Exploratory study of high-strength, low-cost through-bolt with cross-pipe and nut connections for square and roundwood timber frame construction

An exploratory test program was undertaken to determine the withdrawal strengths of through-bolt with cross-pipe and nut connections in the ends of selected timbers. Results of the tests indicate that high strength end connections (25,000 lb.) can be obtained in structural timbers with these connectors, but surface checks and drying splits significantly reduced the strength of the joints and lead to major variations in strength. However, the weakening effect of major drying splits can be reduced by orienting the cross-pipe perpendicular to the plane of the split. Furthermore, average withdrawal strength is increased and variability in strength greatly reduced when the ends of the member are reinforced with some form of strapping or with cross bolts. Construction of joints with the nut located on the outside as opposed to the inside of the pipe provides room for the nut to be tightened in place and greatly increases possible uses of the joint since it allows direct end to end joining of members and other constructions that otherwise Would not be feasible. Cost of the connectors is expected to be low - $0.25 to $0.50 per kip.