Seismic Assessment and Rehabilitation of existing RC Buildings not designed to withstand earthquakes

Abstract

This thesis presents a high fidelity numerical model developed to investigate the seismic performance and structural robustness of an original and retrofitted 10-storey reinforced concrete (RC) framed building. The analysed structure represents a typical existing building in Catania, Italy, that was designed to resist only gravity and wind loading according to the design regulation allowed until the 1981 in that area. The proposed numerical description adopts beam-column elements for beams and columns and special purpose shell elements for modelling RC floor slabs, both allowing for geometric and material nonlinearity. In order to model masonry infills, a novel macro-element is implemented within a FE framework based on an already published discrete formulation. 3D nonlinear dynamic simulations are performed considering sets of natural accelerograms acting simultaneously along all the three space directions and compatible with the design spectrum for the Near Collapse Limit State. To improve computational efficiency, which is critical when investigating the nonlinear dynamic behaviour of large structures, the partitioning approach previously developed at Imperial College is adopted, enabling effective parallelisation on HPC systems. The numerical results obtained from the 3D nonlinear dynamic simulations are presented and discussed, focusing on the variation in time of the deformed shape, inter-storey drifts, plastic deformations and internal force distribution, considering or neglecting the infill panel contribution. The original structure showed a very poor seismic performance, even though the infill panel contribution leads to significant variation in the response it is not sufficient to preserve the structure from the collapse. A never adopted strengthening solution that utilises the synergetic contribution of concentric steel bracing and eccentric steel bracings with dissipative shear links is illustrated and employed to retrofit the original structure. A detailed model of the retrofitting components is implemented within the detailed model for the original building. The results of numerical simulations for the retrofitted structure confirm that the proposed solution significantly enhances the response under earthquake loading, allowing the structure to resist the design earthquake with only limited damage in the original RC beams and columns, highlighting the feasibility of retrofitting for this typical multi-storey RC building structure.