今天，FRP在桥梁建设中的应用技术极大的满足了目前行业发展需求，Composite Advantage LLC公司的Scott Reeve在这篇文章中将和我们讨论FRP在桥梁建设中的优势和劣势。
纤维增强聚合物（FRP）在桥梁施工中已有14年的历史，今天，FRP复合材料将继续为美国和全球交通运输基础设施带来巨大的经济效益。虽然业内早期的预 测显示市场对FRP的大额需求，但是由于建筑业低迷等一些影响，FRP市场并未像预期那样，大幅增长。但是，我们可以做出肯定的成绩是，在过去的十年中， 越来越多的出现了应用FRP桥梁建设技术制造出的专有桥梁。
美国与1996年首次将复合材料技术应用于桥梁建设中，以提高桥梁的耐腐蚀性能，从而延长其使用寿命。复合材料的优势主要体现在更快速的安装时间，更高承 载能力，以及低维护率等方面。因此，从1996年开始，美国有将近100座桥梁都加入了复合材料（全球复材桥梁总数为200多座）。
这些桥梁的建成，不但向人们展示了复合材料的强大技术工艺，而且为桥梁的设计者和政府建设部门提供了更多一种的有价值的可选择原材料。许多早期的复合材料 桥梁项目的成功，使业界对该种桥梁越来越有信心。今天，随着“论证阶段”的完成，FRP桥板被视作传统材料桥板最有力的竞争对手。虽然FRP板材的使用需 求不断增长，桥梁的出资方却开始面临成本上涨的考验，因此桥梁设计者也始终对FRP材料有所顾虑。本篇文章，为最适合、最有价值的桥梁投资者提供了FRP 原料的案例和竞争因素的分析。
除了重量轻，耐腐蚀，高强度，降低生命周期成本，FRP技术还具有更快的安装速度。预装的FRP桥梁面板能够迅速的完成安装工作。而传统的桥梁施工需要耗费大量精力在架设桥梁结构，安装钢筋，浇注混凝土并需等待其凝固。而且仅需挖掘机在施工现场就可完成安装任务。
上图为位于美国俄勒冈州的Clark River 桥，此桥为开河桥，建于1924年，于2002年重新利用FRP面板堆桥梁进行返修
{zd0}优势
对于设计者和投资者来说，FRP板材具有许多优势，其中当然包括灵活的解决方案和长期收益。比如：
轻重
FRP桥板比钢筋混凝土桥面在重量上降低10%~20%。因此使用FRP桥板能够比传统桥面大大降低自身重量。这就意味着新兴桥板的使用能够提高桥梁原有 设计的额定载荷和原有的设计使用寿命。在新型桥梁建设中，由于大大减少了结构件的使用，因此将轻重理念能够渗透到整座桥梁结构之中。由于FRP桥面每块面 板的重量不到6000磅（约2.72吨），因此，使用简易设备即可完成安装工程。挖掘机在施工现场就可完成安装任务。由于安装工程无需使用昂贵的起重机， 这无疑降低了施工成本，而且也不会由于空中架设的电力线路阻碍起重机工作，而影响项目施工进程。
耐腐蚀
钢筋易受腐蚀是导致混凝土桥面早期恶化的主要因素。道路除冰盐的使用，加上高于预期的交通严重负荷，同样加速了桥梁老化速度。由于FRP材料具有较优越的 抗腐蚀能力，因此使用FRP材料制成的桥面板是传统材料的{zj0}替代品，解决了传统材质桥面维护工作繁重的问题。这项性能上的突破，在天气寒冷地区显得尤为 重要：因为那里的桥面不得不时刻面临冰雪或除冰盐水的考验。FRP材质向众人展示了其{zy1}的耐久性能，具有{jj0}的抗腐蚀性能，至少能够保证50年性能不 变。由此，FRP板材的使用寿命能够达到75~100年。
快速安装
在工厂制造桥梁面板并将它们运送到桥梁施工现场，这种方式与传统的水泥现场浇注施工的方式相比，具有如下好处：在受控环境中能够密切监测质量标准；不易受 到天气变化造成的施工延误；最重要的一点，施工效率大幅度提高。一旦桥梁主体结构准备完毕，预装的FRP桥梁面板能够迅速的完成安装工作。而传统的桥梁施 工需要耗费大量精力在架设桥梁结构，安装钢筋，浇注混凝土并需等待其凝固。
高强度结构
