Thesis (M.S.) in Civil Engineering--University of Maine, 2001. / Includes vita. Includes bibliographical references (leaves 226-228 (v. 1)).

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Cast-in-place concrete in composite with steel sections is commonly used in bridge deck constructions. The shear transfer between the concrete and steel section is achieved by shear connectors and the strength calculation of conventional shear connectors, i.e. shear studs, is provided in various design codes in North America. Due to the fact that the strength equation is largely based on experimental results, the applicability of the equation is only warranted where the design matches the experimental configuration of the test specimens. Thus, the codes specify detailing requirement for the stud height and the elevation of the reinforcement mesh in relation to the stud height. However, these requirements, in particular, the elevation of the reinforcement mesh, may be difficult to meet accurately in construction practice. The implications of not meeting the mesh requirement to the strength of the shear stud and the remedy solutions are examined in this study. An experimental program involving the test of thirty-three push-out specimens was designed and conducted with a focus on the shear studs' performance. Testing parameters included reinforcement mesh position, shear stud height, presence of stud head, shear stud spacing, and steel flange surface treatment. In addition, the performance of a new type of shear studs, referred to as adjustable studs, was also studied experimentally. The ultimate load and load vs. slip curves were presented and discussed in the forms of tables and graphs. The failure modes were noted and the relationship between the failure modes and the ultimate capacity was discussed. Ultimate loads obtained from specimens were then used to assess the efficacy of code suggested values. Results showed that depending on the elevation of reinforcement mesh, three failure modes were observed including concrete related failure, combined concrete failure and bent studs and stud shear-off from the steel flange. The elevation of the reinforcement mesh had a significant effect on the ultimate load of the specimen. As the mesh elevation increased from intercepting the stud to being in flush with the top of the stud to above the stud, the ultimate load decreased. Specimens with unheaded shear studs had lower ultimate load than specimens with headed shear studs. Flange treatment had an impact on the ultimate load, where the coating on flanges resulted in a decrease in the ultimate load. Test results also showed that the close placement of the shear studs result in a reduction on the ultimate load when the other parameters were kept the same. In the comparison between conventional and adjustable shear studs, specimens with adjustable studs shared similar failure mode to those with conventional studs, but attained on average lower load capacity. The comparison with the code suggested values showed that the code suggested value is only ensured when double-layer reinforcement mesh is used and placed at code specified elevation. A single layer mesh intercepting the studs resulted in the ultimate load slightly lower than the code value. The code values for adjustable studs are markedly higher than the experimental value, which raises the question whether the code equation for conventional studs is directly transferrable to adjustable studs.

The present study involves analysis and design optimisation of lattice composite structures using symbolic computation. The concept of a homogenised model is used to represent heterogeneous composite isogrid structure as a homogeneous structure with the stiffness equivalent to the original grid structure. A new homogenisation technique is developed and used in the present study. The configuration of a unit cell and the geometrical parameters of the ribs of a composite isogrid cylinder are optimised subject to a strength criterion in order to maximise externally applied loading to provide maximum strength and stiffness of the structure as a whole. The effects of tension and torsion on the optimum design are investigated. Special purpose computation routines are developed using the symbolic computation package Mathematica for the calculation of equivalent stiffness of a structure, failure analysis and calculation of optimum design parameters. The equivalent stiffness homogenisation approach, in conjunction with optimum search routines, is used to determine the optimal values of the design variables. The numerical approach employed in the present study was necessitated by the computational inefficiency and conventional difficulties of linking the optimiser and the FEM analysis package for calculating the stress resultants used in the optimisation process. These drawbacks were successfully overcome by developing special purpose symbolic computation routines to compute stress resultants directly in the program using a new homogenisation approach for the model with equivalent stiffness. In the design optimisation of cylindrical isogrids the computational efficiency of the optimisation algorithm is improved and good accuracy of the results has been achieved. The investigation on the basis of failure analysis shows that the difference in the value of the maximum load applied to the optimal and non-optimal isogrid structure can be quite substantial, emphasising the importance of optimisation for the composite isogrid structures. The computational efficiency of optimisation algorithms is critical and therefore special purpose symbolic computation routines are developed for its improvement. A number of optimal design problems for isogrid structures are solved for the case of maximum applied load design. / Thesis (Ph.D.)-University of Natal, Durban, 2000.

