| This dissertation examines the behavior of, and presents a design and analysis method for, a queenpost beam-truss structure constructed of glass fiber-reinforced plastic (FRP) and prestressed using a Kevlar;The queenpost beam-truss geometry was effective in overcoming the problem of low elastic modulus, as the beam-trusses were about 15 times stiffer, and over 6 times stronger, than the beams alone. Additional strength is possible, since failures occurred in the connections, not the main elements. Connection design is found to be important, since the lack of plasticity in FRP means that no redistribution of loads can occur. Second-order forces in the main beam were significant, especially at high loads. The system was inefficient in carrying highly unsymmetrical loads, due to the absence of a positive connection between the cable and the posts.;Line element finite element models utilizing nonlinear, large deflection capabilities were used to analyze the queenpost beam-truss alone and as part of a frame. Predictions and tests correlated well.;A classical method was developed for the in-plane analysis of a single queenpost beam-truss under symmetrical loads. The non-iterative method takes second-order forces into account in the main beam only. Comparison with experimental results was good. Methods of estimating in-plane forces due to unsymmetrical loads are also presented.;A preliminary lateral-torsional stability analysis was made of multiple queenpost beam-trusses braced against each other continuously (by a bridge deck for example). The beam-trusses are so flexible out-of-plane that they practically buckle under their own weight. The deck shear stiffness was found to be more important than the bending stiffness, but a combination of both was most effective in providing bracing.;A step-by-step method is presented for prestressed single queenpost beam-truss design. A method of approximating the design forces for initial member sizing is given. Using the more accurate analysis method developed, the design can be finalized with one or two iterations. |
