Splices in Plastically Designed Continuous Structures

Plastic design is based on the ductile strength of steel—the ability of structural steel to deform at and above the yield point at a uniform level of stress. If the load on a steel structure is increased sufficiently, the material will pass through the elastic range into the plastic range of stress. At overloads, highly stressed areas are permitted to yield in bending. When such highly stressed portions of a continuous structure yield, they merely refuse to accept larger bending moments and transfer the requirement for additional moment capacity to areas which are stressed to a lesser degree. Thus, as a sufficiently large overload is applied to a continuous structure, the relative size of the positive and negative moments will be readjusted so that the structure can support additional load. This moment redistribution does not take place at the design load. The objective is to design the structural frame so that the redistribution can take place if large overloads are imposed. If the structure is not loaded above the design load, it will act within the elastic range in a manner no different from a structure designed by elastic design procedures.