P-DELTA EFFECT UNDER REPEATED LOADING

Recently, a novel P-Delta method for the design of sway frames was introduced by the writer and demonstrated in conjunction with static proportional loading conditions. The method incorporates the rigid-plastic collapse load and the elastic buckling load of the structure as the two boundary conditions and does not require iterations or a precise trace of the load history. In this paper it is argued and verified by experiments that the P-Delta effect for sway frames can also be predicted by the same method if loadings vary independently. Such loadings can lead to a reduced failure load compared with the static load case due to premature incremental collapse if the so-called shakedown load is exceeded. The presented approach is a simple alternative to much more complex analysis procedures which would have to follow repeatedly the loading and unloading paths until failure is indicated. This has to be done under changing axial forces which requires iterations until the structure stiffness and the axial force level match. © ASCE.