SEISMIC RELIABILITY ASSESSMENT OF ROCKING BEHAVIOUR UNDER NEAR-FAULT EXCITATIONS

Abstract eng:
This paper assesses the seismic reliability of single degree of freedom rocking structures subjected to near-fault excitations within a probabilistic framework. In this context, it proposes a physically consistent and practically useful methodology to scale the rocking behavior for excitations of different intensity and predominant frequency. According to the assumptions of the proposed methodology the definition of both the Engineering Demand Parameter (EDP) and the corresponding limit states is rather straightforward, since when the rocking structure does not overturn it eventually returns to its original configuration without permanent deformation or damage. On the contrary, identifying appropriate intensity measure/s (IM/s) for rocking structures is far from trivial, longstanding challenge. Two groups of dimensionless-orientationless IMs are considered as candidate IMs: one giving the frequency ratio ωg/p and one equivalent with the dimensionless slenderness αg/(gtanα). Using four wellknown strong ground motion parameters (the peak ground velocity, the peak ground acceleration, the predominant period of the pulse and the mean period of the CSGM) six different versions of IMs are examined. In addition, this study, introduces a more ‘holistic’ approach for the description of the rocking fragility using hybrid bivariate IMs. Analytical fragility curves (FCs) for slender, rigid rocking structures are obtained, using either univariate IM/s (conventional FCs) or bivariate IM/s (bivariate FCs). The study shows that while the use of a univariate IM is a simpler approach, it results in increased scatter. On the other hand, the more complex bivariate IM approach utilizes additional information and reduces uncertainty. Further, the study also unveils that when the rocking structure survives the excitation without overturning, the peak response follows a bi-planar distribution. Specifically, it brings forward the existence of critical peak ground motion acceleration, below and above which rocking response scales differently.

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