Analysis of concrete failure under heat preexposure and multi-step loading conditions

This study investigates the effects of elevated temperatures on the mechanical properties of concrete, which is an important consideration in structural applications involving fire or thermal loading, such as buildings, bridges, and tunnels. The objective of this research was to evaluate the behavior of concrete specimens under various temperatures (25°C to 750°C) through a series of comprehensive laboratory tests, including Unconfined Compressive Strength (UCS), Split Tensile Strength (STS), and Multi-Step Cyclic Loading (MSCL) tests. These tests were designed and carried out to assess the energy dissipation and damping characteristics of concrete when subjected to cyclic and seismic loads. Additionally, Ultrasonic Pulse Velocity (UPV) tests and Computed Tomography (CT) scans were carried out to quantify thermal damage and provide insight into the resulting internal changes in concrete specimens. The study provides new insights into the cyclic behavior of thermally damaged concrete, which is an area with significant practical applications but with limited existing studies. Results of this study demonstrate that higher temperatures can significantly reduce the energy dissipation capability of concrete while increasing its damping ratio. The UPV results showed that damage due to cyclic loading was lower, while the total damage was significantly higher under the combined effect of temperature and cyclic loading. These findings can help improve the methodologies for cyclic and seismic design of concrete structures after they have been subjected to elevated temperatures.