Dynamic mechanical properties and numerical research of concrete under different cooling methods after high temperature
摘要
The high temperature from the fire can significantly deteriorate the mechanical properties of concrete, and the cooling process after extinguishing the fire will further change the internal crack evolution and dynamic response of the concrete. Therefore, understanding the dynamic response of concrete after high temperature is crucial for evaluating and analyzing the safety of concrete structures after a fire. This paper takes ordinary concrete as the research object and uses two cooling methods after high temperature: natural cooling and water immersion cooling. Static tensile tests, separated Hopkinson pressure bar (SHPB) dynamic tensile tests, and numerical simulation studies are carried out. The coupled influence of temperature, cooling method, and strain rate on the dynamic splitting tensile performance of concrete is systematically analyzed. The results show that as the temperature increases, the dynamic tensile strength and elastic modulus of concrete generally decrease. When the strain rate is 3.5 s−1, the dynamic tensile strength decreases from 9.54 MPa at room temperature to 3.85 and 4.23 MPa after 600 ℃. Under the same temperature and cooling method conditions, as the strain rate increases, the dynamic tensile strength of concrete significantly increases, and the rate effect is more obvious as the temperature increases. The cooling method has a significant impact on the strength degradation pattern. The maximum increase in dynamic tensile strength of concrete can reach 2.33 times. At 600 ℃, the dynamic tensile strength of the water immersion cooling specimens is slightly higher than that of the air cooling specimens. The numerical simulation results show that the modified K&C model can better reflect the dynamic tensile failure mode and stress–strain response of concrete after high temperature, with the peak stress and peak strain errors controlled within 5%. This paper provides a theoretical basis for the numerical calculation and safety assessment of fire-resistant concrete structures subjected to strong dynamic loads.