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1、精选优质文档-倾情为你奉上外文资料The Tenth East Asia-Pacific Conference on Structural Engineering and ConstructionAugust 3-5, 2006, Bangkok, ThailandStructural Rehabilitation of Concrete Bridges with CFRP Composites-Practical Details and ApplicationsRiyad S. ABOUTAHA1, and Nuttawat CHUTARAT2ABSTRACT: Many old exist
2、ing bridges are still active in the various highway transportation networks, carrying heavier and faster trucks, in all kinds of environments. Water, salt, and wind have caused damage to these old bridges, and scarcity of maintenance funds has aggravated their conditions. One attempt to restore the
3、original condition; and to extend the service life of concrete bridges is by the use of carbon fiber reinforced polymer (CFRP) composites. There appear to be very limited guides on repair of deteriorated concrete bridges with CFRP composites. In this paper, guidelines for nondestructive evaluation (
4、NDE), nondestructive testing (NDT), and rehabilitation of deteriorated concrete bridges with CFRP composites are presented. The effect of detailing on ductility and behavior of CFRP strengthened concrete bridges are also discussed and presented.KEYWORDS: Concrete deterioration, corrosion of steel, b
5、ridge rehabilitation, CFRP composites.1 IntroductionThere are several destructive external environmental factors that limit the service life of bridges. These factors include but not limited to chemical attacks, corrosion of reinforcing steel bars, carbonation of concrete, and chemical reaction of a
6、ggregate. If bridges were not well maintained, these factors may lead to a structural deficiency, which reduces the margin of safety, and may result in structural failure. In order to rehabilitate and/or strengthen deteriorated existing bridges, thorough evaluation should be conducted. The purpose o
7、f the evaluation is to assess the actual condition of any existing bridge, and generally to examine the remaining strength and load carry capacity of the bridge.1 Associate Professor, Syracuse University, U.S.A.2 Lecturer, Sripatum University, Thailand.One attempt to restore the original condition,
8、and to extend the service life of concrete bridges is by the use of carbon fiber reinforced polymer (CFRP) composites. In North America, Europe and Japan, CFRP has been extensively investigated and applied. Several design guides have been developed for strengthening of concrete bridges with CFRP com
9、posites. However, there appear to be very limited guides on repair of deteriorated concrete bridges with CFRP composites. This paper presents guidelines for repair of deteriorated concrete bridges, along with proper detailing. Evaluation, nondestructive testing, and rehabilitation of deteriorated co
10、ncrete bridges with CFRP composites are presented. Successful application of CFRP composites requires good detailing as the forces developed in the CFRP sheets are transferred by bond at the concrete-CFRP interface. The effect of detailing on ductility and behavior of CFRP strengthened concrete brid
11、ges will also be discussed and presented.2 Deteriorated Concrete BridgesDurability of bridges is of major concern. Increasing number of bridges are experiencing significant amounts of deterioration prior to reaching their design service life. This premature deterioration considered a problem in term
12、s of the structural integrity and safety of the bridge. In addition, deterioration of a bridge has a considerable magnitude of costs associated with it. In many cases, the root of a deterioration problem is caused by corrosion of steel reinforcement in concrete structures. Concrete normally acts to
13、provide a high degree of protection against corrosion of the embedded reinforcement. However, corrosion will result in those cases that typically experience poor concrete quality, inadequate design or construction, and harsh environmental conditions. If not treated a durability problem, e.g. corrosi
14、on, may turn into a strength problem leading to a structural deficiency, as shown in Figure1.Figure1 Corrosion of the steel bars is leading to a structural deficiency3 Non-destructive Testing of Deteriorated Concrete Bridge PiersIn order to design a successful retrofit system, the condition of the e
15、xisting bridge should be thoroughly evaluated. Evaluation of existing bridge elements or systems involves review of the asbuilt drawings, as well as accurate estimate of the condition of the existing bridge, as shown in Figure2. Depending on the purpose of evaluation, non-destructive tests may invol
16、ve estimation of strength, salt contents, corrosion rates, alkalinity in concrete, etc.Figure2 Visible concrete distress marked on an elevation of a concrete bridge pierAlthough most of the non-destructive tests do not cause any damage to existing bridges, some NDT may cause minor local damage (e.g.
17、 drilled holes & coring) that should be repaired right after the NDT. These tests are also referred to as partial destructive tests but fall under non-destructive testing.In order to select the most appropriate non-destructive test for a particular case, the purpose of the test should be identified.
