Thesis--Technical University of Denmark. / With Danish resumé. Bibliography: p. [75]-76.

Thesis--Technical University of Denmark. / With Danish resumé. Bibliography: p. [75]-76.

About 1930 Dr. Stephen Szego of Hungary developed the diagrid structure. During the early years diagrid structures were of reinforced concrete. In recent years the structural continuity can be achieved by welded steel beams. The purpose of this thesis is an investigation of a plane diagrid having two sets of grid beams dividing the four 20' edge beams into three equal spaces. These two sets of grid beams are perpendicular to each other. The manner of loading of the panels is uniformly distributed. By reducing some simple equations sixteen simultaneous equations have been obtained instead of twenty-six. By writing the sixteen simultaneous equations into matrix form and then transforming it into computer language, by using two subprograms, solutions are obtained. A study is made to show the effect of moments, deflections, reactions, rot. ations by changing the column size and the ratio of I_EB/I_G. / Master of Science

Thesis (M.S.)--Brigham Young University. Dept. of Civil and Environmental Engineering, 2004. / Includes bibliographical references (p. 173-174).

Thesis (M.S.)--Brigham Young University. Dept. of Mechanical Engineering, 2005. / Includes bibliographical references (p. 211-212).

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 vibration of and wave propagation in periodic cellular structures are analyzed. Cellular structures exhibit a number of desirable multifunctional properties, which make them attractive in a variety of engineering applications. These include ultra-light structures, thermal and acoustic insulators, and impact amelioration systems, among others. Cellular structures with deterministic architecture can be considered as example of periodic structures. Periodic structures feature unique wave propagation characteristics, whereby elastic waves propagate only in specific frequency bands, known as "pass band", while they are attenuated in all other frequency bands, known as "stop bands". Such dynamic properties are here exploited to provide cellular structures with the capability of behaving as directional, pass-band mechanical filters, thus complementing their well documented multifunctional characteristics. This work presents a methodology for the analysis of the dynamic behavior of periodic cellular structures, which allows the evaluation of location and spectral width of propagation and attenuation regions. The filtering characteristics are tested and demonstrated for structures of various geometry and topology, including cylindrical grid-like structures, Kagom and eacute; and tetrhedral truss core lattices. Experimental investigations is done on a 2-D lattice manufactured out of aluminum. The complete wave field of the specimen at various frequencies is measured using a Scanning Laser Doppler Vibrometer (SLDV). Experimental results show good agreement with the methodology and computational tools developed in this work. The results demonstrate how wave propagation characteristics are defined by cell geometry and configuration. Numerical and experimental results show the potential of periodic cellular structures as mechanical filters and/or isolators of vibrations.