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欧洲桥梁研究 在欧洲，一个共同研究的平台随着欧盟的发展诞生了。为了举例说明欧洲的研究方法已经被这种方式所替代，一个典型的案例就是有关英国后张法桥梁被讨论的事，爱丁堡大学给出了这个关于用数字化脉冲雷达鉴定后张法混凝土桥梁孔隙的资源互补的案例。引言利用各研究团体的研究成果去验证大量相关论据是所有研究领域所面临的挑战，这是为了能使研究和实践更好地结合，具有针对性。此外，在欧洲，不容忽视的语言壁垒也是一个巨大的障碍,为了避免再次爆发类似于从1939年至1945的第二次世界大战似的的欧洲内战，欧洲国家有了一个共同的政治目的，成立于20世纪60年代的欧共体便是基于这一目的。它的成立带有很强的政治动机，但英国并非这一组织的成员，因为很多的欧洲国家视英国的利益为单纯的经济利益，直到70年代，英国才加入由欧共体转化而来的欧洲经济共同体。到90年代，欧洲经济共同体扩展为欧洲国家联盟，而此时的欧盟既有共同的政治目标又有建立欧洲共同的货币体系的经济目标。随着经济和政治的发展，土木工程，尤其是桥梁工程至今没能形成某种统一阵线。这缘于英国和其他的欧洲国家迥异的大学教育培养体制，欧洲基金计划如苏格拉底计划、大不列颠（英国）欧洲计划等等。对改变这种局面发挥了独特的作用，苏格拉底计划是以各成员国内互派学生学习为基础，而英国欧洲计划主要是给予一些国家的学术机构和工业伙伴以科研援助；它通常是由一个工业国家牵头。关于知识的传播，目前似乎已出现了2种非常不同的方式、英美主要集中于在相关期刊出版物上发表首要的研究成果，例如ASCE、LCE及其它期刊，而欧洲内陆国家主要集中于在专门会议上展示其重要的研究成果，后者存在着局限性，新的研究成果的发布受到了限制。另外，语言也是难以逾越的障碍，那些以英语作为强势外语的欧洲内陆国家积极参与各种国际会议，如德国、意大利、比利时、以及荷兰和瑞士。然而，那些不以英语为强势外语的欧洲国家对国际会议的参与并不积极，比如法国。欧洲的研究在欧洲，关于桥梁研究的方向基本可分为三种类型：1、砖石结构的拱桥英国拥有大量的石拱桥，某些地区有超过60%的公路桥为古老的石拱桥，这些拱桥当初是为了马车通行而建造的，但这种桥型在欧洲其它地区已比较少见，因为它们在二战中许多已被毁坏。2、混凝土桥梁从20世纪的50年代至70年代，在欧洲涌现了大量的混凝土结构的桥梁，在那个时候，这种构造被视为是免于维修的。欧洲也有大量的使用后张法建造的混凝土桥梁，但这种桥梁中的铁制锚索套管会妨碍雷达对桥梁的检测。这种问题仅是存在于法、英两国。3、钢结构桥梁20世纪六七十年代，这种桥梁在英国遭受冷落，因为人们发现到这种桥需要维修保养。但它仍然被用于大跨径桥梁和铁路用桥，如今，随着英国正在进行的高速公路拓宽计划的实施，这种桥梁又重新受到了人们的青睐。欧洲研究的活跃性一个明确的信息表明专业人员在这个领域的研究工作正在欧洲兴起，但并不代表这种研究方法已经没有了缺陷。为了说明欧洲正在进行这种形式的研究工作，爱丁堡大学给出了一个这种资源互补的案例：运用数字化脉冲雷达对后张法建造的混凝土桥梁的孔隙进行检测。后张法混凝土铁路桥研究Ove Arup和他的合作者对曼彻斯特的一座长160M的后张法分段预制施工建造的铁路桥的上部结构的长期稳定性进行了检测和评估，这种技术已被运用于城市轻轨系统。特别需要关注的是后张力法施工的桥梁的完整性。物理检查、非损伤雷达检测及其它的研究方法均已被用来去调查桥梁中潜在的缺陷。自从1985年2月1日英国威尔士地区的一座名叫Ynys-y-Gwas桥梁突然坍塌以来。采用后张力法分段预制施工的桥梁在长期稳定性方面受到关注。因为这种桥梁可能会毫无预兆地出现脆性断裂，后张法钢绞线在预制段搭接部位的防腐工作是影响这种类型桥梁长期稳定性的主要因素。对容易发生脆性破坏处锚索套管中的沙浆孔隙的鉴定被认为是防腐检测中最为重要的步骤之一。桥梁描述总体布局Besses o th Barn大桥始建于1969年，是一座三跨总长160m的后张法分段预制施工的混凝土铁路桥。它的主跨跨径90米，横跨M62公路和巴利A665公路与Prestwick公路衔接，与A665公路最小桥下净空高度为5.18米，与M62公路的桥下净空则大约为12.5米。桥梁上部结构由空心梯形混凝土箱梁组成。箱体横截面高6.7m，宽4m。桥梁南部分引桥和中央主跨径均采用这种长为1.27M的梯形混凝土箱梁结构，后张法施工。这种箱形构件的作用是支撑用来承受铁轨和行车荷载的现浇混凝土悬臂梁。大桥中跨和南部引桥跨径均采用后张法装配式预制结构，这些后张法预制构件构件包括五种类型的预应力张拉措施。1、缘内部的顶端和底部布置纵向锚索管道，管道内的钢筋束用沙浆封住；2、分布在横隔板部位的腹板两侧挠曲钢筋束，钢筋束被包裹在现浇混凝土内；3、桥梁跨中悬臂梁内布置纵向钢绞束；4、在229mm宽的腹板内侧布置用以提高抗剪切能力的竖直钢绞束；5、布置穿过冀缘底部用以支撑悬臂梁的横向钢绞束。分段施工使用分段预制施工体系是包工单位针对大桥南部和中央跨径建议的备选方案之一，Current thinking认为这种施工体系在对穿越构件铰接点处的钢筋束没有足够的腐蚀措施时可能会导致整个结构的脆性断裂，最初的设计构思是想采用现浇的混凝土结构。检测和评估检测各个阶段的检修工作贯穿在桥梁结构所需的试验中，初期检查主要记录如下的一些明显的缺陷：1、在翼缘上表面的不合格的防水材料。2、空心箱梁内部300mm深度内雨水的渗透情况。3、铰接缝和支座处有关排水装置各种的问题。4、中央跨径下端背面暴露出的纵向裂缝。5、翼缘顶部预应力构件旁边的纵向裂缝。6、现浇混凝土表面大片的剥落部位和暴露在外的生锈的加强筋。评估参照最初的设计构想，评估以下目标项：1、估算现存的承载能力。2、挖掘原始设计资料中在结构上的缺陷部分。3、根据检测出的问题作出判断。检测和评估的结论根据检测和评估，仍然存在着一个主要的可疑因素，它就是埋藏在构件里面的预应力钢绞线、电缆或杆件，虽然从结构原理的角度进行分析，这些假定均不成立。然而，它们一旦被腐蚀，就会对桥梁结构的稳定性带来非常高的风险，这个基本原理已经得到证实。对第一阶段评估的全部内容作如下处理：1、进行详细是材料试验，去判定隐藏在结构内部的情况，特别是予埋后张法钢绞线的沙浆。2、混凝土结构耐久性试验。修理不合格防水材料和混凝土表面的瑕疵。检测方法非损伤雷达检测首期调查包括对预制构件铰接缝裂缝的勘测以及后张法钢绞线管道中预应力筋腐蚀和完整性的检测。然而，对出现问题的严重性会很难做出判断。这座桥梁一共有93个铰接缝，平均每个铰接缝有24根钢绞线贯穿，也就是说，那儿大约有2200个要用来进行检测的部位。一个标准的铰接缝横端面，主梁内部的24根钢筋束很难被检测到，因为除了铰接缝外，钢绞线在施加预应力之后又被现浇的混凝土所包裹。显然，铰接缝处钢筋束完全暴露在外是不切实际的，因此相比较而言，用雷达检测钢筋束管道中的孔隙十分高效的，庆幸的是通过铰接缝的放置钢绞束的钢制管道是断开的，可以用雷达检测管道槽内的钢绞束和孔隙。但是，仍然存在的问题是管道周围的高密度的铁元素会对雷达信号产生强烈的干扰，而实际上在这一宽102mm，150mm800mm的混凝土区域内正埋有许多高致密的钢板。雷达测试试验有三家公司被邀请前来参观和指挥试验研究工作，其中一家放弃，剩下的两家被要求用两周的时间去准备试验和撰写报告，再把他们的研究成果与物理勘探的结果进行比较。为了对比，选定了10个观测孔，小孔是垂直向下钻进导管。这十个小孔中有几个在铰接缝处，还有几个在充满沙浆的管道处。为了便于使用内径表面检测仪，小孔直径必须有25mm宽，结果显示爱丁堡大学的研究成果的准确度在60%左右。