Strength of Steel-to-Steel Screw Connections - Update to Provisions
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2020-10-20
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Abstract
The objective of this research was to review the existing provisions of the AISI S100-16 North American Specification for Cold-Formed Steel Structural Members [1], for screw connections loaded in shear and tension (but not combined actions). This study performed a comprehensive analysis of available steel-to-steel screw connection strength test data, totaling 702 shear tests, 143 pull-over tests, and 335 pull-out tests. The tested strength of these connections was compared to the predicted strength from the existing strength equations in the AISI S100-16 Standard. The validity of the existing equations was evaluated based on how well the predicted strengths matched the tested strengths. From this analysis, recommended adjustments to the equations, factors of safety, and/or resistance were determined and reported. This study found that the existing equations in AISI S100-16 for screw connections loaded in shear do not need to be revised, although the resistance factors for both LRFD and LSD could be increased. For the limit state of pull-over, the existing equations in AISI S100-16 do not need to be revised, while the resistance and safety factors for pull-over could be revised, with distinction between connections with ductile steel and connections with low-ductility steel. This study did not look at the effect of geometry on pull-over, and further investigation is recommended. For the limit state of pull-out, the analysis of available test data indicates that the current nominal strength prediction equation in AISI S100-16 should be revised by including an adjustment factor into the equation. The proposed adjustment factor results in increased usable strength in connections with sheet thickness greater than 0.04 inches. It was found that the pullout resistance factors could be increased slightly.