Current Bridge Market
Whether arching a rushing river or connecting interstate and highway systems, bridges are an everyday part of our nations transportation system. These critical elements knit together communities across the country, providing safe travel of goods and people. Constructing new bridges is a complex, expensive, and time-consuming endeavor; and thus, it is paramount to design effective, sustainable bridges for today as well as future generations.
In 2017, the American Society of Civil Engineers (ASCE) rated the US bridge infrastructure a C+, and noted the average bridge is 43 years old. Considering most of these structures were built with a lifespan of 50 years, and 40% have already reached or exceeded that lifespan, there is significant need to upgrade our bridge infrastructure. More than 188 million trips are taken every day across the nation’s structurally deficient bridges.
As you can imagine, there has been significant evolution in the technology, design innovation, and materials as well as massive change in the type and volume of vehicles using our bridges since their initial construction. Retrofitting existing structures is both costly and labor intensive – more like putting a band-aid on a bullet wound. When new and replacement bridges are built, the Federal Highway Administration (FHWA), state Departments of Transportation (DOTs), and local government are looking to the future and trying to build bridges with longer lifespans and to accommodate future traffic.
Planning for the Future: HDG Steel Bridges
One of the big initiatives in planning for the future is to focus on building 100-year bridges. This is not only to learn from the past mistakes, but also a nod to future generations and sustainable development. If environmentally-friendly, economically-feasible bridges are constructed today, future generations will inherit a better infrastructure system than current conditions. To build sustainable bridges, it is imperative to evaluate the construction materials used to ensure they can not only meet the long design life without significant deterioration, but also without significant cost.
Hot-dip galvanized steel has been used in bridge designs for generations. The economical, long-lasting protection system affords bridge designers the life and minimal maintenance they desire. As with any building material, there are certain best practices for design and service environments that ensure the highest quality, longest lasting galvanized steel bridges. Understanding both the benefits and limitations of galvanized steel will assist bridge engineers in evaluating if hot-dip galvanizing is a solution for their bridge project.
The Short Span Steel Bridge Alliance (SSSBA) is a group of bridge and buried soil structure industry leaders who have joined together to provide educational information on the design and construction of short span steel bridges in installations up to 140 feet in length. The Short Span Steel Bridge Alliance is made up of partners from various sectors of the industry including universities, trade organizations, producers, coaters, fabricators, owners, contractors, fasteners, service centers, and design firms.
The SSSBA developed the eSPAN140.com design tool to help county engineers and bridge owners compare steel to concrete bridges in the short span market. There is a misperception that short span steel bridges are not economical and difficult to design. The eSPAN140.com site will provide a county engineer with a simple, short span steel bridge to put on the table. It provides a Solutions Book with fabricators and manufacturers who can quote the cost of the bridge and produce it according to the selected specifications. The tool is designed to be easy to use, and does not require the county engineer to be a bridge engineer to understand it. More information about SSSBA and their activities is available at shortspansteelbridges.org.
HDG Bridge Case Study
Indian Mill Bridge Rehab, Wyandot County, OH, 2015
Providing access to the historic Indian Mill a gift from the US Government to the Wyandot Indian Nation for their aid during the War of 1812 this truss bridge also holds historical significance. The original, covered bridge was destroyed by a flood in 1913 and replaced by a steel truss structure. In 2010, the community leaders deemed the 100-year old truss functionally obsolete and in desperate need of repair.
Because of the historic significance of the site and how integral the truss bridge had become to the overall landscape, the community and County Engineer were skeptical about the rehabilitation. Some engineering was required to bring the bridge to todays modern standards, but peices of the original 100 year old steel were used.
The bridge is in an area with very short summers and long difficult winters, which made the installation window short. The rough installation environment and weather could cause substantial damage to other coating systems such as paint, and future maintenance would be difficult. Collaboration between the galvanizer, fabricator, and County Engineer and some innovative engineering led to this new bridge that with the help of hot-dip galvanizing will be able to last another hundred years.