Computer oriented methods of design and analysis of thin shell structures are developed. The software, being fully automatic and user friendly, should be competitive even in the commercial environment.
'Shapes' are initially generated by applying multiples of the dominant surface load on a flat membrane acting as a tension structure. Inversion of the shell provides a structure in which compression stresses predominate under the same surface loads. Both the linear two node truss element and the three node triangular flat membrane element formulated using the natural mode technique are utilised to generate and analyse the membrane structure. As the solution is non-linear in nature, various iterative schemes are studied, compared and implemented in the program. In order to reduce the laborious input of nodal coordinates and connectivities, the computer package includes a triangular mesh generator married with an efficient bandwidth and profile reduction routine. Two-dimensional and three-dimensional plotting routines are also developed for inspecting and viewing the discretised and deformed structures.
The combined bending and membrane resistances of the inverted ·shapes' are examined using both flat faceted and isoparametric s hell elements. The flat faceted shell element is formed by coupling the existing membrane with a constant moment plate bending element. The heterosis concept, together with different numerical integration schemes, is employed in the isoparametric formulation. The performance of each of the integration schemes is studied and compared.
Utilising the shell programs, the combined stresses are evaluated on the inverted 'shapes' having various aspect ratios. The optimum configurations in terms of resistance to external loads and/or architectural requirements are obtained. These geometrical configurations can be formed as the basic elements of construction. Repetitive usage of these shapes in cast in-situ or as precast units will require less variation in formwork thus furthur saving cost.
The shape finding routines are extended for the design and analysis of fabric and pneumatic structures. Both practical and aesthetic 'shapes' are obtained.
Examples for roof structures, liquid containing structures, water towers , fabric tents and pneumatic pavilions are presented to demonstrate the versatility and usefulness of the software thus developed .