A simplified strategy for force finding analysis of suspendomes

The suspendome has been widely used as the structural roof system of sports buildings in recent years. It is a kind of hybrid space structure composed of an upper rigid single-layer latticed shell and a lower flexible tensegrity (cable-strut) system. The prestress level in the lower cable-strut system is of great significance for the suspendome structure because it has no initial geometric stiffness (for a rib-ring type) before prestress is introduced into the lower tensegrity system. The traditional solution for calculating the self-internal-force mode and the prestress force level (force finding) is somewhat complicated; in general it is based on the Equilibrium Matrix Theory. In the present paper, a simplified computational strategy for the determination of the self-internal-force mode based on the nodal equilibrium is presented for the tensegrity system in a suspendome which is grounded on a newly developed method: the Local Analysis Method. Two types of cable-strut arrangement, the Levy system and the Geiger system, are addressed, and the characteristic of each type is expounded. An analytical solution for the self-internal-force mode of the lower cable-strut system is put forward together with the equivalent nodal force acting on the upper single-layer dome for the two types of cable-strut arrangement. The determination of the prestress level of the lower tensegrity system is then elucidated on the ground of the initial architectural configuration. the counterbalance of the bearing reaction, the equivalent nodal force, and the wind-induced slackening effect. An illustrative example is appended in the end to validate the efficiency of this simplified method. It is shown that force finding, at the viewpoint of structural design, based on this method is of great accuracy and efficiency. The prestress in the outermost ring generally has the highest level among the cable-strut system, and has the most influence on the structural performance of the suspendome. The results from the studies can be referred to not only for direct design use in practical engineering, but also for the design of similar hybrid space structures. (C) 2009 Elsevier Ltd. All rights reserved.