Study On Flexural Behavior Of Concrete Beam After High-temperature Treatment

The temperature causes damage and performance degradation to concrete beam,such as decline of bending strength and the bending stiffness.In this paper,the appearance and mechanical properties of concrete and high strength steel wire after high temperature were studied.The internal temperature field of concrete was studied by experiment and finite element simulation.The calculation method of bending strength of concrete beams after high temperature was established and compared with the experiment data.The specific work was as follows:(1)The mechanical properties of air cooling and water cooling concrete after high temperature were tested and the results showed that:as the temperature of concrete increased,the color of concrete gradually changed from gray to white and the higher the temperature,the more obvious white colour.When the heating temperature reached 400?,a small amount of debris appeared on the surface with the honeycomb cracks and the higher the temperature,the more cracks and the increase of the width to connection.Cooling mode has a greater impact on the concrete surface cracks,compared with air cooling,water cooling process will lead to the generation of cracks and reduce the compressive strength of concrete.(2)The mechanical properties of air cooling high strength steel wire after high temperature were tested and the result showed that:with rising temperature,the high strength steel wire surface by silver turned into dark red and the ultimate strength decreased obviously when they were heated to 400?500?.If they were heated to 700?,their surface became dark with a minimum ultimate strength.When they were heated to 900?,the ultimate strength of the high strength steel wire had a little rebounded with the dark black surface.(3)The experimental research on temperature field of concrete in high temperature environment was carried out and the results showed that:when the concrete is subjected to high temperature,the temperature of concrete is decreased rapidly from the surface to the inside.The temperature of internal concrete point 55mm away from the surface is about 200 ? lower than the surface temperature.The temperature of internal concrete point 150mm away from the surface is 300?400?lower than the surface temperature.Finite element software was used to simulate the temperature field of concrete under high temperature condition and the calculated results were in good agreement with experiment data.(4)Reduction calculation method of bending strength of prestressed concrete beams after high temperature is proposed.Combining with the high temperature mechanical properties degradation research conclusions,bending strength formula of prestressed concrete beam after high temperature was established and verified with the test beam.The results show that the proposed formula has good accuracy.An effective method for calculating the bending stiffness after high temperature was put forward,which can be used as a reference for engineering practice.