This thesis presents elastic-plastic finite element analyses of seven long span composite open-web steel joists. These analyses account for the incomplete interaction between the concrete slab and the steel joist by modeling the nonlinear behavior of the steel shear connectors. Experimental tests on long span composite open-web steel joists were performed at Virginia Polytechnic Institute and State University. Measurements of joist deflections, member strains, and slip between the concrete slab and steel joist were recorded. The response of the finite element models agree reasonably well with the response of the test prototypes where the shear connector position was known. The finite element model can be generated on any general purpose finite element program that includes beam elements and nonlinear spring elements. The finite element model can give reasonable predictions of deflections and ultimate load capacity of a composite open-web steel joist. / Master of Science

A strength of materials type solution is obtained for the shear stress state in the adhesive layer of a bonded cantilever beam subjected to an end load. The shear stress is constant through the thickness of the adhesive layer and varies from zero at the fixed end to a maximum value at the free end. This maximum value can, under certain conditions, be calculated from knowledge of the load and the beam geometry only. The adhesive's shear modulus can then be determined from a measurement of the shear strain in the adhesive layer. An expression for the beam deflection is also obtained. It contains a coefficient of adhesion which is potentially useful to evaluate surface treatments or other factors leading to different states of adhesion. Fracture mechanics application of the specimen, nonlinear and viscoelastic adhesive behavior are briefly mentioned. / Master of Science

In this study two one-dimensional finite element formulations based on higher-order displacement models have been developed. Both theories account for geometric nonlinearities, a parabolic shear strain distribution through the thickness, and satisfy the shear stress free boundary conditions at the upper and lower surfaces of the beam. The theories also account for the bend-stretch, shear-stretch, and bend-twist couplings inherent to generally laminated composite beams. Further, a coupling between the shear deformation and the twisting is introduced. The lateral strains are assumed nonzero and retained in the formulation. The first model termed SVHSDT also accounts for the continuity of the interlaminar shear stresses at the layer interfaces, while keeping the number of degrees of freedom independent of the number of layers. This theory though is restricted to the analysis of symmetrically laminated cross-ply beams. The formulation has been applied to the linear static and free vibration analysis. The second model termed RHSDT is valid for generally laminated beams. This model has been applied to the nonlinear static and transient analysis of generally laminated beams, free vibration analysis, and impact analysis. The effect of axial stresses on the nonlinear transient response has also been investigated using this theory. For generally laminated beams the lateral strains and the shear-twist coupling were found to have a significant effect on the vibrations frequencies. Also, as expected, initial stresses, boundary conditions and the lamination scheme were found to have a significant effect on the nonlinear responses. / Master of Science

To better understand the behavior of composite beams in buildings, push-out tests were conducted to study the behavior of welded shear studs. Forty-eight solid slab push-out tests were conducted to study how stud tensile strength and concrete properties affect the strength of shear connections. It is shown that raising the tensile strength of a shear connector actually has an adverse effect on the connector's performance and strength. It is also shown that the upper limit for shear strength used in the current AISC specification (Load 1993) is unconservative and a lower upper limit is proposed. Eighty-seven pushout tests utilizing steel deck were also conducted. It is shown how the placement, height, and arrangement of shear studs, as well as the height and gage of steel deck affects the strength of shear connections when stiffened steel deck is used. It is shown that the current AISC specification is unconservative and does not account for the many failure mechanisms associated with connections using steel deck. It is shown how tension within the stud shank, friction at the slab/beam interface, and steel deck strength affect the strength of shear connections. / Master of Science

