Size effect on the plastic rotational capacity of RC elements: critical review of EC8

Abstract

The ductility is an important parameter in the seismic design process of reinforced concrete structures. Under seismic loadings, ductility is required to allow a significant deformation and energy dissipation before the collapse. The plastic design of RC elements under bending loads is based on the formation of plastic hinges. The dissipation is characterised by the rotational capacity of these zones. The non-linearity of these dissipative zones is described by the moment-curvature laws (or moment-rotation curves). The Eurocode 8 (EC8) design code gives empirical formulas to evaluate the moment-rotation curves. The main disadvantage of using this practical design code is that the size effect is not taken into account in evaluating the plastic rotational capacity. In the present paper, a critical review of EC8 regarding the size dependency of the plastic rotational capacity is firstly presented. Furthermore, a performance simplified model is developed to assess the phenomena of size effects and its influence on the ductility behaviour of RC elements under simple bending (without interaction). A comparison with the experimental results from literature shows the ability of the proposed model to describe the size dependency phenomenon. Based on the new developments, news formulas are proposed to improve the EC 8. Finally, a real-life engineering application is carried out in order to highlight the benefits of the EC8 improvements proposed.