复合材料板材具备高强度的安全系数。由于FRP材料没有钢和钢筋硬度高，因此在FRP板材的设计上就需要加强该性能。目前，弯沉检测是用来评价 FRP性能的最主要标准。有时FRP面板的弯沉标准甚至比传统水泥面板标准更为苛刻，这组要是由于FRP无论如何还是被视作业内一种全新的原材料。然而 FRP板材的静态测试数据已经清晰表明，该种材质的桥梁面板已经大大超过的特定性能需求，并且xx能够提供高安全系数。
更低的生命周期成本①
FRP桥面板具有非常优越的防腐性能，因此日常桥梁维护中的成本非常低廉。这同时意味着，FRP桥面板比传统材质面板具备更长的使用寿命。这些因素加在一起，是FRP材质拥有更低的生命周期成本。
前期投入成本与未来收益成正比
将FRP材质应用于一般桥梁结构的最主要好处是具备{zy1}的防腐性能，拥有这一优点将使桥梁具备更长的使用寿命和更低的维护成本。将FRP材质应用于 桥梁中，最主要的是着眼于未来。通常意义上，巨大的收益往往伴随着高昂的价格。对于大多数桥梁业主，在获得未来收益之前，往往需要支付大额的前期成本。对 于一些政府机构，面临繁重的老旧结构改造工程，但是通常资金方面又比较拮据，因此这些机构也很难拿出大笔的前期项目资金。因此作为政府桥梁拥有者的业主是 否有能力投入项目生命周期成本，对于扶持新技术（例如FRP），并将新技术带来的市场收益{zd0}化，是至关重要的。
由于FRP桥面板具有优良的耐久性，节约了更新换代的成本和维护成本。其超过百年的桥梁服务周期能够能够为业主带来前期整体结构投入成本更多的收 益。与传统材质相比，FRP节约的生命周期成本能够大大超过该材质先期较高的成本投入。然而相关机构很少基于预计生命周期成本数据来选择原材料，通常材料 选择的基准主要依赖工程师的经验和判断，以及机构偏好。行业标准的做法，更倾向于如何将建设项目初期投入成本控制在{zd1}范围。
Lewis-draw大桥重新翻新安装了FRP桥面板
市场现状
当FRP首次被引入桥梁市场领域时，就凭借其强大的性能和巨大的收益承诺迅速的占有了市场一定份额。支持这一预测的基础是，仅美国境内的桥梁就超过 了58万座，在这之中，有19.7万座桥梁被检测为需要维护和修缮。庞大的数据表明复合材料还是过高估计了其市场渗透量。14年后，很明显，FRP仍然不 是桥修复材料的{sx}。造成这样的状况有很多原因，但最主要的理由是与传统材料相比，FRP过高的价格。
①生命周期成本((Life Cycle Costing ，LCC)：指产品在整个生命周期中所有支出费用的总和，包括原料的获取，产品的使用费用等，即是指是企业生产成本与用户使用成本之和。
生命周期成本法(LCC)源于20世纪6O年代美国国防部对军工产品的成本计算。随着价值工程、成本企划等先进管理模式的诞生，生命周期成本法在成本管理中越来越多地被运用，它可以满足企业定价决策、新产品开发决策、战略成本管理、业绩评价等的需要。
生命周期成本法是一种计算发生在生命周期内的全部成本的方法，通常被理解为产品生产周期成本法，以此来量化产品生命周期内的所有成本。值得一提的 是，企业生产体系设计的中心环节是系统地衡量产品、资产和劳动力等生产要素，并组合成一体化的功能单元。因此，对于资产和劳动力，同样可以采用生命周期成 本法来分析其成本构成。
FRP的高价格主要是由于：
原材料成本：更优质的材料当然花费更多
{dywe}的桥梁：每一座桥梁都需要单独设计。由于FRP是一项新兴技术，因此就需要额外的设计费用。而这项费用在传统材料中是不需要投入的，因为作为已经发展成熟的传统材料，是拥有一套既定的标准规范和设计程序，适用于整个桥梁工业。
产量低：制造业来讲，制造、销售数量终究还是与收益密切相关。
其他因素包括市场规模，竞争和预算。许多桥梁虽然存在一定的缺陷，但是在主体结构上仍不具备严重问题，并且可以再继续使用几十年。改造乡村地区交通负荷量不高的老旧桥梁，也至少要在几十年以后。
