Category:148 Accelerated Bridge Construction (ABC)

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148 abc.jpg

Accelerated Bridge Construction is defined as constructing a bridge using innovative contracting, planning, design, materials and methods to reduce the on-site construction time. MoDOT has been a leader in accelerated bridge construction since 1972. Our use of precast concrete deck panels is still considered innovative and “new” by many states. There is a continued push to limit the impact of bridge construction to the travelling public even further. The Core Team should discuss the need for accelerated bridge construction very early in the project development process. It will affect the budget, the plans production schedule and the bridge options available.

Time Lapse Video of Bridge Construction
I-44 Bridge
over Gasconade River

If there is a solid reason for going faster than normal, it will then be necessary to ensure the short term goal does not cause long term maintenance issues. For example, a pile cap bent can be constructed more quickly than a drilled shaft bent; but, if used in the wrong streams it could result in accelerated scour or corrosion problems.

The most reliable way to build good bridges faster is to provide an incentive to the contractor to build it more quickly than normal. This will push them to work 24/7 and use higher quality materials that more quickly reach the design strength. It is also the most likely method to avoid future maintenance issues. Other options to consider include using more precast elements such as abutments and eliminating bents when possible.

Regarding cost, one would typically first calculate how many days it would normally take to construct the bridge and then increase the cost estimate by the same percentage that the time frame was shortened. For example, reducing the number of days by 20% below normal will increase the cost by 20%.

There are rare instances where MoDOT may want to spend significantly more money to get a bridge built extremely fast (such as a closure of one weekend). The rule of thumb is when the AADT is greater than 50,000 or the detour is greater than 60 miles, the large cost increase may be justified. In these cases, the replacement bridge can be built next to the existing bridge and then slid into place or it can be built a short distance away and then driven into place with a self-propelled modular transporter (SPMT).