Recent studies at Monash University have shown incremental collapse failure of CHS KT- and YT-joints occurring at loads of up to 18% below the static strength of the joint. Incremental collapse occurs when the joints are subjected to high amplitude, low frequency loads. Current research aims at predicting shakedown failure loads for these joints using the Upper Bound Theorem of Shakedown. This theorem 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, and the elastic response can be determined using finite element analysis. This paper looks at predicting the shakedown load of a T-joint undergoing variable axial loading and in-plane bending moment applied to brace.
Cyclic load tests on CHS connections at Monash University have revealed incremental collapse of the connections occurring up to 18% below the ultimate static collapse load of the joint. Goh and Grundy (1994) applied cyclic loads to the diagonal of a YT-joint, from about 18% to 87% of the static strength, observing that incremental collapse occurred. Milani and Grundy (1996, 1997) followed on, with experimental work on profile cut KT-connections, and innovative KTconnections under variable repeated loads. The innovations consisted of flattening the ends of the brace members of the connection. The findings of this research indicate for the conventional profile cut KTjoints that the shakedown limit was less than the static collapse limit by up to 17%, with a corresponding reduction of 20% in the case of the innovative KT-joints. To date, analytical or numerical determination of the shakedown limit has not been developed. The aim of the current research is to use the Upper Bound Theorem of Shakedown to assess the shakedown limit.
