Evaluation of effect of confinement on the collapse probability of reinforced concrete frames subjected to earthquakes

Abstract

Confinement of reinforced concrete members has repeatedly proven crucial when structures are exposed to strong ground motions. Yet, unconfined concrete is still widely used in developing countries with significant seismic hazard. To quantify the effect of lack of confinement on collapse probability of reinforced concrete frames, incremental dynamic analyses were conducted on two 4-story reinforced concrete moment resisting frame buildings using 5 ground motions. The structures are identical and comply to Eurocode demands except for the fact that one is completely unconfined whereas the other is confined according to the code. The analyses were conducted in OpenSEES using Mander’s material model for confined and unconfined concrete. Based on the results of the analyses, collapse fragility curves were created for each structure. The results show statistically significant effect of confinement on the collapse probability of the reinforced concrete frame. The prabability of collapse is 1.2 and 12 %, respectively, for the code complying and the unconfined structure exposed to a design level earthquake.