New Truss Joint Development Project

Abstract

This project comprises a preliminary investigation into the performance of a novel truss connection system named the Howick Rivet Connector (HRC). The HRC is used to provide a pinned connection between cold-formed steel channel sections through their flanges. The overall project objective was to determine the strength and stiffness of this connection and verify that it performs dependably in realistic assemblages. The HRC was firstly tested in a T-joint arrangement which allowed for a set of design capacities to be derived using both the verification by testing method and calculations based on current design standards. A series of short-span trusses connected with the HRC were then tested. The connection capacity was the same or higher than what was developed from the Tjoint tests and the truss was shown to be significantly stiffer and have a much higher proportionality limit (i.e. range of linear elastic behaviour) than similarly dimensioned conventional screwed truss systems. Finite element models of the T-joint and truss tests were modelled in ABAQUS software. The HRC shear capacity was underpredicted because strain hardening caused by swaging was not included. The bearing capacity of the connections were overpredicted in tests with thin gauge members because geometric irregularities were not included. The truss model predicted both the elastic and inelastic experimental test load profile well. A final series of tests were performed on a rigid moment connection using intersecting truss members and gussets. In an opening moment the connection performed rigidly and failure outside the connection occurred at loads expected from design capacities derived from the Tjoint and truss tests. In a closing moment, premature buckling occurred where members had been cut to allow trusses to interconnect. It is recommended that an extended gusset be used to bypass this limitation. A set of load span tables for residential floor trusses have been created to demonstrate the capabilities and limitations of the HRC. The capacity of the connection can be maximised in bearing by adding washers and in shear by inserting a low-tolerance steel pin. It is recommended that cutting the lips of the chord members is avoided as this ultimately limits the system capacity.