TE||A bridge too far
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A bridge too far
过长的桥梁
英文部分选自经济学人Science and technology版块
Construction technology
建筑工程技术
A bridge too far
过长的桥梁
Crumbling infrastructure worries civil engineers
逐渐损坏的建筑物引发土木工程行业的担忧
THE first bridges were likely to have been built by early man shoving a fallen tree across a stream. Since then, construction techniques have come on a bit—from wood to stone, wrought iron and then steel. In the 20th century, reinforced concrete appeared. Concrete is an immensely strong material, especially when coupled with steel. But the sudden collapse of the Morandi bridge in Genoa this week (pictured), with a tragic loss of life, adds to the concern of civil engineers that many bridges around the world which use reinforced concrete are deteriorating faster than was expected.
早期人类将倒下的树木横过小溪，这可能就是最早的桥梁。从那以后，造桥技术取得了长足的进步，材料也由木头发展成石料、锻铁和钢材。在20世纪，钢筋混凝土问世。混凝土本身即是一种强度很高的材料，与钢材混合后强度更上了一个台阶。但是，本周位于热那亚的莫兰迪大桥突然垮塌，造成人员伤亡，并引发了土木工程界的担忧：全世界有诸多使用钢筋混凝土建造的桥梁，而它们老化的速度大大超过预期。
注释：莫兰迪大桥https://en.wikipedia.org/wiki/Ponte_Morandi
The Genoa bridge is based on a design called a cable-stayed bridge, although it is a somewhat unusual variant. Such a bridge uses one or more towers, from which run cables that support the deck of the bridge. This is different from a suspension bridge, such as the Golden Gate Bridge in San Francisco, in which the cables holding up the deck are suspended vertically from a main cable anchored at either end of the bridge. Cable-stayed bridges are widely used, mainly for spans shorter than those crossed in one go by a suspension bridge.
热那亚大桥采用斜拉桥设计，但又和一般的斜拉桥不完全一样。斜拉桥由一座或多座桥塔作支撑，塔上连接数条斜拉钢缆来承受桥体的重量。悬索桥的设计则与之不同，其主钢缆分别固定在桥的两端，而后其余钢缆纵向悬吊在主钢缆上，并支撑桥体重量，例如旧金山金门大桥。许多桥梁采用斜拉桥设计思路，且主要应用于较短跨度的桥梁，而悬索桥设计适用的桥梁跨度则相对较长。
注释：
斜拉桥https://en.wikipedia.org/wiki/Cable-stayed_bridge
悬索桥https://en.wikipedia.org/wiki/Suspension_bridge
A familiar feature of a cable-stayed bridge is that the cables form a fan-like pattern emanating from the supporting tower. If one of the cables is damaged or breaks, it should be obvious; the loading on the bridge is calculated so that the remaining cables will be capable of holding the structure up. The Morandi bridge is different because it was supported by pre-stressed concrete tendons. The tendons are made from bundles of steel wires tightened to produce compressive strength and then encased in concrete. The bridge was designed by Riccardo Morandi, a proponent of this type of bridge. Only a few have been built around the world.
斜拉桥常见的特征是斜拉钢缆从支撑桥塔处朝桥两端以扇形发射。如果其中一根钢缆损坏或发生断裂，从外部看上去会十分明显；与此同时，桥体重量经过精密计算，确保余下正常的钢缆能支撑住整个结构。莫兰迪大桥的不同之处在于该桥以预应力混凝土桥索作为斜拉支撑材料。这些桥索是由数捆钢筋拉紧从而产生抗压强度，之后用混凝土包裹而成。该桥的设计师里卡多▪莫兰迪很推崇这种桥。在世界范围内只建成数座该类桥梁。
注释：
预应力混凝土https://en.wikipedia.org/wiki/Prestressed_concrete（英文）
Concerns about Genoa’s bridge had been raised in the past. The Italian media has reported that in 2016, Antonio Brencich, a specialist in reinforced concrete at the University of Genoa, described the bridge as a “failure of engineering” and that sooner or later it would have to be replaced. Daniele Zonta, a civil-engineering expert at the University of Strathclyde, in Britain, says that since the opening of the bridge in 1967 the tendons have required continuous monitoring and maintenance.
之前人们就对热内亚大桥表示担忧。意大利媒体报道称，在2016年，热内亚大学（the University of Genoa）的钢筋混凝土专家Antonio Brenchci认为这座桥是 “失败的工程设计”，迟早要重建。英国斯特拉斯克莱德大学（the University of Strathclyde）的土木工程专家Daniele Zonta谈到，自1967年大桥通行以来，桥索的监管和保养就没断过。
Although the design of the bridge is unusual, it is much too early to say if that played any fundamental part in the collapse. And in other respects, the Morandi bridge is far from atypical. All around the world bridges built long ago, particularly those using reinforced concrete, are deteriorating. Even back in 1999, a study found that around 30% of road bridges in Europe had some sort of defect, particularly corrosion of their steel reinforcing or pre-stressed tendons.