雷达测绘为主 内径表面检查仪检验裂缝为辅在完成对桥梁结构雷达检测后，再使用内径表面检查仪来验证被预知的裂缝。结果显示，在超过60%的案例中，雷达的检测是准确的。在其它几个事例中，一些证据表明在管道上面的现浇混凝土层中发现了蜂窝状的孔洞。然而用内径表面检查仪检测时，很难判定裂缝的实际尺寸大小以及在锚索套管中延伸的距离，尽管这些裂缝仅占套管不到25%的部分。但事实上，大多数存在于沙浆表面与套管上部曲面边界上的裂缝要比内径表面检查仪所检测到的要窄得多，（内径表面检查仪的分辨率大约在9mm左右）。在少数几个案例中，在沙浆表面能明显地看到预应力钢绞线，但没有迹象表明有水渗透了进去。而且使用内径表面检查仪是不可能看到钢绞线被腐蚀的情况。数字雷达测试这种测试方法是利用无线电频率的雷达天线的穿透性。有以下几个常用频率：1GHZ，900MHZ，和500MHZ。最高的频率能带来最好的分辩率，但会减小其在混凝土中的穿透深度。最低频率的穿透能力最强，但是分辩率最低。雷达扫描到的数据被记录到GSSISIR系统中，这种系统与雷达发射脉冲和记录数据相对应。雷达天线所收到的数据从模拟信号被转换成了数字信号。这种转换是使用一种16位的模拟信号变流器，它能使数据获得相当高的分辨率，以便用于后续的数据处理。这些数据被显示在一个高分辨率的彩色监测器上。在可视化校对之后，将这些数据储存在一个2.3千兆字节的磁带上，用于后面的分析和处理。首先通过磁带记录下数字化雷达所扫描到的原始数据，再通过相关的设置和处理程序转化为精确和可靠的数据。沿着轨迹做特别的标记，再通过记录元件或天线把这个轨迹描述下来。在大学实验室里进行非破坏性试验后，将所有的数字记录从微机上拷贝下来，（原始数据资料处理将会消耗35兆字节的内存。）后张法分析需要运用特殊的处理软件。这种分析是通过变换的颜色和线形来显示出特征点，也可以通过颜色的变换显示相位的变化。除了这些能变换颜色的设备外，还可能使用用来过滤水平线和竖直线的特殊程序。用一个大型荧屏测试器同时显示原始数据和处理过的数据，从而就能很清晰地看到被处理过数据是在那些地方做过修改的，同时电脑显示器将把反馈信息标注到纵坐标上。一个更为先进的软件能够显示专用雷达脉冲扫描的区域，在单独检测锚索周围状况时，它是一种特别有价值元件。调查研究结果的分析在别处已经有对调查结果非常充分的研究，数字化雷达绘图的本质就是将扫描到的被确认有双重相位位移的节点转化为着色线条，从而缺陷部位即被诊断出来。结论1、一个关于桥梁研究平台的雏形已经在欧洲诞生。2、雷达脉冲波检测技术的运用大大增加了对Besses o th Barn铁路桥评估结论的可信度。3、雷达勘察可以显示后张法钢绞线孔道内部的大部分缺陷区域。然而，即使运用了极其一流的研究手段，也没有迹象表明已发现受拉钢丝的腐蚀原因。Bridge research in EuropeA brief outline is given of the development of the European Union, together with the research platform in Europe. The special case of post-tensioned bridges in the UK is discussed. In order to illustrate the type of European research being undertaken, an example is given from the University of Edinburgh portfolio: relating to the identification of voids in post-tensioned concrete bridges using digital impulse radar. IntroductionThe challenge in any research arena is to harness the findings of different research groups to identify a coherent mass of data, which enables research and practice to be better focused. A particular challenge exists with respect to Europe where language barriers are inevitably very significant. The European Community was formed in the 1960s based upon a political will within continental Europe to avoid the European civil wars, which developed into World War 2 from 1939 to 1945. The strong political motivation formed the original community of which Britain was not a member. Many of the continental countries saw Britains interest as being purely economic. The 1970s saw Britain joining what was then the European Economic Community (EEC) and the 1990s has seen the widening of the community to a European Union, EU, with certain political goals together with the objective of a common European currency. Notwithstanding these financial and political developments, civil engineering and bridge engineering in particular have found great difficulty in forming any kind of common thread. Indeed the educational systems for University training are quite different between Britain and the European continental countries. The formation of the EU funding schemes e.g. Socrates, Brite Euram and other programs have helped significantly. The Socrates scheme is based upon the exchange of students between Universities in different member states. The Brite Euram scheme has involved technical research grants given to consortia of academics and industrial partners within a number of the states a Brite Euram bid would normally be led by an