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.

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.

Fibre composite materials are gaining recognition in civil engineering applications as a viable alternative to traditional materials. Their migration from customary automotive, marine, aerospace and military industries into civil engineering has continued to gain momentum over the last three decades as new civil engineering applications develop. The use of fibre composite materials in civil engineering has now evolved from non-structural applications, such as handrails and cladding, into primary structural applications such as building frames, bridge decks and concrete reinforcement. However, there are issues which are slowing the use of fibre composite materials into civil engineering. Issues include high costs, difficulties in realising potential benefits, general lack of civil engineers' familiarity with the material and relatively little standardisation in the composites industry. For composites to truly offer a viable alternative to traditional construction materials in the civil engineering marketplace, it is essential that these issues be addressed. It is proposed that this situation could be improved by demonstrating that potential benefits offered by composites can be achieved with familiar civil engineering forms. These forms must be well suited to fibre composite materials and be able to produce safe and predictable civil engineering structures with existing structural engineering methods. Of the numerous structural forms currently being investigated for civil engineering applications, the truss form appears particularly well suited to fibre composites. The truss is a familiar structural engineering form which possesses certain characteristics that make it well suited to fibre composite materials. In this research a novel monocoque fibre composite truss concept was developed into a working structure and investigated using analytical and experimental methods. To the best of the author's knowledge the research presented in this thesis represents the first doctoral research into a structure of this type. This thesis therefore presents the details of the development of the monocoque fibre composite (MFC) truss concept into a working structure. The developed MFC truss was used as the basis for a detailed investigation of the structural behaviour of the MFC truss elements and the truss as a whole. The static structural behaviour of the principal MFC truss elements (tension members, compression members and joints) was investigated experimentally and analytically. Physical testing required the design and fabrication of a number of novel test rigs. Well established engineering principles were used along with complex finite element models to predict the behaviour of the tested truss elements and trusses. Results of the theoretical analysis were compared with experimental results to determine how accurately their static structural behaviour could be predicted. It was found that the static structural behaviour of all three principal truss elements could be accurately predicted with existing engineering methods and finite element analysis. The knowledge gained from the investigation of the principal truss elements was then used in an investigation of the structural behaviour of the MFC truss. Three full-scale MFC trusses were fabricated in the form of conventional Pratt, Howe and Warren trusses and tested to destruction. The investigation included detailed finite element modelling of the full-scale trusses and the results were compared to the full-scale test results. Results of the investigation demonstrated that the familiar Pratt, Howe and Warren truss forms could be successfully manufactured with locally available fibre composite materials and existing manufacturing technology. The static structural behaviour of these fibre composite truss forms was accurately predicted with well established engineering principles and finite element analysis. A successful marriage between fibre composite materials and a civil engineering structure has been achieved. Monocoque fibre composite trusses have been developed in the familiar Pratt, Howe and Warren truss forms. These structures possess characteristics that make them well suited to applications as primary load bearing structures.