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Thesis (M.S.)--Rochester Institute of Technology, 1993. / Typescript. Includes bibliographical references (leaves 100-102).

Thesis (MTech (Mechanical Engineering))--Peninsula Technikon, Cape Town,1999 / Smart structures technology featuring a network of sensors and actuators, real-time control capabilities, computational capabilities and host material will have tremendous impact upon the design, development and manufacture of the next generation of products in diverse industries. The idea of applying smart materials to mechanical and structural systems has been studied by researchers in various disciplines. Among the promising materials with adaptable properties such as piezoelectric polymers and ceramics, shape memory alloys, electrorheological fluids and optical fibers, piezoelectric materials can be used both as sensors and actuators because of their high direct and converse piezoelectric effects. The advantage of incorporating these special types of material into the structure is that the sensing and actuating mechanism becomes part of the structure by sensing and actuating strains directly. This advantage is especially apparent for structures that are deployed in aerospace and civil engineering. Active control systems that rely on piezoelectric materials are effective in controlling the vibrations of structural elements such as beams, plates and shells. The beam as a fundamental structural element is widely used in all construction. The purpose of the present project is to derive a set of approximate governing equations of smart composite beams. The approximate analytical solution for laminated beams with piezoelectric laminae and its control effect will be also presented. According to the review of the related literature, active vibration control analysis of smart beams subjected to an impulsive loading and a periodic excitation are simulated numerically and tested experimentally.

An optimization system based on the finite element code CSM Testbed and the optimization program ADS is described. The optimization system can be used to obtain minimum-weight designs of composite stiffened structures. Ply thicknesses, ply orientations, and stiffener heights can be used as design variables. Buckling, displacement, and material failure constraints can be imposed on the design. The system is used to conduct a design study of geodesically stiffened shells. For comparison purposes, optimal designs of unstiffened shells and shells stiffened by rings and stringers are also obtained. Trends in the design of geodesically stiffened shells are identified. An approach to include local stress concentrations during the design optimization process is then presented. The method is based on a global/local analysis technique. It employs spline interpolation functions to determine displacements and rotations from a global model which are used as "boundary conditions" for the local model. The organization of the strategy in the context of an optimization process is described. The method is validated with an example. / Ph. D.

No / Precast concrete hollow core floor units (hcu) are widely used in all types of multistorey steel framed buildings where they bear onto the top flanges of universal beams. The steel beam is normally designed in bending, in isolation from the concrete slab, and no account is taken of the composite beam action available with the precast units. A program of combined experimental and numerical studies was undertaken that aimed at deciding on a suitable approach for the design of composite steel beams that utilize precast concrete hollow core slabs. The results show that the precast slabs may be used compositely with the steel beams in order to increase both flexural strength and stiffness at virtually no extra cost, except for the headed shear studs. For typical geometry and serial sizes, the composite beams were found to be twice as strong and three times as stiff as the equivalent isolated steel beam. The failure mode was ductile, and may have been controlled by the correct use of small quantities of tie steel and insitu infill concrete placed between the precast units.

This article reviews the design and behaviour of composite beams with precast hollow core slabs in multi-storey buildings for gravity loading. A brief history of composite construction and introduction to precast¿composite construction is given, followed by an overview of recent research work on various factors affecting the design. This includes the push-off test procedure, the load¿slip characteristic of the headed shear studs and the design procedures for this type of construction. Finite element modelling of the headed stud shear connectors and the composite beams with precast hollow core slabs are presented. Finally, recommendations and future research work is also suggested.

