Master of Science / Department of Architectural Engineering and Construction Science / Sutton F. Stephens / Trusses have been a common structural system for hundreds of years. The design and analysis of trusses evolved over time to its current state. Most manual truss analyses use the methods of joints and sections under idealized conditions. These ideal conditions, including pinned connections, cause discrepancies between the ideal truss being analyzed and the actual truss being constructed. The discrepancies include joint rigidity, connection eccentricity, and transverse loading. These cause secondary stresses, which induce bending moment into the truss members due to the chord’s continuity. Secondary stresses are most severe in continuous compression chord members. In these members, secondary stresses should be addressed to determine if they are severe and should be included in the truss design, or if idealized analysis will suffice. This report aims to determine the variables that affect the magnitude of secondary stresses in continuous compression chords due to chord continuity. The variables considered are chord stiffness, truss depth, and chord efficiency. Pratt trusses with WT chords were analyzed using the commercial analysis software RISA 3D. Pinned and continuous chord trusses were compared using the interaction value for each chord member. The results were used to determine how these variables affect secondary stresses and how secondary stresses can be predicted. Evaluation criteria were examined to determine the severity of secondary stresses. These criteria examine the radius of gyration, moment of inertia, depth, and section moduli of the chord members, and the moment of inertia of the truss for determination of secondary stress severity. The results of the studies show that secondary stresses increase with increasing member stiffness, decreasing member efficiency, and decreasing truss depth. The necessity for secondary stress consideration can be determined most accurately using the radius of gyration criterion (L/r[subscript]x < 50) for the compression chord.

Thesis (C.E.)--Lehigh University, 1877. / Caption title. Also available online.

Thesis (M.S.)--Oregon State University, 2009. / Printout. Includes bibliographical references (leaves 43-44). Also available on the World Wide Web.

Yes / The aim of this article is to apply and improve the species-conserving genetic algorithm (SCGA) to search multiple solutions of truss topology optimization problems in a single run. A species is defined as a group of individuals with similar characteristics and is dominated by its species seed. The solutions of an optimization problem will be selected from the found species. To improve the accuracy of solutions, a species mutation technique is introduced to improve the fitness of the found species seeds and the combination of a neighbour mutation and a uniform mutation is applied to balance exploitation and exploration. A real vector is used to represent the corresponding cross-sectional areas and a member is thought to be existent if its area is bigger than a critical area. A finite element analysis model was developed to deal with more practical considerations in modelling, such as the existence of members, kinematic stability analysis, and computation of stresses and displacements. Cross-sectional areas and node connections are decision variables and optimized simultaneously to minimize the total weight of trusses. Numerical results demonstrate that some truss topology optimization examples have many global and local solutions, different topologies can be found using the proposed algorithm on a single run and some trusses have smaller weights than the solutions in the literature.

This thesis discusses the optimization of non-periodic open structure continuous-fibre PMFRC parts where yarns extend along 3D paths that maximize the specific structural performance of the resulting part for specific load cases. The work focuses on optimizing the geometry of dry yarn structures using steepest ascent (SA) methods and calculating structural performance of the resulting PMFRC parts using finite element analysis (FEA).

The Long Term Bridge Performance (LTBP) program is an organization within the Federal Highway Administration that inspects, tests, analyzes, and observes, for an extended period of time, a variety of bridge types throughout the United States. Part of the program includes periodic testing of select bridges of a span of 20 years. The Kettle River Bridge located outside of Sandstone, Minnesota was selected for study due to its unique design. The Kettle River Bridge is a historical steel cantilevered deck arched Pratt truss bridge. The bridge was instrumented with 151 strain gauges on various floor and truss members along with eight displacement gauges strategically placed along the truss. All gauges were read simultaneously as the bridge underwent non-destructive live loading. The recorded gauge readings were analyzed to determine bridge behavior and then used in the assistance of calibrating a working finite-element model. After a working model was verified the distribution factors for the interior and exterior floor stringers were determined. By using the controlling distribution factor, a load rating for the bridge was determined for both inventory and operating. The distribution factors and load ratings determined using the working finite-element model were then compared to the AAHSTO LRFD specifications.

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Master of Science / Department of Architectural Engineering and Construction Science / Kimberly W. Kramer / This report is designed to be a valuable tool for any engineer who has had proper instruction in load paths and knowledge of structural steel design but is not familiar with truss systems and has never designed a long-span steel truss. In other words, for someone who knows the math and concepts but not the means, methods, and practical limitations of truss design. By applying their knowledge of engineering concepts and some good judgment with the information in this report they will be able to design an efficient truss. The type of truss considered has a span of 100’ to 200’, is parallel chord, one-way, simply spanned, and constructed of steel. The trusses are evaluated for typically gravity loading and analyzed in two dimensions. Aspects from analysis, layout, fabrication, erection, and transportation are investigated to find ideal methods of design and practical limitations for this type of truss. Once this information is learned it can be to be applied to an individual truss on an individual basis. Engineers need to realize that even though a truss could be designed with the most efficient use of steel it may not be the most economic solution. One must also realize too many variables are present to form rules or equations to always yield the perfect truss. Only by coupling proper design and analysis with knowledge of fabrication and erection will one be able to design an efficient truss.

The stability bracing behavior of trusses was investigated using experimental testing and computational modeling. The laboratory experiments were conducted on twin trusses fabricated with W4x13 sections for the chord and web members. Spans of 48 and 72 feet were used in the tests that included both lateral load tests and buckling tests. Most of the tests were done on the regular (Howe) truss, except the lateral stiffness tests which were also done on the inverted (Pratt) truss. Computational models were developed using the three-dimensional finite element program, ANSYS, which were validated using the laboratory test data. A variety of models were used to simulate both as-built and idealized truss models. The experiments demonstrated that the buckling capacity of the truss with torsional bracing largely depended on the brace stiffness and the number of intermediate braces. Similar behavior was observed in the truss with lateral bracing. The tests results demonstrated that cross sectional distortion dramatically reduces the effectiveness of the torsional braces. The experiments provided valuable data for validating the finite element models that were used to conduct parametric studies on torsional bracing of truss systems. The results from the parametric studies were used to develop stiffness requirements for torsional bracing of trusses. / text

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