2 - Seismic vulnerability assessment of RC structures: research and practice at building level

Abstract

Recent earthquakes exposed the vulnerabilities of Reinforced Concrete (RC) buildings. The majority of the RC building stock in large cities correspond to old buildings where most of them were designed with codes without any seismic provisions, thus leading, most likely, to important seismic vulnerabilities. Good knowledge about the building properties and vulnerabilities and, more importantly, on how to model the behavior of the most relevant components, is fundamental to help analysts and practitioners in the assessment and strengthening of existing RC buildings. This chapter focuses on the description of the main structural characteristics and vulnerabilities of existing RC buildings in Europe and the numerical modeling approaches for their seismic assessment, taking into account those vulnerabilities. The numerical modeling of structural components – beams, columns, and shear walls –, and infills is described and discussed with special attention devoted to important issues such as the simulation of smooth rebars and the consideration of ageing effects. Two representative old RC buildings – a framed and a dual wall-frame – are selected as case studies; these structures are representative of the building stock found in Lisbon, Portugal, and were built between 1960 and 1980. Due to their characteristics, ageing effects and the presence of smooth rebar are taken into account in the development of 3D numerical models of the buildings. The seismic behavior is evaluated through nonlinear static analyses and the N2 method, in its extended version, is used to estimate the target deformation. The seismic safety of the buildings is conducted in terms of demand/capacity ratios (DCR) for each vertical structural element (columns and walls) considering both bending and the shear failure mechanisms. The results show that the seismic performance of the buildings is impaired due to the presence of important vulnerabilities.