Layerwise finite element analyses of geodesically stiffened cylindrical shells are presented In this work. The layerwise laminate theory of Reddy (LWTR) is developed and adapted to circular cylindrical shells. The Ritz variational method is used to develop an analytical approach for studying the buckling of simply supported geodesically stiffened shells with discrete stiffeners. This method utilizes a Lagrange multiplier technique to attach the stiffeners to the shell. The development of the layerwise shells couples a one-dimensional finite element through the thickness with a Navier solution that satisfies the boundary conditions. The buckling results from the Ritz discrete analytical method are compared with smeared buckling results and with NASA Testbed finite element results. The development of layerwise shell and beam finite elements is presented and these elements are used to perform the displacement field, stress, and first-ply failure analyses. The layerwise shell elements are used to model the shell skin and the layerwise beam elements are used to model the stiffeners. This arrangement allows the beam stiffeners to be assembled directly into the global stiffness matrix. A series of analytical studies are made to compare the response of geodesically stiffened shells as a function of loading, shell geometry, shell radii, shell laminate thickness, stiffener height, and geometric nonlinearity. Comparisons of the structural response of geodesically stiffened shells, axial and ring stiffened shells, and unstiffened shells are provided. In addition, interlaminar stress results near the stiffener intersection are presented. First-ply failure analyses for geodesically stiffened shells utilizing the Tsai-Wu failure criterion are presented for a few selected cases. / Ph. D.

The response characteristics of beams and plates made from composite laminates are strongly affected by the shear deformations of their layers. However, incorporation of the shear deformation further complicates the equations of motion and their analysis. As a result the vibration analysis of such structures have been limited to simple free vibration studies such as determination of their frequencies. The forced vibration problems of these structures have been solved by exact methods for only some very simple cases. In this study, a generalized modal approach is presented to solve more general vibration problems of composite beams and plates. The coupled systems of partial differential equations, representing the equations of motion, are uncoupled into modal equations by utilizing the eigenfunctions of the system and its adjoint. A method is presented to obtain these eigenfunctions for beams with arbitrary boundary conditions and for plates with Levy-type boundary conditions. The forced vibration solutions obtained by this method are then used to calculate the random response characteristics of beams and plates subjected to spatially and temporally correlated random loads. In the analysis of beams, both symmetric cross-ply and angle-ply configurations have been considered. In the symmetric cross-ply configuration with no torsional loads, of course, the warping effects are absent. The angle-ply case, however, includes torsion-warping effects and coupled bending-torsion motions. A simple displacement field is introduced to reflect warping in the third-order shear deformation theory. In the analysis of plates also two configurations of the laminates have been considered: symmetric cross-ply and antisymmetric angle-ply. At this time, these are the only two configurations which can be solved by the closed-form modal analysis approach for the Levy-type boundary conditions. In both cases of the beams and plates, the numerical results with and without shear deformations are obtained and compared. The results for no shear deformation are obtained with the classical lamination theory. The results have also been obtained for the first-order shear deformation theory with a somewhat simpler displacement field which has been commonly used in the past by several investigators. The numerical results are obtained for the global response quantities such as frequencies, displacements and crossing rates as well as for the local response quantities such as normal and shear stresses across a cross section. The numerical results obtained with various deformation theories for the frequencies as well as response quantities are compared to evaluate the effect of the shear deformations. For thicker and rigid beams and plates, one observes large differences in the frequencies and responses obtained with (the first- and third-order shear deformation theories) and without consideration of shear deformations (classical theory). For the frequencies and global responses both the first- and third-order theories give about the same results. But for the local response quantities, the results obtained with the two shear deformation theories can also be quite different in some cases. In any case, the results clearly point out the importance of including the shear deformations in thick and rigidly constrained composite beams and plates. Although, in this study only uniform cross section or uniform thickness beams and plates have been considered, it is felt that the eigenfunctions developed herein can also be conveniently utilized with advantage as comparison functions in approximate Rayleigh-Ritz type of approaches to analyze non uniform structures. / Ph. D.

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Advancements in design technology and construction materials have allowed composite floor systems to become longer and shallower. As a result, serviceability considerations rather than strength considerations have started to control designs. Partial continuity in composite floor systems has been suggested as a means by which the serviceability aspects could be improved. A new beam-to-girder connection referred to as a composite semi-rigid beam-to-girder connection is investigated as a possible method to provide partial continuity in floor systems. Four of these connections are evaluated experimentally and analytically to determine their behavior and the feasibility of their use in typical composite floor systems. The results indicate that these connections would improve serviceability aspects of the floor system and would improve the general efficiency of the floor design. / Master of Science