This study investigates the behaviour of the composite beam to column connection with circular web opening through a comprehensive FE analysis. Results showed that the circular web opening is effective to move the plastic hinge away from the column face, and accordingly, the ductility and the energy dissipation of the connection improve significantly. In the previous researches, the composite action was not considered to account for the severest case in terms of the load carrying capacity. However, this study proves that the composite effect should be included since it has a detrimental effect on the ductility and the rotational capacity. It was also concluded that the contribution of the composite action to the load carrying capacity increases with the increase in the opening diameter. Therefore, the calculated negative capacity tends to be very conservative if the composite effect is neglected when the large opening diameter is used.
Keywords: RWS, Plastic hinge, Vierendeel, Circular web, composite beam-column connection.