Mechanical Properties Of Concrete After High Temperature Exposure

Reinforced concrete construction was common, and was extensively used in commercial and industrial buildings. With the gradual rise in fire occurrences in recent years, so the more thorough and quantitative understanding of fire damage to concrete is needed. However, little research has been done to study of concrete behavior under high temperature, and it also can't meet the needs of engineering development. Thus, concrete material and structural behavior in high temperature have become an impending and important research problem.Concrete behavior under high temperature is more complex than one at room temperature, and its mechanical behavior changes along with the variation of the temperature. Restoration and reinforcement of fired structure is based on the temperature and residual strength analysis. The correlation between mechanical behavior and temperature should be considered on the analysis of the residual strength. Therefore, the temperatures used in the study were 100, 300, 500, 600 and 700. And the variation of concrete behavior after being heated to temperature up to 700 was investigated by experimental and theoretical analysis. The correlation between compressive strength and temperature, deposited time, cooling mode was clarified; the loss of compressive strength was analyzed; the different appraising methods of temperature and compressive strength were investigated. Then, the conclusions are as following:1. The correlation between mechanical behavior of concrete and temperature was analyzed at elevated temperature. Characteristics of reinforced concrete structure at elevated temperature were concluded; thermal and mechanical properties of materials was analyzed respectively from two aspects -concrete and reinforcement, and then the conclusions, such as compressive strength gradually reduced with elevation of the temperature, were concluded.2. Experimental investigation on the variation of concrete mechanical behavior with different temperature, cooling mode and deposited time, and formula which shows the coupling correlation between compressive strength and temperature varying based on deposited time is established; research on compressive strength of concrete with different cooling mode (sprayed and natural cooling), and the curve of the compressive strength and temperature varying on cooling mode is obtained; the change of stress-strain curve of concrete for different temperature is analyzed, and standard stress-stain curve and formula are obtained by transforming; research on the correlation of elastic modulus and temperature, the formula between elastic attenuation parameters and temperature is established by regression analysis.3. It is a complex job that appraising building's temperature after high temperature. The methods of appraisal temperature and no-damaged appraisal are given in this paper, and the judgment and assessment of compressive strength are introduced; at last, "fire damaged grading and assessment standard of concrete structure and components'''' is given through studying some information. It can be used in structure assessment, restoration and reinforcement.4. Section temperature distributing of concrete component under high temperature is a transient heat conduction problem. In this paper, the theoretical analysis of temperature field is carried out, and some universal methods are concluded, and also some important further study aspects arebrought forward.In conclusion, the study on mechanical behavior of concrete after high temperature exposure is conducted, and the results may provide many references for practical engineering applications and further study.