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The objective of this research is to develop a flexible design grammar and genetic algorithm representation to be used in a multi-objective optimization method to design efficient steel roof trusses given space dimensions and loading requirements by the user. The goal of implementing the method as a multi-objective problem is to obtain a set of near-optimal trusses for the defined unstructured problem domain, not just a single near-optimal design. The method developed was required to support the exploration of a broad range of conceptual designs before making design decisions. Therefore, a method was developed that could define numerous design variables, support techniques to locate global or near-global optimal designs, and improve the efficiency of the computational procedures implemented. This research effort was motivated by the need to consider structural designs that may be beyond the established conventions of designers in the search for cost-efficient, structurally-sound designs. An effective design grammar that is capable of generating stable trusses is defined in this research. The design grammar supports the optimization of member size, in addition to truss geometry and topology. Multi-objective genetic algorithms were used to evolve sets of Pareto-optimal trusses that had varying topology, geometry, and member sizes. The Pareto-optimal curves provided design engineers with a range of near-optimal design alternatives that showed the tradeoffs that occur in meeting the stated objectives. Designers can select their final design from this set based on their own individual weighting of the design objectives. Trials are performed using a multiobjective genetic algorithm that works with the design grammar to evolve trusses for different span lengths. In addition to evaluate the performance of the developed optimization method further, trials were performed on a benchmark truss problem domain and the results obtained were compared with results obtained by other researchers. The results of the performance evaluation trials for the proposed method, in which the sizing, shape and topology were simultaneously performed, indicated that the method was effective in evolving a variety of truss topologies compared to previous published results, which evolved from a ground structure. The diverse topologies, however, were obtained over several trials instead of being found in a Pareto-optimal set found by a single trial. In addition, the proposed method was not able to locally optimize the member section sizes. Additional trials were performed to determine the benefit of applying local optimization to the member section sizes for a given truss topology or geometry provided by the method. The results indicate that significant weight reduction could be achieved by performing local optimization to the truss designs obtained by the proposed multi-objective optimization method.

Thesis (M.S.)--Oregon State University, 1999. / Typescript (photocopy). Includes bibliographical references (leaves 124-129). Also available online.

Thesis (MScIng)--University of Stellenbosch, 2008. / Bibliography. Also available via the Internet.

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

Thesis (Professional Degree)--University of Missouri, School of Mines and Metallurgy, 1930. / The entire thesis text is included in file. Typescript. Illustrated by author. Title from title screen of thesis/dissertation PDF file (viewed October 12, 2009)

Metal plate splice joints with gaps between butting pieces of lumber were tested in compression to evaluate the effect of gap size on joint serviceability performance. The current design methodology for compression splice joints was also evaluated. Specimens representing floor and roof trusses, with 16 and 20 gauge plates of staggered and aligned tooth configurations were tested for each of two gap sizes. Generally, 20 gauge plates and 16 gauge plates with 1/8” gaps buckled under compression loads while 16 gauge plates with 1/16" maximum gap did not buckle before the gap closed; rather, the gap closed primarily due to slippage between the teeth and the wood. 16 gauge plates generally outperformed 20 gauge plates based on serviceability performance of the test compression splice joints. Furthermore, gap size had less of an influence on joints with 16 gauge plates than on joints with 20 gauge plates. The current practice of sizing plates for compression splices to withstand one-half of the calculated chord force could not be physically confirmed using the study joint serviceability criteria. The test results indicate that basing allowable plate ratings on a per area basis derived from tension tests is misleading. / Master of Science

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Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Civil Engineering, 1980. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Vita. / Includes bibliographical references. / by Pierre Hernando Montauban. / M.S.

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.