The West Gate Bridge
建筑论文代写 The West Gate Bridge fell down on the 15th of October in 1970, it was caused by a few half girders on the west part of the bridge that didn’t fit.
The West Gate Bridge fell down on the 15th of October in 1970, it was caused by a few half girders on the west part of the bridge that didn’t fit. They attempted to fix this with an unusual method which made the situation worse. The bridge buckled and eventually collapsed. It killed the workers while they were on break and only a few were left alive.
The West Gate Bridge started construction in 1968 and was the second longest bridge in Australia. The building process was going well at first though an unusual method was being used throughout the project. About 2 years into construction, problems began to show. There was an imbalance between several steel girders which made them not fix into position. Some engineers proposed putting 10 concrete blocks which weighed 8 tons individually, on each of the girders to put them into place which caused the bridge to buckle.
西门大桥于1970年10月15日倒塌，原因是桥西侧的几根半梁不合适。 他们试图用一种不寻常的方法来解决这个问题，这使情况变得更糟。 桥梁弯曲并最终倒塌。 它杀死了正在休息的工人，只有少数人活着。
西门大桥始建于 1968 年，是澳大利亚第二长的桥梁。 尽管在整个项目中使用了一种不寻常的方法，但最初的建造过程进展顺利。 大约在建设两年后，问题开始显现。 几个钢梁之间存在不平衡，导致它们无法固定到位。 一些工程师建议在每根大梁上放置 10 个单独重达 8 吨的混凝土块，以将它们放置到位，从而导致桥梁弯曲。
The company Freeman Fox & Partners was in charge of build and this was their 20th bridge.
Some of their previous works were The Adome Bridge, Humber Bridge, Erskine Bridge, and Forth Road Bridge. The West Gate Bridge is a cable-stayed bridge in Melbourne, Victoria, Australia which spanned over the Yarra River north of Port Phillip and is an important link to the inner city.建筑论文代写
For the most part, the investigation was mostly interviewing survivors and explaining what happened. The blame was mostly on the engineer who designed it and the engineers who ordered the concrete blocks. It was found that Ward, aka Freeman Fox & Partners were responsible for giving the designs. The bridge was built unevenly and they tried to put concrete blocks on the girders. Their measurements were fixed in the rebuild and there were no problems during the process. It was structural engineer fault due to the failure of measuring properly and allowing to fixing the problem with concrete bricks, which resulted in the bridge buckling. The mess was cleaned up almost immediately. The ambulance got the injured, the firefighters put out the fire and the construction crew cleaned up the wreckage and started over. The bridge was reopened to the public in 1978.
公司 FREEMAN FOX & PARTNERS 负责建造，这是他们的第 20 座桥梁。
在大多数情况下，调查主要是采访幸存者并解释发生了什么。主要归咎于设计它的工程师和订购混凝土砌块的工程师。发现 Ward，又名 Freeman Fox & Partners 负责提供设计。这座桥建得不平整，他们试图在大梁上放混凝土块。他们的测量在重建过程中得到了修复，并且在此过程中没有出现任何问题。由于未能正确测量并允许用混凝土砖解决问题，导致桥梁屈曲，这是结构工程师的错误。烂摊子几乎立刻被清理干净。救护车将伤者救出，消防员将火扑灭，施工人员清理残骸并重新开始。该桥于 1978 年重新向公众开放。
The deck on West Gate Bridge is a continuous steel box girder of 4m in depth with plate thicknesses varying from 10 to 25mm. The overall width including the cantilevers is 37m. Inside, the box girder is divided into three cells by four longitudinal webs and has plated diaphragms every 16m. All plates are heavily stiffened with the majority of stiffeners being the old bulb flat type. The deck is cable supported along its centreline by two sets of cables which pass over saddles at the steel box tower heads and splay out at deck level into cable anchorages within the steel deck box.
Lane arrangement prior to upgrade
|View inside box girder|
The strengthening solution adopted was to prop the existing cantilevers and turn the existing hard shoulder into a running lane. Other options were considered that required widening the carriageway slightly but studies had shown that it was safe to reduce lane widths (to 3.2m in this case) over short distances without adversely affecting road safety. And this proved to be the least expensive option. As well as propping of the cantilevers a lot of internal strengthening to the deck and towers were required to cope with the additional traffic loading.