The present study involves the analysis and design optimisation of composite structures using analytical and numerical methods. Five different problems are considered. The first problem considers the design of laminated plates subject to non-uniform temperature distributions. The plates are optimised for maximum buckling temperature using the fibre angle as the optimising variable. The method of solution involves the finite element method based on Mindlin theory for thin laminated plates and shells, and numerical optimisation. A computational approach is developed which involves successive stages of solution for temperature distribution, buckling temperature and optimal fibre angle. Three different temperature loadings are considered and various combinations of simply supported and clamped boundary conditions are studied. The effect of plate aspect ratio on the optimal fibre angle and the maximum buckling temperature is investigated. The influence of bending-twisting coupling on the optimum design is studied by considering plates with increasing number of layers. The second problem concerns the optimal design of composite pressure vessels. Finite element solutions are presented for the design of hemispherically and flat capped symmetrically laminated pressure vessels subjected to external pressure. The effect of vessel length, radius and wall thickness, as well as bending-twisting coupling and hybridisation on the optimal ply angle and buckling pressure are numerically studied. Comparisons of the optimal fibre angles and maximum buckling pressures for various vessel geometries are made with those for hybrid pressure vessels. In the third problem, the multiobjective design of a symmetrically laminated shell is obtained with the objectives defined as the maximisation of the axial and torsional buckling loads. The ply angle is taken as the optimising variable and the performance index is formulated as the weighted sum of individual objectives in order to obtain Pareto optimal solutions of the design problem. Single objective design results are obtained and compared with the multiobjective design. The effect of weighting factors on the optimal design is investigated. Results are given illustrating the dependence of the optimal fibre angle and performance index on the cylinder length, radius and wall thickness. In the fourth problem, the optimal layup with least weight or cost for a symmetrically laminated plate subject to a buckling load is determined using a hybrid composite construction. A hybrid construction provides further tailoring capabilities and can meet the weight, cost and strength constraints while a non-hybrid construction may fail to satisfy the design requirements. The objective of the optimisation is to minimise either the weight or cost of the plate using the ply angles, layer thicknesses and material combinations as design variables. As the optimisation problem contains a large number of continuous (ply angles and thicknesses) and discrete (material combinations) design variables, a sequential solution procedure is devised in which the optimal variables are computed in different stages. The proposed design method is illustrated using graphite, kevlar and glass epoxy combinations and the efficiency of the hybrid designs over the non-hybrid ones are computed. Finally, the minimum deflection and weight designs of laminated composite plates are given in the fifth and last problem. The finite element method is used in conjunction with optimisation routines in order to obtain the optimal designs, as was the procedure in the first problem. Various boundary conditions are considered and results are given for varying aspect ratios and for different loading types. / Thesis (Ph.D.)-University of Natal, Durban, 1996.

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This thesis investigates the behaviour of hollow and concrete filled steel columns fabricated from thin steel plates. The columns are investigated under axial, uniaxial and biaxial loading. The currently available international standards for composite structures are limited to the design of concrete filled steel columns with compact sections and yield stress of steel up to 460 N/mm2. This thesis consists of both experimental and analytical studies and design recommendations for future use. Three comprehensive series of experimental tests are conducted on hollow and concrete filled steel columns. The principal parameters that have been considered in the test programmes are the slenderness of the component plates, the yield stress of the steel and the loading conditions. In the first test series, three slender hollow steel columns and three slender composite columns are tested under uniaxial loading. The steel utilised is mild steel. High strength steel is utilised in the second test programme. In this test series four stub columns, eight short columns and eight slender columns are tested, each set consists of four hollow and four composite columns. Short columns are tested under axial loading to investigate the confinement effect provided by the steel casing. Slender columns are tested under uniaxial loading to investigate the coupled instability of local and global buckling. The third test programme is quite novel and considers the behaviour of hollow and concrete filled steel columns fabricated with high strength structural steel plate and subjected to biaxial bending. In this test eight short columns and ten slender columns each of them consisting of hollow and composite columns are investigated under biaxial loading. Analytical models are developed herein to elucidate the behaviour of the hollow and composite columns considering cross section slenderness, yield stress and loading conditions. An iterative model considering the coupled global and local buckling in the elastic and plastic range incorporating material nonlinearities is developed to investigate the behaviour of slender columns fabricated from mild steel. An improved deformation control model is developed to investigate the behaviour of slender high strength steel columns considering the confinement effect and local and post-local buckling in the elastic and plastic range. Then a numerical model for biaxial bending is developed to study the behaviour of short and slender concrete filled high strength steel columns under biaxial loading incorporating interaction buckling considering material and geometric nonlinearities. The scope of the thesis presents a wide range of experimental and theoretical studies of an extremely novel nature. It demonstrates the benefit of confinement and the consideration of local and post-local buckling in the elastic and plastic range. It is hoped that this research will contribute to the area of composite steel-concrete structural applications.

Thesis (Ph. D.)--University of Missouri--Rolla, 2007. / Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed November 15, 2007) Includes bibliographical references.

Thesis (Ph. D.)--University of Missouri-Columbia, 1997. / Typescript. Vita. Includes bibliographical references (leaves 223-229). Also available on the Internet.