Stability analysis of truss chords loaded by a combination of axial and lateral forces is studied. A simple model based on beam-column theory is proposed and analyzed. The continuous truss chord is replaced by a beam column loaded by end moments replacing the effect of adjacent members. The solution yields deflections and moments allowing one to compute the stress at any point of the truss chord. Analytical and numerical solutions are applied to an example of a wood truss with a continuous top chord. The numerical solution for the deformations converges rapidly. Non-converging results indicate instability. A new design procedure for wood truss chords subjected to possible buckling is proposed. The procedure is based on the analysis of a beam-column model and a mechanics of materials approach. / Graduation date: 1994

Difficulties in characterizing the dynamic behavior of wood structures have hindered investigations into their performance under dynamic loading. Because of this, wood structures are treated unfavorably in seismic design codes, even though past damage assessment surveys after seismic events indicated generally satisfactory performance. To allow investigations into their performance and safety under dynamic loading, the energy dissipation mechanisms of wood joints and structural systems must be known and the hysteretic behavior modeled properly. This thesis presents a general hysteresis model for wood joints and structural systems, based on a modification of the Bouc-Wen-Baber-Noori (BWBN) model. The hysteretic constitutive law, based on the endochronic theory of plasticity and characterized by a single mathematical form, produces a versatile, smoothly varying hysteresis that models previously observed behavior of wood joints and structural systems, namely, (1) nonlinear, inelastic behavior, (2) stiffness degradation, (3) strength degradation, (4) pinching, and (5) memory. The constitutive law takes into account the experimentally observed dependence of wood joints' response to their past history (Le., the input and response at earlier times, or memory). Practical guidelines to estimate the hysteresis parameters of any wood joint or structural system are given. Hysteresis shapes produced by the proposed model are shown to compare reasonably well with experimental hysteresis of wood joints with: (1) yielding plate, (2) yielding nails, and (3) yielding bolts. To demonstrate its use, the proposed model is implemented in a nonlinear dynamic analysis program for single-degree-of-freedom (SDF) systems. System response from arbitrary dynamic loading, such as cyclic or earthquake-type loadings, can be computed. Three SDF wood systems are subjected to the Loma Prieta accelerogram to obtain their response time histories. Advantages of using the proposed model over currently available models in nonlinear dynamic analysis of more complex systems are identified. A multidegree-of-freedom shear building model incorporating the proposed hysteresis model is formulated but not implemented on a computer. / Master of Science