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Group effects in axially loaded self-tapping screw connections
Highlights Strength variability decreases as more fasteners are added to a connection group. Group strength can be described by isolating effects on the average strength and variability. Unit characteristic withdrawal resistance increases in groups of widely spaced self-tapping screws. A net group effect factor greater than one is possible for widely-spaced screws in withdrawal.
Abstract Connections using self-tapping screws are frequently used in modern timber construction, with screws often assembled in groups to resist large loads. Load carrying capacity and stiffness are maximized when screws are loaded parallel to the screw axis in withdrawal. In the design of multiple fastener connections a group effect reduction is typically applied that has not considered positive effects from reduced strength variability in large groups. Static tests were performed on groups of self-tapping screws loaded axially in withdrawal, with up to 12 widely spaced (10d) screws. The results showed no effective change in average strength with respect to group size, however the variability decreased significantly. Two group effect factors were identified that, together, adjust the 5th percentile strength value for a single screw to that of the group. A group factor was developed that results in an increase in the design strength in larger groups. Connection stiffness was observed to be constant but sensitive to the measured load path. The sensitivity of the results to equicorrelation between screws and construction-induced variability was discussed.
Group effects in axially loaded self-tapping screw connections
Highlights Strength variability decreases as more fasteners are added to a connection group. Group strength can be described by isolating effects on the average strength and variability. Unit characteristic withdrawal resistance increases in groups of widely spaced self-tapping screws. A net group effect factor greater than one is possible for widely-spaced screws in withdrawal.
Abstract Connections using self-tapping screws are frequently used in modern timber construction, with screws often assembled in groups to resist large loads. Load carrying capacity and stiffness are maximized when screws are loaded parallel to the screw axis in withdrawal. In the design of multiple fastener connections a group effect reduction is typically applied that has not considered positive effects from reduced strength variability in large groups. Static tests were performed on groups of self-tapping screws loaded axially in withdrawal, with up to 12 widely spaced (10d) screws. The results showed no effective change in average strength with respect to group size, however the variability decreased significantly. Two group effect factors were identified that, together, adjust the 5th percentile strength value for a single screw to that of the group. A group factor was developed that results in an increase in the design strength in larger groups. Connection stiffness was observed to be constant but sensitive to the measured load path. The sensitivity of the results to equicorrelation between screws and construction-induced variability was discussed.
Group effects in axially loaded self-tapping screw connections
Joyce, Tom (author) / Chui, Ying Hei (author)
Engineering Structures ; 251
2021-10-31
Article (Journal)
Electronic Resource
English
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