Experimental Methods Of The Properties Of Reinforced Concrete Structures And Measuring Methods Of Deformations At Elevated Temperature

Reinforced concrete structures work at normal temperature (less than 60°C) usually. Design and safety checking computations of reinforced concrete structures are according to current codes. But some structures such as workshop at high temperature, chimney, nuclear reactor, etc., work at elevated temperature constantly. Moreover, all kinds of fire accidents result from natural or man-made reasons make structures endure the impact of high temperature more than 1000℃. At elevated temperature, the properties of concrete structures are more complex than them at normal temperature, and the mechanical properties of materials become weak seriously. At the same time, the theoretical analyses on the mechanical behaviours of reinforced concrete structures at elevated temperature are very difficult. To this day, the researches in this field of our country are limited, and there aren't relevant high temperature resistant or fire resistant codes for design of reinforced concrete structures. So the researches of this field can't keep up with the development of construction engineering. Therefore, the researches on the mechanical behaviours of reinforced concrete materials, members and structures at elevated temperature (fire exposure) and the researches on relevant experimental methods become a very important task for us to resolve.In this paper, based on experiments and theoretical analyses, the mechanical properties of reinforced concrete materials and structures and relevant experimental methods are researched. The major contents are summarized as follows:The experimental methods of several kinds of main structural members and the design of stoves for experiments at elevated temperature are introduced in detail.Based on experiments, the mechanical properties of concrete and steel bar at elevated temperature are researched. And the reasons why the mechanical properties of these two kinds of materials at elevated temperature become weak are analysed. On the base of comparison with the properties of these two kinds of materials at normal temperature, the formulas used for calculating the main mechanical indexes of concrete and steel bar at elevated temperature are proposed.The linear variable displacement transducers (LVDT) work at room temperature usually and the highest working temperature of them is less than 150℃, so they can't be used to measure the displacements or deformations at elevated temperature (fire exposure)directly. But LVDT are strongly required to measure the displacements or deformations of structural members at elevated temperarure directly in experiments, so normal LVDT must be improved to adapt the condition of high temperature. In this paper, the methods how to improve LVDT to adapt high temperature are introduced. And the two methods have been certificated as the national patents (Patent Application No. : 200410100477.3 and 200410100478. 8). It is proved by experiments that the improved LVDT can measure the displacements or deformations at elevated temperarure (fire exposure) directly, efficiently and economically.