Engineering modeling of semi-rigid joints with dowel-type fasteners for nonlinear analysis of timber structures

Abstract

Plastic analysis in engineered structures requires ductility of structural components, which in timber structures is primarily provided by joints made of dowel-type fasteners. A prerequisite for nonlinear analysis is realistic modeling of joint stiffness and load distribution in dowel-type joints. A joint model suitable for structural analysis is presented and validated in this contribution. The semi-analytical joint model is based on kinematic compatibility and equilibrium considerations. It accounts for local fastener slip by means of nonlinear elastic springs. Influences of nonlinearity and orientation dependence of fastener slip are assessed. Elastic deformations of the timber in between dowels are however neglected. The model allows for predicting global joint stiffness, as well as load distribution within the joint, taking explicitly the effect of simultaneously acting internal forces into account. Model validation builds upon an experimental database that spans from embedment testing on the material scale up to joint testing on the structural scale. Application examples demonstrate the broad applicability of the model for structural analysis. Moreover, they illustrate effects of assumptions of fastener slip on the joint and structural behavior. Limitations, as well as pros and cons of these assumptions are discussed. Special attention is drawn to load distribution within the joint, since it is important for fastener-based design, currently prescribed by the European design standard. Load distribution in joints is also important for verification against brittle failure modes. As an alternative to fastener-based design, joint-based design, by means of a framework for applying the presented model to plastic design of timber structures with ductile joints, is proposed.