与此同时，基础竞争也在不断向前推进。混凝土目前已改进了其性能，例如密度更低和预制替代品，以此更好的为建筑领域服务。除此之外，混凝土使用简单，价格低廉，而且是业界已知的发展成熟原材料。
预算越来越少，使得桥梁业主不得不少花钱、多办事。这样就促使越来越多的业主选择成本{zd1}的（当然也往往是不经久耐用的）替代品。
不幸的是，桥梁后续的维护者却不得不为业主最初的选择承担后果。研究表明：桥梁业主在材料采购过程中75%~85%不会考虑生命周期成本因素。同时，维修成本也没有太多的考虑。
产量，是评价{zj0}制造工艺的另一项主要参数。对于FRP板材来说，主要有两项生产工艺：
一类是批量生产，板材的制作从开始到结束都是一片片的单独个体。这种工艺通常将树脂导入整个板材模具中。
另一类是拉挤工艺。是一项持续生产过程，生产出未截断的一整块面板。应用拉挤工艺可以生产出面积较大的板材。这种工艺满足了高产量成本效益需求。因此，拉挤工艺也被FRP生产过程中最能减低成本的有效途径。
但是，基于目前桥梁的设计和建造的制约，应用拉挤工艺还未能xx实现。主要是由于每一座桥梁都是{dywe}的，并且都有各自不同的需求。因此，几乎没有“复制”的桥梁。
Steel-grate大桥原先的钢制格板桥面
Steel-grate大桥重新安装了FRP桥面板
FRP板材如何适应今天的市场
在今天的基础设施建设市场领域，尽管FRP复合材料板材在价格上并不具备优势，但是目前桥梁的四类应用，仍将大力推动FRP板材的发展。每一类应用都有一 个至关重要的考虑因素：轻重。设计者必须尽量减低桥梁重量以满足设计和应用需求。除轻重的优点之外，FRP板材还使得桥梁业主获得高效防腐和更长生命周期 的优势。
极具历史意义的钢桁架桥
极具历史意义的钢桁架桥
下承式连续钢桁架拱桥
FRP板材{zj0}应用领域包括：
易于移动的桥梁
成为被历史铭记的钢桁架桥②
具有钢格板的桥梁
行人和车辆的桥梁
下面我们分别对以上四点进行分析：
易于移动
移动式桥梁，主要分布在沿海和港口地区。沿海、河以及五大湖地区的大型港口城市的桥梁，不但要适应重型卡车的行驶需求，而且要满足商业船只航行的需求。这 些卡车要频繁往返于工厂和港口之间。沿海城市的桥梁除了要具有承载交通运输的能力，而且要兼顾商业船只和游艇。在这些地方，主要应用三种桥梁（见下图）， 它们是：提升式桥梁（Lift bridge），旋开桥（Swing bridge），开河桥（bascule bridge）。通常来讲，这些桥梁的桥面钢材或钢筋混凝土材质。桥面的重量对机械设备的投入成本和经营成本将造成直接影响。FRP桥面在众多同类产品 中，重量{zd1}，同时还能够为桥梁上部钢结构提供坚实的基础。目前，FRP桥面已被众多的可移动桥梁所采用。少数情况下，这类桥梁还被应用到繁忙的港口地 区，承载大量的重型卡车的运输工作。
提升式桥梁
旋开桥
开河桥梁
开河桥梁
“保存”历史
轻重的FRP桥板同时还可以应用在极具历史意义的钢桁架桥结构中。许多钢桁架桥建于20世纪中期，它们更多的是承载着历史价值，主要原因是由于它们之中大 多数的额定负荷并不再适用于今天的交通运输要求。FRP确实是减少桥梁自重非常不错的选择。经测算数据为每平方英尺可减低80磅左右。因此，无需更换这些 具有历史意义的桥梁，FRP桥面能够帮助这些已“退休的”老旧的桥梁重新发挥作用。
目前正在进行的一项研究是针对加利福尼亚桥梁进行的。研究的主要内容是将目前的钢筋混凝土桥面与FRP桥面进行性能上的对比。测试结果表明：混凝土桥面为105磅/平方英尺；exothermic桥面为55磅/平方英尺；FRP桥面为16磅/平方英尺。
