三参数Weibull分布的多因素作用下混凝土加速寿命试验

针对中国西部盐渍土地区混凝土耐久性较差的突出问题,设计了模拟自然环境的室内混凝土加速寿命试验,其中包括盐卤腐蚀、干湿循环、冻融循环和太阳辐射。采用动弹性模量作为评价混凝土耐久性失效阈值,得到混凝土加速寿命数据。基于三参数Weibull分布,运用概率分析软件对寿命数据进行分析预测,得到加速寿命分布概要图。结果表明,三参数Weibull分布能够很好地拟合加速寿命数据样本点;其阈值参数可直观反映混凝土开始退化失效的时间;其分布概要图可直观反映加速退化过程中的可靠性,从而为混凝土耐久性评估提供新的可靠性依据。     

一类基于改进Weibull分布模型电力电缆寿命评估方法

对电缆的剩余寿命进行评估是电缆寿命管理的关键环节,以往电缆寿命评估的方法中有Arrhenius方法和Weibull分布模型.对这两种方法分别进行分析,特别是确定Arrhenius模型中激活能的计算,以及应用Weibull分布模型对电缆寿命进行评估.最后以实际电缆的状态监测数据,对简化的Arrhenius模型进行仿真,说明所提出的方法是有效的.     

一类基于改进Weibull分布模型的 电力电缆寿命评估方法

对电缆的剩余寿命进行评估是电缆寿命管理的关键环节,以往电缆寿命评估的方法中有Arrhenius方法和Weibull分布模型。对这两种方法分别进行分析,特别是确定Arrhenius模型中激活能的计算,以及应用Weibull分布模型对电缆寿命进行评估。最后以实际电缆的状态监测数据,对简化的Arrhenius模型进行仿真,说明所提出的方法是有效的。     

半电池电位法近似预测混凝土构件寿命探讨

针对钢筋锈蚀的半电池电位法检测无法定量分析的缺陷,利用锈蚀电位和锈蚀电流间的近似关系,结合法拉第定律,给出了半电池电位法近似预测构件寿命的方法;最后对某一单层厂房改造工程,进行了半电池电位法钢筋锈蚀检测和构件寿命预测。     

二级低高和高低加载下疲劳寿命可靠性预测

基于二维频率ＭＩＮＥＲ准则，本文建立了在二级变幅加载下进行疲劳寿命可靠性预测的系统方法，并用八组较大子样的二级低高和高低加勒下的试验数据进行了验证，验证结果表明，本文方法对疲劳寿命的预测值与试验值吻合良好，具有较好的准确性，简便性和实用性。     

性能贮存可靠性评估及贮存寿命预测方法

在介绍贮存可靠性与条件贮存可靠性的基础上,针对一次性产品的性能贮存可靠性试验的特点,提出了性能贮存可靠性评估及贮存寿命预测的基本思路和方法。通过算例说明了本文提出的评估和预测思路的可行性与合理性,同时也分析了这种贮存可靠性评估和寿命预测方法对于一次性产品的适用范围。     

基于Weibull分布的不同冻融介质下再生骨料透水混凝土耐久性能研究

为探究不同环境下再生骨料透水混凝土(RPC)耐久性变化规律,以3种再生骨料替代率(0、30%、50%)和4种冻融介质(H₂O、3.5%NaCl、5%Na₂SO₄、3.5%NaCl+5%Na₂SO₄)为变量进行冻融试验。定期测定RPC质量损失率和相对抗压强度损失率,对RPC取样并进行扫描电镜(SEM)分析,以冻融试验下RPC相对抗压强度损失率为依据,利用Weibull函数对RPC进行寿命预测。结果表明,同一环境下,RPC质量损失率和相对抗压强度损失率随着再生骨料替代率的增加而增加;同一再生骨料替代率下,3.5%NaCl、5%Na₂SO₄、3.5%NaCl+5%Na₂SO₄均加速RPC冻融破坏,3.5%NaCl+5%Na₂SO₄对RPC质量损失率和相对抗压强度损失率影响最严重。由SEM分析可知RPC内部孔隙和侵蚀产物数量均因循环次数和冻融介质的变化呈现...     

混凝土结构耐久性设计方法与寿命预测研究进展

为量化钢筋锈蚀与余震对钢筋混凝土结构抗震性能的影响,选取两栋按我国现行规范设计的中国东南沿海地区钢筋混凝土框架结构为研究对象,考虑未锈蚀和由低到高三种不同锈蚀率(5%、10%和15%)的四种工况,采用真实主余震序列作为输入,选取Park-Ang损伤指数作为结构损伤指标,开展了主余震序列作用下的未锈蚀与锈蚀钢筋混凝土框架结构的地震损伤评估与易损性分析。计算结果表明：锈蚀率的提高加剧了主余震序列作用下的结构累积损伤,其增长率最大可超过50%。由钢筋锈蚀单一因素引起的结构损伤在主余震累积损伤中的占比最高可超过30%。此外,钢筋锈蚀因素会导致结构的主余震易损性曲线发生显著提升。当锈蚀率较大时,钢筋锈蚀对结构易损性的影响与余震对结构易损性的影响相接近。钢筋锈蚀和余震两个因素的耦合作用会使结构的易损性水平发生更为显著的提升。因此,十分有必要在既有钢筋混凝土结构抗主余震性能评估中考虑钢筋锈蚀因素的影响。     

