Strength of Sawn Lumber and Wood Composite Dowel Connections Loaded Perpendicular to Grain. I: NDS Design Equations

Abstract

Connections are important design elements in timber engineering. Connections loaded perpendicular to grain for structural composite lumber (SCL) materials have received little attention. Connection strength can be determined as the minimum of the Technical Report 12 (TR-12) equations, a generalized form of the National Design Specification (NDS) connection equations, or a shear stress check for reduced beam section. This paper presents test results and compares the 5% offset yield and capacity of double-shear single bolt connections with steel side plates loaded perpendicular to grain to TR-12 equations for solid-sawn lumber and two SCL products. Testing considered three different span/depth ratios and three different loaded edge distances. Splitting failures were observed at the 4D loaded edge distance and mixed mode failures contained splitting at the 7D and 10D loaded edges. The allowable shear stress values dominated the connection at the 4D loaded edge distance and were conservative in some cases. Comparing the TR-12 equations to experimental connection strength, there was little difference for the span/depth ratios and main member materials. Different loaded edge distances demonstrated significant differences between the TR-12 equations and experimental values. The choice of displacement limit for the capacity dowel bearing strength was identified as an important factor in the TR-12 equations.