Post-Earthquake Assessment and Numerical Modeling of Freestanding Heritage Structures

Historic and heritage structures are particularly vulnerable to earthquakes, where damage or collapse can not only lead to loss of a structure but also the loss of irreplaceable heritage. Many heritage structures can be classified as freestanding (detached) structures, including unreinforced masonry walls, classical multi-drum columns, and statue-pedestal systems. However, the seismic response of freestanding structures (sliding, rocking, rock-slide, overturning) is poorly predicted by existing methods due to geometric non-linearities as well as sensitivity to interface conditions and modeling parameters. Previous studies have focused on analytical modeling of simplified systems and/or experimentation under controlled laboratory conditions. In contrast, this paper presents the post-earthquake assessment of multiple statue-pedestal systems following the 2014 South Napa earthquake. The objective is to examine the seismic response of these complex freestanding structural systems, under real-world conditions, to elucidate key characteristics of the response and evaluate the influence of both physical and modeling parameters. In this study, the responses of the selected statues from the Napa area are numerically simulated under original ground motion records. The complex geometries of the statues are represented using meshes generated from lidar-based point clouds obtained during post-earthquake reconnaissance. The responses of the statues are simulated using the Distinct Element Method (DEM) where the statue and pedestal have been modeled as rigid blocks with deformation concentrated at the joints (i.e. interface of statue and pedestal or pedestal and ground). The study analyzes the results of the numerical simulations in comparison to the observed physical response during the earthquake event. Results emphasize the significant impact of ground motion parameters (e.g. directionality), the presence of soil, and modeling parameters such as contact stiffness