汽车空调环境模拟试验室设计及特点

本文阐述了汽车空调系统环境模拟试验室设计及特点，结合国内外汽车空调环境模拟试验室的技术资料分析，提出了汽车空调性能模拟试验技术的发展趋势。     

混凝土结构表层防护方式试验研究

由于客运专线混凝土结构所处环境类型及环境作用类别的多样性，混凝土结构普遍存在着裂缝，通过对混凝土结构表面防护研究，寻找有效措施增加混凝土结构的耐久性。     

先张法预应力混凝土构件裂缝的产生原因及防治

随着我国建筑行业的发展，预应力混凝土构件的应用越来越广泛，它具有建造跨度大、自重轻、节约钢筋等优点。在荷载作用下，预应力混凝土构件与普通钢筋混凝土结构一样，都会不可避免的出现裂缝，影响结构的耐久性和结构性能。本文介绍了先张法预应力混凝土构件裂缝在准备阶段监控的要点和裂缝产生的原因及防治。     

“现代桥梁结构防腐蚀技术论坛”将在上海召开

随着我国经济的迅速发展，桥梁建设进入了一个辉煌时期。特别是沿海地区的高速发展，迫切需要对港口及一些岛屿进行开发和连通，上海国际航运中心洋山深水港及东海大桥的建设就是其中的重要项目之一。沿海恶劣的环境条件对跨海大桥等结构的防腐蚀和耐久性提出了很高的要求。东海大桥建设首次提出了设计基准期为100年的要求。为实现这一目标，国内多家单位共同进行了有关外海桥梁结构耐久性设计与应用技术综合研究，包括结构耐久性设计原则与设计方案、混凝土结构耐久性设计、钢管桩防腐蚀技术、钢结构电弧喷铝防腐蚀技术等，并在工程实践中成功应用，积累了许多宝贵的经验。此外，我国内陆地区已经建成、在建或即将兴建的多座跨江大桥，同样面临工业性气候环境的腐蚀问题。     

混凝土工程施工中泵送混凝土温度裂缝控制

随着建筑施工技术的不断发展,泵送混凝土施工技术得到普及和应用。泵送混凝土不仅能改善混凝土的施工性能,对薄壁密筋结构少振捣或不振捣施工,具有提高抗渗性、改善耐久性特点。本文主要阐述泵送混凝土施工中温度裂缝存在的问题并进行原因分析,提出控制和防止温度裂缝的有效措施,提高泵送混凝土浇筑质量。     

环境模拟技术——一门新的综合性工程技术

环境模拟技术是一门新的边缘技术，主要研究各种自然环境的人工再现技术和在模拟环境下产品的试验技术；环境模拟设备及环境试验技术经历了由单参数模拟到多参数模拟、从静态模拟到动态模拟、从产品环境试验到人机系统环境试验的发展道路；当前发展方向是建立整机的多参数综合动态环境模拟设备和进行多参数综合动态试验及人机系统环境试验；在环模设备中再现各种环境条件，进行产品的环境可靠性试验，从而可更快地发现问题并找出原因，这对于新产品的开发和成品的质量检验具有重要的意义。     

混凝土氯离子电通量测定仪校准技术研究

随着建筑行业仪器仪表技术的发展,大量新型混凝土结构耐久性测量仪器出现,但目前混凝土氯离子电通量测定仪仍然是国内使用量最大、应用最广泛的耐久性计量仪器.为了使混凝土氯离子电通量测定仪对混凝土耐久性进行有效评定,必须采取可靠的计量手段.本文介绍了该类仪器的基本原理,确定了混凝土氯离子电通量测定仪的校准参数和校准所需的标准仪器设备,探讨性地提出了该类仪器的量值溯源方法.     

火力发电厂汽轮发电机基础混凝土施工裂缝控制流程

火力发电厂汽轮发电机基础属于大体积混凝土结构。大体积混凝土指的是最小断面尺寸大于1米以上的混凝土结构,其尺寸已经大到必须采用相应的技术措施妥善处理温度差值,合理解决温度应力并控制裂缝开展的混凝土结构。在大体积混凝土结构中裂缝通常表现为温度裂缝和沉缩裂缝,怎样减少和控制裂缝的出现,有效地保证汽轮发电机基础的的整体性、耐久性、抗震性和抗渗性,是混凝土施工中必须控制的关键因素。本文拟就裂缝的种类和预防控制来叙述汽轮发电机基础混凝土施工的控制流程。     

水工施工中混凝土裂缝分析

随着社会的发展，在水利工程建设和使用中混凝土的质量问题越来越多，尤其是混凝土裂缝问题，直接影响水工混凝土结构的外观和耐久性。所以，对于混凝土裂缝，应通过一些措施以预防、处理为主。     

浅谈大体积混凝土结构的裂缝控制的技术措施

随着我国建筑行业施工技术的不断提高,大体积混凝土技术已广泛应用于高层建筑及水电工程工程项目中,但大体积混凝土结构出现裂缝的现象十分普遍且难以控制,裂缝不仅影响了结构的观感,而且对结构的整体性及耐久性也有较大的影响,因此如何行之有效地控制大体积混凝土结构裂缝的问题是目前所面临的。一个重要课题,本文从大体积混凝土裂缝产生的原因方面出发,结合实际经验及相关技术性资料,总结出一套较为有效的控制裂缝的技术措施。     

