A method for estimating ultimate load of thin-walled I - Beams subjected to patch loading in the plane of the web

The carrying capacity loss of thin - walled I profiles under patch loading has been investigated by many researchers for the last forty years. A large number of researchers have tried to provide a complete mathematical description of this problem, and to develop a procedure for calculating the failure load. The problem is extremely complex. Geometrical imperfections often make the girders vary their behaviour, with geometrical nonlinearity present right from the beginning of load application. Girder collapse develops with buckling propagation in the web. This occurrence is characterised by yielding lines in the web and there is the evidence of complex elasto-plastic state in the girder. To calculate failure load more than 26 mathematical models have been proposed, mainly of empirical or semi-empirical nature. This paper proposes a new mathematical model for calculating ultimate load. The problem of loading in the plane of the web has been analysed. The results were checked on a statistical sample of 658 tested beams, gathered from 29 experimental researches. Already known correction factor is used for horizontally stiffened girders. The proposed model corresponds well to the results of the experiments. Mathematical model is not final and a special effort should be made in order to improve it.