This research project was undertaken to investigate the shear and tensile capacity of arc-spot welds connecting overlapped deck sheets to underlying steel framework. Such connection configurations typically occur in roof deck constructions when steel sheets are stacked at a sidelap or endlap or at both. At these specific locations, the limits on the thickness of the thinnest connected part and on the ratio of supporting steel to sheet steel thickness imposed by the CSA S136 Specification (2007) can be exceeded if thick steel sheets are used. The first step of the project was to determine a welding procedure that would maximize the quality of arc-spot welds when fabricated through thick sheets. It was found that the most important factors to control during the welding of thick steel sheets were the current setting (high intensity), the electrode type (E6011) and the welding technique. During this study welds were fabricated by a certified welder through 1, 2 and 4 layers of steel sheets with thicknesses ranging from 22 gauge (0.76 mm) to 16 gauge (1.52 mm) and a welding procedure was developed for each case. Different sheet steel configurations were used to reproduce the typical loading conditions found in roof deck construction. A minimum of 3 tests were completed for each configuration with each steel sheet thickness. Monotonic tensile resistance tests were carried out on 72 specimens. A total of 107 shear resistance tests were also completed. Of this total, 76 specimens were loaded with a monotonically increasing load while 31 specimens were loaded with a reversed cyclic protocol used to gain insight on the behaviour of arc-spot welds subject to dynamic loading, such as that imposed under seismic ground motions. The resistance, deformation and failure mode was recorded for each specimen. Moreover, the effective weld diameter was recorded for specimens that failed due to weld failure. The results obtained during this study were compared with the current provisions of the CSA S136 Specification to verify if these provisions are applicable to multi-overlap configurations.;During the tensile resistance tests, specimens where the sheet tearing failure mode governed presented an average measured tensile resistance higher than the average resistance predicted by the section E2.2.2 of the CSA S136 Specification . These results showed that the 30% reduction in capacity specified in CSA S136 for specimens fabricated through more than one layer of sheet steel should not apply to specimens governed by the sheet tearing failure mode (Equation E2.2.2-2). However, for specimens that failed due to tensile weld fracture, the average measured resistance was lower than the values predicted by CSA S136, which indicates that the 30% reduction in strength should apply to this case. The 30% strength reduction related to weld failure should also be applied to welds fabricated in standard 1-layer configurations as there is no evidence to suggest that the resistance of arc-spot welds in tension is influenced by the lapped configuration.;The effective weld diameter was recorded for all specimens where weld failure was observed. The average effective weld diameter recorded was larger than the effective weld diameter predicted by CSA S136 Specification . This difference between the measured and predicted values increased as the sheet steel thickness increased. These results demonstrated that a lower limit should be imposed on Equation E2.2.1-5 of CSA S136 to improve its precision when dealing with large thicknesses of sheet steel. In the monotonic shear tests, the average shear resistance recorded was greater than the average resistance predicted by section E2.2.1 of CSA S136. A modification to this section is proposed to improve its overall precision. During the cyclic tests, the results demonstrated that the resistance of the specimens did not decrease after sustaining several loading cycles at load levels smaller than and then equal to the factored resistance. The results from the cyclic tests also showed that ductile failure can occur when the sheet bearing failure mode is engaged. This failure mode was observed for some specimens where the average weld diameter was relatively large when compared to the steel sheet thickness.
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