Tests and models for engineered wood product connections using small steel tube fasteners

Laminated Strand Lumber (LSL) is a type of engineered wood product widely used as a substitute for sawn structural lumber. This is because LSL can be manufactured to have superior mechanical and physical performance to competing products, including high resistance to splitting, high strength and dimensional stability. The authors studied connections in LSL with behaviour of similar connections in sawn Spruce lumber as a benchmark. Proneness to splitting is the Achilles heel of most wood-based construction materials and especially products like sawn lumber and glued-laminated-timber. This characteristic makes it especially difficult to make connections that are mechanically efficient. However, when constructing with LSL it is possible to create connections that not only have desirable response characteristics, but also achieve labour efficiencies. The particular type of connection studied by the authors uses small diameter steel tube fasteners inserted in tight-fitting holes in conjunction with steel plate elements located in slots in ends of joined members and links them together. Tube fasteners are driven perpendicular to the axes of wood members and pass through both those members and steel link elements. Tests were conducted under static tensile loads with multiple-fastener arrangements obeying spaced and end distance rules typical for solid bolts in sawn softwood lumber. The response was highly ductile and failure occurred mainly in the fasteners. Consequently the so-called European Yield Model (EYM) for doweled timber connections yields good predictions of connection strengths. A detailed finite element analysis was also performed to assist interpretation of test results and validate predictions from the EYM beyond the range of test data. The finite element model was developed using the ABAQUS software and results from that model agreed closely with experimental findings in both qualitative and quantitative aspects.