Out-of-plane stability of simply supported beams with knee braces

This paper investigates the buckling of thin-walled beams braced by horizontal knee angles, which is a new practice currently coming into use in Chinese industrial buildings with small and moderate overhead cranes of light or medium duty to improve the stability of simply supported crane runway girders. It was found that this technique increases significantly the elastic buckling capacity of thin-walled beams. The increase in elastic-plastic buckling capacity may also be as high as 40% compared with unbraced beams. Simple formulae are presented for buckling moments of the knee-braced beams. Compared with the results of finite element analysis, the proposed formulae have excellent accuracy in prediction of the critical loads of knee-braced beams under concentrated load at mid-span and uniformly distributed loads. The application of the formulae was explained through an example of a practical crane runway girder.