Strength of Lag‐Screw Connections

Abstract

Lag screws are frequently used to fasten relatively thin, often metal, cleats to wood structural elements. Design values for engineered lag‐screw connections have been based on proportional limit loads derived from limited test data. A new allowable stress design specification and a draft load and resistance factor design (LFRD) specification for engineered wood structures incorporate theoretically based yield equations to calculate connection strength. These equations, based on a set of assumed yielding actions, offer designers much greater freedom and guidance in checking dowel‐type connection strength than has previously been the case. This paper shows the development of yield models and simplified equations for the lateral strength of lag‐screw connections with wood and metal side plates. Experimental data from several sources are presented in verification of the models. Calibration of the yield equations to traditional safety levels for use in codification is described.