Beam-to-column friction connection for earthquake-resilient reinforced concrete frames made with hybrid trussed beams

Beam-to-Column Connections (BCCs) endowed with friction dissipative devices have become suitable solutions to limit or avoid the damage undergone by the surrounding structural members in the case of seismic events. In the context of the low-damage design strategy, very few solutions were proposed for cast-in-place Reinforced Concrete (RC) framed structures, due to the difficulty to design efficient yet economic damage-proof connections. A structural solution that can be adopted to solve the preceding difficulty is the Hybrid Steel-Trussed Concrete Beam (HSTCB). In fact, those HSTCBs endowed with a bottom steel plate are more similar to structural steel members, and can be more easily endowed with a friction device. HSTCBs are often characterized by a small effective depth, which leads to a large amount of longitudinal bars. The latter, passing through a small-sized beam-column joint, make it more prone to be damaged by the cyclic actions induced by an earthquake. To prevent this issue, the use of an innovative friction-based BCC, designed to increase the lever arm of the moment transferred be-tween joint and beam, can effectively reduce the shear force experienced by the panel zone, and thus significantly limiting or avoiding its damage. Within this framework, this paper deals with the proposal of a friction-based beam-to-column connection for RC structures made with HSTCBs. Firstly, the pro-posed solution is described highlighting its innovative features. Then, the design procedure of the beam-to-column friction connection is outlined. After that, a detailed 3D finite element model representing an exterior beam-column joint endowed with the proposed friction connection is developed. Several mono-tonic and cyclic analyses are carried out investigating different design moment values. Lastly, the numerical results are commented, which prove the efficacy of the proposed solution in avoiding damage in beam, column and joint, as well as in ensuring adequate dissipative capacity thanks to its flexural behaviorr characterized by wide and stable hysteresis loops.