National Steel Bridge Alliance
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Why Steel Bridges?
Why use structural steel for bridges? Here are the top 12 reasons:
100-year steel bridges have been built for over 100 years. Many notable, historic, and revered bridges have been built with steel: Golden Gate Bridge, Eads Bridge, and the Brooklyn Bridge to name a few. With appropriate maintenance, these 100-year bridges have proven their resiliency to harsh environmental conditions and extreme events. Steel bridges of today are built with steel materials, coatings, and fabrication techniques that have the potential to be even more resilient than bridges built 100 years ago.
Check out our Steel Centurion series, showcasing a variety of 100-year steel bridges.
Steel bridges can be visually inspected, as all major load carrying components are accessible by inspectors. Special non-destructive inspection techniques are not needed to see the conditions of the main load-carrying components. When necessary, steel bridges can be repaired and remain in service, and not require replacement. Components can be strengthened with additional steel, or components can be removed and replaced without removing the bridge permanently from service.
Superstructures for steel bridges are generally lighter than other building materials which typically result in smaller and less costly foundations. Also, lighter superstructures typically result in reduced seismic forces which can be a major advantage in high seismic regions.
Fabricated off-site with geometrically controlled equipment, structural steel has the advantage of being ready to erect as soon as it reaches the bridge site. Reinforcement and formwork installation is not required. Structural steel erection is not limited to a specific temperature range. Structural steel is often lighter than other materials for the same span, resulting in smaller or fewer erection cranes. The use of structural steel for a bridge project accelerates construction and reduces on-site labor requirements and overall project costs.
Structural steel bridge components can be strengthened and adapted if the need arises in the future to address increased live loadings, new live loadings, roadway widenings, or other changes in configuration. Other materials do not have the same adaptability and oftentimes require replacement for new loadings or changes in configuration.
Steel bridge components can be fabricated and erected for numerous complex geometrical configurations. Steel bridges have the advantage of being able to handle tight curves, large skews, variable width decks, single point urban interchanges, as well as entrance and exit ramp bifurcations that are a necessity within limited owner right-of-way spaces.
Steel has the capability of spanning crossings well over 500 feet, in the form of plate girders, tied-arches, suspension bridges, cable-stayed bridges, and trusses. Many examples, both historic and current, point to steel being the ideal material for long-span structures. Steel offers advantages of controlled fabrication, lighter components, and durability for these long-span applications.
Steel bridges offer owners opportunities in the short span, typical overpass, workhorse bridge market as well. Steel bridges can provide a cost-effective solution for short spans, utilizing standard rolled sections or standard plate girders, as well as modern coating systems. When a quick replacement is necessary for a shorter span, steel offers the ability to be modular in construction, and rolled sections can be made readily available.
Steel bridges achieve reliability through redundant design and construction practices. Effective and efficient redundancy can be achieved through system or member-level mechanisms using engineered damage tolerances that can be coupled with the inspection interval of the bridge. Additionally, exposed tension elements of in-service steel bridges improve the probability of damage detection during routine visual inspections, further increasing safety and reliability.
On average, structural steel produced in the U.S. is composed of 93%-98% recycled content, and 100% of a structural steel frame can be recycled into new steel products (not down-cycled like concrete) including steel scrap from the fabrication process. Steel's high strength-to-weight ratio coupled with a low carbon footprint-1.16 tons of CO2 per ton of fabricated hot-rolled steel-results in an overall reduction of the embodied carbon of a typical structure compared to other framing materials. Simply stated, waste and environmental impacts are minimized when steel is used.
Stiffness, strength in both tension and compression and the ability to bend without cracking or breaking are inherent advantages of structural steel. Compared to all other materials, structural steel has the greatest ability to maintain strength and integrity during extreme events. Steel bridges are not subject to shrinkage or creep under load over time. Even in corrosive environments, applied coatings protect structural steel and add longevity to the bridge. A durable and nonporous material, steel provides value and a significant return on investment.
Off-site fabrication allows for controlled conditions, ensuring a higher quality product configured to precise tolerances. While all bridges experience some type of movement, a structural steel bridge behaves in a predictable manner to provide comfort to the traveling public.