Title: Collapse Assessment of Non-Ductile, Retrofitted and Ductile Reinforced Concrete Frames
Author(s): M. Baradaran Shoraka, K.J. Elwood, T.Y. Yang, and A.B. Liel
Publication: Symposium Paper
Appears on pages(s): 1-20
Keywords: Collapse assessment; Nonlinear analysis; Probability of collapse; Retrofitting; Reinforced concrete moment frames; Seismic safety.
Probability of collapse is currently used to set targets for system performance and response measures of new buildings. This study compares the probability of collapse for new, retrofitted and existing concrete buildings. Retrofitting plays an important role in reducing seismic risk from older concrete buildings. In order to decide on the most appropriate and economical retrofit strategy for an existing structure, it is necessary to assess the risk of collapse of each rehabilitation measure. At present, it is frequently assumed that retrofitting a non-ductile concrete building will enhance the seismic performance such that it can reach the same performance level as a ductile building designed based on current seismic codes. However, based on the evaluation of the concrete frames presented in this paper, typical retrofit schemes (such as: adding an additional lateral force restraint system; increasing ductility of existing concrete columns; and weakening the existing beams) cannot achieve the same performance as modern code-conforming structures. The study finds that retrofitting schemes where the columns or beams are modified such that the frame satisfies the collapse prevention level of ASCE 41-13 have the least beneficial effect regarding seismic collapse safety; and conversely, adding a shear wall will significantly improve the seismic performance in terms of the probability of collapse.