RC beams strengthened with hybridization by CFRP and ECC under extreme temperature difference environments in cold regions

To study the effect of extreme temperature differences caused by fire in cold regions on the flexural capacity of reinforced concrete beams (CER beams) strengthened with carbon fiber reinforced polymer (CFRP) and engineered cementitious composite (ECC), reinforced concrete (RC) beams were taken as the control group. The CER beams were tested at -20 °C, 200 °C, 400 °C, and 600 °C, respectively. The characteristic bearing capacity of RC beams and CER beams degrades obviously under the action of high temperatures in cold regions. The ultimate bearing capacity of RC beams and CER beams decreases by 8.99%/14.02%/20.33% and 26.13%/35.38%/43.57%, respectively, at 200°C, 400°C, and 600°C compared with the initial ambient temperature of -20°C. The extreme temperature difference load in cold regions greatly reduces the flexural bearing capacity of CER beams. The average increase of cracking load, yield load and ultimate load compared with RC beam is 245.67%, 56.58% and 61.97% respectively. It shows that CFRP/ECC hybrid reinforcement has a significant improvement effect on the flexural performance of RC beams under extreme temperature difference environment. In addition, the calculation formulas for the characteristic loads of CER beams under extreme loads in cold regions are proposed in this paper. The results show that the theoretical calculation is in good agreement with the test, and the average error of the characteristic bearing capacity at each temperature is controlled within 8%. The experimental and theoretical research quantifies the mechanical property degradation behavior of CER beams after fire loads in cold regions, which provides a useful reference for subsequent similar research.