Optimum Partial Strengthening for Improved Seismic Performance of Old Reinforced Concrete Buildings with Open Ground Story

Abstract

The paper looks into the problem of partial strengthening of old reinforced concrete buildings with open ground story (pilotis). The strengthening is restricted to the ground story, to keep the cost to a minimum and the building in use during the intervention. Strengthening of the building is achieved using (a) steel bracing in selected bays and (b) reinforced concrete jacketing of ground story columns. Since strengthening the ground story will typically increase the loading to the story or stories above, it is necessary to determine the level of required strengthening that will produce optimum results, i.e. will cause the maximum possible reduction to the building’s vulnerability. In essence, the intervention aims at removing the “soft story” weakness for the said class of buildings and increase its overall seismic resistance. Non-linear static and dynamic analyses are performed in order to determine the seismic behavior of the existing building and the strengthening solutions. Results indicate that increasing both stiffness and strength of the open ground story could effectively improve the behavior of the existing building, removing its inherent weakness due to the soft ground story. However, there exists an upper bound of strengthening, which if exceeded shifts the problem to the upper stories, thus canceling the benefits from the intervention.