18、 In general, there are three types of NDT to investigate: (1) strength, (2) other structural properties, and (3) quality and durability. The strength methods may include; compressive test (e.g. core test/rebound hammer/ ultrasonic pulse velocity), surface hardness test (e.g. rebound hammer), penetra
19、tion test (e.g. Windsor probe), and pullout test (anchor test).Other structural test methods may include; concrete cover thickness (cover-meter), locating rebars (rebar locator), rebar size (some rebar locators/rebar data scan), concrete moisture (acquameter/moisture meter), cracking (visual test/im
20、pact echo/ultrasonic pulse velocity), delamination (hammer test/ ultrasonic pulse velocity/impact echo), flaws and internal cracking (ultrasonic pulse velocity/impact echo), dynamic modulus of elasticity (ultrasonic pulse velocity), Possions ratio (ultrasonic pulse velocity), thickness of concrete s
21、lab or wall (ultrasonic pulse velocity), CFRP debonding (hammer test/infrared thermographic technique), and stain on concrete surface (visual inspection).Quality and durability test methods may include; rebar corrosion rate field test, chloride profile field test, rebar corrosion analysis, rebar res
22、istivity test, alkali-silica reactivity field test, concrete alkalinity test (carbonation field test), concrete permeability (field test for permeability).4 Non-destructive Evaluation of Deteriorated Concrete Bridge PiersThe process of evaluating the structural condition of an existing concrete brid
23、ge consists of collecting information, e.g. drawings and construction & inspection records, analyzing NDT data, and structural analysis of the bridge. The evaluation process can be summarized as follows: (1) Planning for the assessment, (2) Preliminary assessment, which involves examination of avail
24、able documents, site inspection, materials assessment, and preliminary analysis, (3) Preliminary evaluation, this involves: examination phase, and judgmental phase, and finally (4) the cost-impact study.If the information is insufficient to conduct evaluation to a specific required level, then a det
25、ailed evaluation may be conducted following similar steps for the above-mentioned preliminary assessment, but in-depth assessment. Successful analytical evaluation of an existing deteriorated concrete bridge should consider the actual condition of the bridge and level of deterioration of various ele
26、ments. Factors, e.g. actual concrete strength, level of damage/deterioration, actual size of corroded rebars, loss of bond between steel and concrete, etc. should be modeled into a detailed analysis. If such detailed analysis is difficult to accomplish within a reasonable period of time, then evalua
27、tion by field load testing of the actual bridge in question may be required.5 Bridge Rehabilitation with CFRP CompositesApplication of CFRP composite materials is becoming increasingly attractive to extend the service life of existing concrete bridges. The technology of strengthening existing bridge
