Design Guide 21 provides a complete overview of topics related to structural welding, including selection of weld types, weld design, metallurgy, weld repair, weld procedure specifications, quality, inspection, economy and safety. The second edition references provisions in AISC 360-16, AISC 341-16 and AWS D1.1:2015, and contains new chapters dealing with seismic considerations and fracture mechanics as applied to welded connections, and the chapter on fatigue has been expanded. The popular first edition chapter on "special welding applications" has been divided and expanded: more special applications are addressed and a new chapter on "problems and fixes" addresses commonly encountered problems with practical advice to solve the problem.