Flexural behavior of concrete beams reinforced with high-strength steel bars after exposure to elevated temperatures

Abstract

To study the flexural behavior of concrete beams reinforced with high-strength steel bars after exposure to elevated temperatures, flexural tests were conducted on twelve concrete beams reinforced with high-strength steel bars. The influences of exposure temperatures (room temperature, 200, 400, 600, 800, and 1000 °C), holding times (0, 1, and 2 h), yield strength grades of steel bars (600 and 500 MPa), and the number of heating sides (2 and 3 sides) on the flexural behavior of beams, including failure mode, load–deflection response, flexural bearing capacity, ductility, and concrete strain, were investigated. The results showed that all beam specimens presented flexural failure mode. When the exposure temperatures were below 600 °C, the flexural capacities changed negligibly, decreasing significantly when the exposure temperatures exceeded 800 °C. The peak loads of specimens with HRB600 bars after exposure to 800 and 1000 °C decreased by 12.9% and 38.7% relative to that under room temperature. The flexural capacities decreased more significantly when the holding time was 2 h relative to that was 0 h and 1 h, of which peak load decreased by 2.4% and 9.4%, respectively. The number of heating sides had no obvious effects on the load - deflection response of the specimens. The load - deflection curves were similar in the elastic stage and yield stage between the specimens were heated on two and three heating sides. At last, combining the temperature distribution on the cross-section obtained by the elevated temperature tests, the calculation methods on the flexural capacities of concrete beams reinforced with high-strength steel bars after exposure to elevated temperatures were proposed based on the equivalent section reduction method and the material reduction method, respectively. Comparing the calculated results with test results, a good agreement could be noted.