As the State Highway 45N/Interstate 35 interchange grows above the Travis/Williamson County line just north of Austin, older sections of highway must fall to the wayside as they are replaced.

Stomper Demolition of Fort Worth was recently contracted to remove the six-lane, 320-foot-long FM 1325 bridge over one of the busiest sections of highway in Texas. According to TxDOT traffic counts, an average of about 188,000 vehicles per day pass through this area. The I-35 corridor provides at least 70 percent of Round Rock's retail tax base, meaning that weekend shopping is alive and well here.

This past February, over the course of one weekend, a Stomper Demolition crew quickly brought down the old FM 1325 mainlane bridge over I-35, allowing the prime contractor, Archer Western, plenty of time for clean-up.

General contractor Archer Western, subcontractor Stomper Demolition, Construction Manager PBS&J, representatives of the Central Texas Turnpike System, and the Texas Department of Transportation (TxDOT) had spent months organizing the demolition and meeting with community leaders and media to alert drivers of the major 48-hour highway closure. Community awareness has been stressed, according to Randall Rosenbaum, project manager for Archer Western. Once the highway closure was scheduled, notices were sent to area businesses, emergency response agencies, school districts, neighborhood groups, local media, and adjacent businesses. To keep traffic moving as smoothly as possible during a difficult situation, there was also a heavy show of law enforcement and pre-positioned tow-trucks in case of a "fender-bender" with no injuries.

"Our challenge was to develop a demolition plan to get the bridge down without any peripheral damage and within the allotted time," said Pat Todd, owner of Stomper Demolition.

The fee for closing highway mainlanes is high, and running overtime would have cost the contractors $8,000 per hour, per lane. With six lanes closed, that would add up to $48,000 per hour.

"It wasn't enough to have the bridge down by the deadline," Todd explained. "We had to have the bridge down and leave sufficient time for Archer Western to clean up the rubble from the roadway."

The bridge was made up of 40 pre-stressed concrete box beams, each 115 feet long, and nine columns with caps, all supporting 32,000 square feet of bridge deck.

During the early steps of devising their demolition strategy, Stomper had cored the box beams and discovered Styrofoam. The pre-stressed bridge beams had been cast with stay-in-place Styrofoam forms. This would make recycling more difficult, but the chance of showering Austin with the white stuff was a more immediate concern for demolition day. The weather service had predicted north winds of up to 35 miles per hour.

The solution was in a wire fence that Archer Western erected below the new bridge located within inches to the south of the one to be demolished, basically creating a box to catch any lightweight debris before it became airborne. "The containment appeared to be 100 percent," according to Todd.

To accomplish the demolition, Stomper moved in a convoy of five excavators (four 30-ton class and one 20-ton), each mounted with a Kent 8,000-pound hammer attachment. Bruce Bement, Stomper senior project manager, explained, "We use hammers because they make processing faster, and we can control when the structure will fail."

"We have learned to take the beams apart while they're still in the air," Todd said. "We can take them apart by 50 to 75 percent before they fall, so large pieces won't damage the roadway below."

Demolition began at 5 a.m. Saturday. Seven equipment operators, including owner Pat Todd and project manager Bruce Bement, rotated on six-hour to eight-hour shifts. By 1 a.m. Sunday, 19 hours later, the bridge was down. Archer Western was left with 29 hours for cleanup before the I-35 mainlanes were scheduled to reopen.

As demolition progressed, Archer Western workers removed concrete and steel to the side of the highway within the right of way, where other workers removed the steel strand and rebar, according to Rosenbaum. The steel was sold to a recycler, and the concrete was sold to a land developer adjacent to the project, where it will serve as fill material.

Stomper Demolition has taken down several bridges along the Texas I-35 corridor over the past two years, including two prestressed concrete bridges in Buda and Kyle south of Austin, two Loop 340/SH 6 prestressed concrete bridges over I-35 in Waco, and the steel railroad bridge north of Hillsboro.

SH 45N is one of the projects that make up the Central Texas Turnpike System 2002 Project (CTTS-2002 Project) designed to facilitate traffic between Austin and growing communities to the north. For more information, refer to the article, "Streamlining Delivery — Seriously" in the March 6, 2006 issue of Texas Contractor. The article is also available online at www.acppubs.com . Click on "Texas," then "Articles." The CTTS website is www.centraltexasturnpike.org.