Behavior of welded connections after exposure to elevated temperature

This paper reports test results showing how the heating-cooling process like the one occurring during fire action can affect the tensile strength and the deformation after rupture of the welded connections normally used in steel structures. Tests were carried out to assess the values of these properties for butt welded, transverse and longitudinal fillet welded connections after heating. Different configurations of weld specimens, made of Q345 steel, were first heated to a specified target temperature in 200 to 800 °C range, then cooled to ambient temperature, and finally loaded to failure. Cooling in the air and cooling by water jet were the cooling processes used. All connections were designed to fail in the base metal at room temperature. Test results show that butt welded connections attain failure in the weld region when heated to above 400 °C (and cooled under natural cooling) or 500 °C (under water cooling regime), which showing butt welds experience greater tensile strength degradation than the base metal after exposure to larger temperatures. Moreover, natural cooling generally produces higher strength and deformation degradation in butt welds than water cooling. In contrast to butt welded connection specimens, the transverse and longitudinal fillet welded connection specimens experience failure in the base metal throughout 20-800 °C exposure range. Further experimental research on fillet welds is needed to evaluate the residual behavior of fillet welded connections after exposure to elevated temperatures.