举个例子，位于俄亥俄州Ashtabula县的Schaeffer Road大桥，这座钢桁梁桥，建于1936年。这座具有连续三个钢梁跨度的大桥总长度为175英尺（53.34米），宽度为17英尺（5.18米）。地方 政府曾表示，并不想替换这座大桥，由于钢桁架结构是比较有价值的。因此只需更换成FRP桥板，就能够大大减低该桥梁的自身重量，使其继续发挥作用。
有效保护上部结构
FRP桥板是桥梁钢格板的一个有效替代品。虽然钢格板也具有较轻重量，通常为17~28磅/平方英尺。但是，如果接触xx化学品时，上部结构会连带接触这 些物品，使其容易发生腐蚀现象，而且格板表面也随着时间的推移变得平滑，使车辆在雨，雪天气或桥面道路结冰时发生侧滑。在很多情况下，格板的使用是针对上 层覆盖的钢制桥板。因此大桥业主必须选择一种新的钢格板或FRP桥板。原因是由于将钢格板填入混凝土后，会增加到55磅/平方英尺的重量，因此这种做法是 不可行的。FRP的重量仅为16~20磅/平方英尺，因此为{zj0}选择。FRP桥板带来的第二个益处是，位于桥梁附近的企业，宾馆，饭店和公园将不用忍受传 统桥梁带来的噪音。事实证明，使用FRP桥板几乎在车辆行驶到大桥上时，几乎没有什么噪音。因此，一个轻重、表面坚固、耐腐蚀的桥板将大大降低对上部结构 的腐蚀。
为道路减负
第四个应用领域是将原有仅用于行人/自行车通行的桥梁与目前供汽车通行的桥梁相连。尽量减少自重是这样一个项目成功必不可少的因素。如果结构设计上 可行的话，在现有汽车桥梁之上，用FRP桥面扩充出供行人行天桥，将比另外重新修建一座与汽车桥梁平行的行人桥梁更为节约成本。
未来的FRP桥面
随着时间的推移，FRP也会逐渐成为一种给设计者和业主带来更多益处的成熟原材料。任何新型材料的发展都需要时间过程，需要开发出相应的程序，规格，设计知识和业主满意度。FRP材料所具有的{zy1}耐腐蚀和轻重性能会在接下来的14年中被大量应用。
目前的市场发展显示，FRP的{zj0}应用领域为可移动桥梁，钢桁架桥和与目前车用桥梁相连的人行天桥。作为美国交通运输部的一个分支：美国xx公路管理局 （FHWA），提供了各种结构类型桥梁的统计数据表示，目前，美国有883座可移动的桥梁和12 608座桁架桥。虽然这个数字只是美国桥梁总数的一小部分，但是FRP将会成为许多这类型桥梁的“{zj0}拍档”。不仅如此，FRP将为桥梁业主提供{zj0}的解 决方案，同时有利于国家桥梁的整体发展。
②钢桁架：是指用钢材制造的桁架。工业与民用建筑的屋盖结构、吊车梁、桥梁和水工闸门等，常用钢桁架作为主要承重构件。各式塔架，如桅杆塔、电视塔和输电线路塔等，常用三面、四面或多面平面桁架组成的空间钢桁架。
With a 14-year track record of bridge installations under its belt, the fibre reinforced polymer (FRP) composites market continues to offer significant benefits to the transportation infrastructure in the USA and around the world. Although early predictors indicated high volume demand for FRP, quantities have remained somewhat low due to several contributing factors. However, over the last decade specific bridge configurations have emerged that are especially suited to FRP bridge technology.