Finite element modelling of multiple cohesive discrete crack propagation in reinforced concrete beams

This paper presents a finite element (FE) model for fully automatic simulation of multiple discrete crack propagation in reinforced concrete (RC) beams. The discrete cracks are modelled based on the cohesive/fictitious crack concept using nonlinear interface elements with a bilinear tensile softening constitutive law. The model comprises an energy-based crack propagation criterion, a simple remeshing procedure to accommodate crack propagations, two state variable mapping methods to transfer structural responses from one FE mesh to another, and a local arc-length algorithm to solve system equations characterised by material softening. The bond-slip behaviour between reinforcing bars and surrounding concrete is modelled by a tension-softening element. An example RC beam with well-documented test data is simulated. The model is found capable of automatically modelling multiple crack propagation. The predicted cracking process and distributed crack pattern are in close agreement with experimental observations. The load-deflection relations are accurately predicted up to a point when compressive cracking becomes dominant. The effects of bond-slip modelling and the efficiency and effectiveness of the numerical algorithms, together with the limitations of the current model, are also discussed.     

基于离散元的钢筋混凝土梁极限承载力研究

通过PFC2D建立考虑骨料级配的钢筋混凝土梁离散元细观数值模型,开展钢筋混凝土梁极限承载力的研究。混凝土标准棱柱单轴压缩模拟验证了混凝土单元细观参数的准确性。通过修改平行黏结模型获得了适用于钢筋模拟的平行-强化黏结接触模型,钢筋单轴拉伸模拟验证了钢筋单元细观参数的准确性。建立了无缺口钢筋混凝土梁离散元数值模型,在此基础上生成预制缺口钢筋混凝土梁数值模型,根据缺口位置及倾角分为9种工况,分析了各工况下梁的裂缝扩展规律及极限承载力。结果表明:缺口位置对裂缝的扩展过程影响较大,一般起裂位置均位于缺口顶端;缺口倾角仅对裂缝扩展初期有影响,后期裂缝依然会沿竖向发展;缺口梁极限承载力约为无缺口梁极限承载力的95%~98%。     

Lattice modeling of chloride diffusion in sound and cracked concrete

Reinforced concrete structures are frequently exposed to aggressive environmental conditions. Most notably, chloride ions from sea water or de-icing salts are potentially harmful since they promote corrosion of steel reinforcement. Concrete cover of sufficient quality and depth can ensure protection of the steel reinforcement. However, it is necessary to study the effects of material heterogeneity and cracking on chloride ingress in concrete. This is done herein by proposing a three-dimensional lattice model capable of simulating chloride transport in saturated sound and cracked concrete. Means of computationally determining transport properties of individual phases in heterogeneous concrete (aggregate, mortar, and interface), knowing the concrete composition and its averaged transport properties, are presented and discussed. Based on numerical experimentation and available literature, a relation between the effective diffusion coefficient of cracked lattice elements and the crack width was adopted. The proposed model is coupled with a lattice fracture model to enable simulation of chloride ingress in cracked concrete. The model was validated on data from the literature, showing good agreement with experimental results.     

Development of discrete cracks in concrete loaded by shock waves

The non-linear behaviour of statically loaded concrete results mainly from the development of cracks. In addition, highly dynamically loaded concrete is influenced by the failure of micro-pores. Several authors use a damage model to consider both effects. The objective of this work is to test the capability of a discrete crack model to simulate shock wave-loaded concrete. Discrete cracks are modelled using the element-free Galerkin method, which allows cracks to be implemented independently of the mesh. The discrete crack model is used in combination with a fracture process zone to simulate the cohesive behaviour of the cracks in concrete. The behaviour of the micro-pores is described by a compression modulus, which depends on hydrostatic strain (Hugoniot curve). The strain rate effect is considered by modifying the failure surface for calculating crack development. Static and dynamic benchmarks with several concrete beams show good agreement with experimental results. Experiments with concrete loaded by contact detonation show the development of cracks below the crater. The simulation model used shows good agreement with the experimental crack pattern.     

混凝土裂纹扩展过程模拟的扩展有限元法研究

扩展有限元法(theextendedFiniteElementMethod,XFEM)为数值模拟结构裂纹扩展过程提供了一条有效途径。该文介绍了用扩展有限元法对混凝土结构裂纹扩展过程进行数值模拟的实现方法。采用虚拟裂缝模型模拟混凝土非线性断裂行为,针对二维四边形单元推导了详细的有限元列式。采用3种方案对非线性方程系统进行求解,分析了其求解思路并概括了其求解步骤。通过对带初始边缘裂纹的单向拉伸混凝土板的数值模拟,对3种求解方案的计算结果进行了分析和讨论。     

Experimental Study of Strengthening an RC Bridge Deck by Adding a Concrete Overlay

