FRACTURE MECHANISM OF JOINT OF H-STYLE STEEL BEAM-SQUARE STEEL TUBULAR COLUMN AND STUDY ON JOINTS WITH HORIZONTAL HAUNCH AND SLOT HOLES AT BEAM FLANGES

Based on a suggested elliptical fracture model and an elliptical yield model of constructional steel,it was performed for the numerical simulation and fracture analysis on the conventional joint of an H-style steel beam-square steel tubular column tested by low-cycle reversed loading.The results reveal that stress concentrates,seriously at butt weld due to the strong constraint of the column on beam flange and the first crack comes into being at the edge of the butt weld where the geometries change sharply.The conventional joint brittle fracture and the plastic rotation do not meet with the requirement of 0.03rad in the interim guidelines FEMA.Joints with horizontal haunch and slot holes at beam flanges were tested by low-cycle reversed loading and were simulated based on the elliptical fracture model revised by considering residue stress and welding flaws.The results show that the degree of stress concentration at the butt weld of a conventional joint is markedly mitigated by using of horizontal haunch and that the plastic hinges are formed at the reduced beam section duo to the slot holes.For the joint with proper parameters of slot holes and horizontal haunch,the plastic rotation meets with the requirement of 0.03rad in the interim guidelines FEMA and the bearing capacity is equivalent to that of conventional joints.