Extended shear tab connections (either in full-depth or partial-depth configurations) have been widely used to connect simply supported beams to the web of supporting girders. Full-scale laboratory tests of extended beam-to-girder shear tab connections demonstrated the differences between their observed strength and expected design strength calculated according to the AISC design procedure. This difference is attributed to the fact that the AISC design procedure neglects the girder web mechanism and its interaction with shear plate buckling of the tab, which are the main governing failure modes for partial and full depth configuration of extended beam-to-girder shear tabs, respectively. This paper aims to address the effect of flexibility of the girder web on the buckling strength of beam-to-girder shear tab connections. The findings from a finite element (FE) simulation of two beam-to-girder shear tab connections, tested at McGill University, are discussed. Finite element models were developed and calibrated based on the available data from these tests. Furthermore, symmetric boundary conditions were then implemented along the girder axis to represent the situation where the girder supports a beam on each side. This connection configuration will restrict the out-of-plane deformation of the girder web. Results from the FE models demonstrate the effect of the girder web deformation and shear tab configuration on the buckling failure mode and the ultimate strength of extended beam-to-girder connections.