28、s with externally bonded CFRP composites was developed primarily in Japan (FRP sheets), and Europe (laminates). The use of these materials for strengthening existing concrete bridges started in the 1980s, first as a substitute to bonded steel plates, and then as a substitute for steel jackets for se
29、ismic retrofit of bridge columns. CFRP Composite materials are composed of fiber reinforcement bonded together with a resin matrix. The fibers provide the composite with its unique structural properties. The resin matrix supports the fibers, protect them, and transfer the applied load to the fibers
30、through shearing stresses. Most of the commercially available CFRP systems in the construction market consist of uniaxial fibers embedded in a resin matrix, typically epoxy. Carbon fibers have limited ultimate strain, which may limit the deformability of strengthened members. However, under traffic
31、loads, local debonding between FRP sheets and concrete substrate would allow for acceptable level of global deformations before failure. CFRP composites could be used to increase the flexural and shear strength of bridge girders including pier cap beams, as shown in Figure3. In order to increase the
32、 ductility of CFRP strengthened concrete girders, the longitudinal CFRP composite sheets used for flexural strengthening should be anchored with transverse/diagonal CFRP anchors to prevent premature delamination of the longitudinal sheets due to localized debonding at the concrete surface-CFRP sheet
33、 interface. In order to prevent stress concentration and premature fracture of the CFRP sheets at the corners of concrete members, the corners should be rounded at 50mm (2.0 inch) radius, as shown in Figure3.Deterioration of concrete bridge members due to corrosion of steel bars usually leads in los
34、s of steel section and delamination of concrete cover. As a result, such deterioration may lead to structural deficiency that requires immediate attention. Figure4 shows rehabilitation of structurally deficient concrete bridge pier using CFRP composites.Figure3 Flexural and shear strengthening of co
35、ncrete bridge pier with FRP compositesFigure4 Rehabilitation of deteriorated concrete bridge pier with CFRP composites6 Summary and ConclusionsEvaluation, non-destructive testing and rehabilitation of deteriorated concrete bridges were presented. Deterioration of concrete bridge components due to co
36、rrosion may lead to structural deficiencies, e.g. flexural and/or shear failures. Application of CFRP composite materials is becoming increasingly attractive solution to extend the service life of existing concrete bridges. CFRP composites could be utilized for flexural and shear strengthening, as w
37、ell as for restoration of deteriorated concrete bridge components. The CFRP composite sheets should be well detailed to prevent stress concentration and premature fracture or delamination. For successful rehabilitation of concrete bridges in corrosive environments, a corrosion protection system shou
38、ld be used along with the CFRP system.第十届东亚太结构工程设计与施工会议2006年8月3-5号，曼谷，泰国碳纤维复合材料修复混凝土桥梁结构的详述及应用Riyad S. ABOUTAHA1, and Nuttawat CHUTARAT2摘要：在各式各样的公路交通网络中，许多现有的古老桥梁，在各种恶劣的环境下，如更重的荷载和更快的车辆等条件下，依然在被使用着。冲刷、腐蚀和风化对这些古老的桥梁已经造成了破坏，而维修资金短缺更加剧了它们的损坏。一个利用碳纤维增强复合材料（CFRP）来延长混凝土桥梁的使用寿命的想法使桥梁恢复了原有的状态。然而，采用碳纤维复合材料修复
