Modeling the behavior of bolted connections under bending/tension loading

A mathematical model that approximates the load-deformation relationship of single bolted connections in wood structures subjected to bending/tension loading is presented. The model accounts for connections which exhibit nonlinear load-deformation curves virtually from the start of loading.;The mathematical model uses the material properties and the connection dimensions as input, and can predict the general deformation pattern in both the elastic and the post-elastic range. The stress level at which the nonlinear behavior begins is determined from the values of stress at proportional limit entered as input to the program. The value of the observed stress at proportional limit in transverse compression under the connection's washer determined from a test is reduced to account for the difference between the area modeled and the actual area. The stiffness reduction factor that allows for the transition from elastic to inelastic behavior in the wood member also reflects this difference. Allowance is made for initial bolt prestress.;Since the model requires extensive computational efforts, because it is iterative, computations are performed on the CYBER 205 supercomputer. A series of experiments is made to determine the accuracy of the model and it is determined that the prediction capability of the model is generally good. The normalized error with respect to the mean deflection is less than 15% throughout the greater part of the loading range in the majority of cases.;Two wood species are included in the experimental phase of this study: a softwood (lodgepole pine) and a hardwood (hard maple). The wood members are assumed attached to a fixed rigid steel support plate. Analyses of this connection model are made using a plane-stress, two-dimensional orthotropic finite element model. Six-node, linear strain triangular elements are used to represent the structure. An incremental-iterative secant stiffness approach is employed to trace the nonlinear behavior. The principal response investigated is the load versus deformation at the tip of the wood member up to a predetermined deformation level.