Intensity Measure Based on a Smooth Inelastic Peak Period for a More Effective Incremental Dynamic Analysis

Juan Carlos Vielma,Maria Cristina Porcu,Nelson López

doi:10.3390/app10238632

Abstract

The Incremental Dynamic Analysis (IDA) assesses the global collapse capacity of a structure by plotting its maximum inelastic response, obtained through a non-linear time-history analysis, versus the scaled intensity of different input earthquakes. The seismic intensity is often measured through the spectral acceleration at the fundamental elastic period. However, this can produce highly variable results. An alternative method is presented in this paper that relies on the elongated period, calculated either from the Fourier spectrum of the acceleration at a target building point (inelastic peak period) or from a smooth Fourier spectrum (inelastic smooth peak period). By referring to a reference reinforced concrete building and to a set of 10 spectrum-consistent earthquakes, the paper presents the results of a wide investigation. First, the variation in the elongated period as a function of the seismic intensity is discussed. Then, the effectiveness of the proposed method is assessed by comparing the IDA curves to those obtained through the elastic period or through approximate values of the elongated period given in the literature. The results show that the alternative IDA procedure generates curves with less-dispersed collapse thresholds. A statistical analysis shows significant improvements in the results when the inelastic smooth peak period is adopted.

Highlights

Non-linear analyses are the most accurate approach for assessing the seismic behavior of civil structures, since the current codes highly encourage post-elastic dissipative behavior under strong earthquakes
In the guidelines published by the Federal Emergency Management Agency (FEMA) [6,7], incremental dynamic analysis (IDA) is presented as the fundamental basis with which to determine the performance factors of new types of structures, as well as to obtain the collapse thresholds of existing structures while considering the variability of seismic records
The present paper proposes to evaluate the intensity of a scaled ground motion by referring to the earthquake spectral acceleration taken at the inelastic elongated period, the latter being obtained in this case:

Summary

Introduction

Non-linear analyses are the most accurate approach for assessing the seismic behavior of civil structures, since the current codes highly encourage post-elastic dissipative behavior under strong earthquakes. The unified procedure usually adopted to carry out IDA was originally formulated by Vamvatsikos and Cornell in [19]. Their approach is based on a simple transformation of the amplitude of a reference “as-recorded” accelerogram a1 (t) that is uniformly scaled up or down by a scale factor (SF), denoted λ, so that λ ∈ [0, +∞] : aλ = λ a1. By successively integrating the non-linear motion equations under a given earthquake, which is scaled at each iteration with a different SF, the progressive performance of a structure can be assessed from the elastic to the inelastic range until collapse. An engineering demand parameter, namely, the damage measure (DM) should be chosen to assess the structural responses at different seismic intensity levels

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