Abstract
A general summary of double-layer grids is given in the introductory chapter and a basic geometrical classification is suggested. This is followed by a description of the hexagon-on-hexagon grid which forms the subject of this research. The second chapter deals with the rigorous analysis of the frame. The stiffness method is introduced and properties of the stiffness matrix which can reduce computer storage and execution time. The program developed to analyse the grid is detailed, with particular emphasis on its use of the typical joint matrix concept and the handling of very large matrices in the elimination process. The results of the analysis are presented for pinned and rigid modes. The deflections and forces for top, bottom and web members are given for a range of support conditions with a uniformly distributed load, and additional results for symmetrical point loads. Each set of results is preceeded by a summary of the behaviour. The derivation of an analogous anisotropic sandwich plate is described in Chapter 3. The normal isotropic plate equations are formed and the modifications for anisotropic plates stated. The plate properties are calculated from which centre deflection and layer forces are found. These are compared with the rigorous analysis values and are then used as the basis of an empirical maximum 5% error approach. Chapter 4 covers the construction and testing of a model of the grid with suggested reasons for the lack of correlation between test and analytical results. An account is also given of the collapse of the grid under test. An examination of the statical stability of the frame, showing the effect of the number of hexagonal units and the edge geometry on the number of constraints required, is contained in Chapter 5. The geometrical form of instability is presented.