钢筋锈蚀对全珊瑚海水钢筋/混凝土柱大偏心受压性能的影响

通过对不同混凝土强度等级、不同种类钢筋的全珊瑚海水钢筋/混凝土柱（CA/CC）进行大偏心受压性能试验,研究了CA/CC的破坏形态、变形和承载力,建立了荷载-位移、荷载-应变等关系,探讨了CA/CC大偏心受压极限承载力（N_u）的计算模型。结果表明:CA/CC的受力破坏机制和形态与普通骨料钢筋/混凝土柱（OA/CC）基本相似。随着混凝土强度等级的提高,CA/CC纵向受拉钢筋应变开始突变所对应的荷载逐渐增大。在加载过程中,有机新涂层钢筋与珊瑚/混凝土（CA/C）之间产生较大的滑移,使在相同混凝土强度下,普钢钢筋CA/CC的N_u比有机新涂层钢筋CA/CC的N_u大约高7.1%~20.8%。建议在CA/C结构中采用有机新涂层钢筋,能有效的抑制钢筋发生锈蚀,从而延长CA/C结构的有效服役寿命。综合考虑钢筋锈蚀和涂层钢筋滑移的影响,提出了适用于满足高强、高耐久性要求的CA/CC大偏心受压N_u计算模型。      

多因素作用下混凝土寿命的BP神经网络预测

影响混凝土及其结构使用寿命的因素主要包括荷载和自然环境的变化,它们对混凝土结构使用寿命的影响过程是错综复杂的,难以用准确的数学式表达.人工神经网络方法具有无需输入变量与输出变量间复杂的相关假设,也无需确定各种计算参数,从而以消除计算参数确定过程中产生的计算误差的特点,使得其在土木结构工程耐久性方面具有广泛的应用.采用动量～自适应学习速率调整算法以及规则化调整对BP神经网络的泛化能力进行了改进,使其误差平方和达到0.000918,提高了BP神经网络的泛化能力;并用改进的BP神经网络对荷载-复合离子-干湿交替作用下混凝土材料的使用寿命进行了预测,避免了在确定计算参数过程中所产生的计算误差,拓宽了多因素作用下结构混凝土寿命预测新方法.     

氯盐环境下纤维编织网增强混凝土拉伸性能

通过拉伸试验研究了氯盐干湿、氯盐冻融循环和常规环境下纤维编织网层数、种类以及氯盐浓度和循环次数等因素对纤维编织网增强混凝土（纤维/混凝土）拉伸性能的影响。结果表明：三种环境下,增加纤维编织网层数均可提高纤维/混凝土的拉伸性能,且碳纤维编织网较玄武岩纤维编织网的增强作用更明显;氯盐浓度、干湿或冻融循环次数对纤维/混凝土拉伸极限荷载影响不明显;常规环境和氯盐干湿循环下,掺入短切聚乙烯醇（PVA）纤维和耐碱玻璃（AR-glass）纤维均可以提高纤维/混凝土的拉伸极限荷载;氯盐冻融循环下,掺入短切PVA纤维的纤维/混凝土的拉伸极限荷载未有提高,而掺入短切AR-glass纤维的纤维/混凝土的拉伸极限荷载增大。     

Comparative study of different test methods for reinforced concrete durability assessment in marine environment

There are many different test methods to assess reinforced concrete durability. As in marine environment reinforcement corrosion due to chloride attack is the most important degradation process, chloride penetration rate has been compared with different durability tests results (concrete strength, porosity, water absorption, water penetration depth under pressure, capillarity, water and oxygen permeability) carried out on concrete cores obtained from the caissons of seven Spanish wharves. Data have been studied separately, depending on concrete location (chloride penetration rate is faster in submerged concretes than in tidal zone concretes) and cement type (mineral admixtures reduce permeation rate due to pore size refinement). Results show that it is advisable to control concrete water tightness through water penetration under pressure test; additionally, in order to make sure a slow corrosion rate, it should be advisable to control oxygen permeability in tidal zone concretes.     

