Energy-based damage index for concentrically braced steel structure using continuous wavelet transform

The seismic damage level of a structure is assessed using damage indices that are based either on modal parameter (e.g., period, mode shape and damping ratio) or on non-modal parameter (e.g., drift ratio and displacement). The interstorey drift based non-modal parameter damage index is widely used by the engineers and researchers in damage assessment. However, the interstorey drift based damage index does not take into account the effects of the number of inelastic cycles experienced by the structure to determine the damage. In this study, a new energy based damage index that takes into account the number of inelastic cycles (i.e., total energy dissipated by the structural systems) is proposed for concentrically braced frame (CBF). The continuous wavelet transformation (CWT) technique is applied to compute the dissipated energy during ground shaking. Three concentrically braced frame structures of varying height and braced configuration are selected to assess the capability of the proposed damage index. Further, the proposed damage index is compared with commonly used drift based index. On the basis of this study, the correlation between the energy based and drift based indices is very high in minor damage levels, however, the correlation is decreasing with increasing level of damage due the effect of the number of inelastic cycles. Therefore, the energy based damage index provides more reliable estimate of damage for structures responded in the nonlinear range.