WELDING COLD-FORMED STEEL

1 1 Light Gauge STEEL Engineers Association 1 TECH NOTE (560-b1) 10/99 TECHNICAL NOTEOn COLD-FORMED STEEL ConstructionLight Gauge STEEL Engineers Association z Washington, z Toll-Free: 1 (866) 465-4732 z $ COLD-FORMED STEELSUMMARY: In COLD-FORMED STEEL construction, WELDING is a viable connection method. Of the various forms ofwelding, arc WELDING is most commonly used to join both COLD-FORMED STEEL members and hardware of roof trusses, panelization of walls, and hardware connections are all ideal applications wherewelding may be the preferred joining method. This Tech Note provides information on the applicable codes,processes, procedures, design considerations, fabrication and 1welding (GTAW), and submerged arc WELDING (SAW).SMAW ( )Shielded metal arc WELDING (SMAW), commonly known asstick electrode WELDING or manual WELDING , is the oldest ofthe arc WELDING processes.

2 Versatility, simplicity and flex-ibility characterize it. The SMAW process commonly is usedfor tack WELDING , fabrication of miscellaneous components,and repair WELDING . SMAW has earned a reputation for de-positing high quality welds dependably. It is, however, slowerand more costly than other methods of WELDING , and is moredependent on operator skill for high quality welds and is dif-ficult to use on thin ( )The flux cored arc WELDING process offers two distinct ad-vantages over shielded metal arc WELDING . First, the elec-trode is continuous. This eliminates the built-in starts andstops that are inevitable with shielded metal arc WELDING . Notonly does this have an economic advantage because the op-erating factor is raised, but the number of arc starts and stops,a potential source of weld discontinuities, is reduced. Another major advantage is that increased amperages can beIntroductionWelds used to connect COLD-FORMED STEEL may be either arcwelds or resistance welds.

3 In building construction, how-ever, welds are generally made using the arc WELDING pro-cess. Resistance welds are commonly used for connectingthin sheet steels in the automotive or appliance. Arc weldingis the process of fusing material together by an electric arc,usually with the addition of weld filler design of welds for COLD-FORMED STEEL construction istypically governed by the Specification for the Design ofCold- formed STEEL Structural Members (AISI 1996) and theANSI/AWS Structural WELDING Code Sheet STEEL (AWS1998). Both the AISI and AWS documents contain require-ments for the following types of welds: (1) groove weld, (2)arc spot weld (puddle weld), (3) arc seam weld, (4) filletweld, (5) flare groove weld and (6) plug most common weld type to connect sheet-to-sheet orcross section-to-cross section is the fillet weld. Groove weldsare commonly used during the roll forming process to con-nect flat sheet of one coil to the subsequent coil.

4 Arc spotwelds, also called puddle welds, are used extensively to at-tach deck and panels to bar joists or hot-rolled welds on STEEL where at least one of the connected partsis equal to or less than in. in nominal thickness shall bemade in accordance with AWS The AWS weld-ing code provides guidelines for the following: workman-ship, technique, qualification, and ProcessesAWS defines WELDING electrodes that appropriatelymatch the strength of the approved base metals. The weld-ing code lists the following as approved WELDING processes:shielded metal arc WELDING (SMAW), gas metal arc WELDING (GMAW), flux cored arc WELDING (FCAW), gas tungsten arc22 Light Gauge STEEL Engineers AssociationTECH NOTE (560-b1) 10/99used with flux cored arc WELDING , with a corresponding in-crease in deposition rate and productivity. Several .035 diameter electrodes are specifically designed forwelding galvanized sheet ( )Submerged arc WELDING (SAW) differs from other arc weld-ing processes in that a layer of fusible granular material calledflux is used for shielding the arc and the molten metal.

5 Thearc is struck between the workpiece and a bare wire elec-trode, the tip of which is submerged in the flux . Since the arcis completely covered by the flux , it is not visible and theweld is made without the flash, spatter, and sparks that char-acterize the open-arc processes. The nature of the flux is suchthat very little smoke or visible fumes are released to the is typically not used for thin material unless the pro-cess is ( )Gas metal arc WELDING (GMAW) utilizes equipment muchlike that used in flux cored arc WELDING . Indeed, the twoprocesses are very similar, except GMAW uses a solid ormetal cored electrode and leaves no appreciable amount ofresidual slag. Gas metal arc has been a popular method ofwelding in the fabrication shop and isideal for sheet STEEL . However,GMAW is not generally used in thefield due to the potential loss of shield-ing gas.

