Abstract

Today space trusses are designed using linear elastic theory, and the load carrying capacity of the truss is considered to be limited by the failure of a new critical members. Because of high redundancy, and due to practical constraints in selecting member sizes, only a portion of the member strength is used. Attempts have been made to utilize the remaining strength of the members by providing a means of transferring load from critical compression members to the understressed members. However because of the brittle buckling characteristics of compression elements, when they fall in the economic range of slenderness, postbuckling reserve capacity of compression members cannot be developed. Load transfer must thus be made before compression members reach their capacity. One part of this study is concerned with the modification of space truss behaviour by introducing nonlinearity in the chord members prior to attaining their maximum load. The amount of nonlinearity required to increase the load capacity of the truss by an economically justifiable amount has been studied, and the feasibility of the proposed system was confirmed by tests on the elements and on an assembled full scale truss. As an alternative, transfer of load from critical chord elements to the understressed chord elements can be achieved by the selective removal of internal bracing members. A means to determine the optimum selection of diagonals to be removed has been established. The above techniques were applied to four space trusses which were similar in size and proportions, but which varied in their support conditions and the distribution of member sizes. It was further considered whether the combination of the two techniques, of nonlinear chord behaviour and diagonal removal, could further improve the capacity, or whether each, when optimum, leads to the same load carrying capacity.