Date of Award
Doctor of Philosophy (PhD)
Civil Engineering and Engineering Mechanics
The central focus of research undertaken concerned the strength and behaviour of separated double chord rectangular hollow section (RHS) K-joints. Peripherally the concepts of the twin member shear beam is introduced as a simple and inexpensive bridging for revealing the intrinsic structural properties of such joints.
The finite element method has been used to investigate the stiffness characteristics of the separated joint. The RHS chord member is idealized by a thin plate representing the inner web and a channel representing the top and bottom flanges and the outer web. The stiffening effect by the channel is incorporated through its condensation into a boundary stiffness matrix to be added to the inner web stiffness matrix.
The proposed finite element formulation includes rectangular plate elements in the inner web plate and a variety of beam elements in the channel forming grillage. The formulation considers both bending and in-plane actions. Material nonlinearities of the joint are assumed to be adequately represented by the Von Mises yield criterion and the associated plastic flow rule. While geometric nonlinearities have been excluded, this was deemed reasonable for the range of displacements considered in this study.
To verify the finite element model, a number of experiments were conducted on twin shear beams with the objective of making definitive statements about the joint performance to be anticipated for the finite element model. Twenty-four specimens were tested in the Applied Dynamics Laboratory of McMaster University. Test results showed a definite improvement in structural performances for both increased depth and a decrease in the gap.
From experimental result, a local deflection limit criterion was suggested to define a range of permissible displacements in double chord joints. Such a criterion was based upon that presented in the literature for single chord joints.
A verification of the finite element model was made using the experimental data of the twin shear beams and it exhibited good correlation. A model of sensitivity analysis was then carried out with the objective of furthering understanding of the behaviour of such structural components.
The model was extended to the general model called EPAC-RHS (Elasto-Plastic Analysis of RHS Connections). In the process of this extension, triangular plane stress-plate bending elements were introduced to accommodate an arbitrary joint assembly of K and N configuration. In addition, member preloads were accounted for in EPAC-RHS.
Theoretical results of simulated K-joint models were compared with experimental data of K-joints obtained from the literature. While strength predictions were somewhat conservative, very good agreement of elastic response was observed for all tests.
A yield line theory was developed for which two strength models, trapezoidal and conical were proposed. Their predicted strengths were compared with experimental loads at the limiting deflections suggested. Good agreement with the tests was found particularly for the trapezoidal model. The twin shear beam models were then extended to be applicable to K-joints by taking into account both the reduction in strength due to chord axial preload and the horizontal component of the diagonal force. Theoretical results were compared with previous experiments on K-joints and exhibited reasonable correlation.
Mitri, Hani Sabri, "Separated Double Chord RHS Joints" (1984). Open Access Dissertations and Theses. Paper 3287.