Seismic fragility of RC framed and wall-frame buildings designed to the EN-Eurocodes

Abstract

Fragility curves are constructed for a portfolio of prototype regular RC frame and wall-frame buildings designed and detailed to EC2 and EC8. The aim is to use EC8’s own seismic performance assessment methods and criteria for existing buildings to evaluate how EC8 achieves its performance goals for new RC buildings. The overall conclusion is that these goals are met in a very consistent and uniform way across all types of buildings considered and their geometric or design parameters, except for RC walls of Ductility Class Medium, which may fail early in shear despite their design against it according to EC8. In fact, these walls do not perform much better than those of braced systems designed to EC2 alone. Therefore, wall shear seems to be an aspect in EC8 worth looking at again. Another finding is that the slenderness limits and the lateral bracing requirements of EC2 for 2nd-order effects under factored gravity loads place severe restrictions on the size of columns and walls, which, although ignored in ordinary seismic design practice, materially impact the outcome of the design and, to a smaller extent, the seismic fragilities of the building’s members. Mixing in the same building columns with significantly different stiffness most often penalizes the more flexible ones and not the stiff, despite their smaller deformation capacities. Another finding is that the reduction in fragility from higher design peak ground accelerations is disproportionately low. Even buildings designed for gravity loads only, but in full accordance to EC2, possess substantial seismic resistance.