Improving the Seismic Performance of Existing Old Pilotis Type Buildings By Strengthening Only the Ground Story

Abstract eng:
The present paper deals with the problem of partial strengthening of old Reinforced Concrete (RC) buildings with open ground floors (pilotis). The strengthening is restricted to the ground level, so that the cost is kept to a minimum and the building remains in use during the intervention. Since strengthening of the ground story will typically transfer the problem to the story or stories above, it is necessary to determine the amount of required strengthening so that the net result will be an optimum, i.e. the maximum possible reduction of the building’s vulnerability. In essence the intervention is aimed at increasing the overall seismic resistance for the said class of buildings by removing the “soft story” weakness. This limited intervention is not generally expected to bring the building up to the standards of seismic safety implied by the new codes. For dealing with this problem, plane RC frames corresponding to symmetric buildings, as well as non-symmetric buildings in plan, representative of the old building stock in Greece, are designed in accordance with the old codes (RC code and Code for earthquake resistant design). Subsequently they are subjected to a set of code compatible accelerograms and using nonlinear time history analyses conclusions are drawn regarding the effectiveness of ground story strengthening. Evaluation of their seismic performance is based on Part-3 of Eurocode 8 for assessment and retrofitting of buildings. It is shown that strengthening only the open ground story can effectively reduce the vulnerability of pilotis type buildings by removing the inherent weakness. For non-symmetric buildings, appropriate selection of the bracing location and size, can also improve building performance by reducing the ground story stiffness eccentricity and the consequent torsional response.

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