Fatigue Behavior of Reinforced Concrete Beams with Temperature Differentials at Room and Low Temperature

This paper investigates the fatigue behavior of reinforced concrete beams at low temperatures compared to similar beams tested in fatigue at room temperature. Four large-scale steel-reinforced beams ($200\times 400\times \mathrm{4,200}\mathrm{mm}$) were fabricated and tested. All of the beams had temperature differentials over their depth to simulate solar radiation and in-service temperature of the bridges. Two beams had stirrups while the other two had no shear reinforcement. One beam of each type was tested at room temperature and the other at low temperature. The beams were cyclically loaded to failure with a stress range representative of the ratio of live to dead loads found in most bridges. This study showed that the fatigue life of the reinforced concrete improved at low temperature and this improvement was much more pronounced when shear reinforcement was not present. In fact, low temperature changed the mode of failure of the reinforced concrete beams without stirrups from shear to flexural fatigue failure as a result of the higher shear strength and stiffness of the reinforced concrete, the lower number of cracks with smaller widths, and improved fatigue properties of steel at low temperature. The results showed that the fatigue life of the reinforced concrete beam without shear reinforcement at room temperature primarily depended on the concrete and concrete-to-steel bond while fatigue lives of the other beams depended on the stresses in the tensile reinforcement. The strains and stiffness degradation were much lower in the low-temperature beams compared to their room-temperature counterparts. The findings of this study showed that the contribution of concrete to the performance of the beam under either static or cyclic load becomes more pronounced at low temperatures.