Experimental and numerical investigation on post-fire seismic performance of light weight aggregate reinforced concrete beams

Abstract

The stringent demand for designing fire-resistant structures in recent years has triggered a good deal of effort into theoretical and experimental studies. Structures may be exposed to seismic loading after a fire in the course of their lifetime, resulting in the reduction of their integrity. This study examines the seismic performance of damaged light weight aggregate reinforced concrete beams by exposure them to elevated temperatures. Accordingly, a set of 8 light weight and normal weight concrete prisms were cast and tested under quasi-static reversed cyclic loading after exposure to temperatures of 25, 250, 500 and 750 °C. The stress-strain relationship, residual deformations, strength and stiffness degradation, energy dissipation capacity and cracking pattern of light weight beams were compared to those of the normal weight counterparts. The experimental results revealed that the light weight beams, although with lower compressive strength at ambient temperatures, show better seismic performance when exposed to elevated temperatures as compared to their normal weight companions. On this account, the residual deformations of the entire set of beams decreased with increasing the thermal exposure level. However, this was less pronounced in the case of lightweight prisms. In addition, the energy dissipation capacity of normal weight prisms was higher than that of the lightweight beam specimens at ambient temperature. Nonetheless, the dissipated energy in lightweight concrete overtook that of normal weight concrete as the temperature was increased. Moreover, the beams under investigation were numerically modeled in OpenSees through fiber section models in order to verify the obtained experimental results. The fire effect was applied in the compressive strength reduction of the beam specimens based on experimental results, such that each heat-exposure level relatively decreased the compressive strength of prisms. The results confirmed that the numerical responses obtained from material models in OpenSees could provide the characteristics of the beam capacity as well as the strength and stiffness degradation behavior in good accord with the experimental results.