industrialist.In terms of dissemination of knowledge, two quite different strands appear to have emerged. The UK and the USA have concentrated primarily upon disseminating basic research in refereed journal publications: ASCE, ICE and other journals. Whereas the continental Europeans have frequently disseminated basic research at conferences where the circulation of the proceedings is restricted.Additionally, language barriers have proved to be very difficult to break down. In countries where English is a strong second language there has been enthusiastic participation in international conferences based within continental Europe e.g. Germany, Italy, Belgium, The Netherlands and Switzerland. However, countries where English is not a strong second language have been hesitant participants e.g. France.European researchExamples of research relating to bridges in Europe can be divided into three types of structure:Masonry arch bridgesBritain has the largest stock of masonry arch bridges. In certain regions of the UK up to 60% of the road bridges are historic stone masonry arch bridges originally constructed for horse drawn traffic. This is less common in other parts of Europe as many of these bridges were destroyed during World War 2.Concrete bridgesA large stock of concrete bridges was constructed during the 1950s, 1960s and 1970s. At the time, these structures were seen as maintenance free. Europe also has a large number of post-tensioned concrete bridges with steel tendon ducts preventing radar inspection. This is a particular problem in France and the UK.Steel bridgesSteel bridges went out of fashion in the UK due to their need for maintenance as perceived in the 1960s and 1970s. However, they have been used for long span and rail bridges, and they are now returning to fashion for motorway widening schemes in the UK.Research activity in Europe It gives an indication certain areas of expertise and work being undertaken in Europe, but is by no means exhaustive.In order to illustrate the type of European research being undertaken, an example is given from the University of Edinburgh portfolio. The example relates to the identification of voids in post-tensioned concrete bridges, using digital impulse radar.Post-tensioned concrete rail bridge analysisOve Arup and Partners carried out an inspection and assessment of the superstructure of a 160 m long post-tensioned, segmental railway bridge in Manchester to determine its load-carrying capacity prior to a transfer of ownership, for use in the Metrolink light rail system.Particular attention was paid to the integrity of its post-tensioned steel elements. Physical inspection, non-destructive radar testing and other exploratory methods were used to investigate for possible weaknesses in the bridge.Since the sudden collapse of Ynys-y-Gwas Bridge in Wales, UK in 1985, there has been concern about the long-term integrity of segmental, post-tensioned concrete bridges which may be prone to brittle failure without warning. The corrosion protection of the post-tensioned steel cables, where they pass through joints between the segments, has been identified as a major factor affecting the long-term durability and consequent strength of this type of bridge. The identification of voids