混凝土结构碳化寿命预测模型分析

混凝土碳化是影响结构耐久性的重要因素.根据碳化寿命准则,对现有混凝土结构碳化寿命预测模型进行分析比较,并用试验值或实测值验证.还对混凝土结构碳化寿命预测模型的影响因素进行了分析,对混凝土结构耐久性设计以及施工和维护期间应控制的影响因素提出了建议.     

A comprehensive probabilistic model of chloride ingress in unsaturated concrete

Corrosion induced by chloride ions has become a critical issue for many reinforced concrete structures. The chloride ingress into concrete has been usually simplified as a diffusion problem where the chloride concentration throughout concrete is estimated analytically. However, this simplified approach has several limitations. For instance, it does not consider chloride ingress by convection which is essential to model chloride penetration in unsaturated conditions as spray and tidal areas. This paper presents a comprehensive model of chloride penetration where the governing equations are solved by coupling finite element and finite difference methods. The uncertainties related to the problem are also considered by using random variables to represent the model’s parameters and the materials’ properties, and stochastic processes to model environmental actions. Furthermore, this approach accounts for: (1) chloride binding capacity; (2) time-variant nature of temperature, humidity and surface chloride concentration; (3) concrete aging; and (4) chloride flow in unsaturated conditions. The proposed approach is illustrated by a numerical example where the factors controlling chloride ingress and the effect of weather conditions were studied. The results stress the importance of including the influence of the random nature of environmental actions, chloride binding, convection and two-dimensional chloride ingress for a comprehensive lifetime assessment.     

Sustainable design of reinforced concrete structures through embodied energy optimization

As the world struggles to reduce energy consumption and greenhouse gas emissions, much attention is focused on making buildings operate more efficiently. However, there is another, less recognized aspect of the built environment: the embodied energy of buildings, which represents the energy consumed in construction, including the entire life cycle of materials used. Architects and structural engineers extensively perform designs of buildings with steel and reinforced concrete-materials that, to different degrees, are energy intensive. This presents an opportunity to use structural optimization techniques, which have traditionally been employed to minimize the total cost or total weight of a structure, to minimize the embodied energy. With this in mind, an analysis is carried out to determine the implications, from the point of view of cost, of optimizing a simple reinforced concrete structural member, in this case a rectangular beam of fixed moment and shear strengths, such that embodied energy is minimized. For the embodied energy and cost values assumed, results indicate a reduction on the order of 10% in embodied energy for an increase on the order of 5% in costs.     

Life-cycle reliability analysis of shield tunnels in coastal regions: emphasis on flexural performance of deteriorating segmental linings

In contrast to reinforced concrete (RC) structures on land, RC shield tunnels in coastal regions deteriorate rapidly after their construction because of the combined effects of multiple mechanical and environmental stressors. In this paper, by considering the coastal hazards associated with chloride and the impacts of hydrostatic pressure, a novel approach is presented to estimate the life-cycle structural performance of a shield tunnel that has undergone deterioration due to chloride-induced steel corrosion. Deterioration processes in segmental linings are investigated via corrosion-accelerated experiments on individual segments, and the combined effects of corrosive agents and loads are emphasized. Monte Carlo simulation is used to estimate the time-variant failure probability of shield tunnels in a marine environment. In an illustrative example, the effects of structural location, hydrostatic pressure and material properties on the life-cycle reliability of shield tunnels are investigated.     

Evaluation and Bayesian dynamic prediction of deterioration of structural performance

The deterioration of structural performance is a time-variant process with a large amount of uncertainties and incompleteness of load and environmental effects. It seems inevitable that the prediction of structural deterioration should be based on a philosophy of information updating. In the present paper, a new model system for structural performance prediction is introduced based on Bayesian dynamic linear model (DLM) theory. The system can implement Bayesian updating on the prediction of the time series process of structural deterioration. It can effectively incorporate useful information through the deterioration process of structures to update the prediction. Intervention and monitoring techniques are also designed to ensure the stability of the model system. This paper also defines an indicator of the so-called ‘condition index’ to evaluate the structural performance. Using condition indexes, the qualitative condition rating of structural performance based on visual inspection in current engineering practice can be integrated into the Bayesian DLMs. Case studies validate the advantages of Bayesian DLMs. The information updating has a favourable effect on reliability analysis and life prediction. The condition indexes are simple and convenient used in practice.     

