In the construction of traditional composite bridges whose structure consists of plate girders, the concrete slabs of the decks are often casted before launching. These thin-walled webs are occasionally reinforced with longitudinal stiffeners to increase bending and shear strengths, and for bridges erected by incremental launching, these stiffeners also provide an enhancement for patch loading resistance. Experimental works have shown that ultimate resistance to patch loading is highly dependent on the size, relative position and shape of the longitudinal stiffener. Nonetheless, a comparison between those three factors should be carried out in order to establish the optimum configuration of longitudinal stiffening for webs under compressive forces. Hence, this study attempts to compare the increase of ultimate strength of a slender I-girder subjected to concentrated load using open and closed section types of stiffeners, evaluating three different stiffeners configurations: i) a single open section stiffener, ii) multiple open section stiffeners, and iii) a single closed section stiffener. The nonlinear computations were performed using a finite element analysis parametric model, where the relative position and size of the stiffeners are varied to cover a wide range of geometries.