Abstract
The study evaluates two alternative seismic intensity measures (IMs) that reduce the collapse capacity dispersion of inelastic non-degrading single-degree-of-freedom (SDOF) systems vulnerable to the P-delta effect. This dispersion of collapse capacity is caused by record-to-record variability, which refers to frequency content variation of the ground motions used in the dynamic analyses. This reduction (of dispersion) is achieved utilizing efficient elastic pseudo-spectral acceleration based IMs. The first set of evaluated IMs is based on the spectral pseudo-acceleration averaged in a certain period interval between the structural period and an elongated period. The “optimal” lower bound of the period interval corresponds to the structural period of vibration, since naturally in an SDOF system no higher modes effects do exist. The “optimal” upper bound of the period interval for averaging, referred to as elongated period, is found to be 1.6 times the system period. The second IM considered in the study is the 5 % damped spectral pseudo-acceleration at the system period in the presence of gravity loads, which is a single target IM. The most widely accepted IM, the 5 % damped pseudo-spectral acceleration at the system period without P-delta, serves as the benchmark IM. The results show that both proposed IMs lead to a reduction of the collapse capacity dispersion compared to the benchmark IM outcomes. The IM based on the averaged spectral acceleration of the “optimal” period interval is more efficient up to a negative post-yield stiffness ratio of 0.45, while the single target IM based on the system period in the presence of gravity loads is superior for extreme negative post-yield stiffness ratios larger than 0.45. Additionally, the sufficiency and the scaling robustness property of the considered IMs with respect to the natural logarithm of the record-dependent individual collapse capacities is discussed for a wide range of structural configurations.
Highlights
The second generation of performance-based earthquake engineering (PBEE) methodologies (FEMA P-58-1 2012; FEMA P-695 2009) considers the inherent uncertainties in response prediction within a probabilistic framework
The results show that both proposed intensity measures (IMs) lead to a reduction of the collapse capacity dispersion compared to the benchmark IM outcomes
The IM based on the averaged spectral acceleration of the ‘‘optimal’’ period interval is more efficient up to a negative post-yield stiffness ratio of 0.45, while the single target IM based on the system period in the presence of gravity loads is superior for extreme negative post-yield stiffness ratios larger than 0.45
Summary
The second generation of performance-based earthquake engineering (PBEE) methodologies (FEMA P-58-1 2012; FEMA P-695 2009) considers the inherent uncertainties in response prediction within a probabilistic framework. Since there is no unique definition of intensity of an earthquake record, several IMs have been proposed They can be classified into (a) elastic ground motion based scalar IMs (Adam and Jager 2012b), such as peak ground acceleration (PGA), peak ground velocity (PGV) and peak ground displacement (PGD); (b) elastic and inelastic spectral based IMs such as spectral acceleration and spectral displacement at the fundamental period of the structure, as well as spectral values related to higher modes effect or period elongation (Cordova et al 2001; Haselton and Baker 2006; Luco and Cornell 2007; Bianchini et al 2009; Kadas et al 2011; Cantagallo et al 2012; Vamvatsikos and Cornell 2005; Bojorquez and Iervolino 2011); and (c) vector valued IMs (e.g., Baker and Cornell 2005; Vamvatsikos and Cornell 2005). 4 a single target IM is introduced for the collapse capacity assessment of P-delta vulnerable non-deteriorating SDOF systems This IM is the 5 % damped pseudo-acceleration at the period of vibration in the presence of gravity loads, TSPDDOF and referred to as ‘‘P-delta’’ IM, SaðTSPDDOFÞ.
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