This paper presents a study devoted to the definition of technical solutions for improving the seismic performance of steel-concrete composite beam-to-column joints. In particular, this investigation is focused on the role of the concrete slab in how to increase the transferring capacity of the compressive forces between slab and partially encased composite columns. Based on the approach proposed by the Eurocode 8, the bearing capacity of the concrete slab in compression is globally schematized using strut & tie mechanisms. On the basis of this model, the numerical analyses and the experimental results were utilized to study the effect of different variables in the overall behaviour of joint. A parametric study was undertaken using the validated model performed using ANSYS finite element program. The parametric numerical analyses were executed to study the effect of relevant parameters (concrete class, reinforcing bar diameter and column steel profile) on the performance of both the resistant internal mechanisms of concrete slab and the slab-column connecting mechanism. Based on the obtained results, the friction and the cohesion factors existed in the design shear formula, proposed by AASHTO and EN1992- 1-1. From this study, it can be concluded that, the column inertia and concrete compressive strength are the main factors in joint behaviour. More and over, the cohesion factor can be taken as a percentage from concrete compressive strength to allow a practical tool to anticipate the ultimate strength of the slabs.