混凝土结构与钢结构材料性能的先进监测技术

介绍了对混凝土结构和钢结构的材料性能进行监测的先进技术,包括自动监测技术和人工检测技术两大类,以通过采用这些技术,及时发现结构材料的性能退化,从而有效保障结构安全。     

钢筋混凝土中钢筋的氯诱导腐蚀

钢筋的氯诱导腐蚀是钢筋混凝土中钢筋腐蚀的最主要的原因之一,它会引起钢筋表面钝化膜的局部破损。混凝土中氯离子来自于采用的受污染的原材料和外界环境中氯离子的渗入。测定氯离子的阀值是众多研究的主要目标之一。由于氯离子阀值受许多因素影响,目前尚无确定的阀值。因此,对受氯离子污染的混凝土来说,对氯离子的活性及钢筋的状态的监测尤其重要。许多电化学方法,例如半电池电势、直流极化电阻、电化学阻抗谱和静电脉冲技术等已经广泛应用于研究和现场监测中,实践证明这些技术也是非常有力的工具。本文对钢筋氯诱导腐蚀的现状作了详细概述。     

温福铁路CX-SUN混凝土外加剂作用机理研究

温福铁路处于东南沿海地区,台湾海峡西岸,许多桥梁位于海水和地下水侵蚀环境,为了确保设计使用年限达到100年以上,针对东南沿海环境温福线铁路桥梁混凝土抗腐蚀,提高耐久性,应用了CX-SUN抗侵蚀外加剂。CX-SUN海工高性能混凝土抗侵蚀外加剂产品,可解决钢筋混凝土因长期遭受地表海水和地下水中各种化学物质的侵蚀破坏而过早丧失服役现象,使混凝土使用年限提高20~30年。     

纤维塑料筋(FRP筋)在混凝土结构中的应用

为解决钢筋混凝土结构中钢筋锈蚀的问题,国内外普遍开展了纤维塑料筋（FRP筋）来代替普通钢筋的应用研究.FRP筋具有耐腐蚀、抗拉强度高、电磁绝缘性好及弹性模量低等特点,国外早已大力开展了对FRP材料的力学特性、加工工艺和结构性能研究,并将其用于钢筋混凝土结构,且在试验研究和工程应用等方面均取得了丰硕的成果.本文在对目前研究成果进行分析的基础上,主要介绍了国内外有关FRP筋的最新研究进展.     

Life-cycle cost analysis of reinforced concrete structures in marine environments

Chloride-induced corrosion of carbon steel reinforcement is the main cause of deterioration of reinforced concrete (RC) structures in marine environments. One of the ways to protect RC structures from corrosion is to use corrosion-resistant stainless steel reinforcing bars. However, stainless steel is between six and nine times more expensive than carbon steel. Thus, its use can only be justified on a life-cycle cost basis. In the paper a time-variant probabilistic model was presented to predict expected costs of repair and replacement which was then used to calculate life-cycle costs for RC structures in marine environments under different exposure conditions. Results of the life-cycle cost analysis can be applied to select optimal strategies improving durability of RC structures in marine environments, including the use of stainless steel reinforcement.     

An improved tie force method for progressive collapse resistance design of reinforced concrete frame structures

Progressive collapse of structures refers to local damage due to occasional and abnormal loads, which in turn leads to the development of a chain reaction mechanism and progressive and catastrophic failure. The tie force (TF) method is one of the major design techniques for resisting progressive collapse, whereby a statically indeterminate structure is designed through a locally simplified determinate structure by assumed failure mode. The method is also adopted by the BS8110-1:1997, Eurocode 1, and DoD 2005. Due to the overly simplified analytical model used in the current practical codes, it is necessary to further investigate the reliability of the code predictions. In this research, a numerical study on two reinforced concrete (RC) frame structures demonstrates that the current TF method is inadequate in increasing the progressive collapse resistance. In view of this, the fundamental principles inherent in the current TF method are examined in some detail. It is found that the current method fails to consider such important factors as load redistribution in three dimensions, dynamic effect, and internal force correction. As such, an improved TF method is proposed in this study. The applicability and reliability of the proposed method is verified through numerical design examples.     

论混凝土结构施工阶段安全性

近年来大量工程事故统计资料表明,混凝土结构在施工阶段的安全性已成为突出问题。本文作者在分析事故原因的基础上,总结了国内外关于施工阶段安全性研究进展,并提出了目前急待解决的几个问题。     

Some considerations on the performance cycle analysis of concrete girders in France

A performance assessment of corroded reinforced concrete (RC) structures requires an acute understanding of both material deterioration and its impact on structural behaviour, in order to evaluate its durability, safety, serviceability and remaining service life. The corrosion phenomenon is usually due to carbon dioxide and chloride ions. More generally, the environmental conditions may determine what kind of deterioration mechanism can produce structural degradation depending on relative humidity, temperature, severity of the surrounding environment, materials properties, etc. Consequently, the performance cycle prediction of reinforced concrete structures involves many factors, which introduce uncertainties. A probabilistic approach as opposed to a deterministic one is therefore more appropriate to generate reliable cycle predictions. This paper focuses on the application of the principles of such a probabilistic approach to calculate for a typical set of RC bridges in France, the critical times corresponding to every performance cycle, considering both chloride-induced corrosion and carbonation, but also concrete cracking and spalling. For this purpose, the impact of the environment on the RC structures and the principal material properties are taken into account in this analysis. A methodology is also provided for roughly assessing serviceability cycles from visual inspections.     

