土木工程建筑外文翻译外文文献英文文献欧洲桥梁研究.doc

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:Defective waterproofing on the exposed surface of the top flange.Water trapped in the internal space of the hollow box with depths up to 300 mm.Various drainage problems at joints and abutments.Longitudinal cracking of the exposed soffit of the central span.Longitudinal cracking on sides of the top flange of the pre-stressed sections.Widespread sapling on some in site concrete surfaces with exposed rusting reinforcement.AssessmentThe subject of an earlier paper, the objectives of the assessment were:Estimate the present load-carrying capacity.Identify any structural deficiencies in the original design.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. 欧洲桥梁研究欧洲联盟共同的研究平台诞生于欧洲联盟。为了说明欧洲的研究方法已经被这种方式所替代，一个典型的案例是后张桥在英国爱丁堡大学进行了讨论，对数字脉冲雷达识别后张预应力混凝土桥梁孔隙互补的情况。引言利用各研究小组的研究结果验证了大量的相关参数是所有研究领域面临的挑战，这是使研究和实践更有针对性的的结合。此外，在欧洲语言是不能忽视的是一个巨大的障碍，为了避免类低于1939到1945第二次世界大战一样的欧洲内战， 60年代的第二十世纪的欧洲共同体的建立是基于欧盟各个国家这样共同的目的。它是建立在一个强大的政治动机之上，但英国不是欧盟一员，因此许多欧洲国家视英国的为纯粹的经济利益，直到20世纪70年代英国加入欧洲共同体进入欧洲经济共同体。在90年代，欧洲经济共同体扩展为欧洲联盟，在这个时候，欧洲联盟既有共同的政治目标，也有建立一个共同的欧洲货币体系的经济目标。随着经济和政治的发展，土木工程特别是桥梁工程一直没有能够形成统一战线。这是由于英国和其他欧洲国家不同的大学教育培训体系，欧洲基金计划，如苏格拉底计划，英国欧洲计划等。扮演一个独特的角色来改变这种状况，苏格拉底方案是以国内交换生学习为主，而英国的欧洲计划则是给一些国家的学术机构和产业界的合作伙伴提供研究援助；这通常是由一个工业国家领导的。传播知识，现在似乎已经出现了两个非常不同的方式，英国和美国主要集中在将研究结果发表在相关的期刊，例如ASCE、LCE和其他期刊，和欧洲大陆国家主要集中于重要研究专题会议上展示研究成果，后者在研究成果上发布具有局限性。此外，语言是很难克服的障碍，在英语是一种强势语言的国家里，在欧洲内陆国家积极参加各种国际会议，如德国，意大利，比利时，荷兰和瑞士。然而，英语不是一种强大的语言国家里，在国际会议上不活跃，如法国。欧洲的研究在欧洲，桥梁的研究方向可分为三种类型：1圬工拱桥英国有最大的砖砌拱桥。在英国的某些地区，多达60%的道路桥梁是石砌石拱桥，这些最初为马拉交通建造的。这在欧洲其他地方不太常见，因为它们在二战期间，它们大多数已经破坏了。2混凝土桥在20世纪50年代、到70年代的时候，欧洲出现了大量的混凝土结构桥梁，在那时，这一结构被认为是免维护的。欧洲还使用了很多后张法建造的混凝土桥梁，但铁制锚索套管会影响桥梁雷达监测。这个问题只存在于英法两国。3钢结构桥在上世纪60年代和70年代被认为是对维修的需求，这种桥在英国被冷落了。但它仍然被用于大跨度桥梁和铁路桥梁，现在，这种桥应用于英国正在进行的公路扩建工程行。欧洲的研究活动一个明确的信息表明，在这一领域的研究工作正在欧洲星期，但它并不意味着这中研究的方法没有缺陷。为了说明欧洲研究正在进行的类型，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。总体布局Besses oth 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