1 September 1999
8-1. INTRODUCTION. A weldment may contain metals of different compositions, and the
components of the framing system may be rolled shapes, pipes, tubes, or plates. In general,
all metals are weldable, but some are much more difficult to weld than others. Certain types of
reinforcing steels used in concrete and masonry construction can be very difficult to weld.
Various types of joints are used to connect framing components, including butt joints, corner
joints, edge joints, lap joints, and T-joints. Various types of welds are used in joining steel
components together, and several different welding processes can be used to make the weld.
Structural engineers involved in the design of weldments must be familiar not only with the
various types of joints and types of welding procedures, but also with the effect welding
position has on the selection of welding procedures, and with the effect factors such as base
metal composition, electrode selection, preheat and interpass temperature, wire feed speed,
travel speed, post weld treatment, ambient temperature, etc., have on weld performance.
Volume change effects due to temperature gradients that occur due to welding, joint restraint
conditions, and weld toughness are factors which must also be considered to assure
weldments will be free from cracks that could reduce joint capacity and ductility. Corner joints
and poor weld termination can cause stress concentrations that can also lead to weldment
8-2. BASIS FOR DESIGN. Weldments will comply with the American Welding Society (AWS)
AWS D1.1, "Structural Welding Code - Steel". AWS D1.1 contains many prequalified joint
details that are known to produce quality weldments when fabricated in accordance with AWS
Welding Procedure Specifications (WPS). WPS's are required for all welding, including
prequalified procedures. Additional guidance on welding can be found in TI 809-26, "Welding
Guidance for Buildings."
8-3. ARC WELDING PROCESSES. The most popular arc welding procedures are Shielded
Metal Arc Welding (SMAW) and Flux Core Arc Welding (FCAW). The SMAW process is
defined as "an arc welding process that produces coalescence of metals by heating them with
an arc between a covered metal electrode and the work. Shielding is obtained from
decomposition of the electrode covering. Pressure is not used and filler metal is obtained from
the electrode." The FCAW process is defined as " an arc welding process that produces
coalescence of metals by heating them with an arc between a continuous filler metal
(consumable) electrode and the work. Shielding is produced by a flux contained within the
tubular electrode. Additional shielding may or may not be obtained from an externally supplied
gas or gas mixture". Shielding refers to methods used to prevent the molten weld metal from
coming in contact with gasses contained in the surrounding air. These gases, especially
oxygen, nitrogen, and hydrogen, are the most detrimental to weld quality. Other types of arc
welding processes are carbon arc welding (CAW), gas tungsten arc welding (GTAW), plasma
arc welding (PAW), submerged arc welding (SAW), and gas metal arc welding (GMAW). The
type of base metal usually determines which welding processes can be used.