Application of finite element analysis in shakedown analysis of CHS joints

Recent experimental programs at Monash University on CHS KT-joints and CHS YT-joints have shown incremental collapse occurring at loads up to 18% below the static strength of the joint. Incremental collapse occurs when the joints are subjected to high amplitude, low frequency repeated loads. Little theoretical analysis has been undertaken thus far and current research aims at predicting shakedown loads for these joints. The Upper Bound Theorem of shakedown is used to assess the shakedown limit, and this requires an envelope of elastic response of the structure to all load cases, and a kinematically admissible strain rate. The kinematically admissible strain rate is basically a valid collapse mechanism and can be quantified using yield line analysis. One advantage in the use of the Upper Bound Theorem of Shakedown is that a simple elastic envelope of stresses is required with the only areas of interest being the yield lines. The elastic stress envelope can be determined using finite element analysis, and is the topic of this paper.