Study On Shear Mechanism And Probabilistic Shear Strength Of Corroded Reinforced Concrete Columns

Reinforced concrete (RC) columns are the major load-bearing components for various engineering structures such as building and bridges. During the service period of the RC columns, aggressive environmental action often induces the corrosion of stirrup and longitudinal reinforcements as well as spalling of concrete cover, which significantly reduces the load-bearing capacity of the RC columns, and even makes the failure mode of the RC columns change from ductile flexural failure to brittle shear failure. However, the mechanism of shear strength for corroded RC columns is complex and there are lots of influential factors with significant uncertainties. Therefore, study on probabilistic shear strength of corroded RC columns plays an important role in the safety assessment of existing RC structures. The main contents of this thesis are as follows:(1) An improved model for critical crack angle of RC column which takes into account the axial load effect was developed based on the variable angle truss theory and by adopting the correction factor of the axial load. Meanwhile, a probabilistic model of critical crack angle for RC column was also developed by combining with the Bayesian theory and the Markov Chain Monte Carlo (MCMC) method. The proposed probabilistic model not only could describe the probability distribution characteristics of critical crack angle of the RC column reasonably, but also provides a foundation for the analysis of the shear strength of RC columns.(2) Based on the variable angle truss-arch model, an improved deterministic model for shear strength of RC column was established by taking into consideration the influence of axial load ratio on the critical crack angle as well as the deformation compatibility between the variable truss model and arch model. Meanwhile, a probabilistic model for shear strength of shear-critical RC column was developed by combining with the Bayesian theory and the MCMC method. The proposed probabilistic model could describe the probabilistic characteristics of shear strength for shear-critical RC column reasonably. Moreover, this model provides a benchmark to calibrate the confidence level of traditional deterministic models. Furthermore, the proposed probabilistic model provides an efficient way to determine the characteristic values of shear strength of shear-critical RC column according to a predefined confidence level.(3) The shear mechanism of corroded RC column was explored by taking into account the influence of steel corrosion on the reduction of the steel area and yield strength, the loss of effective shear cross-section area of RC columns, the change of shear-critical angle of RC columns. Based on shear strength model of un-corroded RC columns, a deterministic model for shear strength of corroded RC column was proposed by introducing the important parameters such as the steel cross-section area loss and the correction factor of the axial load ratio. Moreover, a probabilistic model for shear strength of corroded RC columns was established by combining with the Bayesian theory and the MCMC method. The proposed probabilistic model provides a foundation for the evaluation of shear strength for corroded RC columns.