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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

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 thesis presents a research project aimed at advancing the treatment of cold-formed steel (CFS) structural reliability in roof trusses. Structural design today relies almost exclusively on component-level design, so structural safety is assured by limiting the probability of failure of individual components. Reliability of the entire system is typically not assessed, so in a worst-case scenario the system reliability may be less than the component reliability, or in a best-case scenario the system reliability may be much greater than the component reliability. A roof truss itself, is a subsystem with several possible failure modes that are being studied in this test program. These trusses are constructed of CFS members that nest with one another at the truss nodes and are connected by drilling fasteners through the mated surfaces, as well as having steel sheathing fastened to the top chords for lateral bracing. Presented in this paper is a series of full-scale static tests on single cold-formed steel roof trusses with a unique experimental setup. The test specimens were carefully monitored to address multiple failure modes: buckling of the top chord, buckling of the truss webs, and any connection failures. This research includes the experimental results, the computed system reliability of the trusses as well as their relationship between the components reliability.

M. S.