Impact of ground-motion duration on nonlinear structural performance: Part I: spectrally equivalent records and inelastic single-degree-of-freedom systems

Abstract

In current seismic performance-based assessment approaches, nonlinear dynamic analysis of structures generally relies on ground motions selected based on their pseudo-spectral accelerations, with little or no consideration for ground-motion duration. Part I of this study, presented in this article, attempts to comprehensively quantify the impact of ground-motion duration on the nonlinear structural performance of case-study inelastic single-degree-of-freedom systems for shallow-crustal seismicity conditions. The effect of duration is decoupled from that of ground-motion amplitude and spectral shape by assembling sets of spectrally equivalent long- and short-duration records. Such sets are employed in incremental dynamic analyses of a wide range of computational models incorporating in-cycle and cyclic strength and stiffness deterioration. The structural response is quantified in terms of peak- and cumulative-based engineering demand parameters. Formal hypothesis testing is used to assess the statistical significance of duration’s impact on the median structural capacity of the considered structural systems. Furthermore, the derivation of duration-dependent fragility and vulnerability relationships demonstrates that ground-motion duration effectively impacts the nonlinear structural performance of various systems, and it should be accounted for in current practice. The fragility median values for highly deteriorating structural systems under long-duration ground motions are found to be up to 21% or 34.0% smaller than the short-duration counterpart if a peak- or cumulative-based engineering demand parameter is adopted, respectively.

Accounting for earthquake‐induced ground‐motion duration in building‐portfolio loss assessment

“…The fragility and vulnerability models explicitly account for the ground-motion duration since 𝑎𝑣𝑔𝑆𝐴 and 𝐷𝑠 5−95 can jointly describe part of the variability of the developed PSDMs. It can be noticed from the results that ground-motion duration mainly impacts the higher DSs (i.e., DS3 and DS4), while the lower DSs (i.e., DS1 and DS2) are slightly affected (i.e., the variability in the probability of exceeding a DS as a function of 𝐷𝑠 5−95 only increase for higher DSs); confirming that DSs less severe than collapse are impacted by duration as shown in Otárola, Gentile, et al 14 and Otárola, Sousa, et al 15 As ground-motion duration increases, the probability of exceeding a DS for a given IM level increases (i.e., lower fragility median values are obtained); this explains why the vulnerability model exhibits a steady rise in the loss ratio due to duration. Since both the fragility and vulnerability models indicate an increasing trend in DS exceedance probability and LR, respectively, when 𝑎𝑣𝑔𝑆𝐴 and 𝐷𝑠 5−95 levels increase, it is inferred that duration can effectively impact the damage/loss estimates.…”

“…45 This allows capturing the cumulative damage due to increasing ground-motion duration (e.g., in ref. 14,15). Vulnerability models are then derived by combining the above fragility models with a building-specific damage-to-loss model.…”

“…Similar behaviour is presented in different empirical damage models, such as the Park and Ang damage index. 78 Nevertheless, the impact of duration on these relationships cannot be inferred directly without performing a relevant comparative analysis against relationships derived using different ground-motion records with different durations (e.g., using separate sets of short-and long-duration ground motions; for further discussion, see Otárola, Gentile, et al 14 ). Figure 7C and D show the fragility and vulnerability models obtained using 𝑎𝑣𝑔𝑆𝐴 and 𝐷𝑠 5−95 in a vector-valued format.…”

“…Literature describing how duration influences structural fragility for different damage states (DSs) and the detailed quantification of such influence is not widely available (e.g., in refs. 12,13); therefore, this modelling challenge was recently tackled using two different approaches in Otárola, Gentile, et al 14 and Otárola, Sousa, et al 15 In the first approach, the effect of duration was decoupled from the effects of ground-motion amplitude and spectral shape by assembling sets of spectrally equivalent long-and short-duration ground-motion records similarly to other authors (e.g., in ref. 16).…”

“…Literature describing how duration influences structural fragility for different damage states (DSs) and the detailed quantification of such influence is not widely available (e.g., in refs. 12, 13); therefore, this modelling challenge was recently tackled using two different approaches in Otárola, Gentile, et al 14 . and Otárola, Sousa, et al 15 .…”