Report - PEER - University of California, Berkeley

EVALUATION OF INELASTIC DISPLACEMENTS IN DETERIORATINGSYSTEMS USING AN ENERGY-BASED APPROACHHaluk SUCUOĞLU 1 and M. Altug ERBERIK 1ABSTRACTSeismic performance of deteriorating systems is investigated by employing an energy-basedapproach. Low-cycle fatigue principle forms the basis of the analytical hysteresis model, whichis based on two deterioration parameters. These parameters are calibrated by usingexperimental data in the literature obtained from reinforced concrete specimens subjected toconstant and variable amplitude displacement cycles. The effect of stiffness and strengthdeterioration is studied by evaluating the ratio of the maximum inelastic displacements ofdeteriorating and non-deteriorating (elasto-plastic) systems (C 2 coefficient), calculated under 40ground motion components recorded on stiff and soft sites. The results revealed that C 2 isindependent from the yield strength and ductility characteristics, whereas it is stronglyinfluenced from the level of deterioration and the site class. The values proposed in FEMA-356capture the calculated trends in general, however they require better tuning with a morecomprehensive classification of deteriorating systems by focussing on the characteristics ofexisting vulnerable buildings.Keywords: C 2 coefficient; Strength deterioration; Energy-based hysteresis; Low-cyclefatigue; Inelastic displacement.INTRODUCTIONDeterioration in the mechanical properties of concrete, steel and masonry structuresare observed usually under repeated cyclic loading in the inelastic range due to lowcycle fatigue. When these types of structures are subjected to strong ground motions,deteriorations in the stiffness and strength lead to larger displacements henceincreased damage. Maximum inelastic displacements of equivalent SDOF systemscan be approximated from the maximum displacements of the associated elasticSDOF systems either by using equivalent linearization, or by applying a set ofdisplacement modification coefficients (Miranda and Ruiz-Garcia, 2002). This studyfocuses on the displacement coefficient that represents the effect of stiffness andstrength deterioration on the inelastic displacement response, with reference to theinelastic response of a non-deteriorating elasto-plastic system.1 Department of Civil Engineering, Middle East Technical University, Ankara 06531, Turkey421