Time-varying Performance Analysis Of Corroded RC Frame Structure In General Atmospheric Environment

The RC structures in the service environment,due to the influence of concrete carbonization,steel corrosion and other factors,the mechanical properties of the materials and the effective cross-sectional area of the components will be degraded,which will increase the damage probability of the structure under the external load,and affect the safety and applicability of the structures.In addition,whether structural design parameters or external load excitation,there are random factors,which need to be considered as an uncertain problem to study the time-varying mechanical properties of RC structure.Based on the probability density evolution theory,the time-varying mechanical properties and failure modes of RC beams and columns in general atmospheric environment are analyzed.Then,the time-varying vulnerability of RC frame structure under different service years is studied.There are:(1)For the time-varying compressive strength of concrete,which is less studied at present,a time-varying model is established by Bayesian information updating method,which not only inherits the rational understanding of its laws,but also is closer to the actual situation.(2)Based on the existing reproducing kernel collocation analysis method for solving the generalized probability density evolution equation,expands the probability density function to the second order by introducing the Taylor formula,and establishes a solution scheme with higher calculation accuracy.(3)The time-varying limit state equation of corroded RC beams and columns is established based on the models of the bending capacity,the shear capacity and load effect in general atmospheric environment.The limit state equation is applied to the probability density evolution method,and the time-varying reliability of corroded RC beams and columns is solved.Monte Carlo simulation is used to prove that the method of this paper can achieve good calculation accuracy under the premise of saving a lot of time cost.It can be seen that the ratio of the reinforcement radio to the stirrup radio determines the failure mode and its transformation to some extent.Increasing the stirrup diameter and the concrete cover depth can delay the degradation of mechanical properties of corroded RC beams and columns.For corroded RC columns,increasing lateral load and forward eccentricity will decrease the time-varying reliability of the columns.With the increase of vertical load,the bending time-varying reliability of corroded RC columns increases first and then decreases,and the shear time-varying reliability will increase.(4)Taking a seven-layer RC frame structures as an example,through comprehensively considering the randomness of structural parameters and external excitation.Seismic vulnerability curves with 6 target ages and 4 performance levels are formed,and then the time-varying vulnerability surfaces with the continuous change of curing age are established.The results show that the time-varying vulnerability cures are inconsistent in different service ages,and are related to the performance level.With the increase of structural failure performance level,the different of vulnerability cures between different service ages is lager.