This is achieved by using strong-motion acceleration data available on the Center of Engineering Strong Motion Data (CESMD) website. A framework is developed for processing and analyzing the strong-motion acceleration data obtained from building stations monitored by the California Strong Motion Instrumentation Program (CSMIP). The building stations comprise multiple stories and types of seismic force-resisting systems. The higher-mode effects are assessed by comparing the spectral response factors defined as the ratio between the floor spectral response acceleration and the ground spectral response acceleration at a determined modal period. The design acceleration coefficients are computed based on the design provisions. The design acceleration coefficients are compared with the peak floor accelerations first computed at the center of rigidity of each instrumented floor and then interpolated to the remaining floors. The center of rigidity is estimated using the measured strong-motion data by implementing a method available in the literature. The periods of the first, second, and third translational modes are estimated using the measured strong-motion data by evaluating simplified and analytical expressions provided in the literature. The floor diaphragm design acceleration coefficients per ASCE/SEI 7-22 are modified to consider the intensity of the measured ground motions and the estimated level of inelastic response of the building stations induced by the measured ground motions. Based on this, the modified acceleration coefficients are named design-based intensity-dependent acceleration coefficients.  Two metrics are used to compare the modified acceleration coefficients with the measured peak floor accelerations over the height of the buildings.  Comparing the spectral response factors at the second- and third-mode periods with those at the first-mode periods for different buildings confirms the need to consider the characteristic dynamics of the buildings to estimate the design forces for floor diaphragms, as done in ASCE/SEI 7-22 Section 12.10.3. The design-based intensity-dependent acceleration coefficients based on ASCE/SEI 7-22 Section 12.10.1 can significantly underestimate the peak floor accelerations if the ground spectral response accelerations at the higher-mode periods are considerably larger than the ground spectral response acceleration at the first-mode period. The design-based intensity-dependent acceleration coefficients based on ASCE/SEI 7-22 Section 12.10.3 reasonably predict the peak floor accelerations if the ground spectral response accelerations are reasonably estimated. The modified acceleration coefficients based on ASCE/SEI 7-22 Section 12.10.3 can capture the increased peak floor accelerations caused by either the higher-mode ground spectral response accelerations or the higher-mode response contribution characteristic of the dynamic properties of the building stations. However, some assumptions considered in ASCE/SEI 7-22 Section 12.10.3 need to be further revised.