This thesis deals with the behaviour and design of triangular trusses fabricated from Hollow Structural Sections (HSS), with two Warren-type web planes and a single tension chord. Experimental programs are described in which triangular truss segments and simplified joints were tested in order to investigate the behaviour of compression web members and tension-chord welded joints. The mechanics of joint deformations are analysed in relation to the yield line theory, and simple models are shown to give a good prediction of the joint stiffnesses and strengths. Complex yield line models are investigated, but are slightly or not superior to the simple models. Recommendations are established covering the design of tension and compression chord joints, as well as chord and web members. The design of a 22 m span triangular truss is outlined.

No description available.

The element and system models for linear and nonlinear space trusses were formulated and implemented relative to cylindrical coordinates. Nonlinear equilibrium paths were traced using the modified Riks/Wempner method. Two radially symmetric reticulated domes which exhibit snap-through instability and which were subjected to radially symmetric loads were analyzed both linearly and nonlinearly. Along with the entire structures, "pie slices" of the structures were also analyzed. Accuracy was observed by comparison of element forces or of critical load values to those previously presented for these trusses. Reduction of computational effort from analysis of "pie slices" was studied, as were suppression and generation of bifurcation buckling modes. Structural models in cylindrical coordinates were found to greatly reduce computational effort by analysis of "pie slices" of radially symmetric structures with radially symmetric loads, and analysis of "pie slices" provided qualitative information regarding buckling mode geometries when techniques for branching onto bifurcation paths failed. / Master of Science

M.S.

Joining wooden rafters with plywood gusset plates using helically threaded nails to form roof trusses has been widely developed in recent years. Actually, the nailed member has proven to be extremely strong and stiff, but it is not perfectly rigid. The effect of non-rigidity of joints in resisting bending and thrust are investigated in this paper. The purpose of this study is to determine the rotation and slip of truss members relative to plywood gussets which influence the moment, shear, and axial load of each member. Experimental work was conducted on several timber joints in an effort to determine their actual characteristics. The theoretical analysis of relative rotation was based on the assumption that a rafter member is supported by a continuous elastic foundation; i.e. by equally spaced nails. It yields results which are reasonably close to those found experimentally. The Moire Fringe effect was introduced to measure the rotation of the wooden chords relative to the gusset plates of small model joints. A model truss with semi-rigid joints was tested. Strain were measured with SR-4 gages and deflections with dial gages The results were applied full scale designs by model analysis techniques / M.S.

An experimental testing program was conducted to determine the compression member performance in post-buckling region. These results are compared with an analytical computer program developed by Portland State University under Bonneville Power Administration Contract 79-80BP 24005. The paper presents the sensitivity of the performance of single angle compression members to various parameters such as length to radius of gyration ratio, eccentricity, end conditions and yield stress. The effect of local buckling on long member performance is also documented.

The post-buckled performance of cross-braced single angles was experimentally determined. The results of this study will be used by the Bonneville Power Administration for the analysis of member performance in transmission towers.

M. S.

The Astoria-Megler Bridge is a 6.6 kilometer (4.1 mile) long bridge, connecting Oregon and Washington on US 101, with a continuous steel truss main span of 376 m (1232 ft). It is the second longest main span bridge of this type in the world. Due to vortex shedding, some of the long truss verticals exhibit wind-induced torsional vibrations. These vibrations can create large numbers of repeated stress cycles in the truss verticals and the gusset plate assemblies. The members and connections were not designed for such conditions and the impact of this behavior on the service life of the bridge is uncertain. A full-scale representation of one of the truss verticals observed to exhibit such wind induced torsional response was fabricated and tested in the Structural Engineering Research Laboratory at Oregon State University. Experimental data of the rotational behavior and the stress distribution along the vertical were collected using inclinometers, an angular rate sensor, and uniaxial and rosette strain gages. The data collected were compared with existing analytical methods and predictions from finite element models. The observed experimental results including twist angle, stress distribution, and stress magnitude were well captured by both the finite element model and the analytical equations. Using analytical expressions, the fatigue lives of the existing bridge verticals were predicted based on assumed storm duration and recurrence. / Graduation date: 2013