in grouted tendon ducts at vulnerable positions is recognized as an important step in the detection of such corrosion.Description of bridgeGeneral arrangementBesses o th Barn Bridge is a 160 m long, three span, segmental, post-tensioned concrete railway bridge built in 1969. The main span of 90 m crosses over both the M62 motorway and A665 Bury to Prestwick Road. Minimum headroom is 5.18 m from the A665 and the M62 is cleared by approx 12.5 m.The superstructure consists of a central hollow trapezoidal concrete box section 6.7 m high and 4 m wide. The majority of the south and central spans are constructed using 1.27 m long pre-cast concrete trapezoidal box units, post-tensioned together. This box section supports the in site concrete transverse cantilever slabs at bottom flange level, which carry the rail tracks and ballast.The center and south span sections are of post-tensioned construction. These post-tensioned sections have five types of pre-stressing:1. Longitudinal tendons in grouted ducts within the top and bottom flanges.2. Longitudinal internal draped tendons located alongside the webs. These are deflected at internal diaphragm positions and are encased in in site concrete.3. Longitudinal macalloy bars in the transverse cantilever slabs in the central span .4. Vertical macalloy bars in the 229 mm wide webs to enhance shear capacity.5. Transverse macalloy bars through the bottom flange to support the transverse cantilever slabs.Segmental constructionThe pre-cast segmental system of construction used for the south and center span sections was an alternative method proposed by the contractor. Current thinking suggests that such a form of construction can lead to brittle failure of the entire structure without warning due to corrosion of tendons across a construction joint，The original design concept had been for in site concrete construction.Inspection and assessmentInspectionInspection work was undertaken in a number of phases and was linked with the testing required for the structure. The initial inspections recorded a number of visible problems including:1、 Defective waterproofing on the exposed surface of the top flange.2、 Water trapped in the internal space of the hollow box with depths up to 300 mm.3、 Various drainage problems at joints and abutments.4、 Longitudinal cracking of the exposed soffit of the central span.5、 Longitudinal cracking on sides of the top flange of the pre-stressed sections.6、 Widespread sapling on some in site concrete surfaces with exposed rusting reinforcement.AssessmentThe subject of an earlier paper, the objectives of the assessment were:1、 Estimate the present load-carrying capacity.2、 Identify any structural deficiencies in the original design.3、 Determine reasons for existing problems identified by the inspection.Conclusion to the inspection and assessmentFollowing the inspection and the analytical assessment one major element of doubt still existed. This concerned the condition of the embedded pre-stressing wires, strands, cables or bars. For the purpose of structural analysis these elements、had been assumed to be sound. However, due to the very high forces involved,、a risk to the structure, caused by corrosion to these primary elements, was identified. The initial