Cyclic earthquake-type performance of one-bay single-story reinforced concrete (R/C) frames retrofitted with an encased R/C panel

The in-plane behaviour of one-bay single-story reinforced concrete (R/C) frames, retrofitted by jacketing of their columns together with a cast-in-place encased R/C panel, was studied numerically when subjected to cyclic seismic-type horizontal loading. The influence of such an encased R/C panel is examined, when it is connected with the surrounding frame with or without steel ties. From preliminary numerical results is concluded that an encased panel results in a considerable increase of the stiffness and the bearing capacity of such a system, especially when steel ties are present at the interface. The presence of steel ties moderates the amplitude of the forces transferred at the narrow column-to-beam joint regions in a direction normal to the interface through the contact/gap mechanism; thus it, mitigates the possibility of crushing the encased panel and/or parts of the columns or beams at these regions. Thus, an encased R/C panel connected by the appropriate steel ties with the surrounding R/C frame, has a beneficial effect on the seismic behaviour of this type of structural system. Experiments were performed in order to quantify the behaviour of such steel tie connections at the interface under a stress field similar to the one that develops at this part of the encasement during seismic type loading. Such measured behaviour is in agreement with the assumptions made concerning the behavioural characteristics of these steel ties in the preliminary numerical analysis. Next, simple and advanced numerical simulations of the tested connection detail are also examined in an effort to validate numerical tools that can serve the purpose to quantify such a transfer of forces for connection details that can be used in design. It was concluded that the described advanced numerical simulation is a quite valid numerical approach.