How Are the Equivalent Damping Ratios Modified by Nonlinear Engineering Demand Parameters?

Abstract

Abstract. When attempting to predict the seismic response of reinforced concrete (RC) structures, a trade-off has to be found out between a realistic representation of the dissipations through material behavior law and a numerically more efficient modeling with a controlled computational demand such as a Rayleigh-type damping model. Anyway, constitutive laws only describe internal dissipation and actually need a complementary dissipation term often chosen as a proportional damping matrix to take into account external dissipation sources such as interactions with the environment. Decoupling these two contributions in global dissipation measurement from experimental tests is still challenging. To address this problem, a numerical study based on an experimentally identified structural model is here presented. To this end, an experimental campaign has been carried out on RC beams set up on the AZALEE shaking table of the TAMARIS experimental facility operated by the French Alternative Energies and Atomic Energy Commission (CEA). In this paper, the experimental campaign is first presented. Secondly, a suited constitutive model is formulated and identified from the experimental results. Third, numerical dynamic experiments are carried out in order to assess the influence of several parameters on the energy dissipation and on the equivalent viscous damping ratio through two different methods. The validity of these results is assessed on a numerical case where a nonlinear model and an equivalent linear model are compared with each other. Experimental results of dynamic tests are also used as reference in order to estimate the additional viscous damping necessary to take into account the whole energy dissipation.

Energy dissipation models for RC members and structures

“…Even after omitting this cycle, tests of non‐precracked specimens suggest an energy dissipation before yielding corresponding to a mean viscous damping ratio of 8.4% (8.4% in rectangular beams/columns, 11.2% in walls, 6.7% in circular columns), almost regardless the amplitude (Figure A). This value agrees well with predictions for one‐story RC buildings but exceeds the value of 5% in code elastic spectra, the values recommended in Pacific Earthquake Engineering Research Center for nonlinear response history analysis, or those that suit the measured low‐amplitude response in RC buildings with energy dissipation sources not included in the model or derived from the dynamic response of slender walls or from cyclic tests of beams . So, great caution is needed in using the average value of 8.4%.…”

Dissipations in reinforced concrete components: Static and dynamic experimental identification strategy

“…Despite the fact that experimental data do not give information regarding ductility coefficient values lower than 4, the EVDR is expected to increase in the first place until a maximum is reached. This hypothesis has been studied in [22] through numerical simulations performed on a hysteretic model calibrated on experimental data. It is shown in the same study that the EVDR not only depends on the ductility coefficient but also on the current cycle amplitude of displacement itself.…”

“…In an ideal case, all the progressive loading procedure should be carried out at each degradation level (from zero to the current degradation state) in order to uncouple the both influences. This aspect has been investigated in the aforementioned paper [22].…”

Effect of the viscous damping on the seismic response of Low-rise RC frame building

“…Energy dissipation and ductility are part of diverse parameters that influence viscous damping ratio [12,13]. The viscous damping matrix is fundamental in nonlinear time history analysis to calculate the inelastic deformation.…”