A Study on Compressive Strength and Strain Behavior of Concrete at High Temperatures<BR>-Chapter 1 Introduction-

Abstract

Although reinforced concrete structures are generally considered to be resistant to fire, there are cases where large quantities of combustibles are present, the fire continues for a long time, or where the long-term load on the structural members is high, and thus the construction could collapse [1]. Even when structures are built using reinforced concrete, their fire resistance should not be regarded as unquestionable.In particular, when comparing high-strength concrete with normal-strength concrete, there could be a significant decrease in the strength at high temperatures [2], and since degradation in the bearing force due to spalling [3] can also be expected, it is used in actual constructions only after its load bearing ability and its ultimate strength are confirmed by means of a fire resistance test [4].Generally, the deflection behavior, the cross-sectional temperature and the fire resistance time are measured in the fire resistance test. Although it is essential to understand the distribution of stress on the structural members during fire by constructing a strength formula for the members exposed to fire, since the temperature of the ambient environment can reach 1000°C, the temperature of the members increases significantly as the fire progresses. Naturally, strain gauges tested at ambient temperature become unusable at such high temperatures, and it becomes difficult to explore the stress and the strain in the cross-sectional plane directly through experiments. As a result, the construction of the strength formula for members exposed to fire is considered a challenging task.Mathematical analysis becomes a powerful tool for obtaining the information about stress and strain in the cross-sectional plane that cannot be obtained through fire resistance tests. Moreover, following the expansion of performance design in the field of fireproofing, it is projected that there will be increasingly more opportunities to investigate the fire resistance properties of structural members through mathematical analysis in the future. However, the reliability of mathematical analysis is often questioned, which determines the need for improving the accuracy of the analysis.Since whether the analysis is successful depends strongly on the material model, there is a need to adopt a model which provides an adequate treatment of the mechanical properties and the behavior at high temperatures at the level of the material.The behavior of concrete at high temperatures has been the subject of research for