recommendations which completed the first phase of the assessment were:1. Carry out detailed material testing to determine the condition of hidden structural elements, in particularthe grouted post-tensioned steel cables.2. Conduct concrete durability tests.3. Undertake repairs to defective waterproofing and surface defects in concrete.Testing proceduresNon-destructive radar testingDuring the first phase investigation at a joint between pre-cast deck segments the observation of a void in a post-tensioned cable duct gave rise to serious concern about corrosion and the integrity of the pre-stress. However, the extent of this problem was extremely difficult to determine. The bridge contains 93 joints with an average of 24 cables passing through each joint, i.e. there were approx. 2200 positions where investigations could be carried out. A typical section through such a joint is that the 24 draped tendons within the spine did not give rise to concern because these were protected by in site concrete poured without joints after the cables had been stressed.As it was clearly impractical to consider physically exposing all tendon/joint intersections, radar was used to investigate a large numbers of tendons and hence locate duct voids within a modest timescale. It was fortunate that the corrugated steel ducts around the tendons were discontinuous through the joints which allowed the radar to detect the tendons and voids. The problem, however, was still highly complex due to the high density of other steel elements which could interfere with the radar signals and the fact that the area of interest was at most 102 mm wide and embedded between 150 mm and 800 mm deep in thick concrete slabs.Trial radar investigations. Three companies were invited to visit the bridge and conduct a trial investigation. One company decided not to proceed. The remaining two were given 2 weeks to mobilize, test and report. Their results were then compared with physical explorations.To make the comparisons, observation holes were drilled vertically downwards into the ducts at a selection of 10 locations which included several where voids were predicted and several where the ducts were predicted to be fully grouted. A 25-mm diameter hole was required in order to facilitate use of the chosen horoscope. The results from the University of Edinburgh yielded an accuracy of around 60%.Main radar survey, horoscope verification of voids. Having completed a radar survey of the total structure, a baroscopic was then used to investigate all predicted voids and in more than 60% of cases this gave a clear confirmation of the radar findings. In several other cases some evidence of honeycombing in the in site stitch concrete above the duct was found. When viewing voids through the baroscopic, however, it proved impossible to determine their actual size or how far they extended along the tendon ducts although they only appeared to occupy less than the top 25% of the duct diameter. Most of these voids, in fact, were smaller than the diameter of the flexible baroscopic being used (approximately 9 mm) and were seen between the horizontal top surface of the grout and the curved upper limit of the duct. In a very few cases the tops of the pre-stressing strands were visible