SAFETY AGAINST BRITTLE FRACTURE OF WELDED GUSSET PLATE JOINTS OF TRUSS MEMBERS WITH H-SECTION

摘要

Cut-outs in gusset plates are increasingly used with welded connections of H-shaped web members of truss girders. This is because this construction eliminates tolerance problems during fabrication of the truss girders. The width of these cut-outs is equal to the height of the connected H-section. Its length is somewhat longer than required for the design length of the web member to allow for tolerances. The connection is by longitudinal side fillet welds. Tension tests with full size specimens have shown that this structure may be prone to brittle fracture even at ambient temperature. This is because of residual stresses with large tensile components and the high stress concentration in the gusset plate close to the ending web member. The residual stresses are due to the gap between truss member and gusset plate and the large in-plate-stiffness of both of them. The stress concentration in the gusset plate at the end of the truss member is by three effects: The stress increases due to global continuity conditions at the end of the longitudinal side fillet weld, to local effects from welding at the starting point or end point of the weld and to the remaining cut-out in the gusset plate at the end of the web member - which is comparable to the fracture mechanics situation of a central crack in a plate. This situation is investigated by experiments and analyzed by FE-calculations. The investigation includes modifications of the structure to improve its ductility.