# The Optimum Design of Pin-jointed Space Structures with Variable Shape

*The shape of a structure often plays a significant part in deciding its cost. In this paper a method is proposed for the design of pin-jointed space frames which includes the shape, i.e. their geometry and topology, as a variable to be decided not by the designer but by the method itself. The method includes stress, serviceability, buckling and stiffness requirements as constraints to be satisfied, while the cost of the material is minimised. In doing so the self-weight of the structure, which is changing during the design process, is fully considered as a design variable. To reduce cost, members are allowed to be grouped together so that those in a group have the same cross-section. However, a member is allowed to have a variable length as the joints at its end are allowed to move in a 3-dimensional space. Examples are given of the design method which include a dome and a transmission tower.
Professor K.I. Majid and X. Tang*