R.C. beam to column connection failure assessment and limit state design

Abstract

Reinforced concrete beam-to-column connections have a fundamental role in determining the seismic performance of buildings. As a matter of fact, modern seismic codes impose a series of detailing provisions that try to prevent failure in beam–column joint, leading the failure to beam ductile plastic hinges. The complexity of the transferring of forces inside the joint makes the codes to adopt overestimated actions and underestimated resistance of this fundamental element of building frame. Moreover, a well designed joint gives a large amount of ductility that can’t be safely used because it can jeopardize the overall equilibrium when it dissipates through fragile mechanisms. Because of this complexity, unfortunately any clear consensus on methods for identifying their modes of failure hasn’t been found inside the scientific community. This paper wants to confirm a method for identifying connection failure mechanisms, which employs a number of indices relating to the connection resistance mechanisms that are determined solely from the connection mechanical and geometrical properties. The method here presented allows the identification of the specific mode of failure for an existing joint and adopts a correct design for a new joint. The method is validated against the results of 72 experimental tests carried out on beam–column connections sourced from the published literature, showing a quite accurate result. Test database considers connections designed with normal strength and high strength concrete and steel, but don’t consider tests carried on bad designed connections, i.e. those using plain bars, hooks, lack of shear reinforcement in beams. Finally a new joint capacity design approach, which aims to ensure good connection performance at the serviceability, damage limitation and ultimate limit states, is suggested.