Myths and Realities About Steel Bridges

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Steel Bridge Construction: Myths & Realities (4.3 MB PDF) —American Iron and Steel Institute

Myths and Realities

Myth: Concrete lasts forever without maintenance.: Reality: Concrete is affected by the same environmental deterioration factors as steel. Its performance is also affected by quality of materials and design.
Myth: Concrete bridges outlast steel bridges.: Reality: There is no credible statistical evidence to support the notion that concrete bridges outlast steel bridges.
Myth: Weathering steel performs only under ideal climatic conditions: Reality: Weathering steel performs successfully when designed and detailed according to the published FHWA and Industry guidelines for its use. There are many cases of weathering steel bridges not conforming to the guidelines that are also performing well.
Myth: Steel Is Not Recommended For Short Spans.: Reality: Due to changing designs and prices for both steel and concrete members, the relative economics of span and cost of each material has also changed. In many cases, the most economical steel span may be close to or the same as for the concrete design. In some cases where 250-foot to 350-foot segmental prestressed concrete spans are used, the most economical steel spans may be shorter than for concrete.
Myth: Bridge joints are essential.: Reality: Experience has shown that jointless bridge decks can be designed to provide a durable and costeffective structure.
Myth: Steel bridges require traditional fabricated steel bearings rather than bearing pads usually specified in prestressed concrete designs.: Reality: There are simpler steel reinforced, or fiber reinforced elastomeric pads and preformed fabric pads that are both more economical and often mechanically superior to the traditional fabricated steel bearings.
Myth: Painting or repainting of steel bridges is an insurmountable problem.: Reality: There are cost-effective ways of repainting existing bridges. For new construction, there are modern high-performance coatings which comply with EPA standards and which can provide a minimum service life of 25 years prior to first paint maintenance.
Myth: Bridges at the end of their calculated fatigue life or those experiencing localized fatigue problems have to be replaced.: Reality: Fatigue life applies only to details. Localized fatigue problems can generally be fixed quickly and easily with no reduction in live load capacity or life of the bridge. During the life of a steel bridge structure, certain details may exhibit fatigue cracking. These localized fatigue cracks do not mean that the entire structure has exceeded its service life. Many fatigue cracks can often be easily repaired by drilling holes at the tip of the cracks to stop crack propagation, if the driving force is removed or in other cases, bolting splice plates over the crack. After this retrofitting is performed, there is no reduction in live-load capacity or remaining service life of the bridge. Much of this retrofitting and repair can be completed without interrupting traffic.
Myth: Modular prefabricated short-span steel bridges are only temporary structures.: Reality: Modular prefabricated short-span bridges, as compared with so-called panel bridges, are typically permanent structures.
Myth: Modular prefabricated short-span steel bridges are limited to a one-size-fits-all scheme.: Reality: Modular prefabricated short-span steel bridges are custom engineered to meet individual specific requirements.
Myth: There are limited options with modular prefabricated short-span steel bridges.: Reality: There are numerous options available.
Myth: Timber decks on modular prefabricated short-span steel bridges do not hold up and the timber treatments leach harmful chemicals into the environment.: Reality: Treated timber continues to be used as a decking material for permanent bridge installations. Properly treated and detailed the treated timber will last the design life of the bridge. Timber treatment continues to advance with preservative choices and manufacturing techniques to minimize impact on the environment.
Myth: Steel is not competitive for simple-span bridges less than 140 feet in length.: Reality: Prefabricated modular steel bridges compete favorably with other materials when considering the greater use of shop labor vs. field labor, the speed at which they can be installed and the significant reduction in time required to close a given roadway to the public.
Myth: Corrugatedsteel pipe or corrugated steel plate bridges do not last, as they tend to rust out.: Reality: With proper attention to design details and appropriate coating one can expect a service life up to 100 years.
Myth: Reinforced concrete pipe lasts forever.: Reality: Concrete pipe is susceptible to deterioration from aggressive soils and road salts as well as lack of soil stability.
Myth: Corrugated steel is flexible and not appropriate under high fills.: Reality: Corrugated steel material for bridges has the ability to perform under fill heights exceeding 100 feet.
Myth: If corrugated steel pipe or corrugated steel plate is used as a bridge one is obliged to disturb the natural waterway.: Reality: There are options available to avoid disturbing the waterway.
Myth: Corrugated steel pipe and corrugated structural plate bridges cannot compete with comparable reinforced concrete structures.: Reality: Corrugated steel bridges compete very favorably with reinforced concrete bridges.
Myth: Although able to provide long-term protection under adverse environmental conditions, galvanizing on plate-girder and rolled-beam bridges is prohibitively expensive.: Reality: Due to the relatively stable price of zinc metal over the past 20 years, the initial cost of hot-dip galvanized plate girder and rolled beam steel for bridges is very competitive with painted steel and even less expensive in many cases.

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Single-lane Modular Bridge Specifications (Weathering)
28 KB .doc

Multi-lane Modular Bridge Specifications (Weathering)
32 KB .doc

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