Multifiber finite element model based on enhanced concrete constitutive law to account for the effects of early age damage on the seismic response of RC structures

Abstract

RC structures get damaged over time due to several phenomenons such as shrinkage, thermal deformations, creep and corrosion. This damage starts at early age and continues during the lifetime of the structures. In order to account for the effects of early age damage on the seismic response of RC structures, a research project combining both an experimental and numerical part was conducted. In the experimental part, two types of portal frames that evolved either in endogenous conditions (by covering them using a plastic sheet to limit drying shrinkage) or in non-endogenous conditions (no imposed covering, thus similar conditions as in site constructions) during early age, were constructed and tested at the end of 28 days using static cyclic and pseudo-dynamic tests. Experimental tests performed and monitoring techniques used (ambient vibration, digital image correlation, optical fiber) showed that early age drying shrinkage can cause an increase of the seismic vulnerability of RC structures (50% decrease of the fundamental frequency, 33% lateral drift increase). This article presents the multifiber finite element model based on enhanced constitutive law which allows describing the early age damage due to shrinkage, creep, thermal and mechanical strains and to simulate the static and dynamic response of the portal frames. The resolution of a THC (Thermo-Hygro-Chemical) problem allows calculating shrinkage and temperature time evolutions. In the model, creep is calculated using three viscoelastic Kelvin Voigt models in series with the μ damage law for concrete (through the resolution of an internal equilibrium at the fiber level) whereas steel is accounted for using a Menegotto model. Results obtained using the numerical model were compared to experimental ones in order to validate the proposed model.