Laser measurements on experiments on plate girders with a very slender web under pure bending

This paper is about the laser measurements as part of the research on the distribution of a certain amount of steel over the flanges and the web of an I-shaped plate girder to achieve the maximum bending moment resistance [1]. In many steel structures standard hot-rolled sections are used. These sections are divided into specific types in Europe and similar profiles in the USA. The range of hot-rolled sections is limited and therefore fabricated plate girders are used. Double symmetric I-shaped plate girders are built up with steel plates for the top and bottom flange and the web, welded together to a cross-section. Using this type of plate girders, a high degree of optimisation of material use is possible by using different plate thicknesses and widths for the flanges and thickness and height for the web. In the thesis the main topic for optimisation is the bending moment resistance of a plate girder. The maximum bending moment resistance appears for plate girders with a lot of material in the flanges and with a large web height. The web thickness has to be as small as possible and so the web slenderness has to be as large as possible. The limitation of the web slenderness is according to the Eurocode and the American standard based on flange induced buckling. The web of cross-section class 4 buckles and this buckling is during experiments measured by lasers. This paper gives an overview of the results of the laser measurements. Based on these measurements, it is concluded that flange induce buckling is not a limitation for the web slenderness. High web slenderness can be applied and the bending moment resistance increases enormously and the stiffness increases even more. Because of this, the use of HSS becomes of high interest.