西门大桥桥面为连续钢箱梁，深4m，板厚10-25mm。 包括悬臂在内的总宽度为 37m。 在内部，箱形梁被四个纵向腹板分成三个单元，每 16m 有一次镀膜隔板。 所有板都经过严格加固，大多数加强筋是旧的灯泡扁平型。 甲板由两套缆索沿其中心线支撑，这些缆索越过钢箱塔头处的鞍座，并在甲板水平展开到钢甲板箱内的缆索锚固处。
Modeling with LUSAS
Very early in the project Flint & Neill decided to create a shell element model of the whole cable-stayed bridge structure in LUSAS. Peter Robinson, one of the project’s engineers involved said, “Ordinary desktop computers are now capable of running a shell model of the entire bridge. Which is great for modeling the distortion and shear lag stresses around the cable anchorages in wide boxes such as West Gate.” A rigidity matrix was defined to model the orthotropic effect of the stiffened plates. Linear elastic analysis was used to allow load combinations to be assessed.
|LUSAS model of West Gate Bridge, showing the permanent load deflection and cable creep||Live load modeling 建筑论文代写|
使用 LUSAS 建模
在项目初期，Flint & Neill 决定在 LUSAS 中创建整个斜拉桥结构的壳单元模型。 参与该项目的工程师之一 Peter Robinson 说：“普通的台式计算机现在能够运行整个桥梁的壳模型，这非常适合模拟西门等宽箱体中电缆锚固周围的变形和剪力滞应力。 .” 定义了刚度矩阵来模拟加筋板的正交各向异性效应。 使用线性弹性分析来评估载荷组合。
Load cases considered
For the permanent load case a survey carried out in 2007 showed that the central span of the bridge had deflected by around 330mm over the years due to the creep and sagging of the cables. Although the stretching of the cables didn’t change the tensions in them very much it did add considerably to the stresses in the deck. When sagging at mid-span and when hogging at the towers. In the LUSAS assessment model, the initial stress in the cable stays was adjusted to represent creep and the deck profile was matched to that of the 2007 survey. An as-built profile was also modeled to allow re-tensioning of the cables in the future.
For live loading, the traffic load definition was specific to West Gate Bridge and was derived from weigh-in-motion data. Where the weights of vehicles crossing the bridge were recorded and analysed to derive the extreme loading. Traffic loads were generated using Autoloader traffic load optimisation software. Which required the creation of over 700 traffic loadcases to assess maximum stress along the box girder, and in the bearings and cables. For wind loading static loadcases were derived from the gust buffeting response of a spine model.
Because of the history of the bridge the handling of the construction loads was a particularly sensitive issue,
made all the more difficult because the bridge was overstressed under the existing eight lane traffic loading. For reasons of safety, it was required to position concrete barriers along the bridge during the upgrade works which added considerable weight. It was decided to limit the loads during construction to the maximum theoretical 8 lane loading before the strengthening had started. This was achieved by modelling the full sequence of gantry movements and resulted in night time lane restrictions for a long period and restrictions on the allowable movements of gantries.
|Modelling of construction loading|
对于永久荷载工况，2007 年进行的一项调查表明，由于电缆的蠕变和下垂，多年来，桥梁的中心跨度已经偏移了大约 330 毫米。尽管缆索的拉伸并没有太大改变它们的张力，但是当在跨中下垂和在塔架处拱起时，它确实大大增加了甲板的应力。在 LUSAS 评估模型中，调整了斜拉索中的初始应力以表示蠕变，并且甲板剖面与 2007 年调查的剖面相匹配。还对竣工轮廓进行了建模，以允许将来重新张紧电缆。
对于活荷载，交通荷载定义是特定于西门大桥的，它来自动态称重数据，其中记录和分析过桥车辆的重量以推导出极端荷载。交通载荷是使用 Autoloader 交通载荷优化软件生成的，该软件需要创建 700 多个交通载荷工况，以评估箱梁以及轴承和电缆中的最大应力。对于风荷载，静态荷载工况源自脊柱模型的阵风抖振响应。
由于桥梁在现有的八车道交通负荷下承受了过大的压力，因此变得更加困难。出于安全原因，在升级工程中需要沿桥设置混凝土护栏，这增加了相当大的重量。在加固开始之前，决定将施工期间的载荷限制为最大理论 8 车道载荷。这是通过对龙门运动的完整序列进行建模来实现的，并导致长时间的夜间车道限制和对龙门架允许运动的限制。
Because Flint & Neill chose to create a shell element model of the whole bridge in LUSAS it was straightforward to refine the mesh in certain areas of interest to investigate localised effects. This had other benefits too as Peter Robinson explains: “Having a single global shell model meant that there was no need to worry about specifying boundary conditions or applying suitable loading as would be required for looking at regions of the structure using separate localised models, and this was a big plus.” He continues: “The model also showed how the distribution of loads in the webs and diaphragms of the anchorages took place. It’s worth pointing out that for the assessment carrying out the analysis with LUSAS was only half the story. We also had the task of checking against all the element (member) capacities which, for stiffened structures such as this box girder, can be very complex.”
