Project Case Study: High-speed engineering

July 2008 » Feature Articles
The dual challenge of engineering a NASCAR speedway is creating a surface that allows racecars to travel at high speeds while preventing them from hurtling into space. At Tennessee’s Bristol Motor Speedway, that task was exacerbated by the need for cross-sections that encourage drivers to race side by side. In addition, the track redesign had to be built within the confines of the existing seating arrangement without negatively affecting sight lines from any part of the track.
Greg Delaney, P.E., LEED AP

Speedway redesign highlights engineering and construction innovation.

Project
Bristol Motor Speedway, Bristol, Va.

Civil Engineer
Eberly & Associates, Inc., Atlanta

Application
3-D modeling and continuously reinforced concrete pavement meet design and construction challenges for variably banked speedway.

The dual challenge of engineering a NASCAR speedway is creating a surface that allows racecars to travel at high rates of speed while preventing them from hurtling into space. At Tennessee’s famed Bristol Motor Speedway (BMS), that task was exacerbated by the need for cross-sections that encourage drivers to race side by side—a sight modern NASCAR fans have come to expect—while accommodating the speed at which they race.

Prior to its recent redesign, Bristol’s cross-sections compelled drivers to run single file. This was because of a slight but noticeable waviness in the concrete surface, as well as a banking transition that created a distinct disadvantage for drivers traveling further away from the infield. Adding to the project’s challenges was the fact that the redesign had to be built within the confines of the existing seating arrangement without negatively affecting sight lines from any part of the track.

As viewed from the turn two suites, NASCAR drivers give the new track a workout.

 

The design also had to avoid giving an advantage to one particular travel lane (racing groove) on the track. In the cross-section, the lower car would have a shorter path, but move at lower speed due to the flatter grade. The upper car would benefit from higher speed but travel a longer route. The redesign required a zero-sum result: Two equal cars traveling exactly side by side would complete the turns at precisely the same time.

Finally, the project team had only five months between the existing track’s demolition and Bristol’s first scheduled race in August 2007. All of this at a track that was considered legendary among fans and drivers alike in its longstanding configuration.

Tinkering with success
BMS is the toughest ticket in NASCAR. With more than 160,000 seats, the stadium reaches to the sky. Bristol is a "short track"—a little longer than a half-mile, compared with 2.5 miles At Daytona—so races there often resembled roller derby in cars as they bumped and jostled for position.

Rebuilt from asphalt to post-tensioned concrete paving in 1992, Bristol has been such an exciting and unique experience that no one really wanted to touch it for fear that the magic may be lost. BMS President and General Manager Jeff Byrd said of the planned redesign, "It scared us to death. We had the number-one product in NASCAR, we’d sold out more races in a row than anyone, the drivers had just rated it their favorite speedway, and the fans always voted it their favorite place to watch a race. Here we had something with a tremendous market share, more successful than any other entity of its kind, and we were going to change the basic formula."

Despite understandable trepidation, Bristol’s leadership group realized it had no choice. The existing concrete surface—with four jointed segments—was deteriorating rapidly. In early 2007, crews had to go out every night with a concrete saw and cut inch-long joints on all four corners because the track was pushing up along the wall. Concerned that the post-tensioned concrete would let go and the track would crumble, BMS decided that this was its opportunity to redesign the track to allow for side-by-side racing.

"We were running out of time and we had to decide what the track was going to be," said Jeff Byrd. "We could have just left the configuration as it was, but we got everyone in the same room and decided that variable banking was the best option. All the drivers were telling us to go with it. It was a giant leap of faith, but everyone lined up behind it because we thought it was the right thing to do for the future of the track."

The project team’s challenge was determining a concrete paving design that could withstand the stress of a slope that varied from 15 percent to 57 percent on the turns. The solution was to use continuously reinforced concrete, which allows the surface to expand and contract incrementally.

One of the project team’s first tasks was to develop a 3-D model in AutoCAD that simulated cars traveling at the upper and lower ends of the cross-section under various design scenarios. However, since roadway design reference books do not offer guidelines for cars traveling faster than 80 mph, the team reverted to mathematical formulas and pure physics to get the answers it needed for cars racing 125 mph to 210 mph. To create the high-tech computer model, the project team developed and inputted algorithms, just as engineers had done long before the computer age.