海工混凝土结构的腐蚀与防护

阐述海工混凝土结构的腐蚀机理和影响因素，结合当前研究成果，介绍了相应的防腐蚀机理与防护方法。     

Bayesian assessment of the characteristic concrete compressive strength using combined vague-informative priors

Bayesian statistics can be used in order to determine the characteristic value of an unknown distribution based on a limited number of test samples. In cases where no previous test results are available, most often a Bayesian method based on vague prior information is used. The assumption of a vague or uniform prior results in a conservative approach in cases where only a limited number of test results are available. However, in case of concrete, prior information on concrete strength can be found in literature or country-specific prior information can be determined. Therefore, the use of a combined vague-informative prior is of particular interest, more specifically in the form of scaled inverse-χ² distributions that can be used for updating the standard deviation of the strength distribution of concrete. The differences between the use of a vague and a combined vague-informative prior are investigated through Monte Carlo simulations. Because prior information is taken into account, the uncertainty regarding the standard deviation of the predictive strength distribution is significantly reduced.     

施工期钢筋混凝土结构的安全性

介绍了施工期建筑结构安全分析的内容,分别阐述了钢筋混凝土结构施工期荷载,抗力及可靠度的特点,并对目前国内外施工期建筑结构的安全分析研究进展进行了总结和展望,以期促进施工期钢筋混凝土结构安全性分析。     

体外预应力混凝土结构研究进展

阐述了体外预应力结构的发展概况及其特点，分析了体外预应力结构承载力的研究方法与进展，介绍了桥梁修复工程中的体外预应力技术，指出了体外预应力技术在我国的发展前景。     

Modeling of steel and concrete strains between primary cracks for the prediction of cover-controlled cracking in RC-beams

After cracking, the intact concrete between two consecutive primary cracks remains elastic and the maximum concrete stress is less than the tensile strength of concrete. However, under increasing loading, cover-controlled cracks occur at the steel-concrete interface causing a loss of bond and hence a loss of tension stiffness. The cover-controlled cracks are internal concrete cracks that initiate at steel rib location and are contained within the concrete cover. In this paper, steel and concrete strain distribution between two consecutive primary cracks are modeled based on a linear assumed distribution of the bond stress at the steel-concrete interface. The accurate calculation of the tensile concrete strain allows introducing new criteria for cover-control cracking initiation based on a peak value of steel stress calculated at crack location.     

核心型钢混凝土组合结构体系应用前瞻

主要介绍了核心型钢混凝土组合结构体系在高层住宅建筑中的应用前景和性能优势,分析了核心型钢混凝土组合结构体系在国内外的研究现状,并探讨了核心型钢混凝土组合结构目前存在的主要问题.对21个不同配钢形式的核心型钢混凝土柱试件进行截面非线性分析.分析结果表明,各种形式核心配钢均能有效提高柱截面在较高轴压比下的曲率延性系数.介绍了2个核心型钢混凝土组合结构工程实例.在综合分析基础上,提出了核心型钢混凝土组合结构体系的抗震设计建议和深入研究思路.     

Half a century of reinforced concrete electric poles maintenance: inspection,field-testing,and performance assessment

Application of reinforced concrete (RC) poles as overhead electrical transmission line supports has become of great interest during recent years worldwide. The higher strength, longer life, and the potential to span longer distances than steel poles are the key reasons behind this tendency. A great variety of architectural shapes, relatively low maintenance costs, and high electrical resistance make RC a prominent alternative to steel. The drawbacks related to the application of RC poles include the high self-weight and vulnerability to damage. Self-weight might be reduced by prestressing the reinforcement and/or forming a tubular structure for the poles. However, both of these options might increase the vulnerability of the supports. Moreover, long-term processes (deterioration of concrete and corrosion of steel reinforcement) complicate the prediction of structural properties. This paper presents results of the everlasting inspection of the overhead electric power distribution system in Lithuania: technical state of more than 500 RC supports was assessed; selected poles were tested until failure. A specific point of this research is that most of the inspected supports were under maintenance since the middle of last century. The inspection results were used for developing the technical condition of RC pole evaluation scale proposed in this paper.