Estimating equivalent viscous damping ratio for RC members under seismic and blast loadings

It can be learned that the equivalent viscous damping (EVD) ratio as a function of displacement ductility is a crucial parameter in the application of the displacement based method. A set of generalized expressions are proposed herein for estimating the EVD ratio for individual and multiple reinforced concrete (RC) members. For individual RC members under seismic loads, the EVD ratio was derived based on their hysteretic response and hysteretic energy dissipated under fully reversed cyclic loading. Because of the nature of blast loads only the energy dissipated up to maximum displacement was considered to estimate the EVD ratio for individual RC members under blast loads. For multiple degree of freedom systems consisting of RC members, the EVD ratio was derived based on equating the total energy dissipated in the system to the sum of the energy dissipated by its individual members. Analytical studies presented here and elsewhere indicate that the EVD ratio is highly dependent on the damaged displacement ductility, which can be directly correlated to damage. These analytical results along with the expressions to compute the EVD ratio for RC members under seismic and blast loads are presented and discussed in this paper.