Journal of Constructional Steel Research 59 (2003) 561–586 www.elsevier.com/locate/jcsr Resistance of longitudinally stiffened I-girders subjected to concentrated loads Carlos Graciano * , Bernt Johansson Division of Steel Structures, Department of Civil and Mining Engineering, Lulea ˚ University of Technology, S-971-87 Lulea ˚, Sweden Received 18 May 2002; received in revised form 29 June 2002; accepted 1 July 2002 Abstract This paper presents a design procedure for the determination of the ultimate resistance of longitudinally stiffened girder webs to concentrated loads. The influence from the longitudinal stiffener is considered in the slenderness parameter l, through the buckling coefficient k f . This procedure is harmonized with other design procedures currently used for describing buckling problems in steel structures. An expression is developed for the buckling coefficient based on finite element analysis. The interaction between the web plate with flanges and a longitudinal stiffener was considered in the analysis. The ultimate strength according to the design pro- cedure presented herein and the results are compared with available experimental results. The interaction with bending is also investigated.  2002 Elsevier Science Ltd. All rights reserved. Keywords: Plate girder; Buckling; Resistance; Patch loading; Longitudinal stiffeners; Ultimate resistance 1. Introduction Longitudinal stiffeners increase the resistance of steel girder webs subjected to concentrated forces, commonly referred to as patch loading. Despite the amount of experimental research carried out on the effect of longitudinal stiffening on patch loading resistance very little has been done to quantify this increase, which in most design codes has been disregarded. * Corresponding author. Present address: Departamento de Meca ´nica, Universidad Simo ´n Bolı ´var, Apdo. 89000 Caracas 1080-A, Venezuela. Tel.:+58-212-9064060. E-mail address: cgracin@usb.ve (C. Graciano). 0143-974X/03/$ - see front matter  2002 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0143-974X(02)00046-9