Factors influencing the repair costs of soft-story RC frame buildings and implications for their seismic retrofit

Abstract

This paper examines the factors affecting the repair costs following major earthquakes, of reinforced concrete (RC) frame buildings with non-ductile detailing typical of construction practices in Italy and other parts of the world during the 1950s and 1960s. Two configurations of a RC frame structure, one with full infills and the other with partial infills, are numerically studied. Results of incremental dynamic analyses confirm that the partial infill RC structures, in which soft-story mechanisms form in the open story, are more likely to collapse. However, by undertaking a loss estimation study for different scenarios it is shown that the lower losses that are expected due to the reduced damage of non-structural components in upper levels could be an advantage of soft-story buildings provided that the collapse propensity is reduced at the first level. It is further shown that losses in soft-story buildings will be strongly affected by the repair value of the structural and non-structural components at the soft-story level relative to other levels and the magnitude of P-Delta effects. These observations indicate that an effective retrofit strategy, that would reduce both monetary losses and the probability of collapse, could be achieved by increasing the deformation capacity at the soft-story level without altering the isolating effect that the soft-story mechanism provides to the levels above and without any further intervention in the stories above. The changes in losses resulting from such a conceptual retrofit solution are presented in order to illustrate the merits of such an approach, that should therefore become the focus of future research.