冰冻海域PC梁氯离子随机扩散模型及起蚀概率评估

Chlorion Random Diffusion Model and Corrosion Initiation Probabilistic Assessment for PC Beam in Freezing-thawing Marine Environment

为构建冰冻海域预应力混凝土(PC)梁的钢筋起蚀概率评估方法,进而为承载能力等性能衰减预测提供关键时间参数,首先开展了室内氯离子扩散试验,确定扩散系数的温度影响函数及冻融循环次数影响函数。其次,基于长期暴露试验,研究了扩散模型中的龄期衰减系数、胶凝材料组成的影响及表面氯离子浓度的时变规律,构建了氯离子确定性扩散模型,通过与暴露试验结果对比验证了模型适用性。进一步对模型中关键参数实现随机性表征,建立了氯离子随机扩散模型。最后,分析了钢筋起蚀评估目标可靠指标,引入基于风险函数的时变可靠性分析,构建了冰冻海域PC梁钢筋起蚀时变概率评估方法,并依托胶州湾跨海大桥非通航孔PC梁阐述方法的应用。结果表明:氯离子扩散系数随温度升高、冻融循环次数增加近似呈线性增长趋势,随服役时间延长,PC梁表面氯离子浓度先增长,而后趋于稳定;评估基准期为1 a,20 a时,起蚀目标可靠指标分别建议为2.46,1.13;钢筋起蚀时间对混凝土拉应力水平十分敏感,混凝土平均拉应力水平从0 MPa增大至1 MPa时,起蚀时间缩短40%,PC梁运营阶段常见压应力水平对起蚀时间影响较小。

In order to establish a method for evaluating the probability of corrosion initiation of steel bars of prestressed concrete(PC)beam in freezing-thawing marine environment,and to provide key time parameters for predicting the attenuation of performance,such as load carrying capacity,firstly an indoor chlorion diffusion experiment is carried out,the temperature effect function of diffusion coefficient and the effect function of freezing and thawing cycles are determined.Second,based on the long-term exposure experiment,the age attenuation coefficient,the influence of cementitious material composition and the time-varying rule of chlorion concentration on the surface of diffusion model are studied,the deterministic diffusion model of chlorion ion is established,and the applicability of the model is verified by comparison with the exposure test.Furthermore,the key parameters of the model are characterized by randomness,and the chlorion ion random diffusion model is established.Finally,the time-dependent reliability analysis based on risk function is introduced,the time-dependent probability evaluation method of steel bar corrosion for PC beam in freezing-thawing marine environment is constructed,and the application of the method is illustrated with the Jiaozhou Bay Bridge non-navigable hole PC beam.The result shows that(1)the chlorion diffusion coefficient increases linearly with the increase of temperature and freeze-thaw cycles,and the chlorion concentration on the surface of PC beams increases first and then tends to be stable with the increase of service time;(2)when the base period is 1-year and 20-year,the reliability indicators of the initiation target are suggested to be 2.46 and 1.13 respectively;(3)the corrosion initiation time of reinforcement is very sensitive to the tensile stress level of concrete,when the average tensile stress level of concrete increases from 0 MPa to 1 MPa,the corrosion initiation time decreases by 40%,and the common compressive stress level has little effect on the corrosion initiation time of PC beams.