尽管这座大桥的设计不走寻常路，但是把桥梁崩塌的责任归因于设计还为时过早。另一方面，莫兰迪大桥坍塌绝非个例。全世界范围内，那些很早建成的、尤其是使用钢筋混凝土的桥梁正在老化。甚至早在1999年的一项研究表明，欧洲30%的公路桥都存在某些缺陷，尤其是对钢筋和预应力筋的腐蚀。
A report from the American Road & Transportation Builders Association in January is even more sobering. It reckoned that 54,259 of that country’s 612,677 bridges are “structurally deficient”. These problem bridges have an average age of 67 years and are crossed by vehicles 174m times every day. At the present rate of repair and replacement, it will take 37 years to remedy all the problems, says Alison Premo Black, the organisation’s chief economist.
今年一月，美国道路交通建造商协会（the American Road & Transportation Builders Association）发表的报告更加发人深省。报告认为，全国共612677座桥梁中，有54529座存在“结构上缺陷”。有问题的桥梁平均寿命67岁，每天车辆通行量达1.74亿次。该协会的首席济学家Alison Premo Black说，以现在的修补和置换速率，需要37年才能补救所有问题。
What is going wrong with these bridges? The difficulty is that concrete, or rather the steel used to reinforce it, can fail in a number of ways. Salt, ice and the pounding of weather can cause tiny fractures in the concrete’s surface. As these cracks creep inward, they let in water. Once the water reaches the steel reinforcing or tendons, it corrodes them. This enlarges the cracks, which can cause the concrete to fall apart. That this is happening is evident from rusty streaks on crumbling concrete.
这些桥梁出了什么问题？问题就在于混凝土，或者更确切地说，用于加固混泥土的钢材会以各种方式发生故障。盐、冰和气候的侵袭会导致混凝土表面出现细小的裂缝。裂缝会缓慢地向深处蔓延时，水便顺着这些缝隙流进混凝土中。水一旦接触到钢筋或桥索，就会造成腐蚀。随后裂缝会因此扩大，造成混凝土瓦解。从破裂的混凝土可以看到斑斑锈迹，就知道发生什么了。
Heavy traffic
拥挤的交通
Other factors compound the deterioration of bridges, such as a constant cyclic vibration from traffic, says Mehdi Kashani, an expert in structural mechanics at the University of Southampton, in Britain. This is troublesome for bridges designed in the 1960s, when traffic flows were lower, cars were smaller and lorries much lighter. On top of that, extreme weather can take a toll, with heat and cold expanding and contracting the structure, floods eroding away foundations and high winds buffeting the bridge. This is why regular inspections and maintenance are essential.
英国南安普顿大学（the University of Southampton）结构力学专家迈赫迪·卡沙尼（Mehdi Kashani）称，还有其他因素会加剧桥梁的老化，譬如交通带来的连续性周期振动。这给20世纪六十年代设计的那些桥梁造成了不小的麻烦，因为当时的交通流量较少，汽车更小，卡车也要轻得多。除此之外，极端天气也会造成桥梁的老化，极热极冷的天气会导致桥梁结构热胀冷缩，洪水会侵袭桥梁基座，狂风会冲击桥体。因而，定期检查和维护是必不可少的。
New methods of monitoring structures are available to help engineers spot problems before they become critical. Instead of the arduous task of climbing up bridges or erecting scaffolding, camera drones can easily take a close-up picture of just about any part of a bridge. Electronic sensors can provide regular readings of any movement in the structure. And laser scanners are capable of picking up fine details and displaying them as a three-dimensional image. All this should help, but only if regimes exist to ensure that careful monitoring and preventive maintenance take place. If such tasks are skipped, for whatever reason, the result could be disaster. “The Genoa bridge is not the first to fall down,” says Dr Kashani. “And unfortunately it will not be the last.”
检测桥梁结构的各种新技术有助于工程师在问题变得棘手之前就发现它们。无须费力地攀爬桥体或搭建脚手架，载有摄像头的无人机能轻而易举地拍下桥梁任何部位的特写。电子传感器可以定期读取桥梁结构中发生的任何变化。激光扫描仪能够捕捉到微小的细节并以三维图像的方式呈现出来。这些技术帮助很大，但前提是政府能确保监测和预防性维修被认真执行下去。无论出于什么原因而跳过这些措施，结果都可能是灾难性的。“热那亚大桥不是第一个坍塌的，”卡沙尼博士说道，“不幸的是，它也不会是最后一个。”
Repair or replace?
翻修还是重建？
Monitoring and repair are not the only options. When bridges were being built in the 1950s, 60s and 70s, many were expected to last for more than 100 years. But the decay of reinforced concrete leads some civil engineers to think that such bridges may have a life of only 50-60 years. That means thousands of bridges are coming to the end of their days. Refurbishment is possible, but it is slow and very costly. It might end up being more expensive than building a new bridge.
