ESTIMATING THE RISK OF ROCKING SYSTEMS VERSUS LIFESPAN

Abstract eng:
There is a wide range of applications where the connections of structural and non-structural elements to their surroundings are not capable of transferring tensile stresses. In the simplest case this results into free standing bodies, while in more complicated cases these connections may form frames or columns as in the case of ancient Greek and Roman temples. The response of such objects when subjected to ground excitations is a rich dynamic response dominated by rigid body motions that overall can be characterized as rocking. Failure of rocking elements occurs mainly due to exceedance of a displacement or rotation criterion. This is in contrast to the standard response of structural elements where failure is usually associated to a stress or strain criterion. This further means however, that design codes developed for the latter category are not necessarily applicable for the case of rocking systems. Additionally due to the geometric non-linearity involved in rocking models, standard tools that are based on linear systems, such as the concept of a resonant frequency, are not directly transferable. Instead, the estimate of rocking systems is inherently related to a suitable selection or generation of ground motions that will allow for a realistic calculation of the associated probability of failure. In this work, the authors will present a method for estimating the risk of rocking systems based on the ground generation model presented in [1]. The probability of failure curves of a rocking body will then be presented versus an expected lifespan, which is an engineering quantity of interest that can be directly associated to existing regulations. The effect of the seismicity of a region on the probability of failure will be explored. The presented method will finally be illustrated for the case of precarious rocks.

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