Seismic behaviour and damage characteristics of corroded reinforced concrete beam-column joint

• Main Author: Zhang, Xinchen
• Other Authors: Li Bing
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2021
• Subjects: Engineering::Civil engineering::Structures and design
• Online Access: https://hdl.handle.net/10356/148144
• Institution: Nanyang Technological University

Environmental deterioration of reinforced concrete (RC) in terms of reinforcement corrosion is a common problem faced by existing RC structures. Both serviceability and durability will be threatened. In humid and sultry environment, the diffusion of chloride will speed up the corrosion process and cause the damage. If the damaged RC structures are situated in the seismic-prone zone, the safety of the structures will be threatened under earthquake. Therefore, it is important to make further investigations on the seismic performance of corroded RC structures with corroded reinforcements under earthquake loading. Moreover, monitoring the damage state of corroded RC structures during earthquake for providing early warning is also indispensable. In this study, three experimental investigations were conducted. The first test series was focused on the corroded exterior beam-column joint. Total eight intact and corroded joint specimens with different corrosion level of reinforcement and column axial force ratio were tested subjected to simulated seismic loading. Hysteretic response, lateral load resistance, stiffness, crack pattern, failure mode, energy dissipation capacity, etc. were examined. Experimental results showed that the seismic performance of corroded RC exterior beam-column joint specimens were significantly deteriorated. It was also observed that higher level of column axial force ratio had positive effect on joint specimens with higher corrosion level of reinforcement. The second test series consisted of eight uncorroded and corroded interior beam-column joint specimens. The parameters studied in this test series were also reinforcement corrosion level in terms of mass loss and axial force ratio of column. Similar to the experiment results of test Series 1, corrosion of reinforcements significantly affected the seismic performance including peak lateral resistance, ductility, energy dissipation capacity, etc. Larger axial force helped increase the hysteresis behaviour of corroded specimens and avoid pure brittle joint shear failure. Based on the collected test data, a constitutive shear stress-strain model for corroded RC joint was calibrated and validated. A good correlation was obtained between the results from analytical model and experimental observation. The last test series consisted total three uncorroded and corroded specimens with same column axial force ratio from test Series 2. During the loading process, the damage state of these specimens was monitored based on acoustic emission (AE) technique. By analysing the AE signals collected, it was found that AE technique was also effective on health monitoring of corroded RC members. A good correlation was found between AE hits and amplitude analysis results and experimental crack patterns. A further analysis based on b-value and AE intensity indicated the development of microcracks and macrocracks. Empirical damage level prediction formulas based on AE signals were proposed, which showed promise in potential applications of structural engineering. A numerical investigation was conducted based on finite element (FE) modelling. A non-linear finite element model was proposed in current study to further demonstrate the seismic behaviour of corroded RC beam-column joint with considering the deterioration due to corrosion of reinforcement. The FE model was validated by the available experiment study. An extensive parametric study was conducted for study more parameters that might influence the seismic behaviour. Based on the parametric study results, validated empirical equations were proposed to predict the shear strength of corroded RC beam-column joint. In addition, the behaviour of corroded RC interior and exterior beam-column joint specimens were analytically studied based on the developed Strut-and-Tie (STM) model. Deteriorated bond mechanism and material properties due to the corrosion of reinforcements were incorporated in the STM model. An acceptable correlation was found between the possible STM model and joint crack pattern observed in experiment. Parametric study was also conducted by adopting the STM to investigate the influence on joint internal force flow. Results showed that column axial force ratio exceeding 0.2 for exterior corroded RC joint, and 0.3 for interior corroded RC joint became detrimental.