“This project demonstrated that concrete can lead the way for further applications in marine use.”

M. Myint Lwin

 

Special Solution Bridges

Pier 5 Fender Replacement on the I-10 Mississippi River Bridge

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This project’s creation of modular, precast concrete open-cell boxes for use as pier fenders, replacing steel and timber versions, offers potential for many bridges around the country. The fenders on the I-10 bridge over the Mississippi River in Baton Rouge, La., typically are about 14 ft (4.3 m) wide, 11 ft (3.4 m) deep and 13 ft (4.0 m) tall. They begin 19 ft (5.8 m) below the water’s surface and extend 45 ft (14 m) above water, completely surrounding the pier.

“This was the first use of such a precast concrete system for pier protection, and it can provide more resistance than the existing system,” says Myint Lwin, a member of the transportation awards jury. “This project demonstrated that concrete can lead the way for further applications in marine use.”

The fenders protect a subshaft between the top of the caisson and the pier columns. It achieved the design-impact loading of a six-hopper barge column, a three-tanker barge column, or a ship of 100,000 deadweight tonnage traveling at 14.7 ft/sec (4.48 m/s).

Precast concrete modular boxes provided the structural core and formwork for the closure pours between box sections and the pier shaft. This eliminated the need to erect formwork in the field. All modules were cast prior to site work beginning to speed construction, which was further enhanced by attaching composite marine timbers and applying coal-tar epoxy prior to shipping.

The modular boxes allowed erection to be completed with vertical alignment guides. The boxes are gravity supported on the distribution block and braced for impact by concrete fill between the back of the precast concrete and face of the pier shaft. The open cell at each joint between boxes was filled with concrete to distribute shear and anchor a tieback. The mass of the system and remaining open cells allow for controlled crushing of the boxes to absorb and deflect impact.

Of the 138 modules used on the project, 100 were side modules, 20 were corner modules, 10 were nose modules, and 8 were created as replacement sections for future repairs from major impacts.

Minor impacts will create limited damage, which was demonstrated during construction. As work progressed, one of the piers was struck by a commercial barge just off-center at the pier nose. The damage was repaired with a marine-timber replacement.

“This design really opens the doors for the use of precast concrete in this situation around the country,” says Kevin Eisenbeis, a member of the transportation awards jury. “There are a number of bridges around that need updates to their fendering system, and this provides a great economical solution.”

Location: I-10 over the Mississippi River, Baton Rouge, La.
Owner: Louisiana Department of Transportation and Development, Baton Rouge, La.
Engineer: Modjeski and Masters Inc., New Orleans, La., www.modjeski.com
Contractor: Weeks Marine, Houston, Tex.
Precaster: Standard Concrete Products, Theodore, Ala., www.standardconcrete.net
Bridge length: 3315 ft (96 m)
Pier protection area: 420 ft (128 m) long, 48 ft (15 m) high