Fracture Resistance of a Cracked Concrete Beam Post-strengthened with FRP Sheets

Fibre-reinforced plastic (FRP) composites have been increasingly used in rehabilitation and strengthening of concrete structures. Significant increases in stiffness and strength have been achieved by applying this technique. However, there is concern about the ductility or toughness performance of FRP/concrete hybrid structures, which is critical in the application of this technology. This paper presents a new theoretical method to predict the fracture resistance behaviour of FRP post-strengthened concrete flexural beams. No slip between the FRP and plain concrete matrix is assumed and Mode I fracture propagation is considered. The model is valid for a wide range of span-to-depth ratios and any crack length. The influence of the bridging stresses provided by the fracture process zone (FPZ) at the tip of a fictitious fracture is examined. The effect of various material and geometric parameters on the resistance curve and toughness of the hybrid structure is discussed, based on the numerical results from the developed theoretical formulae. The results provide a useful insight into the strengthening/toughening and the design of FRP sheet/concrete beam structures.     

Lifetime evaluation of concrete structures under sustained post-peak loading

Experimental tests on crack propagation in concrete under constant post-peak loading are simulated using the finite element method and the cohesive crack model, in both Mode I and Mixed-mode conditions. The time-dependent behaviour of concrete in the process zone is due to the interaction and growth of microcracks, a phenomenon which, for high constant load levels, turns out to be predominant over linear viscoelastic creep in the bulk material. In mechanical systems based on this type of material behaviour (creep and strain-softening taking place simultaneously), the initial value problem is non-parabolic, i.e., the error at one time level is affected by the accumulation of errors introduced at earlier time levels. Despite these difficulties, the scatter in numerical failure lifetime vs. load level turns out to be negligible in Mode I conditions and practically acceptable in Mixed-mode conditions. Therefore the time-dependent behaviour of the process zone can be inferred solely from the results of direct tensile tests.     

钢管超高强混凝土的强度及本构关系预测

为安全有效的应用超高强混凝土，通过加载测荷载一应变关系的方法，对钢管超高强混凝土的力学性能进行了研究。研究结果证明，超高强混凝土经钢管约束后，塑性得到很大的改善，改善的幅度随套箍指标中的增加而增加，为彻底改善超高强混凝土的塑性，套箍指标中应≥0．48。推导出钢管高强超高强混凝土强度的计算公式和预测其本构关系的数学模型，结果证明强度计算值和本构关系预测结果与实测值吻合良好。     

混凝土工程冬期施工管理的几个问题

混凝土冬期施工管理中主要存在除冻剂的使用及质量控制、混凝土强度等级、测温工作、受冻临界强度检验等方面问题。文章结合工程质量检验实际情况,进行了具体分析。     

横山土石坝扩建的构造和应力变形分析

本文对１９９５年１２月已竣工验收鉴定的横山扩建坝的构造、主要特点和评价作了概要介绍。重点说明了扩建成混凝土面板堆石坝的设计要点和理论方法、老坝心墙拱效应、深混凝土防渗墙的应力状况。结合原型内部观测成果，作了对比分析研究。     

混凝土质量通病防治的措施

混凝土工程施工时,经常发生一些质量通病,这些质量通病很难根除,在施工时只能进行防治,从裂缝蜂窝、麻面、孔洞、露筋、缝隙、夹层、缺棱掉角、表面不平整、强度不够、均质性差等9个常见的质量通病产生原因和防治方面来进行探讨.     

大体积混凝土全数字化温度监测系统

本文针对大体积混凝土水化热过程中的温度监测要求提出一种全数字化测温系统。该系统能及时监测大体积混凝土内部温度变化和各测点之间温差等信息并以报表、图形、曲线等方式向用户显示,从而指导保养工作、确保工程质量。该系统还对采集的数据进行处理、分析;并可按照用户需求自动生成相应的报表、曲线。     

采用自流式混凝土对地下室墙体的加固处理

自流式混凝土(BY-40灌浆料)是一种高强胶结材料,以水泥及特选骨料掺加多种外加剂复合经特殊工艺配制而成,有较好的流动性,较低的泌水率,同时能保证在较短的时间里达到较高的抗压强度,从而加固钢筋混凝土墙体.BY-40灌浆料具有广泛的适用范围,采用BY-40灌浆料对有质量缺陷墙体的加固具有良好的效果,但目前采用这种自流式混凝土应用还较少,本文结合实例,介绍它对地下室墙体加固补强的施工和检测.     

Performance updating of concrete bridges using proactive health monitoring methods

Uncertainties associated with modelling of deteriorating bridges strongly affect management decisions, such as inspection, maintenance and repair actions. These uncertainties can be reduced by the effective use of health monitoring systems, through which information regarding in situ performance can be incorporated in the management of bridges.The objectives of this paper are twofold; first, an improved chloride induced deterioration model for concrete bridges is proposed that can quantify degradation in performance soon after chlorides are deposited on the bridge, rather than when initiation of corrosion at the reinforcement level takes place. As a result, the implications of introducing proactive health monitoring can be assessed using probabilistic durability criteria. Thus, the second objective of the paper is to present a methodology for performance updating of deteriorating concrete bridges fitted with a proactive health monitoring system.This methodology is illustrated via a simple example of a typical bridge element, such as a beam or a part of a slab. The results highlight the benefits from introducing ‘smart’ technology in managing bridges subject to deterioration, and quantify the reduction in uncertainties and their subsequent effect on predictions of future bridge performance.     

混凝土路面裂缝原因分析及防控措施

本文对贵溪冶炼厂混凝土路面破坏现象进行深入研究 ,分析了混凝土路面裂缝的原因 ,提出了防控混凝土路面裂缝的措施