1 September 1999
8-4. WELDING POSITIONS. Welding positions include the flat position, the horizontal
position, the vertical position, and the overhead position. Certain welding processes have
limitations on which welding positions can be used. The structural engineer designing the
weldment must be familiar with these restrictions, and make sure the type of weldment
specified can actually be applied as intended considering access conditions, weld position,
and any environmental conditions that could adversely influence weldment fabrication.
8-5. WELDMENTS SUBJECTED TO EARTHQUAKE AND CYCLIC LOADING CONDITIONS.
Certain types of welds are not permitted to join members that may experience cyclic loadings
due to earthquake ground motions, or due to vibratory motion caused by equipment. Partial
penetration butt joints in tension, intermittent groove welds, and intermittent fillet weld are
examples. Special Moment Resisting Frames (SMRF's) and Ordinary Moment Resisting
Frames (OMRF's) used for earthquake resistance must be capable of performing in the
nonlinear range (beyond yield) during major earthquakes. For SMRF's this means the
weldments designed for beam column joints must have greater strength than the connected
members so that yielding occurs in the beam span away from the beam column joint. Welded
steel frame design for seismic resisting moment frame systems is covered by the American
Institute of Steel Construction (AISC), Seismic Provisions for Structural Steel Buildings".
8-6. WELDMENT STRENGTH AND DUCTILITY. Base metals selected for components of the
structural framing system must possess certain strength and ductility characteristics. It is
important that the electrodes for joint weldments, as well as welding procedures, be selected to
produce a joint with strength and ductility properties equal to, or superior to, those of the base
8-7. ENVIRONMENTAL FACTORS IMPORTANT TO WELDMENT PERFORMANCE.
Cracking can occur due to environmental factors such as the presence of moisture, and low
ambient temperatures. Field welding should be avoided as much as possible. However, when
field welding is required, especially under adverse environmental conditions, it is important that
AWS welding specification procedures be followed to the letter. Preheating and inter-pass
temperatures are critical if cracking is to be prevented. Preheating also helps to drive of
excess surface moisture, and retards the cooling rate thereby minimizing temperature
gradients. Controlling cool-down rates, especially during cold weather, is critical if cracking is
to be eliminated.
8-8. WELDING REINFORCING STEEL. The welding of reinforcing steels is covered by AWS
D 1.4, "Structural Welding Code - Reinforcing Steel." Most reinforcing steel bars can be
welded. However, the preheat and other quality control measures that are required for bars
with high carbon equivalents are extremely difficult to achieve. It is recommended that carbon
equivalents be limited to 0.45 percent for No. 23 bars (No. 7 bars) and higher, and to 0.55
percent for smaller bars. ASTM A615, Grade 60 reinforcing steel will most likely not meet the
aforementioned carbon equivalent requirements. However, reinforcing bars meeting ASTM
Specification A706 have a low carbon equivalent, are easy to weld, and should be considered
when welding is required. Mechanical connectors are another way of connecting reinforcing
bars. Mechanical connectors are covered in Chapter 4.