6 A variety of shielding gasesor gas mixtures may be used. Carbondioxide (CO2) is the lowest cost gas,and while acceptable for WELDING car-bon STEEL , the gas is not inert but ac-tive at elevated temperatures. This hasgiven rise to the term MAG (metalactive gas) for the process when (CO2)is used, and MIG (metal inert gas)when predominantly argon-based mix-tures are ( )Gas tungsten arc WELDING (GTAW) ortungsten inert gas (TIG), as it is some-times known, is a process where coa-lescence is produced by heating withan arc between a tungsten electrodeand the base metal. The hot tungstenelectrode, arc, and weld pool areshielded by an inert gas or mixture of inert gases. Filler metalmay be added, if needed, by feeding a filler rod into the weldpool either manually or automatically. The weld quality ishigh, however, GTAW is usually not used for production sinceit takes more time to produce a weld than any other 2 Figure 3 Figure 43 Light Gauge STEEL Engineers Association 3 TECH NOTE (560-b1) 10/99 WorkmanshipAWS stipulates that the surfaces to be welded shall besmooth, uniform, and free of imperfections.

7 When weldinggalvanized sheet, suitable ventilation shall be provided. Also, WELDING of sheet steels shall not be done when the ambienttemperature is lower than 0 F, when the surfaces are wet, orwhen the welder is exposed to inclement weather. The partsto be joined shall be brought into close contact to facilitatecomplete fusion. The closeness of the two parts can not beover-emphasized, especially for arc spot welds. If any gapexists between the members prior to spot WELDING , the strengthof the weld may be substantially reduced. Also, to obtainconsistently sound welds, the WELDING current must be WELDING Procedure Specifications (WPSs),which are exempt from WPS qualification tests, can be es-tablished based on the applicable WELDING code provisions inAWS A WPS is a written set of instructions that de-fines the joint details, WELDING electrodes, base metals, elec-trical parameters, and other procedural variables.

8 Any timewelding is performed in accordance to AWS a writtenWPSs must be used, even for prequalified the WELDING parameters do not conform to theprequalified status, the WELDING procedure must be qualifiedby testing. This happens, for instance, when a base metalother than those in the approved list are used, or when thejoint detail does not match one of the prequalified details. AProcedure Qualification Record (PQR) is used to record theactual values of the WELDING procedure test. After the weldedspecimens pass the destructive tests, a qualified WELDING Pro-cedure Specification can be Procedure Specifications are the responsibility ofthe manufacturer or the contractor. The required tests, testmethods, and required results areprescribed by AWS Oncea contractor has qualified a weld-ing procedure, the procedure shallbe considered qualified for its requires only visualinspection of welded sheet steeljoints.

9 The visual inspection shalldetermine compliance with con-tract documents. Particular em-phasis shall be placed on verify-ing proper location, size, andlength of a weld, in addition tothe bead shape, reinforcement, and undercut. Inspectors arealso responsible for confirming that qualified or prequalifiedWPSs and qualified welder are used in performing the ConsiderationsOf primary importance to the structural design engineer isthe strength of a welded connection. Strength equations forthe six weld types are stipulated by the Specification for theDesign of COLD-FORMED STEEL Structural Members (AISI1996) which is in general agreement with the Structural Weld-ing Code Sheet STEEL (AWS 1998). The paramount differ-ence between the strength of a welded connection in COLD-FORMED STEEL and a welded connection in hot-rolled STEEL isthe dominance of sheet tearing as an alternate failure the design provisions provide guidance on deter-mination of the weld strength, the design is generally limitedby the tearing of the base design engineer must also consider workmanship, qual-ity, and inspection when determining if a weld is an appro-priate connection EquationsA design equation is a mathematical relationship that modelsthe failure of a welded connection.

10 The following is an over-view of the Specification s strength equations for the com-mon weld Weld. The strength of a groove weld depends on thetype and direction of load application. For example, when agroove weld is subjected to either tension or compressionnormal to the axis of the weld, the strength of a groove weldis defined by the yield strength of the sheets being connected,that is AISI Equation However, when the weld ex-periences shear, both the weld strength and the connectedsheets must be investigated (AISI Equations and ).Figure 544 Light Gauge STEEL Engineers AssociationTECH NOTE (560-b1) 10 Structural WELDING Code STEEL . The American WELDING Society, Structural WELDING Code Sheet STEEL . The American WELDING Society, Procedure Handbook of Arc WELDING . 13th Edition. The James F. Lincoln Arc WELDING Foundation, for the Design of COLD-FORMED STEEL Structural Members.