In this work, methods for rapid analysis and design of composite curved C-section frames subjected to axial tensile loading are developed. Failure is predicted using polynomial in-plane and interlaminar failure criteria. Interlaminar stresses can be directly computed only from three-dimensional finite element models, but the computational expense of these models is prohibitive. Therefore, approximate two-dimensional analysis methods are used here to predict interlaminar stresses in the curved corner regions between the web and flanges and at the free edges of the flanges. A response surface design approach is used to approximate the failure response using a minimum number of finite element analyses. Large degree of freedom 2D/3D global/local finite element models are selectively used in conjunction with the smaller 2D shell element models in the design process to improve the response surface polynomials. This combined use of simple and complex analyses is known as variable complexity modeling. Two design case studies are conducted, one with two design variables and one with five design variables. Three different objective function formulations are used in the two design variable case, minimum weight, maximum strength, and combined minimum weight and maximum strength. Only the minimum weight formulation is used in the five design variable case due to the complexity of the design space. The design studies demonstrate the accuracy and efficiency of the proposed approach. / Master of Science

The stresses and deformations in cross-ply composite tubes subjected in circumferential temperature gradients are studied. The motivation behind the study is the anticipated use of composite tubes in space structures where the tube is exposed to the heat of the sun on one side and the cryogenic temperatures of space on the other. Experiments were performed to measure the functional form of the temperature gradient and the displacements. It was found that the form of the temperature gradient, T(Ɵ), can accurately be represented by T(Ɵ) = A + BcosƟ¸ and that the displacement of the tube is parabolic in the axial coordinate. Two types of analytical solutions were developed: an exact elasticity U solution and an approximate solution. The approximate solution includes a linear variation of the material properties with temperature and uses the principle of complementary virtual work in conjunction with a Ritz approximation on the stress field. The elasticity solution predicts that high tensile stresses could crack the matrix. The effect of including temperature-dependent material properties is to reduce the circumferential dependency of the stresses. / Master of Science

The increasing use of laminated composites in moving structures such as aircraft has led to a need for an efficient and accurate procedure for performing transient bending analysis of laminated composite plates. Classical theory is inadequate because it neglects transverse shear deformation, rotatory inertia, and geometric nonlinearities. In this thesis, a theory to account for transverse shear deformation and rotatory inertia is combined with the von Karman theory of geometric nonlinearities to develop the nonlinear governing equations of laminated composite plate bending. A finite element program is developed to solve these equations, using the Newmark direct integration technique to integrate the equations in time. Apparently, this constitutes the first transient finite-element analysis of laminated composite plate bending which accounts for transverse shear deformation, rotatory inertia, and geometric nonlinearities. The program accuracy is verified by comparison with results previously reported in the literature. Finally, results of a study of various material and plate geometry parameters are presented. The results of the parametric study show that transverse shear deformation, rotatory inertia, and geometric nonlinearity may all have a profound effect on the predicted bending response. In addition, the effects of material orthotropy, plate aspect ratio, plate thickness, lamination scheme, and load magnitude are shown to be significant. Computational constants such as the Newmark coefficients, the time-step size, and the element mesh are also investigated, and appropriate observations are made on the computational aspects of the program. / Master of Science

Studies on the effective moment of inertia of girders that support concrete slabs using joist seats as the horizontal shear connections, and a cost efficiency analysis comparing composite and non-composite floor systems that meet vibrations design standards, were conducted. The first study was undertaken because over-prediction of girder effective moment of inertia was the suspected cause of several recent vibration problems in floors supported by widely spaced LH-series joists. Eight purpose-built floors of the type in question were subjected to experimental tests of girder effective moment of inertia and girder frequency. Frequencies were tested for two live loading cases. Three separate test configurations were made with each floor by changing the seat-to-girder connections between bolted, welded, and reinforced. In the study, 1) the accuracy of the current design practice is assessed, 2) a new relationship was proposed, and 3) suggestions for finite element modeling are made. In recent years, composite construction has been used to improve cost efficiency by reducing structural weight and in some cases by reducing story height. However, vibration problems are a design consideration in composite floors because lighter floors tend to be more lively. It is not clear if cost savings can be made with composite construction if vibrations are considered in the design. To compare the cost of composite and non-composite floors that satisfy AISC/CISC Design Guide criterion for walking excitation, four typical size bays were analyzed using commercial design software that finds the least expensive member configuration for a given bay size. All acceptable bay configurations of member sizes and spacing were evaluated for least non-composite and composite costs, then these results were compared. The findings show that composite construction can be more economical when initial dead load deflections do not control the design. / Master of Science

