An efficient modified flanges only method for plate girder bending resistance calculation

Abstract

The very popular “Flange Only” method suggested in the BS 5950 for calculation of bending resistance of plate girder with Class 4 slender web is studied and compared with the more complicated effective width method adopted by the EC3. It is shown that within all practical range of web depth to thickness ratio, that the flanges only method is conservative but sometime may be inefficient. Based on the study of these two methods, a very simple modification factor, which can be obtained conveniently by hand calculation, is proposed to improve the efficiency of the flanges only method. It is shown that the proposed modified flanges only method, while still always remains conservative, could be able to estimate the bending resistance of the girder more accurately than the original flanges only method. In most cases, the bending resistances predicted by the proposed method are within the range of 94% to 97% of those predicted by the more complicated effective width method.