Characterization of Submerged Arc Welds from the World Trade Center Towers: As-Deposited Welds and Failures Associated with Impact Damage of the Exterior Columns

摘要

Intact and aircraft impact-damaged welds from the exterior columns of the World Trade Center towers were evaluated. The fillet welds joining the various steel plates composing the built-up box columns were primarily deposited using submerged arc welding. Characterization of undamaged joints revealed that the welding procedures employed were appropriate relative to contemporaneous standards; no visible surface flaws or subsurface defects were observed. Impact damage of the welds consisted of fracture primarily initiating at and traveling through the heat-affected zone (HAZ) of the steel plates that had rolling planes perpendicular to the travel direction of the aircraft. Failure occurred in this region due to the lower cross-sectional area of the plate and the degraded HAZ mechanical properties (i.e., ductility, toughness with respect to the base plate). Based upon the low-energy, ductile fractures (little plate thinning, slanted fracture surfaces) observed, the failure of the joints absorb only a small fraction of the energy from the impact of the aircraft.