Development of a uniaxial hysteretic model for dowel-type timber joints in OpenSees

Abstract

Dowel-type joints are commonly used as shear connections in many types of timber structures. The load-deformation hysteretic behavior of dowel-type joints usually dominates the structural seismic performance. In this paper, a novel phenomenological uniaxial hysteretic model for dowel-type timber joints is developed. It has the following features: (1) the model fits various dowel-type joints including nails, screws, and bolts, as well as grouped joints, and agrees well with experimental data; (2) the envelope curve can be asymmetric or have low initial stiffness, defined by any of the three models: exponential, Bézier, or piecewise linear; (3) the hysteresis captures the force intercept variation, single-side loaded behavior, and smooth transition, with parameters easy to identify; and (4) the strength and stiffness degradation models consider the displacement or secant stiffness history, as well as the energy dissipation history, yet is kept simple with few defining parameters. The uniaxial model can be incorporated into the open-source software OpenSees as a “uniaxial material” named DowelType. Cyclic loading experiments on (1) Wood-Framed (WF) sheathing-to-framing nailed joints, (2) Cross-Laminated Timber (CLT) screwed joints and metal connectors, and (3) Glued-Laminated Timber (GLT) steel plate bolted connections are presented, and the results are calibrated to the DowelType model and existing Pinching4 and SAWS models in OpenSees, with a Genetic Algorithm (GA) based parameter identification procedure. Comparison of the simulation results indicates that the DowelType model can capture more of the characteristics that have been experimentally observed in dowel-type joints and connections than the existing models, with improved consistency and computational efficiency.