On the use of bubble functions in stability analysis

Bubble functions are finite element modes that are located entirely within a single element. Elements with such modes have an added complexity, and are generally not favoured in linear analysis. This is because the extra element complexity is not rewarded with a commensurate improvement in performance. The use of bubble elements in buckling analysis is examined, taking frame elements as a starting point. Two formulations are presented, and the greatly improved performance of these is demonstrated. The results indicate that the efficiency of bubble formulations needs to be re-thought.