Numerical Simulation of Thermal Stresses in Prismatic Concrete Beams Reinforced with FRP Bars under Low Temperatures

Abstract

The thermal properties of fiber reinforced polymer (FRP) bars particularly in the transverse direction are higher than those of hardened concrete and steel bars. The difference in transverse thermal characteristics between FRP bar and concrete generates radial tensile stresses within concrete at the interface of FRP bars/concrete under low temperatures. These thermal stresses may cause circumferential cracks in concrete at the interface and eventually the reduction of the bond that can affect significantly the serviceability of reinforced concrete structures. This paper presents a nonlinear numerical simulation of thermal stresses in prismatic concrete beams reinforced with glass FRP (GFRP) bars submitted to low temperatures when the confining action of concrete is asymmetric. The non linear numerical analysis shows that the first circumferential cracks start to develop within concrete at FRP bar/concrete interface at a temperature decrease DT_cr varied between -30°C and -25°C for prismatic concrete beams reinforced with GFRP bars having a ratio of concrete cover thickness to FRP bar diameter (c/d_b) varied from 1.0 to 3.2. Furthermore, the depths of circumferential cracks propagated from the interface through the concrete cover increase with the decrease of the thermal load DT (from -25 °C to -50 °C). These depths did not reach the outer surface of the concrete cover under low temperatures up to -50 °C. Also, the radial tensile stress at FRP bar/concrete interface increases with the increase in the ratio c/d_b. The cracking thermal loads and thermal stresses predicted from nonlinear finite element model are compared to those evaluated with analytical models. Comparisons between numerical and analytical results in terms of cracking thermal loads and thermal stresses are presented.