海洋大气环境下轴压腐蚀钢构件承载力时变模型及时变可靠度研究

The steel members in marine atmospheric environment are prone to produce corrosive damage. The corrosion not only weaken the effective section, but although reduce elastic modulus and yield strength, which leads to reduction of bearing capacity of steel members. However, all specifications use design formulas which are based on time-independent reliability to appraisal steel structures. Because the time-independent reliability assume that bearing capacity do not change with time, that is clearly incompatible with actual state of steel structure in marine atmospheric environment, so it is necessary to put forward a new appraisal theory based on time-dependent reliability. The time-dependent model of corrosion depth and constitutive model of corroded steel will be built in this project based on corrosion experiment, and the constitutive model can reveal the influence law of mechanical property parameters by corrosive damage. Based on the axial compress test of corroded steel member and Monte-carol stochastic finite element method, the relationship between bearing capacity and corrosion depth will be discussed, then the new time-dependent model for bearing capacity of corroded steel member will be built. Then, a new method for calculate time-dependent reliability of corroded steel member will be put forward on the basis of first passage mechanism, and a new appraisal method will be built . This project will provide theoretical support for safety assessment of existing steel members, and it has significant theoretical and engineering value.

海洋大气中的盐雾会导致钢构件产生腐蚀损伤，腐蚀不仅会削弱钢构件的截面面积，还会降低钢材的弹性模量和屈服强度等力学性能指标，从而导致钢构件承载力下降。然而，我国现行鉴定规范评定腐蚀构件时，仍套用基于传统可靠度理论建立的设计规范公式，由于承载力不变假定与腐蚀构件承载力时变规律不符，导致评定结果偏于不安全，故亟须建立一种时变可靠度评定理论。本课题首先基于钢材腐蚀试验，建立腐蚀深度时变模型和腐蚀钢材本构模型，揭示腐蚀损伤对力学性能参数的影响规律；继而基于腐蚀钢构件轴心受压试验和蒙特卡罗随机有限元法的结果，分析承载力的平均值和标准差随腐蚀深度变化的规律，建立腐蚀钢构件受压承载力时变模型；进而基于“首次超越破坏理论”，推导建立时变可靠度直接计算方法，并据此提出一种腐蚀构件安全性评定方法。研究成果可为海洋大气环境下的既有腐蚀钢构件评定提供理论依据，具有重要的理论意义和工程实用价值。

沿海地区尤其是处于苛刻海洋大气环境中的钢结构不可避免地存在着腐蚀损伤。腐蚀不仅会削弱钢构件的有效承载面积，而且腐蚀引起的钢材表面不平整会导致应力集中，进而影响钢材的弹性模量、屈服强度、极限强度等力学性能指标。目前关于腐蚀钢构件承载力和时变可靠度的理论尚不完善，开展相关研究具有重要的理论价值和应用价值。本课题采用试验研究、理论分析和有限元模拟分析的手段，系统研究腐蚀钢材的本构模型、腐蚀钢柱和腐蚀钢柱的承载力时变规律以及腐蚀构件的时变可靠度计算方法。本课题的研究内容如下：1.系统开展了腐蚀钢材拉伸试验，采用大气暴晒和中性盐雾加速腐蚀获得不同腐蚀时长的腐蚀试件，通过拉伸试验得到试件的弹性模量、屈服强度、极限强度等力学性能指标；2.开展了海洋大气和模拟海水环境下腐蚀圆钢管轴压承载力研究试验、腐蚀H型钢梁抗弯承载力研究试验、腐蚀H型钢柱力学性能研究试验；3.采用串联系统模型简化计算时变可靠度，利用重要抽样法在计算效率上的优势，给出了基于重要抽样法的锈蚀构件时变可靠度计算方法。研究结果如下：1.建立了腐蚀拉伸试件的串联分段模型和腐蚀钢材的不确定性本构模型，揭示了锈蚀钢材力学性能参数与腐蚀损伤参数之间的关系；2.通过试验获得不同腐蚀深度和不同长细比轴心受压构件的荷载-位移曲线和整体稳定承载力，提出了改进的稳定系数-正则化长细比计算公式；3.通过试验获得了不同腐蚀深度和不用截面的受弯构件的荷载-位移曲线和整体稳定承载力，提出了可考虑初始偏心的梁整体稳定承载力计算公式；4.给出了基于重要抽样法的锈蚀构件时变可靠度计算方法；5.建立了钢材腐蚀深度时变模型和常用截面带腐蚀参数几何特性计算公式，进而建立了腐蚀钢构件抗力退化模型。