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.

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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

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.

The purpose of this study is to investigate the static and dynamic stability of an elastic truss model. The truss model· is subjected, separately, to static loads, dynamic step loads, and dynamic impulse loads. For each loading, the results are presented in the form of stability boundaries and displacement criteria. For the static loading, the stable equilibrium displacement fields are determined by minimizing the energy of the model. The type of failure, limit or bifurcation, and the critical load magnitudes, are determined based on plots of load-frequency curves. For the dynamic loadings, the magnitudes of the critical load are based on the criterion presented by Budiansky and Roth. The stability boundaries for the static loading and the dynamic step loading are compared. It is found that the static critical load values are three to seven times the magnitude of the dynamic step critical loads. It is found that the truss model shows a local and global failure for a certain class of loading. The magnitudes of the critical loads for local instability are significantly less than the magnitudes of the critical loads for global instability when the loading is symmetric or near symmetric. It is found that the critical load magnitudes for a symmetric loading are much larger than for an asymmetric loading. Constant displacement curves (based on displacement constraints for the truss model) are also presented. These results are helpful in indicating loading configurations to which the response of the truss model is sensitive. / 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.

This study utilizes state of the art information concerning roof truss behavior to simulate the effect of strength property correlations on roof truss reliability. Also, research efforts to define lumber property correlations are summarized. Computer models were constructed to simulate the behavior of five common roof truss patterns. The patterns studied were the Fink, double W, triple W, triple W farm, and flat Howe trusses. Monte Carlo simulation, based on 50,000 trials, was used to calculate probabilities of failure for each truss pattern, and level of strength property correlation. The simulated trusses were subjected to a 50 year maximum lifetime snow load distribution plus a dead load distribution. Bending, tensile, and compressive strength properties were modeled by a weighted least squares regression analysis. Modulus of elasticity was used as the independent strength predictor, and was modeled by a Weibull distribution. The residual strength correlations in the regression models were varied between simulations from 0.0 to 0.9. Member stresses were calculated using a pin joint analysis modified by load factors derived from the Purdue Plane Structures Analyzer. Truss failure was determined by a weakest link analysis which used failure criterion developed from current truss design equations. The influence of lumber property residual correlations on roof truss reliability was defined. The probability of failure increased as the levels of correlation increased, but the difference in magnitudes were considered insignificant. Also, the ratio of snow to dead load was found to be affect wood truss reliability. / 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