Study On Shear Mechanism And Probabilistic Shear Strength Model Of Corroded Reinforced Concrete Beams

Reinforced concrete(RC)beam is one of the most important components of civil engineering structures(such as buildings and bridges),which may occur flexural failure or shear failure subjected to combined actions of moment and shear force.Since shear failure is a brittle failure,shear strength analysis of RC beam is of great significance for safety evaluation and design of engineering structures.Meanwhile,due to the action of corrosive environment,steel reinforcement in concrete often corrodes.Corrosion of steel reinforcement may not only lead to cracking and spalling of cover concrete,but also cause the effective bearing area and mechanical property of steel reinforcement decrease,resulting in reduction of shear strength of corroded RC beam.Due to the fact that the shear mechanism of corroded RC beam is quite complex and the influential factors such material and geometric parameters exhibit significant randomness,development of probabilistic shear strength of corroded RC beam is of great significance for design and redesign of corroded RC beam.In view of this,this thesis focuses on the analysis of shear mechanism and probabilistic shear strength model of corroded RC beam.The main contents of this thesis are as follows:(1)Based on the modified compression field theory(MCFT),a deterministic model of critical diagonal crack angle for RC beam which takes into account the influences of elastic modulus ratio,reinforcement ratio,stirrup ratio and shear span ratio was developed by introducing the correction factor of shear span ratio.Then a probabilistic model of critical diagonal crack angle for RC beam which takes into account the influences of both aleatory and epistemic uncertainties was developed by combining with the Bayesian theorem and the Markov Chain Monte Carlo(MCMC)method.Analysis results show that the proposed probabilistic model can describe the probabilistic distribution characteristics of critical diagonal crack angle,which provides the foundation for probabilistic shear capacity analysis of RC beam.(2)Based on the modified compression field theory(MCFT),stress equilibrium condition,deformation compatibility condition,material constitutive law and the model of critical diagonal crack angle,a deterministic model for shear strength of RC beam which takes into account the influences of sectional size,compressive strength of concrete,yield strength of transverse steel,shear span ratio,reinforcement ratio,stirrup ratio and other factors was established first.Then a probabilistic model for shear strength of RC beam was developed by using the Bayesian theory and Markov Chain Monte Carlo(MCMC)to take into account the influences of both epistemic and aleatory uncertainties.Analysis results show that the proposed probabilistic model not only can describe the probabilistic distribution characteristics of shear strength of RC beam,but also can provide a benchmark to calibrate the confidence level of traditional deterministic models and determine the characteristic values of shear strength of RC beam with predefined confidence levels,which provides an efficient way for probabilistic safety evaluation and limit state design of RC beam.(3)Based on shear strength model of RC beam,a deterministic model for shear strength of corroded RC beam which takes into account the influences of reinforcement corrosion on yield strength of transverse steel,stirrup reinforcement ratio,stirrup ratio,critical diagonal crack angle,RC beam sectional area and other factors was established first.Then a probabilistic model for shear strength of corroded RC beam was developed by using the Bayesian theory and Markov Chain Monte Carlo(MCMC),which provides the foundation for probabilistic safety assessment and re-design of corroded RC beams.