39、受损混凝土桥梁的指导和规范还非常有限。在本文中对无损探伤、无损检测和利用碳纤维复合材料修复已遭侵蚀的桥梁的方法进行了介绍。此设计对碳纤维增强混凝土桥的延性，及其应用后效果也进行了讨论和介绍。关键词:混凝土腐蚀，钢筋锈蚀，桥梁修复，碳纤维复合材料1 简介在这里存在几个有害的外部环境因素影响着桥梁的耐久性。这些因素包括但又不仅限于化学物的侵蚀，受力钢筋的锈蚀，混凝土的碳化，化学物质的聚合反应。如果桥梁维护不好，这些因素可能导致结构的受损，如结构边缘不稳定或结构损毁。为了修复日渐恶化的现存桥梁，应当对其作彻底的评估。目的是通过大致检测剩余耐久度和承载力，评定出所有现存桥梁的真实情况。应用碳纤维复合材
40、料可以恢复混凝土桥梁最初的状况并延长其使用年限。在北美、欧洲和日本，碳纤维复合材料应经得到深入的研究和广泛的应用。碳纤维复合材料的几个设计指南也已经被应用于强化混凝土桥梁。然而，采用碳纤维复合材料修复损坏的混凝土桥梁的指导和规范还非常有限。本文通过合适的例子给出了修复受损混凝土梁桥的准则，列出了评估、无损检测、碳纤维复合材料复原受损混凝土桥梁。碳纤维复合材料的成功应用由于良好的细节设计，它主要考虑了集中力在碳纤维复合材料中依靠混凝土与碳纤维复合材料接触面间的粘合剂转移。此设计对碳纤维增强混凝土桥的延性和反应的效果也进行了讨论和介绍。2 混凝土桥梁的损坏桥梁的使用年限应该给予极大地关注。越来越多
41、的桥梁在达到设计使用年限之前出现令人侧目的破损。这些过早出现的损坏使得桥梁的结构可靠性和安全性成为1副教授，雪城大学，美国2讲师，斯巴顿大学，泰国了值得考虑的问题。总的来说，桥梁的损坏与考虑它的花费多少是紧密相关的。在很多情况下，损坏问题的根源是混凝土结构中受力钢筋的腐蚀。通常由混凝土保护层预防受力筋的腐蚀。然而，这些具有代表性的问题，如混凝土质量差、不适当的设计或施工和周围恶劣的环境导致了钢筋的腐蚀。如果不及时处理像钢筋腐蚀这种耐久性问题，可能会引起受力不均问题，进而导致结构失稳，如图1所示。图1 钢筋的锈蚀导致的结构失稳3 损坏的混凝土梁桥墩柱的无损检测为了设计一个成功的新式系统，应该对桥
42、梁现有的情况作彻底评估。评价现有桥梁的元素或体系需要翻看asbuilt图纸，才能准确的评估出现有桥梁的状况，如图2所示。根据评估的目的，无损测试应该包括的内容：强度的检测，盐度，腐蚀率，混凝土中碱含量等等。虽然大多数的无损测试对现有桥梁不会造成任何损坏，一些无损检测可能导致的轻微局部损伤（如钻洞取芯），在无损检测完毕后应予以修复。这些测试也被叫作部分破坏性测试,但属于无损检测。裸露的钢筋裂缝平行于锈蚀的钢筋剥离（敲击有空心声音）弯剪/剪切裂缝图2 混凝土桥墩可见缺陷正面图为了针对特殊情况选择最合适的无损检测，应该明确测试的目的。一般来说,有三种类型的无损检测进行调查：（1）强度；（2）其他结构
43、性质；（3）质量及耐久性。强度测试的方法可能包括：抗压测试（如轴心抗压、反弹测试仪、超声波脉冲速度检测）；表面硬度测试（如反弹仪测试）；贯入度试验（如温莎探针）；拉拔试验（锚索抗拔试验）。其它结构测试方法还包括：混凝土保护层厚度（保护层测量）；定位钢筋位置（钢筋定位器）；钢筋尺寸（某些钢筋定位器、钢筋数据扫描仪）；混凝土的湿度（含水量测试仪、水分测定仪）；混凝土裂缝检查（外观鉴定、回音法、超声波脉冲回波速度检查法）；混凝土分层剥离（锤击试验、超声波脉冲回波速度检查法、回音法）；缺陷和内部开裂（超声波脉冲回波速度检查法、回音法）；动态弹性模量（超声波脉冲回波速度检查法）；泊松比（超声波脉冲回波速
44、度检查法）；混凝土板或墙的厚度（超声波脉冲回波速度检查法）；碳纤维复合材料剥离（锤击试验、红外线温度记录技术）；混凝土表面缺陷（外观鉴定）。质量和耐久性试验方法包括：钢筋锈蚀率现场试验，现场检测剖面氯化物，验定钢筋锈蚀率，测试钢筋电阻率，现场测定碱质与粒料反应活性，混凝土碱度测定（碳化测定），混凝土的渗透性（现场渗透性试验）。4 损坏的混凝土梁桥墩柱的无损探伤对一个现有混凝土桥梁结构特征的评估由各种信息组成，如图纸、构筑物的检查记录，无损检测的分析数据和桥梁的结构分析。评估过程可以概括如下：（1）计划评估；（2）预备评估，主要包括现有文件检查、实地检查、材料检验和初步分析；（3）初步评估，主要
45、有检查阶段，审查阶段和完成阶段。（4）有关成本影响的分析。如果上述提供的信息，不足以用来进行高水平的评估。那么，我们做完上述的初步评估的步骤之后，可以再做一个详细的、深入的评估。对于某个现存损坏的混凝土桥梁成功地分析评估应当考虑桥梁的实际情况及它的各部分的损坏程度。如果在适当的一段时间内很难完成如此详细的分析，那么就可能需要谈及的依靠现场试验得到的实际桥梁的评估。5 碳纤维复合材料修复受损桥梁的应用碳纤维复合材料的应用延长了既有混凝土桥梁的使用年限而变得越来越引人注目。在桥梁的外部粘结碳纤维复合材料加强现有桥梁的技术被广泛应用在日本（纤维增强塑料板）和欧洲（多层纤维板）。在20世纪80年代，这
46、些材料被应用于加强既有混凝土桥梁，最先是被用来替代钢板，后来被用来替代钢套作为桥墩的耐震补强。碳纤维复合材料由纤维强化复合材料与合成树脂基质粘结在一起组成。纤维以其独特的结构性能使两者良好复合。树脂基质支撑并保护着纤维，将外施荷载以剪应力的方式传递给纤维。大部分在建筑市场上能买到的碳纤维复合材料加固系统都是由单向纤维嵌套在树脂基质中构成，最具代表性的是环氧树脂。碳纤维的有限的极限应变可能会限制强化涂层中的元素的形变能力。然而，在交通荷载作用下，结构在破坏之前且全局的形变在可接受的程度内，碳纤维复合材料板与混凝土基质之间局部的脱胶是被允许的。碳纤维复合材料可用于增加包括盖梁在内的桥主梁的抗弯及抗
47、剪强度，如图3所示。为了增加碳纤维复合材料加强的混凝土主梁的延性，防止由于混凝土基质与碳纤维复合材料接触面之间产生局部脱胶而造成的纵向板过早剥离，应将用于增强抗弯强度的纵向碳纤维复合材料板、横向板及对角板互相锚固。为了防止在混凝土构件的转角处产生应力集中和碳纤维复合材料板过早断裂，这些转角应当是不小于50mm（2.0英寸）半径的圆角，如图3所示。图3 碳纤维复合材料混凝土墩柱弯剪强度的加强由于钢筋的锈蚀而导致的钢筋截面面积的损失和混凝土保护层的损坏是混凝土桥梁构件损坏的根本原因。因此应该时刻注意像这样可能会导致结构失稳的损坏。碳纤维复合材料对受损桥梁结构的修复如下图4所示。弯曲裂缝弯剪/剪切裂缝图4 碳纤维复合材料对受损桥梁的修复6 概要和结论在上文中对测评桥梁、无损测试和对受损混凝土桥梁的修复进行了介绍。钢筋的锈蚀可能会导致混凝土桥梁的构件发生弯曲或者剪切破坏。由于碳纤维复合材料的应用延长了现有混凝土桥梁的使用年限，因此越来越多的人正在对它投入关注。碳纤维复合材料可以被应用于增加构件的抗弯剪强度，也可以被用来修复混凝土桥梁的受损构件。碳纤维复合材料可以很好的应用于防止应力集中和构件过早的破裂及损坏。在极易被腐蚀的环境中，防腐蚀的碳纤维复合材料体系应当被应用，以便成功的修复受损的混凝土桥梁。专心-专注-专业