Plastic Design Applied to Trusses

Plastic design is increasing in popularity as a method of designing one- and two-story unbraced frames and braced multistory frames. The method of design discussed herein allows an extension of plastic design concepts to the design of trusses. The method is not proposed for the design of individual members of the truss system, because truss compression members will generally buckle prior to deforming enough for load redistribution. However, using the method will allow continuous and fixed ended trusses to be designed for lower resisting moments at a section than would normally be determined using an indeterminate analysis approach. For example, the method presented allows a continuous truss to be designed to support gravity moments as opposed to those higher moments determined from an elastic analysis. Consequently, the truss chord members are designed for smaller forces, thereby resulting in a direct savings in truss cost.