Abstract Scope |
Two long-span tapered steel plate girders fractured in a brittle manner where a hanger, designed to support the floor below, extended through an opening cut the girder bottom flange. The two girders spanned 87.3 ft (26.5 m), were 8-ft (2.4 m) in depth at the hanger, with flanges 4-in (100 mm) thick and 36-in (915 mm) wide. Two similar girders that used a different cutting sequence for the opening did not fracture. The investigation of the fractures included flange steel mechanical properties, the condition of the thermal cut surface, the welding sequence, applied loading, and residual and applied stresses. The investigation established a plausible cause of fracture in the two girder flanges, as well as why the other two girders did not fracture. Several recommendations are offered to minimize the risk of future fractures, including additions to fabrication and material standards, modification of joint details, changes to thermal cutting procedures, requirements for surface finishing, and requirements for testing. |