Study Of Sharp Cooling Thermal Effects On Concrete Box Girders Strengthen With CFRP

In recent years, with the deterioration of the environment and the increasing of traffic volume, the early bridge structure have different degrees of disease, reinforcement has been mentioned schedule, because of many advantages, CFRP reinforcement technology is used widely by engineer. Crack which is lead to changing temperature is a major factor affecting the safety of bridge structure, the temperature stress caused by temperature load is getting more and more attention by the engineering community, domestic and foreign scholars have made fruitful results which is about research on temperature effect. But, because of CFRP reinforcement technology appear relatively late, correlation test and theory research tend to its mechanics and use properties, the CFRP reinforced box girder temperature effect of the research is less. Differ from that of the thermal coefficient of CFRP and concrete, especially the difference of thermal expansion coefficient is orders of magnitude, it will make the effect of CFRP reinforced concrete box girder temperature produces new characteristics, therefore, CFRP reinforced concrete box girder temperature effect research is of great significance.Experimental research about the sudden cooling temperature effect on concrete box girders reinforced with CFRP had been conducted on. Four pieces of reinforced concrete beam had been made, including three pieces by pasting the different forms of CFRP, heat preservation material be used to create the different conditions, through the experiment, the temperature value of the measuring point and strain value of the measuring point is got. At the same time, the environment temperature is got. During the experiment, the ANSYS is used to calculate the temperature field of the test beam under different conditions, and it is also used to calculate the longitudinal normal stress of the test beam in different time. The main research contents and achievements are summed up as follows:Under the action of drops in temperature abruptly,the temperature gradient model and the temperature of paste CFRP experiment beams and no paste CFRP beam is consistent, the temperature gradient of roof can be fitting into mansard, temperature gradient of web can be fit for quadratic parabola. Because bottom negative temperature difference not be taken into account in the “General Code for Design of Highway Bridges and Culverts”, the difference exist in the measured data and the General Code for Design of Highway Bridges and Culverts. But the cooling mode which is mentioned in BS-5400 is more close to the measured data. Under the action of drops in temperature abruptly, paste CFRP will change the stress time varying law of box girder, no paste CFRP test beam of each measuring point stress will increase, when the temperature gradient is maximum, the temperature stress is the biggest, with continuous, cooling temperature gradient decreases gradually, the temperature stress everywhere is close to zero gradually; For CFRP strengthening box girder, with the temperature down, stress of roof surface continues to increase, bottom temperature stress also by the tensile stress to compressive stress.