|Detailed modelling around cable anchorage||Stresses in anchorage plates|
Codified checks were carried out to BD56 and to IDWR (Interim Design and Assessment Rules). These rules were drawn up in the 1970s following the collapse of bridges such as Milford Haven and West Gate Bridge and were felt by Flint & Neill to be the most appropriate assessment tool for the upgrade project. Localised modelling and nonlinear analysis with LUSAS was used to improve torsional buckling capacity of the bulb-flats beyond codified values resulting in a reduction of the strengthening required being obtained.
|View of bulb flat stiffened plates showing different types of strengthening||Analysis of bulb flat stiffened section of box|
由于 Flint & Neill 选择在 LUSAS 中创建整个桥梁的壳单元模型，因此可以直接在某些感兴趣的区域细化网格以研究局部效应。正如 Peter Robinson 解释的那样，这还有其他好处：“拥有单一的全局壳模型意味着无需担心指定边界条件或施加合适的载荷，因为使用单独的局部模型查看结构区域所需的，并且这是一个很大的优势。”他继续说道：“该模型还显示了锚固腹板和隔板中的载荷分布是如何发生的。值得指出的是，使用 LUSAS 进行分析的评估只是故事的一半。我们还有任务检查所有单元（构件）的能力，对于像这个箱梁这样的加筋结构来说，这可能非常复杂。”
对 BD56 和 IDWR（临时设计和评估规则）进行了编码检查。这些规则是在 1970 年代在 Milford Haven 和 West Gate Bridge 等桥梁倒塌后制定的，Flint & Neill 认为这些规则是升级项目最合适的评估工具。使用 LUSAS 进行局部建模和非线性分析，以提高球扁钢的扭转屈曲能力，使其超过规定值，从而减少所需的强化强度。
At the start of the strengthening project a lot of work was done to improve the access to the box girder. This saw the enlargement of the central reserve manholes, end pier soffit openings, internal walkways and of the diaphragm and inner web openings where possible. The outside of the bridge has seen the addition of 528 cantilever props, which were installed over a 12 month period using gantries slung beneath the cantilevers. Substantial strengthening was carried out inside the box to the bottom flange and webs.建筑论文代写
This took the form of extra stiffening to the existing stiffeners and the addition of some new stiffeners. The box walls and diaphragm around the pier bearings required heavy strengthening in an already congested area. Prestressing strands were also used inside the box girder to overcome tension overstress in the bottom flange plate and overstress at the splice plates. The prestressing extends over a 60m length of flange, passing through holes drilled in the flange stiffeners, with plated anchorages at each end. Additional stiffening of the towers was also required requiring the fitting of new plates in the region where the tower penetrates the deck level and for these close tolerance bolts were used to avoid weakening the existing structure.
|Installation of cantilever props||Prestressing of bottom flange|
在加固项目开始时，做了很多工作来改善箱梁的通道。这见证了中央储备检修孔、端墩拱腹开口、内部走道以及隔膜和内部腹板开口的扩大。桥的外部增加了 528 个悬臂支柱，这些支柱是使用悬臂下方悬挂的龙门架在 12 个月内安装的。箱体内部对底部法兰和腹板进行了大量加固。
这采取了对现有加强筋进行额外加强的形式，并增加了一些新的加强筋。桥墩轴承周围的箱壁和隔板需要在已经拥挤的区域进行大量加固。箱梁内部还使用了预应力钢绞线，以克服底部翼缘板中的张力过应力和拼接板上的过应力。预应力延伸超过 60m 的翼缘，穿过翼缘加强筋中钻出的孔，每端都有电镀锚固。还需要对塔架进行额外加固，需要在塔架穿过甲板水平面的区域安装新板，并且使用这些紧公差螺栓来避免削弱现有结构。
It is possible to take any of a number of points as that from which stemmed the later events leading ultimately to the failure. One such starting point is certainly the manner in which spans 10-11 and 14-15 were erected.
There are a number of ways in which these spans might have been erected. The simplest is probably to erect all the boxes or half boxes and connect them together up in the air resting on temporary false work. This is a straightforward method, but a lot of temporary supports would be required, many of them founded in the water.建筑论文代写
Another method is cantilever erection in which the half boxes would be lifted up into position by means of a travelling crane running out on the spans, starting at piers 10 and 15 respectively, and have their outer ends supported on a succession of temporary trestles. The last temporary trestle would be at mid-span, and beyond this the remaining four boxes would be cantilevered until box 8 landed on pier 11 (or pier 14).建筑论文代写
In this scheme it would be necessary to support the ends of the boxes on temporary packings on top of the trestles, so as to tilt them slightly upwards. Thus, after allowing for the downward deflection of the cantilever under dead load, its outer end would still be at a sufficiently high level to land on its bearings on pier 11 (or pier 14).
The advantages of both these schemes are that the lifts are relatively light and although the connections between the boxes have to be made up in the air. They present no special difficulties because each box is small and there will be little, if any, distortion along the edges of the projecting flange plates at the longitudinal splices.
