Plastic energy dissipation and ductility of symmetric reinforced and over-reinforced RC elements' sections

It is clear today that the existing spectral-acceleration based the seismic design method has several limitations. First of all, it does not into account the cumulative plastic deformation demands in earthquake resistant structure. The important factors that affect the RC section plastic energy dissipation (FED) and ductility are symmetric reinforcing of the section and over-reinforcing. The purpose of this paper is to propose the method of the calculation of RC element FED and its ductility taking into account the variety of the section reinforcement. The alternating direction of the seismic force at each second half cycle leads to corresponding changes of stress values and signs in the reinforcement. Thus, the compressive zone is periodically over-reinforced and the tensile one is poorly reinforced. In this case, the reinforcement cannot contribute to the section FED, and ductility of the section decreases significantly. This is the main cause of RC element failure under strong earthquakes in seismic zones. The compression zone of a symmetric reinforced section undergoing large-eccentric compression acts as under axial compression, and there is no redistribution of the internal forces in such a section. This is the main cause of a compressed element failure under strong earthquakes, since RC columns in the seismic zone usually have symmetric reinforcement. Nevertheless, symmetric reinforcement is necessary as a result of the alternating direction of the seismic forces. The FED and ductility factor calculation methodology, given in this paper, can be used for RC structures seismic design codes.