The United States has over 617,000 bridges, many of which are past their expected 50-year service life, as the average age is 60 years. While large bridges get more media attention and funding, smaller spans (20 to 60 feet [33 to 18 meters]) are equally important yet often overlooked.
These shorter span bridges typically consist of either steel or concrete girders resting on abutment walls. Just because a bridge has a shorter span does not make it immune from a costly replacement for the owner, which is likely to be a local city, town, or village. These types of bridge owners often do not have the same funding opportunities as a state department of transportation or regional toll authority does.
Cost-Effective Solutions for Local Governments
Local municipalities often face significant costs for replacing shorter span bridges made of steel or concrete girders. Municipal governments can address the urgency and funding scarcity by using buried structures for bridge applications. This approach helps public administrators "do more with less" and implement solutions in less time.
Buried structure technology enables a new bridge or the replacement of an existing bridge to be constructed for a lower initial cost compared to traditional girder and abutment structures. A “buried” bridge is a soil-structure interaction system that can use the in situ soil for most—in some cases all—of the backfill surrounding the structural component. The structural elements consist of either galvanized steel corrugated plate, aluminum corrugated plate, or precast reinforced concrete arch sections, which are mass produced in off-site factories and easily shipped to the jobsite.
Additional project savings are realized if the structural element is corrugated metal plate because the structural materials for an entire bridge can be delivered to the jobsite in one truckload. In comparison, a traditional girder bridge requires multiple deliveries because of the load and size constraints of only hauling one girder per truckload.
Lower Installation & Labor Costs
Other factors that yield a lower installed cost for soil-structure interaction systems include savings on labor and equipment in addition to a larger pool of contractors who are qualified to build the structure. Buried structures, especially those built with metal plates, can be constructed using smaller work crews and ordinary equipment. By comparison, crews on girder/abutment bridges include a wider array of trades and require larger specialized equipment, such as cranes for setting girders and large concrete spreader machines for bridge deck pours. The ability to use basic crews and equipment on buried structures allows municipalities to receive more competitive bid proposals from a more diverse group of contractors. These factors collectively enable local government agencies to implement bridge replacements at 15 to 50 percent less cost than traditional girder/abutment bridges.
Accelerated Bridge Construction
Depending on the circumstances, the schedule for a bridge replacement project is just as or more important than the budget. Buried structures allow for accelerated bridge construction (ABC). Whether the soil-structure interaction system consists of precast concrete elements or metal plates, the construction is modular, which facilitates speed and efficiency because of ease of handling in the field. Additional efficiencies are achieved using prefabricated foundations and end treatments (i.e., headwalls and wingwalls). It is feasible for a deficient bridge to be replaced with a brand new buried structure in one month or less.
