A 3D kinematic model for assessing the seismic capacity of the Frigidarium of the Baths of Diocletian

The Frigidarium of the Baths of Diocletian in Rome is one of the largest extant heritage structures built with unreinforced masonry material. The structural capacity of the Frigidarium to resist lateral accelerations generated by an earthquake is assessed by pushover analysis based on a limit kinematic approach. A 3D solid model of the Frigidarium modular section is subdivided into rigid blocks by cutting planes corresponding to the fracture surfaces determined by a preliminary nonlinear FE analysis. The blocks are then connected by rotational hinges to form a mechanism anchored to a base platform that translates horizontally with increasing acceleration. The mechanism, initially in static equilibrium, is eventually driven into dynamic conditions by the inertial forces generated by the moving platform. The intensity of the acceleration at the limit of the static condition (i.e., at the moment of impending motion) defines the structural capacity. A series of tests is conducted to evaluate the sensitivity of the model to changes in fracture orientation and hinge location, and to the introduction of friction between two blocks. Based on the current results, the capacity can be assessed at about 0.4g.