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Cover Story - October 2003
Bridge Construction
Out With the Old, In With The New As Crews Replace Span Over Lake Belton

By Mark Rea

Innovative techniques in precast concrete bent cap connections are being used by the Texas Department of Transportation as it replaces an antiquated bridge over Lake Belton along State Highway 36 in Bell County.

Groundbreaking for the $20 million project took place in September 2002 to replace the existing bridge that was constructed in the early 1950s. "The existing structure is 45 to 50 years old," said Paul Hoffman, Belton area construction inspector for TxDOT.
"It was built using the old pin-and-hanger method, and it's just tired."

The project features some of the most unique cap-to-column connections ever used by TxDOT on the bridge's 32 hammerhead bents.

Each 75-ton precast cap features predrilled holes in the bottom that fit over separate No. 11 reinforcing steel receiver bars embedded into the top of each column. The caps are lifted onto the columns and then adhered with a special grouting mixture, called Master Flow 928. The grout, which has the consistency of a smooth milk shake, is injected into the voids through a pressurized system for a solid connection.

Hoffman said the advantage of erecting the caps in such a way is increased efficiency in time and safety.

"The safety aspect is phenomenal," he said. "You don't have to have men out there suspended 40 ft. in the air, over the water, constructing that cap. Instead, you simply float the cap out there, lift it and set it into place."

The entire lift can be accomplished in about one hour. It then takes one day to dry-pack it, another day for the grouting, and two to three days later, the proper strength of 3,000 psi is achieved in the mixture so that beams can be placed.

"The conventional way takes two weeks, so you can easily see the savings in time as well," Hoffman added.

General contractor Midwest Foundation Corp. of Tremont, Ill., provided its own cranes as well as platform barges for drilling, pouring concrete and material storage, and a tugboat to maneuver the platforms into position.

The bridge features 124 columns, each 5 ft. in diameter, 26.5 ft. tall and containing an average of nearly 70 cu. yds. of concrete. Every two columns along the length of the bridge are fitted with one 75-ton precast cap. The caps were fabricated by San Antonio-based Bexar Concrete Works Inc., which designed a special transport trailer to bring the caps from the casting yard to the site.

TxDOT also employed an extensive use of precast concrete on a $41 million bridge project spanning Lake Ray Hubbard on State Highway 66 northeast of Dallas. That project was completed last year and spurred the state highway department to continue its use of precast in future bridge construction.

"By using more precast caps and more precast elements, this is kind of a testing ground for future TxDOT bridge projects," Hoffman said. "We can cut the construction time down substantially by using these techniques, and hopefully apply these techniques to the interstate system in the future. We want to get to the point where we can go in, construct a new bridge quicker than ever before and minimize the impact to traffic."

Getting Started

Construction began with excavation at the westernmost part of the job site. Austin-based Garey Construction crushed the excavated material, which consisted mainly of Texas limestone, and used it to build the header of the new bridge on the west side of Lake Belton. After excavation, the first of the shafts were drilled on dry land at the west end of the project.

Once those drills shafts were completed, crews from Round Rock-based ATS Drilling LP went to the east end and drilled shafts, after which the columns were poured. After that, workers boarded their equipment onto barges and began underwater drilling.
Piers were drilled to depths of up to more than 50 ft. below the 20-ft.-deep lake.

As drill shafts were completed, crews placed the tie beams, poured the columns and situated the 75-ton caps into place. Transit Mix of Belton supplied the ready mix for the project, which Midwest Foundation crews placed by bucket. More than 190,000 cu. yds. of concrete will comprise the project, featuring Class C, Class SS and Class S mixtures.

Even with the added safety of installing the bridge caps, the intrinsic nature of construction on water made for some interesting challenges.

"This was my first time working on the water, so that made this project very unique for me," said Charles Lyles, construction inspector and project manager for TxDOT.
"Making large lifts on solid ground is pretty straightforward stuff, but when you're on the water, it's a whole lot different.

"On water, you have motion and momentum, and when you're lifting a piece of concrete that weighs 75 tons with a 300-ton crane, it sometimes makes it a little difficult to put it just where you want to put it when you want to put it there."

Hoffman added that weather conditions also played a role in the erection of the precast caps. "It makes it very interesting, especially when you have some wind," he said. "We have lifted some of those caps in 20-mph winds, and you have to have extremely well-qualified personnel operating that equipment. To their credit, the lifts went very smoothly."

Three-Phased Project

The project is divided into three phases. The first, expected to be completed in January, features construction of the headers to the bridge on either side as well as the path of the new structure. Once the new bridge is complete, traffic will be routed onto the new structure and demolition of the existing bridge will begin.

Since Lake Belton is supervised by the U.S. Army Corps of Engineers, the project required special permitting to eliminate as much disturbance as possible to the wildlife, bird sanctuaries and fish habitats in the area. The Environmental Protection Agency and Texas Commission on Environmental Quality have kept tabs of the work as well.

As a result, the existing structure will be carefully demolished and then placed in the lake to promote an even better ecostructure.

"We will salvage the existing columns and create a new fishing habitat in the lake," Hoffman said. "The contractor will break up the columns, transport them to another location and then stack the chunks on the lake bottom to create the new habitant. Even though this old structure has outlived its usefulness as a highway bridge, it will live on and continue to be useful."

Final paving of the approaches and the installation of signage will complete the project next fall. Approaches to the bridge on SH 36 will be asphalt pavement, with the bridge deck consisting of 8-in. continuously reinforced concrete pavement poured atop precast panels.

The new 0.8-mi. bridge will feature four lanes - a pair of 12-ft. main lanes with 10 ft. shoulders heading both east and west on SH 36.

 

PROJECT TEAM
GENERAL CONTRACTOR: Midwest Foundation Corp., Tremont, Ill.
OWNER: Texas Department of Transportation, Austin
LOCATION: State Highway 36 over Lake Belton, Bell County
CONCRETE SUPPLIER: Transit Mix, Belton
PRECAST PANELS : Bexar Concrete Works Inc., San Antonio
REBAR SUPPLIERS : Capital City Steel, Austin; SMI, Seguin
REBAR PLACEMENT : J.L. Steel Ltd., Roanoke
DRILLING: ATS Drilling LP, Round Rock
EXCAVATION: Garey Construction Ltd., Austin

USEFUL SOURCES

For additional information regarding this project, check these sources:

  • Innovative uses of precast concrete caps on Texas bridges are contained in a white paper available at www.txdot.state.tx.us/brg/Publications/Innovative_1.pdf.
  • To learn more about MasterFlow 928 premixed, non-shrink, rheoplastic grout, visit this Web site: www.masterbuilders.fi/Mfeng928.pdf.
  • A map of the Lake Belton area is available on the Internet at www.texasoutside.com/centraltexas/lakebelton.htm.

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