Composite technology made its first appearance on a US bridge project in 1996 in response to the need for corrosion resistance and long life. The performance advantages of composites translated into faster installation times, improved load-carrying capability and literally no maintenance. Since then, nearly 100 US bridges have been rehabilitated with composites (with a total of more than 200 bridges worldwide).
These installations have helped demonstrate the technology’s capabilities and introduced a valuable material option to bridge designers and owners. Many early installations were demonstration projects where research and development funding was available to introduce FRP to the bridge industry. Now, with much of the demonstration stage completed, FRP decking is judged on a competitive basis against traditional material options. And while the usage of FRP decking has grown, bridge owners have been challenged by cost premiums and bridge designers have been slower to accept the material. The following evaluations, case studies and competitions help bring into focus where FRP materials can provide the best fit and the highest value to owners.
Great advantages
For designers and bridge owners FRP decking offers a number of advantages that can provide dynamic solutions as well as long term benefits.
Light weight
FRP bridge decks weigh only 10-20% of a structurally equivalent reinforced concrete deck. Using an FRP deck to replace a concrete deck reduces dead load significantly. This means load-rated structures may be re-rated to their original design capacity or ageing structures may be kept in service longer before being replaced. In new construction, lighter dead load can translate into savings throughout the structure, as the size of structural members and foundations can be reduced accordingly. Since FRP deck panels usually weigh less than 6000 lb each, simpler equipment can be used to install the deck. Backhoes or excavators that are already at the site are sufficient. Expensive cranes are not required which reduces installation costs in all cases and occasionally is a major functional benefit when overhead power lines limit crane usage.
Corrosion resistance
Corrosion of reinforcing steel is the leading cause of premature deterioration of concrete bridge decks. Use of road de-icing salts, combined with higher-than-anticipated traffic loads, accelerates this corrosion. Because FRP materials are not susceptible to corrosion, FRP bridge decks offer a great alternative to conventional materials for this major maintenance issue. This benefit is most important in cold climates with snow or coastal areas with salt water. FRP materials have demonstrated excellent durability in corrosive chemical environments for 50 years without degradation. This provides a strong basis for the expected 75-100 year life for FRP decks.
Quick installation time
Fabricating deck panels in a factory and shipping them to the bridge site offers several advantages over cast-in-place concrete: quality can be closely monitored in a controlled environment; the potential for weather delays is greatly reduced; and most significantly, bridge down-time can be substantially reduced. Once the superstructure is prepared, prefabricated FRP deck panels can be installed quickly, compared to the labour intensive process of erecting formwork, placing rebar, pouring and curing concrete, and removing the formwork needed to construct a cast-in-place deck.
High strength
Composite decking provides high strength with very high safety factors. Since FRP material is not as stiff as steel and rebar, the stiffness performance requirements drive the design of FRP decks. Deflection criteria have become the most important performance check. Deflection criterion for FRP decking is often more conservative than concrete deck criteria – partially because FRP is still considered a somewhat new material and because end users want to minimise reflective cracking in the wear surface. But static tests of FRP decks clearly demonstrate that the decks greatly exceed specified performance requirements and provide high safety factors.
Lower life cycle costs
Corrosion resistance results in very low maintenance of FRP decking which translates to lower future maintenance costs. It also means that FRP decks will last longer than traditional materials. These add up to lower life cycle costs for FRP.
