Development of Plastic hinge Models for Corroded Reinforcement in RC Beams

Abstract

Earthquake can cause great amount of damage to humanity among all-natural hazards. In order to avoid collapse of building during major earthquakes, most of the multistoried buildings are designed and detailed to combine strength and ductility. To attain the required ductility, they need to be proportionally adjusted to ensure that in the event of a large earthquake, the beam swing failure mode takes precedence over the cylindrical swing failure mode. The designated area in the structure (called a potential plastic hinge) is designed to withstand inelastic deformation, while the rest of the structure undergoes elastic deformation. Dynamic performance of building is determined through these plastic hinges once yielding has occurred. Also, deformation capability of plastic hinge in RCC structure are dependent on quality of steel. Reinforcing steel bars have been corroded to different levels due to environmental effects in already existing structures. Further, corroded reinforcements will not allow the structure to behave as ductile moment resisting building during earthquake. Therefore, incorporating plastic hinge model of corroded RC beams to make sure weak beam- strong column behaviour is the base of this research to prevent collapse of RC structures during earthquakes. In this work, plastic hinge model of RC beam under flexure loading incorporating the effect of 10%, 20% and 30% corrosion in reinforcement bar has been attempted. Nonlinear behaviour of Reinforced Concrete structures is observed using developed plastic hinge model. The study of the effect of corroded old reinforcement is done on the plastic hinge parameters of RCC structures. For this, the effect of different grade of concrete and different reinforcement bar along with the condition of reinforcement (bars have been corroded outside the beam) on a RC beam is studied under flexure loading. The beams are simply supported under four-point loading to ensue flexure behaviour. The moment carrying capacity is increased when the concrete grade is increased. For the same concrete grade when yield strength of the reinforcement is increased, there is a decrease observed in curvature value. Also, plastic hinge length is maximum in the RC beams with no corroded bars used and decreases as the corrosion level increases in all four cases. Further, the bars when inside the RC beam is experimentally investigated to different durations by impressed current corrosion technique as a pilot study using two cases for comparison. However, the work has been extended by taking corrosion of reinforcement outside before casting the beam. Also, reinforced concrete (RC) beams have been analysed through nonlinear finite element modeling considering the effect of reinforcement corrosion loss observed. Plastic hinge model with corroded reinforcement is developed after comparing experimental and analytical results. Then, a simple empirical equation is reported for maximum moment including the percentage of corrosion, using soft computing technique of Genetic Programming (GP). The efficacy of developed hinge models of corroded RC beams on a two-storey frame by performing pushover analysis analytically is investigated. Base shear decreased with increase in level of corrosion as observed from pushover curve. It is observed that corrosion-induced damage in RC structures can effectively be incorporated in developing plastic hinge models for seismic analysis of Reinforced Concrete buildings. This will greatly help the seismic assessment of the remaining bearing capacity of the steel bars, which will greatly help in formulating the design strategy of the existing Reinforced Concrete frame structure.