AISC LRFD 1.pdf

229Comm. JCHAPTER JCONNECTIONS, JOINTS, AND FASTENERSJ1. GENERAL PROVISIONS5. Splices in Heavy SectionsSolidified but still-hot filler metal contracts significantly as it cools to ambienttemperature. Shrinkage of large welds between elements which are not free tomove to accommodate the shrinkage causes strains in the material adjacent to theweld that can exceed the yield point strain. In thick material the weld shrinkage isrestrained in the thickness direction, as well as in the width and length directions,causing triaxial stresses to develop that may inhibit the ability of ductile steel todeform in a ductile manner. Under these conditions, the possibility of brittle fractureincreases.When splicing ASTM A6/A6M Group 4 and 5 rolled sections or heavy weldedbuilt-up members, the potentially harmful weld shrinkage strains can be avoidedby using bolted splices or fillet-welded lap splices or splices that combine awelded and bolted detail (see Figure C-J1.1). Details and techniques that performwell for materials of modest thickness usually must be changed or supplementedby more demanding requirements when welding thick material. Also, the provisionsof the Structural Welding Code, AWS D1.1, are minimum requirements thatapply to most structural welding situations; however, when designing and fabricatingwelded splices of ASTM A6/A6M Group 4 and 5 shapes and similarbuilt-up cross sections, special consideration must be given to all aspects of thewelded splice detail.Fig. C-J1.1. Alternative splices that minimize weld restraint tensile stresses.LRFD Specification for Structural Steel Buildings, December 27, 1999AMERICAN INSTITUTE OF STEEL CONSTRUCTION