Upfront costs equal future benefits
The primary benefit of FRP for general bridge structures is corrosion resistance which delivers long life and very low maintenance. Most of the value of FRP for bridges is in the future. As with most things, great benefits typically come with a higher price tag. The economic difficulty for most bridge owners is paying a premium cost upfront to enjoy future benefits. Given the high demands of an ageing infrastructure with limited funding, government entities also have a difficult time paying for future benefits. The ability of government bridge owners to account for the true and total life cycle costs of their structures is critical to helping newer technologies like FRP bring their benefits and full value to the market.
Because of the projected durability of FRP bridge decks, savings in deck replacement and maintenance costs over a 100-year bridge service life cycle could be much greater than the initial cost of the entire structure. The life cycle cost savings can be shown to more than offset the relatively high initial cost of FRP materials when compared to conventional material. However, long-range durability claims are viewed by the construction industry with some skepticism. Furthermore, few public agencies select materials based on projected life cycle costs. Instead, materials are chosen based on the engineer’s experience and judgment, agency preferences, and industry standard practice, usually with a strong bias toward minimising initial construction cost.
Market realities
When FRP was first introduced into the bridge market, the strong benefits held promise for FRP to capture a reasonable share of the market. The cornerstone supporting this projection was that there are more than 580 000 bridges in the USA alone and about 197 000 of those have been rated as deficient. These large numbers led to the composites industry over-estimating the amount of market penetration. After 14 years, it is evident that FRP is still not the material of choice for bridge rehabilitation. There are a number of reasons for this, but the main reason is the price premium for FRP when compared with traditional materials.
FRP’s price premium is due to:
raw material costs – better materials cost more;
individual bridges – each bridge requires a separate design. Since FRP is a new technology, there are additional design costs not carried by traditional materials with established standard specifications and design procedures already familiar to the bridge industry;
low volume – higher volume is still needed to capture greater manufacturing economies
Other factors include real market size, competition and budgets. Many bridges counted as deficient are still structurally adequate and can be operated for decades. The need to rehabilitate older bridges in rural areas with low traffic count is also decades away.
At the same time, baseline competition has continued to move forward. Concrete has enhanced its value through property improvements, more options like low density, and pre-cast alternatives. Concrete is simple, known and inexpensive.
Budgets are shrinking which leaves owners with having to fix more with less. This pushes owners to select the lowest cost (and often lowest lasting) alternative.
Unfortunately, personnel that may inherit the bridge will have to deal with the consequences associated with that initial choice. Life cycle cost studies have shown that 75-85% of the costs are not considered in the purchase decision. Maintenance costs are also not given much consideration.
Volume, regardless of the product, is another major parameter in selecting the best manufacturing process. For FRP decking options, there are two primary manufacturing processes.
One is a batch process in which deck panels are made from start to finish as individual parts. This process infuses resin throughout the fibreglass lay up resulting in an integrally moulded deck panel.
Pultrusion, the second mainstream option, is a continuous manufacturing process which produces constant cross section parts. The pultrusion process can produce a high volume of shapes which can be finished into deck panels. This process offers a cost effective approach for high volume demand. When the potential for high volume was first anticipated with FRP technology, pultrusion was seen as the best process for lowing cost premiums.
With the constraints that have surfaced in bridge design and construction, these volumes have not been attained. One key constraint is that every bridge has a unique configuration and varying requirements. Replication is rare.
Where FRP decks fit today
In today’s infrastructure market, four bridge applications continue to make strong use of FRP composites despite the cost premium. Each application has a critical requirement for light weight to meet the design and operational objectives. In these cases, owners still receive the benefits of corrosion resistance and a longer life cycle while gaining the value of a light weight deck.
The applications where FRP decks are great matches are:
movable bridges;
historic steel truss bridges;
bridges with steel grating; and
pedestrian deck additions to vehicle bridges.
