Shear capacity and tension capacity of arc-spot welds for multi-overlap deck panels

Arc-spot welds fabricated in multi-overlap configurations are found in roof deck construction when steel sheets are stacked at a sidelap or endlap. A welding technique that maximizes the quality of arc-spot welds fabricated through several layers of thick sheets is presented. Weld specimens were fabricated through 1, 2 or 4 layers of steel sheets with thicknesses ranging from 0.76 to 1.52 mm (22 to 16 gauge). The most important factors to control during the welding are the current (high intensity), the electrode type (E4311) and the welding technique. Various sheet steel/weld configurations found in roof deck construction were included. Adequate weld quality could be achieved in all cases except that welds were undersized when the ratio of the thickness of the underlying material to total sheet thickness was less than 0.7. A total of 72 tension tests and 107 shear tests were completed. Of those, 31 shear specimens were loaded with a reversed cyclic protocol to examine the behaviour of arc-spot welds subject to seismic loading. All other specimens were loaded under monotonically increasing displacement. The results were compared with the provisions of the CSA S136 North American Specification for the Design of Cold-Formed Steel Structural Members. The CSA S136 equations for shear and tension resistance of arc-spot welds are generally conservative, even for welds fabricated through multi-overlap configurations with total sheet steel thicknesses exceeding the 3.81 mm limit. Nonetheless, modifications to the equation for the effective diameter and to Equations E2.2.1.2-2, E2.2.2-1, and E2.2.2-2 are recommended.