Effect of Low Temperature on the Static and Fatigue Behaviour of Reinforced Concrete Beams with Temperature Differentials

Abstract

This research conducted herein comprises two phases: experimental and numerical. In the experimental phase, the effect of low temperature and temperature differentials on the static and fatigue behaviour of eight large-scale reinforced concrete beams is examined. Additionally, the accuracy and performance of two novel sensor technologies, Digital Image Correlation (DIC) and Fibre Optic Strain Sensors (FOS), in monitoring crack widths, deflections and strains in reinforced concrete members are investigated. In the numerical phase, a nonlinear finite element modelling and analysis study is conducted on statically determinate and indeterminate reinforced concrete beams with and without temperature differentials. The results of the static tests showed that the strength, ductility, and cracking load of the beams increased at low temperature. The results also demonstrated that the number, depth, and widths of the cracks decreased at low temperature. The fatigue testing showed that the fatigue life of the reinforced concrete beams improved at low temperature 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 (i.e., delayed fatigue crack initiation and reduced fatigue crack growth rate at low temperature). Calibration tests conducted to correct DIC and FOS readings for temperature showed that both DIC and FOS systems are affected by temperature, and that the response of each DIC camera setup is uniquely affected by temperature changes. The DIC and FOS measurements showed that these structural health monitoring techniques produce promising results and are capable of measuring crack widths and strains to a similar level of accuracy as conventional strain gauges. However, the external FOS have the advantage of being able to measure the strains in concrete in compression and give an indication of the strains in the tensile reinforcement. The numerical results showed that the finite element models are capable of predicting the load displacement behaviour (i.e., cracking, yield, and ultimate loads) as well as cracking patterns for statically determinate and indeterminate reinforced concrete beams with and without temperature differentials at room and low temperature. The modelling also showed that indeterminacy (fixed-ends) substantially increases the ultimate strength of the reinforced concrete (up to 110%).