Inelastic spectra to predict period elongation of structures under earthquake loading

Abstract

Summary Period lengthening, exhibited by structures when subjected to strong ground motions, constitutes an implicit proxy of structural inelasticity and associated damage. However, the reliable prediction of the inelastic period is tedious and a multi‐parametric task, which is related to both epistemic and aleatory uncertainty. Along these lines, the objective of this paper is to investigate and quantify the elongated fundamental period of reinforced concrete structures using inelastic response spectra defined on the basis of the period shift ratio (Tin/Tel). Nonlinear oscillators of varying yield strength (expressed by the force reduction factor, Ry), post‐yield stiffness (ay) and hysteretic laws are examined for a large number of strong motions. Constant‐strength, inelastic spectra in terms of Tin/Tel are calculated to assess the extent of period elongation for various levels of structural inelasticity. Moreover, the influence that structural characteristics (Ry, ay and degrading level) and strong‐motion parameters (epicentral distance, frequency content and duration) exert on period lengthening are studied. Determined by regression analyses of the data obtained, simplified equations are proposed for period lengthening as a function of Ry and Tel. These equations may be used in the framework of the earthquake record selection and scaling. Copyright © 2015 John Wiley & Sons, Ltd.

Application of a Damage State Method Based on Period Elongation for Time Variant Vulnerability of Degrading Reinforced Concrete Buildings

“…The probability of damage state exceedance in the numerical results for the case studies of the aftershock sequences of the Thessaloniki (1978) and the Northridge (1994) follows a similar trend to the failure probability during the aftershock sequence period as estimated by Iervolino et al [5]. Moreover, the assumption that period elongation of ΔΤ = 60 % corresponds to a state near collapse is in agreement with the empirical estimations by Katsanos and Sextos [10].…”

“…Only in extreme cases of severely degrading buildings a ratio of 2.0 was estimated. Katsanos and Sextos [10] also proposed an empirical function for period elongation based on the structural period and the force-reduction factor. Moreover, they showed that PGA has a low correlation with the predominant inelastic period in contrast to spectral acceleration.…”

“…According to these relationships the period elongation corresponding to EMS-98 [12] damage grade 1, 2 and 3-4 is equal to 20 %, 43 % and 65 % and is independent of the number of storeys. The period elongation ratio has been observed to be in an analogy to the stiffness and the force-reduction factor (ratio of the maximum seismic force to yield force) of SDOF oscillators [10] while the effect of earthquake magnitude, distance and soil conditions has been estimated to be of minor significance.…”

Yield frequency spectra and seismic design of code‐compatible RC structures: an illustrative example

“…To avoid any such bias, the 2D frame model was subjected to 300 strong ground motions obtained from the PEER NGA Database [32], with a wealth of different characteristics in terms of seismological parameters (earthquake magnitude, sourceto-site distance and rupture mechanism), amplitude and frequency content as well as soil conditions, in which the motions were recorded. A comprehensive description of the selected earthquake records can be found elsewhere [33].…”

Forecasting Time-Variable Earthquake Risk for Reinforced Concrete Buildings During Aftershock Sequences Based on Operational Earthquake Forecasting and Resonance Period Elongation

“…Among the solutions available, monitoring the elongation of the fundamental period of buildings is a practical, efficient way to assess earthquake damage. Fundamental period (or frequency) is assumed to be a proxy for apparent structural stiffness and structural health [9][10][11][12][13]. For instance, the residual stiffness of masonry buildings from period measurements has been used to study the effect of seismic damage accumulation on macroseismic intensity assessment [9].…”