Study On The Decay Law Of Shear Capacity Of Reinforced Concrete Beams In Marine Environment

The position of the bridge in the entire transportation network is very important,and it can be said that it is the pivot project of the entire transportation system.China's bridge construction is also developing rapidly with the increase of national infrastructure investment.With the increase of service time of reinforced concrete bridges,problems such as steel corrosion,concrete carbonization and concrete spalling have followed,especially in coastal and offshore areas.The problem of rust damage of concrete structures is very serious.Many projects need to be spent on repairing them soon after they are completed,and even scrapped in advance.Corrosion of reinforced concrete in marine environment is mainly attributed to chloride ion erosion.Under the action of chloride ion erosion,the mechanical properties of steel bars inside the bridge are degraded,resulting in the decline of shear capacity and flexural capacity of reinforced concrete beams.Bending damage or shear failure.Since shear failure is brittle failure,the evaluation of the shear capacity of reinforced concrete beams is particularly important for practical engineering design and safety analysis.In view of this,this paper mainly focuses on the calculation method of shear capacity of reinforced concrete in offshore environment and carries out a series of researches.The main contents of the main research work include:(1)Through a large number of literature investigations,the current research on the key factors affecting the RC beam's shear capacity decline,the calculation method of RC beam shear capacity,and the calculation method of RC beam shear capacity are analyzed.Some of the problems in the process are summarized and a series of studies are conducted on these issues.(2)In order to investigate the retarding effect of steel bars in the diffusion process of chloride ions,the diffusion behavior of chloride ions in reinforced concrete was realized by alternating implicit finite difference method.The corrosion inhibition effect of steel bars on steel bar corrosion rate,steel bar deblurring time and concrete protection was discussed.The relationship between the cracking time and the factors such as the diameter of the steel bar,the thickness of the protective layer,the chloride ion concentration on the concrete surface and the free chloride ion diffusion process inside the concrete were found.In addition,the results show that the bar resistance causes uneven distribution of the chloride ion concentration field in the vicinity of the steel bar.This aggregation effect becomes more and more significant with the increase of the diameter of the steel bar and the thickness of the protective layer,but gradually with the extension of the diffusion time.Weakened.Moreover,in the offshore environment,the steel block effect has a significant effect on the corrosion rate of steel(3)Based on the RC beam shear capacity test database,the fixed angle softening truss theory(FASTM)is used to calculate and analyze 367 sets of RC rectangular section simply supported beams with reinforced concrete.The reinforced concrete beam body under the limit state of shear capacity is analyzed statistically.According to the behavior of force,four groups of statistically significant regression relationships were found.An explicit algorithm for shear capacity of RC beams based on FASTM theory was proposed.Without iteration,the calculation results unconditionally converge and the applicability is high.By comparing with MCFT theory and Chinese norms,it is found that the explicit algorithm probabilistic model can not only reasonably describe the probability distribution characteristics of RC beam shear capacity,but also predict the shear capacity of RC beams more reasonably.The shear bearing capacity characteristic value at the confidence level.In addition,the theoretical prediction results of shear capacity of fastm are indeed affected by the shear span ratio.When the shear span is small,the prediction results of fastm theory are small,and when the shear span ratio exceeds 3.0,the theoretical prediction results are obviously larger.When 1.5 < ? ? 3.0,the failure form of the beam is typical shear compression failure,and the error between the calculated results of fastm explicit algorithm and the experimental values is less than 18%.(4)Based on the explicit algorithm of shear capacity of RC beams,considering the influence of steel corrosion on the yield strength and reinforcement ratio of steel bars,a corrosion condition is established which meets the static equilibrium condition,coordination equation and material constitutive equation.The calculation model of the shear capacity of RC beams,including deterministic and probabilistic models.Compared with the collected shear strength test results of 96 corroded RC beams at home and abroad,the shear capacity calculated by the method is in good agreement with the experimental values,and can be used for the analysis of shear capacity of corroded RC beams.On this basis,the time-varying bearing capacity model of RC beams in offshore environment is proposed.Then,by collecting a large number of offshore environmental parameters,based on Monte Carlo simulation technology,the failure process of RC beam bending shear competition in offshore environment is simulated.The results show that in the offshore area,the stirrups are rusted before the longitudinal reinforcement.In the early stage of corrosion,the failure mode of the beam changes from bending failure to shear failure,but in the later stage of corrosion,the bending capacity of the beam is degraded compared with the shear capacity.The faster,from the shear failure mode to the bending failure,there is a bending shear competition failure phenomenon.