above the grout but no sign of any trapped water was seen. It was not possible, using the baroscopic, to see whether those cables were corroded.Digital radar testingThe test method involved exciting the joints using radio frequency radar antenna: 1 GHz, 900 MHz and 500 MHz. The highest frequency gives the highest resolution but has shallow depth penetration in the concrete. The lowest frequency gives the greatest depth penetration but yields lower resolution.The data collected on the radar sweeps were recorded on a GSSI SIR System 10. This system involves radar pulsing and recording. The data from the antenna is transformed from an analogue signal to a digital signal using a 16-bit analogue digital converter giving a very high resolution for subsequent data processing. The data is displayed on site on a high-resolution color monitor. Following visual inspection it is then stored digitally on a 2.3-gigabyte tape for subsequent analysis and signal processing. The tape first of all records a header noting the digital radar settings together with the trace number prior to recording the actual data. When the data is played back, one is able to clearly identify all the relevant settings making for accurate and reliable data reproduction.At particular locations along the traces, the trace was marked using a marker switch on the recording unit or the antenna.All the digital records were subsequently downloaded at the Universitys NDT laboratory on to a micro-computer.（The raw data prior to processing consumed 35 megabytes of digital data.） Post-processing was undertaken using sophisticated signal processing software. Techniques available for the analysis include changing the color transform and changing the scales from linear to a skewed distribution in order to highlight、突出certain features. Also, the color transforms could be changed to highlight phase changes. In addition to these color transform facilities, sophisticated horizontal and vertical filtering procedures are available. Using a large screen monitor it is possible to display in split screens the raw data and the transformed processed data. Thus one is able to get an accurate indication of the processing which has taken place. The computer screen displays the time domain calibrations of the reflected signals on the vertical axis.A further facility of the software was the ability to display the individual radar pulses as time domain wiggle plots. This was a particularly valuable feature when looking at individual records in the vicinity of the tendons.Interpretation of findingsA full analysis of findings is given elsewhere, Essentially the digitized radar plots were transformed to color line scans and where double phase shifts were identified in the joints, then voiding was diagnosed.Conclusions1. An outline of the bridge research platform in Europe is given.2. The use of impulse radar has contributed considerably to the level of confidence in the assessment of the Besses o th Barn Rail Bridge.3. The radar investigations revealed extensive voiding within the post-tensioned cable ducts. However, no sign of corrosion on the stressing wires had been found except for the very first investigation. 出处： 出处：天工网
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