The nonlinear behavior of continuous-fiber-reinforced metal-matrix composite structures is examined using a micromechanical constitutive theory. Effective lamina and laminate constitutive relations based on the Aboudi micromechanics theory are presented. The inelastic matrix behavior is modeled by the unified viscoplasticity theory of Bodner and Partom. The laminate constitutive relations are incorporated into a first-order shear deformation plate theory. The resulting boundary value problem is solved by utilizing the finite element method. · Computational aspects of the numerical solution, such as the temporal integration of the inelastic strains and the spatial integration of bending moments are addressed. Numerical results are presented which illustrate the nonlinear response of metal matrix composites subjected to extensional and bending loads. Experimental data from available literature are in good agreement with the numerical results. / Ph. D. / incomplete_metadata

Thesis (MScEng (Civil Engineering))--Stellenbosch University, 2008. / Introduction South Africa is currently experiencing a significant increase in infrastructure investment. Forecasts by BMI-BRSCU have shown that the building and construction industry is expected to grow considerably to 2010, before languishing slightly to 2015. This growth will be driven in particular by investment in non-residential building (41% growth) and construction (73% growth) activities. Even beyond 2015 however, the demand will still be high on the construction industry to provide infrastructure for South Africa’s growing population. South Africa is also facing a serious shortage of engineers, technicians and other skilled workers in the construction industry. This places high demands on designers and contractors to provide services and to realise projects in ever-reducing time periods and at less cost. These conditions have made it increasingly difficult to maintain the required quality of construction in an industry where mistakes can lead to disastrous consequences. Recent advances in structural materials, structural systems and the way in which projects are handled, now enables a new look at the possibilities of combining pre-fabrication with on site work. This method, known as Hybrid Concrete Construction (HCC), has the potential to revolutionize the South African construction industry if applied correctly. Local research into this technique is however required and it is the aim of this thesis to draw attention to this subject. Key Findings Hybrid Concrete Construction (HCC) can be applied to any structural project, it will however not necessarily be successful. A structure needs to be adapted from the very start to suit a particular construction method. This ensures that all the advantages of the selected construction method may be achieved. Adapting a structure to a different construction method requires a mutual understanding and commitment from all project participants, including the architect, engineer, contractor and client. HCC also requires a certain degree of repetition in a project to be financially viable. A theoretical cost exercise was performed where only the material and erection costs were considered. In this exercise, HCC was found to be slightly less expensive than other construction methods for the Office Building of more than 10 storeys. HCC was also found to be significantly faster than other construction methods for the Office Building of more than 3 storeys. The time calculation was however based on the simplified time estimates from one source. Because of HCC’s shorter estimated construction period, the client can expect to earn revenue from a much earlier date. This decreases the relative cost of a HCC project. This advantage, however, needs to be quantified for chosen South African projects. On-site safety is still an important issue with HCC projects. Labourers are not accustomed to this construction method and it may be necessary to alter current skill development programs to include a crane safety course. The training of qualified riggers and crane operators should receive priority if HCC is to develop in South Africa. This preliminary investigation has shown that Hybrid Concrete Construction (HCC) can be feasible for the South African market. Further investigation is however required to determine the parameters for which HCC would be the preferred construction method. Recommendations Based on the findings and conclusions of this investigation, the following recommendations are made. The following actions should be undertaken by individual South African companies: · Develop relationships with external project partners · Train competent riggers and crane operators The South African concrete industry should invest in the following actions: · Invest in mass-producing precast concrete facilities · Develop a central database of South African projects with information on time, costs, project concepts and layouts to be used as a guideline for decision making · Develop local guidelines for the production and application of self compacting concrete · Compile guidelines for the design and construction of HCC and precast concrete construction in South Africa · Develop a local hidden corbel type connection to its full potential