The present contribution focuses on the experimental investigation of moisture distribution profiles of a reinforced concrete bridge deck determined before, during and after adding a concrete overlay. By means of a non‐destructive system, the mass water content distributions were measured in the existing bridge deck as well as in the concrete overlay. Furthermore, the in situ measurements were accompanied by a comprehensive laboratory test programme. Water desorption isotherms and ultimate drying shrinkage strain were determined on specimens made of both the substrate and overlay concrete. Moreover, moisture distributions and shrinkage strains were measured on concrete prisms stored under uniform climatic conditions. Comparison of in situ measurements with lab test results allows a better understanding of the impact of environmental influences on the bonded overlay behaviour. Comparison of in situ measurements with previous lab test results allows the assessment of the effectivity of surface preparation by high‐pressure water jetting and, hence, the examination of the significance of results from composite lab tests for real bridge decks strengthened by overlays. A comparison of an experimental and numerical study of restraint effects exerted from the substrate concrete on the overlay will be presented in an accompanying paper.     

混凝土裂缝端部粘聚力的计算

混凝土裂缝端部断裂过程区的粘聚力分布是导致混凝土断裂呈现非线性特性的重要原因。基于混凝土的断裂特性和虚拟裂缝端部存在粘聚力的分析模型，并通过分布函数的特性分析，提出了粘聚力分布函数的两种简化表达式：一为单参数待定式，另一为双参数待定式。由变形体叠加原理，推导出计算单参数待定函数公式和计算双参数待定函数代数方程组。进而通过裂缝张开位移实测数据即可求得粘聚力分布，并且给出了适当的算例分析和讨论。     

Quantifying shrinkage cracking in fiber reinforced concrete using the ring test

Tensile stress can develop in concrete when rest raint prevents the concrete from shrinking freely in response to drying, chemical reaction, or temperature reduction. When these tensile stresses exceed the tensile strength of the concrete, visible cracking may be expected to occur. While several test methods have been developed to assess a material's potential for early-age shrinkage cracking, this paper describes the use of the ‘ring-test’ for assessing the performance of a fiber reinforced concrete. An equation is presented that enables the residual stress that develops in the concrete ring specimen to be estimated. This expression is used to approximate the stress that is transferred across a crack. It is shown that for conventional fiber reinforced concrete (i.e., the mixtures described in this paper) the pre-peak mechanical properties (elastic modulus, splitting tensile strength and free shrinkage) are not influenced greatly by the addition of fibers. Rather, fibers appear to influence shrinkage-cracking behavior only after the crack begins to open. To better understand the role of fibers in mitigating early-age shrinkage cracking passive acoustic emission testing was used. Acoustic emission measurements indicate microcracking due to the heterogenous nature of the concrete and the presence of moisture gradients. The acoustic emission results highlight how a single crack begins to form into a visible crack. Finally, an approach is presented for estimating crack-width based on the strain data measured from the ring test. The role of the specimen geometry is discussed for comparing the ring test with field applications.     

Reliability of reinforced concrete beams in limit state of cracking— failure rate analysis approach

The reliability of a reinforced concrete beam with respect to the limit state of crack width under monotonically increasing short-time loading conditions is estimated using the Monte Carlo technique and failure rate analysis. Using both methods the reliabilities of 24 beams whose test results are available in the literature and three beams tested in the laboratory have been determined for a limiting crack width of 0.2 mm. A comparison of the reliabilities obtained using failure rate analysis with those obtained directly from Monte Carlo simulation shows good agreement. From failure rate analysis it is found that a two-parameter Weibull distribution can be used to describe the failure life of a reinforced concrete beam with respect to the limit state of crack width. The mean moment to failure of each beam determined from failure rate analysis is compared with the experimental moment to failure.     

Application of DSCM in prediction of potential fatigue crack path on concrete surface

Prediction of potential fatigue crack paths on the surfaces of concrete structures was a difficult task in the past. To complete this task a Finite Element Method simulation by computers is usually employed, but bearing in mind that the numerical results are not always consistent with the experimental ones because of the effects of various environmental factors and construction quality on concrete structures. In order to inspect the damage process during the service life of structures and to confirm their detailed plan of repair and reinforcement, a new non-destructive technology is used for on-line health inspection of many important concrete structures in the world. Fortunately, along with the development of Digital Speckle Correlation Method (DSCM) in the last two decades, this new non-destructive technique has presented many advantages. To testify the feasibility and accuracy of this system, two series of concrete specimens were tested under flexural fatigue loading and a software UU^© matched to DSCM was employed in this work. DSCM can get full-field and local displacements by comparing two speckle images on target surfaces before and after deformation. Then the full-field and local strain fields on these regions can be deduced from the longitudinal and transversal displacements. By analysis of these strain fields, the starts of potential fatigue crack paths can be predicted precisely. It is testified that DSCM system is accurate and effective in on-line prediction of potential fatigue crack path of specimens made of heterogeneous materials under flexural cyclic loading. The fractural mechanisms of the two concrete series under flexural cyclic loading were discussed. Note that the fatigue testing conditions should be kept still and clean in order to produce precise results of DSCM system.