Shrinkage during solidification of large welds in structural steel members causes, in adjacent restrained metal, strains that can exceed the yield-point strain. In thick material, triaxial stresses may develop because there is restraint in the thickness direction as well as in planar directions. Such conditions inhibit the ability of a steel to act in a ductile manner and increase the possibility of brittle fracture. Therefore, for members subject to primary tensile stresses due to axial tension or flexure in buildings, the American Institute of Steel Construction (AISC) specifications for structural steel buildings impose special requirements for welded splicing of either group 4 or group 5 rolled shapes or of shapes built up by welding plates more than 2 in thick. The specifications include requirements for notch toughness, removal of weld tabs and backing bars (welds ground smooth), generous-sized weld-access holes, preheating for thermal cutting, and grinding and inspecting cut edges. Even for primary compression members, the same precautions should be taken for sizing weld access holes, preheating, grinding, and inspection.
Most heavy wide-flange shapes and tees cut from these shapes have regions where the steel has low toughness, particularly at flange-web intersections. These low-toughness regions occur because of the slower cooling there and, because of the geometry, the lower rolling pressure applied there during production. Hence, to ensure ductility and avoid brittle failure, bolted splices should be considered as an alternative to welding.
(AISC Specification for Structural Steel Buildings Allowable Stress Design and Plastic Design and Load and Resistance Factor Design Specification for Structural Steel Buildings, American Institute of Steel Construction; R. L. Brockenbrough, Sec. 9, in Standard Handbook for Civil Engineers, 4th ed., McGraw-Hill, Inc., New York.)
