Short Span Steel Bridges 
Mason County (WA) Installs Buried Steel Bridge With Local Crews, Saves Money
Article provided by Contech Engineered Solutions and the National Corrugated Steel Pipe Association
This 30′ 8″ span x 9′ 8″ rise Deep Corrugated Box Culvert was chosen to replace an undersized 50 year old galvanized steel structural plate pipe arch. The existing pipe arch was still structurally sound after 50 years but needed to be replaced for fish passage purposes. Salmon species such as chinook, coho, pink, chum and sockeye salmon are all native to Mason County.
The new deep corrugated box culvert has a wide enough span to carry the full bank width streambed inside of it. The deep corrugated box culvert was supplied with 6″ x 2″ corrugated steel structural plate headwalls and wingwalls that were reinforced with galvanized steel welded wire grid strips. In addition, the structure sits upon galvanized Steel Express Foundations that were infilled with concrete after the structure was in place.
The buried steel bridge was both purchased by Mason County and installed with Mason County’s own road crew.
Steel Box Culvert Installed by Local Road Crew
From foundations to the top of the headwalls, this structure is galvanized steel and utilizes both 15″ x 5.5″ corrugations and 6″ x 2″ corrugations. The structure was both purchased by Mason County, Washington, and installed with Mason County’s own road crew. The County was impressed with the speed of construction and the low number of days for the detour. The ability for counties to be able to purchase and install the structure themselves provides a cost savings to the Mason County residents.
The Steel Express Foundations were placed and secured in one day.
Quick Construction Protects Environment, Allows Safe Passage for Fish
The Steel Express Foundations were placed and secured in one day and since the crew had pre-assembled all the rings of the box culvert on the side of the road, the structure was completely assembled the following day by picking individual rings and setting them. The 6″ x 2″ corrugated headwalls and wingwalls were then installed in typical MSE installation sequence with reinforcing strips placed at regular lift heights, then well graded gravel was placed and each lift compacted accordingly. The ability to quickly construct a project on-site helps to protect the environment and allow safe passage for native fish.
Contact Information:
Joel Hahm, PE
Contech Engineered Solutions LLC
Senior Engineer
Office: 970.347.2208
Mobile: 970.590.7907
joel.hahm@conteches.com
What are buried steel bridges?
Buried steel bridges provide an economical choices for bridge replacement or bridge rehabilitation.
They essentially are a corrugated steel pipe or structural plate pipe systems that is “buried” with backfill to carry loads through soil-structure interaction. This means the bridge structure itself and the backfill soils surrounding the structure interact with each other to support the loads. In effect, the backfill material is part of the bridge.
Because of this interaction, the bridge structure is typically lighter, and there can be significant savings in structure costs.
There are also many cases where buried bridges can carry heavier loads than traditional bridges because of the benefits of spreading vehicle loads through the fill. Buried bridges do not require abutments; and unless foundation soil conditions are poor, do not typically
require deep foundations.An additional benefit with buried bridges is that they can be tailored to site conditions and geometric requirements. The design includes inputs for site soils and backfill, meaning that locally available materials can often be used in construction and the structure can be tailored to fit the needs of the site and the owner’s requirements.
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