Structural behaviour and approximate analysis of a double layer grid.

Double-layer grids are a relatively new form of three-dimensional skeletal structure which have come into use during the last two decades or so. They are usually metallic structures used to provide a flat cover for large unobstructed areas. The exact analysis of double-layer grids, even with the aid of an electronic computer, is an onerous task and approximate methods are often used instead. The approximate methods developed have their drawbacks, their reliability has not always been checked and the knowledge about the structural behaviour of double-layer grids still remains limited. In this thesis, the structural behaviour of a type of double-layer grid is investigated by exact analysis and suitable approximate methods are developed. The results of exact analysis for a large number of different conditions are presented in Chapter Two, and lead to certain important conclusions about the structural behaviour as given in Chapter Six. In Chapter Three an original method is developed for approximate analysis of double-layer grids. The formulation is general, suitable for electronic computation and results in substantial savings. A computer programme was written to check its reliability, and the errors were small in all cases considered. The technique developed in Chapter Four consists in deriving a simple interpolation function, which can be used to approximate the displacements and forces in the grid for different values of a variable feature in the grid. It provides a means to study the structural behaviour of double-layer grids and other structures, and is suitable to be used in optimization processes. An experimental investigation carried out as a counter check on the experimental analysis is presented in Chapter Five. Details of the computer programme and a computational technique developed for the exact analysis of the grids are given in Appendices A and B. Appendix C contains a paper, the material of which is associated with the method developed in Chapter Three