Evaluation of maximum strength and optimum haunch length of steel beam-end with horizontal haunch

Since the 1995 Hyogoken-Nanbu Earthquake, the use of horizontally haunched beams has been increasing to prevent brittle fractures of beam flanges in the vicinity of steel-beam-to-boxed-column connections of moment-resisting frames. The author has already proposed a design method based on experimental studies. This method produces ductile beam-to-column connections, because it predicts the fracture mode and an optimum haunch length by comparing a beam’s local buckling strength with that of fracture perpendicular or diagonal to the beam-axis. However, strength-formulas for local buckling used in the method have recently been amended, so the design method needs to be revised and its applicability verified. The revised design method has been applied to test results of twenty-nine horizontally haunched beam specimens designed by the author and other researchers to confirm its effectiveness. Results show that the revised method closely matches the test results. Furthermore, it produces more accurate fracture modes and optimum haunch lengths, except where the haunches incorporate stiffeners. A formula for the optimum haunch length is also proposed. A rough value of the optimum haunch length is about 25 to 35% of the beam depth.