有可能将许多点中的任何一点作为导致后来导致最终失败的事件的根源。一个这样的起点当然是跨度 10-11 和 14-15 的架设方式。
另一种方法是悬臂架设，其中半箱将通过在跨度上运行的行车吊升到位，分别从桥墩 10 和 15 开始，并将它们的外端支撑在一系列临时支架上。最后一个临时栈桥将在中跨，除此之外，其余四个箱子将悬臂直到箱子 8 降落在 11 号码头（或 14 号码头）。
在这个方案中，有必要在支架顶部的临时包装上支撑箱子的末端，以便将它们稍微向上倾斜。因此，在允许悬臂在恒载下向下偏转后，其外端仍将处于足够高的水平，以靠在 11 号墩（或 14 号墩）上的轴承上。
Both these schemes have the further advantage that they permit the early placement of concrete in 10-11 (14-15) since the temporary props or false work can be left in position while concrete is being placed.
This not only gives a solid working platform from which future stages can be cantilevered out. It also provides a more effective composite action between steel and concrete for the bridge in its service condition.
Another method of erection would be to assemble the whole span 14-15 or 10-11 on the ground and jack it up into place on the piers. This scheme has the advantage that all the boxes can be connected together at ground level instead of up in the air. But the total weight to be lifted would be some 1,200 tons to a height of 170 feet. And the jacking operation would be slow and costly. Nevertheless, many bigger spans have been erected in this way and the operation should be reasonably straightforward with no unforeseen difficulties.建筑论文代写
The method proposed by WSC for erection of spans 10-11 and 14-15 was to assemble each span in two halves on the ground-full length and half width.
Each half span was then lifted by jacking straps to the top of the pier, landed on a rolling beam and moved across into position. The cross-diaphragms in the centre panels of each box were assembled on the ground in the south half spans.
In joining the two half spans together, it was therefore necessary not only to correct. Any difference in their vertical camber but also to pull them together horizontally. It should then be possible to connect all the cross-diaphragms at the centre panels . And also the full lengths of the longitudinal splices in the upper and lower flanges.
两个方案的另一个优点是它们允许在 10-11 (14-15) 提前放置混凝土，因为临时支柱或虚假工作可以在放置混凝土的同时保持原状。
另一种安装方法是将整个跨度 14-15 或 10-11 组装在地面上，然后将其用千斤顶顶到桥墩上。这种方案的优点是所有的盒子都可以在地面连接在一起，而不是在空中。但是要提升到 170 英尺高的总重量将是大约 1,200 吨，并且顶升操作将缓慢且成本高昂。尽管如此，以这种方式建造了许多更大的跨度，并且操作应该相当简单，没有不可预见的困难。
WSC 提出的用于安装跨度 10-11 和 14-15 的方法是将每个跨度在地面全长和半宽上分成两半。
Compared with cantilever erection, the adopted scheme had the advantage that much more of the assembly of the boxes could be done on the ground and no temporary props were required.
Compared with lifting the whole of each span in one, the adopted scheme had the advantage that each half span naturally had only half the weight. So that the lifting operation would be halved in magnitude, although it had to be done twice.
There were a number of serious disadvantages however, in lifting each span in two longitudinal halves. Each half span was asymmetric so that there was a horizontal bowing outwards, amounting to about H inches from the centre line at mid-span. Moreover, the upper and lower flanges each projected some 10 feet towards each other at the longitudinal centre line. And substantial temporary stiffening and bracing were needed, particularly on the upper flange which was stressed in compression, to prevent these projecting flanges from buckling. It was also essential to ensure that the two half spans were accurately assembled on the ground before lifting. And that their vertical cambers were the same within at least 1 inch or preferably ! Inch in order to avoid having to carry out a slow, difficult job of correcting the cambers up in the air. 建筑论文代写
This is not to say that the method could not have been successfully adopted, provided that very careful forethought had been given to dealing adequately with all the potential difficulties. But these difficulties are substantial and that may be the reason why no evidence could be found that this method of erection had ever been attempted before. Anywhere in the world, under conditions similar to those prevailing at the West Gate Bridge.
然而，在将每个跨度提升为两个纵向半部时存在许多严重的缺点。每个半跨是不对称的，因此水平向外弯曲，距离中跨中心线大约 H 英寸。此外，上下翼缘在纵向中心线处彼此相对突出约 10 英尺，需要大量临时加固和支撑，特别是在受压时受压的上翼缘，以防止这些突出的翼缘屈曲。确保两个半跨在提升前准确地组装在地面上并且它们的垂直弯度在至少 1 英寸或最好是相同的范围内也很重要！英寸，以避免必须进行缓慢，困难的工作来纠正空中的外倾角。