监测和维修并非唯一的选择。20世纪50-70年代间建造的桥梁，很多桥梁预计使用100多年。然而由于钢筋混凝土受到腐蚀，一些土木设计师推测这些桥梁的寿命可能仅有五六十年。这意味着成千上万座桥梁的寿命已近尾声。重新翻修虽可行，但却耗时又费钱；最终也许会比修建一架新桥更为耗资。
New structures can also take advantage of advances in engineering. There has been huge progress in materials science, so much so that it is now possible to tinker with the internal structure of substances to make concrete more robust and steel better at resisting rust. Ultra-high-performance concrete is already being made in some countries to toughen buildings against such things as earthquakes and bombs. Apart from just sand and cement, other ingredients are added to these super concretes, such as quartz and various reinforcing materials. In some tests, the addition of plant fibres has been shown to produce markedly stronger concrete.
新的桥梁可以利用更为先进的工程技术。材料科学取得了巨大的进步，进步大到可以更改物质的内部结构，使混凝土更坚固，钢铁的抗氧化能力更强。有些国家已经制造出超高性能的混凝土用以加固建筑，可以防震和防弹。除了沙子和水泥，这些超强混泥土还混入了其他材料，比如石英和其他加固物质。一些测试表明添加植物纤维能制造出更坚固的混泥土。
Self-healing concrete is also being explored. Different methods can be used, but the basic idea is that, should cracks appear in the surface, they will trigger a chemical reaction that seals them up again.
可自行修复的混泥土也在研发中。能使用的方法有许多，但基本的原理是—当表面出现裂缝时，它们会引起化学反应再次封住裂缝。
Wholesale replacement of elderly bridges would be an expensive exercise, however.The Governor Mario M Cuomo Bridge, which opened as a replacement for the old Tappan Zee Bridge which crosses the Hudson River in New York, is expected to become fully operational later this year. It is also a cable-stayed bridge, but one of a more traditional design. It is expected to cost some $4bn. The old bridge, built largely from steel and concrete in the 1950s, was knocked up for some $60m, which in today’s terms would be a bargain $564m. The Tappan Zee Bridge was predicted to have a lifetime of only 50 years; it managed nearly 62. Its replacement is supposed to last for a century. Time will tell.
然而，大规模地替换掉旧桥将产生巨额费用。一座横跨纽约哈德逊河的塔本吉桥（Tappan Zee Bridge）将重新修建，取名马力奥‧科莫桥（Governor Mario M Cuomo Bridge），预计在今年年末全面开通。这也是一座斜拉桥，只是使用了更传统的设计，预计耗资40亿美金。旧桥建于1950年，主要材料为钢铁和混凝土，当年匆忙建成耗费了6千万美金，换算成今天的价格为56400万美金。塔本吉桥预计的使用寿命只有50年，它却为人民服务了将近62年。新建的桥预计能存在一个世纪。时间将会验证一切。
翻译组：
Nikolai，男，小硕, science追随者
Frank，男，小硕，经济学人的死侍
Li Xia, 女， 爱爬山的健身小白， 美食狂人
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Xingyi，男，小硕，经济学人爱好者
Helga，女，笔译民工，经济学人爱好者
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观点|评论|思考
本次观点由Muyi全权执笔
Muyi，文产小研，经济学人初段读者
大约在公元前1世纪，古罗马御用工程师马可·维特鲁威（Marcus Vitruvius Pollio）就曾在他的《建筑十书》中提出一切建筑物都应当恰如其分地考虑“坚固、方便、美观”的主张。而今“安全、美观、功能”仍旧是与桥梁质量息息相关的三大主要因素。安全性的完备是保证桥梁质量的基础；功能性的优劣是桥梁经济与价值的保证；而桥梁造型的美观则是价值增值的砝码。
近代桥梁建设随着大工业与交通运输的发展，至今已有200余年历史。随着“一桥飞架南北，天堑变通途”，当今的桥梁建设无论是从结构、材质还是外观造型都已发生了质的飞跃。桥梁建造是人类突破自然束缚的方式之一，也正是因为桥梁的存在让江河湖海不再能阻挡人类丈量土地的步履。但随着车速的提高、交通负荷的加重和环境的变化，现代桥梁的安全性、耐久性便受到了考验，以热那亚公路桥坍塌为代表的桥梁坍塌事故便是样例。事件发生后，BBC在相关报道中提出了热那亚事故发生的几种可能解释，其中便涉及区位和自然环境因素、公路桥管理不善、桥体本身构造缺陷、交通压力繁重以及事发时的恶劣天气等5大原因。
由于各种因素的制约，桥梁事故难以彻底消除。但如何尽最大可能减少事故，重视从桥梁管理、技术避防、建造使用和后期养修等层面的检查应对，让新兴桥梁科技能够更好的福利大众，让桥梁建设能够当起对对社会、历史的负责的态度，我想，这才是保障桥梁能够经历时间和风雨考验的基础。
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