Fatigue life prediction of fiber reinforced concrete under flexural load

This paper presents a semi-analytical method to predict fatigue behavior in flexure of fiber reinforced concrete (FRC) based on the equilibrium of force in the critical cracked section. The model relies on the cyclic bridging law, the so-called stress–crack width relationship under cyclic tensile load as the fundamental constitutive relationship in tension. The numerical results in terms of fatigue crack length and crack mouth opening displacement as a function of load cycles are obtained for given maximum and minimum flexure load levels. Good correlation between experiments and the model predictions is found. Furthermore, the minimum load effect on the fatigue life of beams under bending load, which has been studied experimentally in the past, is simulated and a mechanism-based explanation is provided in theory. This basic analysis leads to the conclusion that the fatigue performance in flexure of FRC materials is strongly influenced by the cyclic stress–crack width relationship within the fracture zone. The optimum fatigue behavior of FRC structures in bending can be achieved by optimising the bond properties of aggregate–matrix and fiber–matrix interfaces.     

Service life prediction of repaired concrete structures under chloride environment using finite difference method

Service life of concrete structures under chloride environment can be predicted by formulations based on the mechanism of chloride ion diffusion. This mechanism can be mathematically described using the partial differential equation (PDE) of the Fick’s second law. One-dimensional PDE can be solved analytically by assuming constant surface chloride ion concentration and constant diffusion coefficient. However, the solution becomes more complicated when two additional conditions are included, i.e., concrete cover repair or replacement and time dependent variation of the surface chloride ion concentration and diffusion coefficient. In this paper, a numerical finite difference based formulation is proposed to effectively accommodate these two additional conditions. By virtue of numerical computation, the nonlinear initial chloride ion concentration can be treated in point-wise manner and both the time dependent surface chloride ion concentration and diffusion coefficient can be iteratively updated. Based on a Crank–Nicolson scheme within the finite difference method, a proper formulation accounting for space-dependent diffusion coefficient was derived; chloride ion concentration profiles are obtained and the service life of repaired concrete structures under chloride environment is predicted. Numerical examples and observations are finally presented.     

Toward a probabilistic design of reinforced concrete durability: application to a marine environment

This work aims to propose a complete design methodology for concrete durability problems based on a probabilistic method including an original chloride diffusion modelling compatible with the new performance-based approaches. This is illustrated by the study of a concrete immersed in sea water. The physical and chemical processes that lead to the corrosion of the concrete reinforcement bars are presented first. A chloride penetration model based on Fick’s second law is proposed. Next, the durability modelling parameters chosen among the durability indicators (Baroghel-Bouny, Concrete design for structures with predefined service life—durability control with respect to reinforcement corrosion and alkali–silica reaction, 2004; Alexander et al., Mater Struct 41:921–936, 2008) are assessed. They depend on the concrete formulation and the chemical composition of the cement. These indicators are characterized by their statistical distributions, which are realistically specified from a wide literature review. The whole probabilistic modelling is included in a Bayesian network so that it can be easily updated to include new experimental data. The evaluation of the time dependant corrosion risk is estimated for two types of cement: CEM I and CEM I with silica fume. The result shows the effect on the Lind–Hasofer reliability index of the type of cement, the concrete quality and the design options. The quality is integrated through the mean value and the standard deviation of the modelling parameters. The method could be used either directly for cover design or for semi-probabilistic design code calibration.     

Influence of chloride threshold value in service life prediction of reinforced concrete structures

Extensive studies have been reported on the development of service-life prediction of reinforced concrete structures in the last two decades. Service life of a reinforced concrete structure is dependent on the corrosion process, specifically chloride threshold value. Chloride threshold value is a distinctive property and is dependent on several factors such as the supplementary cementitious material used, presence of surface cracks, water to binder ratio, type of steel reinforcement, exposure conditions, measurement methods, etc. Although chloride threshold value is an influential parameter in service-life prediction, a definitive chloride threshold value considering these factors is not reported in the existing literature and standards. Moreover, values adopted in many analytical tools for service life predictions based on the type of steel reinforcement alone are not appropriate and leads to inaccurate calculations. There is a gap in the available literature in understanding the selection of suitable chloride threshold values to be adopted for a specific system. Therefore, it is imperative to study the variation of chloride threshold value with exposure conditions as well as other influencing parameters, to achieve proper service life prediction. In the paper, several influencing parameters on chloride threshold value and its significance on prediction method are comprehensively reviewed. Moreover, suitable recommendations are highlighted for Indian and international standards at the later part of the study.     

The durability properties of polypropylene fiber reinforced fly ash concrete

This paper reports of a comprehensive study on the durability properties of concrete containing polypropylene fiber and fly ash. Properties studied include unit weight and workability of fresh concrete, and compressive strength, modulus of elasticity, porosity, water absorption, sorptivity coefficient, drying shrinkage and freeze–thaw resistance of hardened concrete. Fly ash content used in concrete mixture was 0%, 15% and 30% in mass basis, and fiber volume fraction was 0%, 0.05%, 0.10% and 0.20% in volume basis.     

锈蚀对钢筋混凝土结构耐久性的影响研究

钢筋混凝土结构在工程建设中得到广泛的应用,然而结构中的钢筋锈蚀是影响钢筋混凝土结构耐久性的主要因素。文章阐述了混凝土结构的耐久性理论,锈蚀影响混凝土耐久性的因素以及预防锈蚀的措施等。