John Zudell, senior construction manager for SMI, said, "The geometry at Bristol is extremely unique. You have to take into account how fast the racecar is and how severe the banking is; it’s a complicated format. This is cutting-edge, new stuff. We had a huge spreadsheet with all the calculations that was as wide as my office. There’s no DOT manual you can go to for this."

Development of the horizontal and vertical locations and elevations of the cars at any point on the track set the favored racing grooves. From there, the entire track surface required mapping in a 5-foot-by-5-foot grid for construction staking so that no bumps or dips were introduced during installation and the finished track delivered the required racing grooves.

Workers pump concrete for the new track surface.

Contractor Baker Construction Services used GPS-guided grading technology to shape the complicated geometry of the subgrade. Baker Concrete (no relation to Baker Construction) then placed 13,000 cubic yards of concrete on the 0.53-mile, 55-foot-wide track: 5 inches of lean concrete with no reinforcement overlain with a 7-inch, continuously reinforced surface course. Double lugs were built at the beginning and end of each banked turn.

The team used a slope paver for paving the track, which has a parabolic surface with variable banking ranging from 24 to 30 degrees. The team also cut contraction joints using a specially fabricated sawing jig to work on the steep banks.

Baker Concrete adapted a finisher provided by Gomaco Corp. to create a one-of-a-kind concrete screed with customized guide rails that will only work at Bristol. To ensure that the finisher didn’t lift off the top rail, two team members provided about 400 pounds of counterweight until a more permanent solution was discovered—a boat anchor.

Success and satisfaction
On Aug. 25, 2007, the Sharpie 500 race went off without a hitch. While some fans were disappointed that cars were not bumping or crashing as often as previously, pure racing enthusiasts and the drivers in the race were ecstatic.

"I think the changes enhance the racing tenfold," said David Hoots, NASCAR managing event director. "You took away a configuration that lent itself to only one lane of racing and opened up the possibility of multiple lanes of racing, and that was very evident in the August events at Bristol Motor Speedway last year. And any time there’s wear on a surface, whether it’s asphalt or concrete, it’s going to wear itself in and it will only improve."

Expressing the near-unanimous sentiment of the drivers, Ryan Newman said, "The people at Bristol and the speedway itself did a great job in redoing the speedway. The track is better, racing-wise, than it ever has been. I look forward to going there."

Newman will get his next chance in August 2008 as the Sharpie 500 returns to Bristol Motor Speedway.

Greg Delaney, P.E., LEED AP, is vice president and principal with Eberly & Associates, Inc., a land planning, civil engineering, and landscape architecture firm based in Atlanta.

Speedway experience

Eberly & Associates’ experience with speedways began with Bruton Smith’s purchase of Atlanta Motor Speedway in 1989. Smith, chairman of Speedway Motorsports, Inc. (SMI), immediately recognized that the track seemed to be built backwards from a parking lot and access perspective.

Following the project team’s reconfiguration design and construction of the East Turn Grandstands, the Petty Grandstands, The Champion Grandstands, and the Allison Condominium Towers, the start/finish was relocated to the former back straight. This novel "tri-oval" configuration greatly improved site lines for seating and the new track layout resulted in side-by-side racing at record-high speeds.

In 1997, with the comprehensive transformation complete, Atlanta’s entire 43-car field ran faster than the old track record and the pole speed of 197.5 mph became the fastest lap for any non-restrictor-plate track in NASCAR. Further, the redesign effectively became the model for future track redesigns at Texas Motor Speedway, Las Vegas Motor Speedway, and Lowe’s Motor Speedway.

At Las Vegas, for example, the project team gutted the entire 100-acre infield and constructed new pits, fan access areas, and a media center. Additionally, Las Vegas is an international destination city, and the NASCAR venue at LVMS is the perfect place to showcase the sport. So the team steepened the track to 20 degrees in the turns and narrowed it to 55 feet to heighten the racing thrills. The cars ran for the first time on the completely demolished and rebuilt Las Vegas Motor Speedway in April 2007.


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