Experimental Investigation On Behaviors Of Concrete Under Sub-high Temperature

Under continuous heat, the performance of Concrete changes significantly. This will make concrete crack, the deformation of its structural members increase and the carrying capacity decline. At home and abroad, a great deal of research on the performances of concrete under high-temperature have been done, but most of them are about high-temperature range (500℃above). Due to the lack of researches on sub-high temperature range (≤500℃), a number of high-temperature design codes and rules are formulated on the base of some simple assumptions; at home, concrete structures under long-term heating, when the temperature is not high, are treated as under normal temperature, not reflecting their actual situation influenced from temperature action. Based on actual engineering structures, this paper is to study the performance of concrete under sub-high temperature and to provide reference for design of relative engineering structures.Based on needs of the structural design for the thermal power plant, this research is to formulate a model by using finite element software ANSYS, to calculate the temperature distribution of its coke ovens and chimney concrete, and to propose the experimental scheme. A total of 137 standard prism specimens and 18 cube specimens were made for the experiments. This research mainly includes the regularities of concrete strength and deformation. The temperature range between 100℃and 500℃is divided into 9 grades. And these factors of specimen heated to uniform temperature distribution and longer time for different action temperatures are also examined.Through the experimental results, the changing regularities of weight loss rate of concrete, and the compressive strength, the peak strain, the elasticity modulus and the relationships of stress-strain of prism specimens with the increase in temperature or lasting time for a given temperature are discussed. The corresponding formulae are proposed and compared with the existing experimental results.The experimental results showed that, under sub-high temperature, with the increase in temperature, the weight loss rate has an increase tendency while the effect of lasting time for a given temperature on it is not apparent. Under different lasting time for a given temperature, the decaying of concrete compressive strength with increase in temperature follows a similar pattern. Temperature range from 100℃into 250℃, the decaying of compressive strength of prism specimen is apparent. Concrete strength decaying for this temperature range must be considered in practice. In the temperature range above 250℃, the decaying has a linearly decreasing tendency. The rising phase of stress-strain curves under different temperature and different temperature lasting time has a similar shape and can be described with a same equation. This paper proposes several fitting formulae that can reflect performance of concrete under sub-high temperature and can be applied to concrete structural fire-resistant design of actual engineering.The effects of water vapor migration on the strength of concrete under sub-high temperature are also examined. Based on the existing research results and the necessary assumptions, this paper makes modeling calculations by using ANSYS.