Post-fire residual mechanical properties of steel butt weld — Experimental study

Butt weld connection is one of the most commonly used connection types in steel structures, and its post-fire mechanical property is crucial for the estimation of the residual mechanical capacity of steel structures after building fires. To study the mechanical properties of butt weld connections after being exposed to high temperatures, Q235 and Q345 butt weld specimens were designed, heated to various high temperatures between 400 °C and 800 °C, and then naturally cooled to room temperature. Tensile tests were conducted on these butt weld specimens to obtain the force–displacement curves and relevant mechanical properties (yield and ultimate strengths) at various temperatures. The following conclusions were obtained from the test results: (1) The post-fire mechanical properties of the butt weld specimens were affected by material grade and heating temperature; (2) when the temperature exceeded 600 °C, the yield and ultimate strengths of the Q235 and Q345 butt weld specimens began to decrease; the strength reduction of the latter was greater than that of the former; (3) when the temperature was 800 °C, the yield strength and ultimate strength of Q235 decreased to 87% and 91% of the ambient-temperature yield and ultimate strengths, respectively; and (4) the yield and ultimate strengths of Q345 decreased to 83% and 87% of those at room temperature. Computational formulas for the yield and ultimate strengths of the butt weld specimens at high temperatures were also fitted and verified with test data to provide a safety evaluation method for steel structures after a fire.