Abstract Distribution of longitudinal shear along an interface between steel and concrete parts of various composite truss bridges from elastic phase up to plastic collapse is presented. With respect to the authors’ previous experimental research reported in references, the numerical analysis and the Eurocode approach concerning distribution of the longitudinal shear flow is studied in detail. The main interest is devoted to elastic and elastic–plastic distribution of the flow corresponding to the design level of bridge loading and plastic collapse. The analysis covers both the common elastic frame 2D modelling of the shear connection used by designers and the 3D GMNA (geometrically and materially non-linear analysis) using ANSYS software package. Results of the various models are mutually compared and confronted with provisions of Eurocode 4 for composite bridges. The non-linear distribution of the longitudinal shear, required for correct design of shear connection of composite steel and concrete bridges (in both ultimate limit state including fatigue and serviceability limit state) significantly depends on rigidity of the shear connection and densification of the shear connectors above truss nodes. These issues are analysed in parametrical studies, commented and finally some recommendations for practical design are suggested.