Easy to move
Movable bridges are found mostly in coastal and port areas. Large port cities on the coasts, rivers and Great Lakes have bridges that must accommodate heavy truck traffic to ports as well as have the capability to accommodate the passage of commercial ships. Coastal cities with rivers and intercoastal waterways have bridges handling local traffic as well as commercial ships and pleasure craft. These bridge types include lift, swing and bascule bridges. Traditionally, the decks for these bridges are steel grate or steel/concrete. Deck weight has a direct effect on the cost of the mechanical equipment and the operational costs. FRP decking is the lowest weight option. It provides a solid decking surface to protect the superstructure and is preferable to steel grating. FRP decking has been used on a number of movable bridges. In a few cases, these bridges are in port areas and carry a significant percentage of heavy truck traffic.
Saving history
Light weight decking is also valuable in the case of the historic steel truss bridge. Many steel truss bridges were constructed in the first half of the 1900s and carry historic value for their community. Many of these bridges are load rated since they were not designed for current vehicles. FRP is a great option for reducing dead load. This reduction can be as much as 80 lb/ft2. Rather than replacing the historic bridge, FRP decking enables the community to keep the bridge and still handle higher loaded vehicles.
A recent design study for a California bridge compared the current concrete deck with an exothermic steel/concrete deck and an FRP deck. The concrete deck came in at 105 lb/ft2, the exothermic deck at 55 lb/ft2 and the FRP deck at just 16 lb/ft2.
One example is Schaeffer Road bridge in Ashtabula County, Ohio. This steel truss bridge was built in 1936. It is a three-span continuous steel beam bridge with overall dimensions of 175 ft long and 17 ft wide. The local community did not want a replacement bridge because it valued the steel truss structure. The FRP deck at 18 lb/ft2 saved enough weight to remove the load rating on the bridge.
Covering the superstructure
FRP decking provides an effective replacement option for cases involving bridges with steel grating. While steel grating offers a light weight of 17-28 lb/ft2, exposure to water and chemicals quickly takes its toll on the grating and exposed superstructure underneath. The serrated grating surface becomes worn over time and vehicles lose traction during rain, snow or ice. In many cases, the superstructure was designed for the weight of the steel grate deck. Bridge owners must either opt for a new steel grate or an FRP deck. Since filling the steel grate with concrete can add up to 55 lb/ft2 to the weight, this option is not viable. FRP offers a weight of just 16-20 lb/ft2 making this option preferable. A second benefit of the FRP deck is that businesses, hotels, restaurants and parks located near the structure enjoy a reduction in noise with the quieter FRP deck. A lightweight, solid surface deck is the right answer to reduce corrosion of the superstructure.
Share the road (and the bridge)
The fourth case application is attaching pedestrian/bicycle bridges to existing vehicle bridges. With more communities requesting bicycle paths and pedestrian connectivity, an attractive alternative to building completely new bridges is to cantilever the pedestrian bridge off the vehicle bridge structure. Minimising dead load is essential to the success of such a project. If structurally feasible, adding to the vehicle bridge is more cost effective than constructing a new pedestrian bridge parallel to the vehicle bridge.
FRP decking has been used in this way for the Tower Bridge in Sacramento, California. The Tower Bridge is a historic lift bridge with existing walkways on both sides of the bridge. The walkways were only 3 ft wide and could not adequately accommodate pedestrian and bicycle traffic. The long term growth of both riverfronts depended on safe and easy access. Weight limitations on the center span could not accommodate the desired 10 ft wide concrete sidewalk.
Next on deck for FRP
Over time, FRP will continue to mature as a beneficial option for designers and owners. It takes time for any new material to develop the procedures, specifications, design knowledge and owner comfort level to be a standard alternative. The value that FRP brings with its corrosion resistance and light weight will increase its usage over the next 14 years.
The realities of the current market shows that the best applications for FRP are movable bridges, steel truss bridges and pedestrian bridges that cantilever from existing vehicle bridges. The Federal Highway Administration (FHWA), a division of the United States Department of Transportation, offers statistics on bridges by structure type. Currently there are 883 movable bridges and 12 608 truss bridges in the USA. While this is only a small percentage of the total number of US bridges, FRP will be a ‘good fit’ for many of these bridges and will provide an optimum solution for their owners while demonstrating the strong benefits of FRP to the entire bridge community.
