In recent years there had been wide use of non-linear analysis for evaluation of reinforced concrete existing structures in areas of highly seismic risk. In the case of poor anchorage condition slippages of longitudinal bars become significant and govern the global response invalidating the classical full bond condition. This often happens in old structures reinforced with smooth bars and where inadequate detailing rules are applied (such as insufficient lap splice, poor confinement within end regions of elements). Due to lateral loads, beams and columns converging in a joint are subjected to bending moments acting in same direction and, hence, longitudinal bars passing-through joint panel are pulled-out at one end and pushed-in at the other end. This loss of anchorage within joint panel provides a reduction of resisting bending moments and an increment of connection flexibility due to bar slips.

Starting from a literature review, a first approach to study bar anchorage within joint panel is discussed in this paper. The study is addressed, by accounting for slippages, to reproduce the equilibrium conditions of joint panel and to provide a stress-strain relationship of a passing-through bar when anchorage failure occurs. The modified steel model incorporating bond-slips of a bar is used (Braga et al. 2012, D'Amato 2012). The model provides a stress-strain relationship accounting for both steel elongation and bar slip.

Braga F., Gigliotti R., Laterza M., D'Amato M., Kunnath S., 2012. "A modified steel bar model incorporating bond-slip for seismic assessment of concrete structures". ASCE, Journal of Structural Engineering, Vol. 138, No. 11, pp. 1342-1350.

D'Amato M., Braga F., Gigliotti R., Laterza M., Kunnath S.. 2012. "Validation of a modified steel bar model incorporating bond-slip for seismic assessment of concrete structures". ASCE, Journal of Structural Engineering, Vol. 138, No. 11, pp. 1351-1360.