In contemporary structural engineering there is a general trend to avoid vertical stiffeners in plate girders, except at the supports. This is of a special interest in crane girders or for the launching of the bridge girders during construction. In our experimental and theoretical research the local buckling in the zone of load introduction for the plate girders (welded I girders) subjected to localized (patch) loading on a flange has been considered. The girders without vertical (transversal) stiffeners in loaded zone, but with and without horizontal (longitudinal) stiffeners, are considered. The critical and ultimate loads (carrying capacity) manifesting as buckling in the zone of load introduction are evaluated and the influence of different parameters are analyzed. Influence of the length of the patch loading is specially studied. The main results are published in referred journals and cited more than 100 times in international journals, at international conferences and in master and PhD thesis. A proposal for taking into account the influence of longitudinal stiffeners (Marković, N., Hajdin, N. A Contribution to the Analysis of the Behaviour of Plate Girders Subjected to Patch Loading, J. Construct. Steel Research, Vol. 21, No 1-3, 1992, pp163-173) was applied in the British standard BS 5400 (edition from 2000), for the design of steel bridges, where it was used together with Roberts expression for unstiffened girders.
The presented project was initiated as a part of broader research in steel structures directed by Prof. Nikola Hajdin and carried out at the Faculty of Civil Engineering University of Belgrade and the Serbian Academy of Sciences and Arts. Besides the University of Belgrade, the international cooperation also included the University of Cardiff (with T. M. Roberts), the Academy of Sciences of the Czech Republic in Prague (with M. Skaloud) and later with Civil Engineering, Faculty in Podgorica (with Prof. D. Lučić). Although the subject is intensively studied during last decades, further experimental as well as theoretical research is in progress especially in connection with the work on unified European standards for the design of civil engineering structures – Eurocodes.