14 Reasons to Use Structural Steel For Bridges
Article provided by the National Steel Bridge Alliance.
#1 Resilience
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.
#2 In-Service Inspectability
Steel bridges can be visually inspected, as all major load-carrying components are easily accessible by bridge inspectors to efficiently evaluate their in-service condition.
Main-load carrying components are not hidden from the bridge inspector’s eyes, and typically do not require costly specialized equipment or non-destructive testing methods to determine their condition.
Bridge inspectors are able to touch the main load-carrying components and obtain physical measurements of any possible deterioration, providing evaluators the data necessary to appropriately load rate the structure.
#3 Accelerated Construction Schedule
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.
#4 Maintainability and Repairability
When necessary, steel bridges can be efficiently repaired and remain in service, and not require complete replacement. Components can be strengthened with additional steel, or components can be removed and replaced without removing the bridge permanently from service.
Impacts and damage from over height vehicles below the bridge are often easily corrected with well-documented heat-straightening techniques. Maintenance, repairs, and rehabilitation of a steel bridge can often occur with all or a portion of traffic maintained on the structure, while extending the in-service usefulness of the existing bridge
#5 Lightweight Superstructure
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.
#6 Complex Geometries
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.
#7 Future Modification and Adaptability
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.
#8 Workhorse Bridges
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.
#9 Reliability and Redundancy
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.
#10 Reduced Waste and Pollution
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.
#11 Long-Span Construction
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.
#12 Quality and Predictability
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.
#13 Railroad and Transit Applications
Steel bridges are well suited for railroad and transit applications due to the high strength and stiffness that steel can provide as deck girder, through-girder, or truss type bridges.
Steel’s high strength to weight ratio is ideal for supporting rail live loads which are nearly five times as heavy as traditional highway live loads. The stiffness characteristics provided by steel bridges can be exploited to meet the more stringent live load deflection and operational requirements of rail and transit loading.
#14 Long-Lasting and Durable
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.
Does steel provide a cost-effective solution for short span bridges?
Short span steel bridges deliver significant cost savings because of steel’s light weight, the allowance of smaller abutments, rapid installation, and the use of lighter equipment and local crews. Steel also delivers durability with an expected service life of more than 100 years for many bridges, considerable life cycle advantages, and minimal maintenance requirements over the service life of the structure.
Dr. Michael Barker, University of Wyoming, explored the initial costs, life cycle costs, future costs, and bridge life of 1,186 typical steel and concrete state bridges in Pennsylvania built between 1960 and 2010. He compiled a database from PennDOT historical data comparing five types of bridges, including concrete precast I-beam, box adjacent, and box spread bridges, and steel rolled beam and welded plate girder.
Results showed steel I-beams have the lowest average deterioration rate; have the longest average expected life (81 years); offer the lowest average initial and life cycle costs for short bridges; and have lower average future costs compared to initial costs.
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