The displacement coefficient method in near‐source conditions

Abstract

The use of nonlinear static procedures for performance-based seismic design (PBSD) and assessment is a well-established practice, which has found its way into modern codes for quite some time. On the other hand, near-source (NS) ground motions are receiving increasing attention, because they can carry seismic demand systematically different and larger than that of the so-called ordinary records. This is due to phenomena such as rupture forward directivity (FD), which can lead to distinct pulses appearing in the velocity time-history of the ground motion. The framework necessary for taking FD into account in probabilistic seismic hazard analysis (PSHA) has recently been established. The objective of the present study is to discuss the extension of nonlinear static procedures, specifically the displacement coefficient method (DCM), with respect to the inelastic demand associated with FD. In this context, a methodology is presented for the implementation of the DCM toward estimating NS seismic demand, by making use of the results of NS-PSHA and a semi-empirical equation for NS-FD inelastic displacement ratio. An illustrative application of the DCM, with explicit inclusion of NS-pulse-like effects, is given for a set of typical plane R/C frames designed under Eurocode provisions. Different scenarios are considered in the application and nonlinear dynamic analysis results are obtained and discussed with respect to the static procedure estimates. Conclusions drawn from the results may help to assess the importance of incorporating NS effects in PBSD

Analytical modelling of near‐source pulse‐like seismic demand for multi‐linear backbone oscillators

“…Be that as it may, it has been shown that as long as disaggregation of NS hazard can provide the necessary information on the probabilistic distribution of T p conditional on the design scenario of interest, analytical models containing pulse period as a predictor variable can be employed to estimate NS seismic demand or assess performance‐based objectives under NS conditions. This was demonstrated in for the case of single‐stripe pushover‐based simplified analysis using an earlier equation for NS‐FD inelastic spectra . More pertinent to the present model is the illustrative example included in , where a methodology for probabilistically incorporating T p into the calculation of NS inelastic demand at increasing levels of seismic intensity was demonstrated for a simple bilinear system.…”

Near -Source Pulse-Like Seismic Demand for Multi-Linear Backbone Oscillators

“…In fact, the model acts like an R-μ-p TT relation, which must be combined with site-specific information on pulse period and likelihood of directivity. As such, it could be employed in a manner analogous to the methodology of [5] in order to render a static non-linear procedure, for example the capacity spectrum method [17], applicable in NS conditions.…”

“…Initially, these static nonlinear procedures made recourse to inelastic spectra derived for simple elastic-perfectly-plastic or bilinear oscillators. One such procedure applicable in NS conditions has been suggested in [5]. However, the request for demand estimates that delve deeper into the inelastic range and arrive at quantifying collapse capacity (definition to follow), led researchers to also investigate the seismic demand of oscillators with more complex backbone curves such as the trilinear backbone depicted in Figure 2.…”

Pulse‐like versus non‐pulse‐like ground motion records: Spectral shape comparisons and record selection strategies

“…In a similar manner, Chioccarelli and Iervolino proposed a close‐impulsive spectrum, which is a target spectrum generated via a GMPE with pulse considerations based on the scenarios most contributing to the hazard (in terms of magnitude, distance, and T p ) obtained from disaggregation. Baltzopoulos et al, however, demonstrated that adopting a target spectrum for pulse‐like record selection is not yet feasible, due to the scarcity of such recordings. Following this premise, they based their record selection on maintaining consistency of the pulse period distribution with the site hazard, regardless of the spectral shape of the motions.…”