Retrofit of structures: strength reduction with damping enhancement

A new procedure to retrofit existing structures subjected to seismic excitation is proposed. The main features of this procedure are to reduce maximum acceleration and associated forces in buildings subjected to seismic excitation by reducing their strength (weakening). The weakening retrofit, which is an opposite strategy comparing with the conventional strengthening, is particularly suitable for buildings having overstressed components and foundation supports or having weak brittle components. However, by weakening the structure large deformations are expected. By adding supplemental damping devices it is possible to control the deformation within desirable limits. The structure retrofitted with this strategy will have, therefore, a reduction in the acceleration response and a reduction in the deformations, depending on the amount of additional damping introduced in the structure. An illustration of the above strategy is done by evaluating the inelastic response of the structure trough a spectral procedure, modified to fit structures with additional damping. The results are compared with a dynamic nonlinear analysis. Both methods show that the retrofit solution is feasible and simplified techniques can be used for evaluation.