Heterogeneous Constitutive Modeling and Material Damping in Reinforced Concrete Frame Elements in Seismic Loading

Abstract eng:
In inelastic civil engineering structural models, the imparted seismic energy is dissipated by three types of mechanisms: i) energy radiation in the surrounding environment, ii) hysteretic response of nonlinear elements, and iii) additional damping. If i) and ii) rely on models with sound physical basis (boundary conditions, nonlinear restoring forces), it is not the case for iii). Rayleigh proportional viscous damping is commonly used as an additional energy dissipation source to represent damping not otherwise explicitly accounted for in the inelastic structural model, especially at low-amplitude level. However, it is well known that controlling the amount of energy dissipated by Rayleigh damping is very challenging [1,2]. In this paper, we show that introducing spatial variability in parameters of the material constitutive law allows representing some specific features of the concrete behavior in cyclic loading such as local hysteresis loops, even at low-amplitude level. This has the potential for providing a physically sound basis for material damping representation in reinforced concrete structural elements, as will be illustrated by numerical experiments on a cantilever beam with either quasi-static axial loading or dynamic bending excitation, as well as by the simulation of a frame tested on a shaking table [3]. Practically, fiber frame elements are used and, in each fiber of the control sections, heterogeneity in parameters of the nonlinear constitutive law is introduced according to the fluctuations of a 2D random field [4]. The objective here is to observe the influence of this heterogeneity on each single realization of the random medium, without any statistical analysis involved. To this end, it is numerically shown that discretizations of the frame element sections into fibers and of the random field can be performed such that there is no significant influence of the realization of the random field in the structural response. This research is supported by a Marie Curie International Outgoing Fellowship within the 7th European Community Framework Programme (proposal No.275928).

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