Size Effect on Rotational Capacity of Reinforced Concrete Beams Numerical Investigations vs Eurocode 8

Abstract eng:
The ductility is a very important parameter in the seismic design process of reinforced concrete structures. Under seismic loading, ductility is required to allow a significant deformation and energy dissipation before the collapse. The plastic design of beams under bending-loads is based on the formation of plastic hinges. The dissipation is characterized by the rotational-capacity of these zones. The nonlinear seismic analysis of reinforced concrete structures could be performed using a global approach based on the direct use of moment-curvature laws in zones of plastic hinges. Concrete is known to be a quasi-brittle material. Its cracking behavior depends on the specimen’s size. At the scale of engineering structures, the concrete has a brittle behavior due to the phenomenon of the size-effect. The design codes produce general empirical formulas fitted by test data. The reinforced concrete structures in daily practice are generally much larger than the testing laboratory samples. Do not take into account of the size-scale effect leads to an unsafe design. Numerical models are required to reproduce the effect of scale-change on the structural design. In the context of the seismic design, the experimental observations confirm the dependence of the ductility on the structural dimension. Hence, the size-scale effect should be considered in the seismic design process. To establish the momentrotation curves needed in dynamic non-linear analysis of RC structures, Eurocode 8 gives empirical formulas to provide 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 rotational capacity which produces a bad estimation of the energy dissipation. In this present paper, a global model is proposed in order to into account the phenomena of size effects and its influence on the ductility assessment. Both compression and tensile behavior are described by stress-strain curves where the localization process is taken into account. A comparison with the experimental results is firstly performed in order to validate the proposed model. Furthermore, a comparison between the EC8 and the proposed model regarding the diagram providing the rotational capacity of RC beams as a function of the relative neutral axis positions x/d is proposed.

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