By Mark Rea

Changing the skyline of downtown Austin could be considered risky at any time, but doing it with a 33-story high rise office tower in the midst of economic bad times raised more than a few eyebrows.

However, when the $137 million Frost Bank Tower is completed in November at Fourth Street and Congress Avenue, the Capital City will welcome a new architectural landmark that could also help revitalize the downtown area as the exclusive location for office space.

The Austin office of Atlanta-based Cousins Properties Inc. developed the concept for the unique downtown high rise and assembled a team in 2001 that included Dallas-based Constructors and Associates Inc. as general contractor. In addition to building what many experts believed was an extremely risky project given the economic climate, Cousins turned to a contractor with no previous experience in multi-story high rises.

"I think it's safe to say that many people viewed this as a high-risk endeavor," said Constructors president Bob Albanese. "It was going to be the tallest building in downtown Austin and started in the middle of an economic downturn."

Cousins had worked with Constructors in the 1990s on construction of the Frost Bank Plaza in Austin. That relationship, along with the contractor's continued presence in the Austin area, allowed Constructors to put together a bid package that earned the high-profile contract.

"To earn this project, assemble a great team and then bring it to life makes us extremely proud," Albanese said.

Groundbreaking took place in November 2001 for the 1 million sq. ft. building, which will boast an 11-story parking garage base with room for up to 1,500 vehicles. Atop the parking structure will be a 22-level glass and Italian limestone tower featuring 500,000 sq. ft. of prime office space.

Construction began with demolition of several clubs, restaurants, retail shops and a bank. Crews drilled piers - with average diameters of 52 in. - for the footprint of the structure to an average depth of 30 ft. In the center of the footprint is a 6-ft.-thick concrete mat slab to anchor the square core of the building.

"The reason for the mat slab was because we had to place all of the electrical transformers and switch gears underground in a vault," said Constructors senior project manager George Allen. "We felt that since we were excavating for that and the elevator shafts, a mat slab would be beneficial so that we could capture some more space under the building."

Workers excavated to a depth of 28 ft. for the mat slab, which contains about 1,500 cu. yds. of concrete. The slab was completed in just two pours.

The square core was unique from an architectural standpoint because most similar office buildings feature rectangular cores.

"It definitely differs from what we typically do," said Brian Eason, project architect and vice president for Dallas-based HKS Inc. "The square core has some large spans for concrete structuring and that's a unique feature. Normally, the spans would be placed straight through the core, but here all the beams come off the corner at an angle. That was a challenge as far as concrete forming was concerned, but a feature that really sets the building apart from any other."

Capform Inc. of Carrollton handled all of the structure's formwork.

Compaction of the site also held some special obstacles for work crews. Surrounding the new building are several longtime Austin structures, some of which are more than a century old and protected as historical buildings.

"The last thing we wanted to do was shake those old foundations too much," Eason said. "We had some anxious moments when the drilling rigs fired up, but everything worked out well."

Specialized Concrete

The Frost Bank Tower features several types of concrete, including a 10,000-psi mixture for the foundation's columns and shear walls especially designed by Robert Hill of Dallas-based structural engineer Brockette Davis Drake.

"Starting off with 10,000 psi was certainly something unusual," said Constructors project superintendent Barry McManus. "The mixture was so rich that it initially took about three days to set. Of course, we needed that mix to set in one day. But Robert made an adjustment from a chemical imbalance in the initial mix and that resulted in the perfect mix."

The entire core area is comprised of shear walls around the elevator areas with all exterior girders tied in. Each shear wall consists of concrete between 10,000 psi on the lowest level to 5,000 psi on the upper floors. Interior concrete beams average 20¾ in. by 30 in. until reaching transfer floors where the weight of the upper tower is transferred onto huge girders tied to the cores. Beams on the transfer floors are as large as 80 in. wide and 40 in. deep, while the concrete girders average 30 in. by 6 in.
Austin-based Capital Aggregates supplied the more than 62,000 cu. yds. of concrete for the project and Pumpstar of Buda used an 8,000-psi, twin-engine diesel to get the mixtures to the upper levels.

"We tried not to pour with the tower cranes because of their limited use and the fact that the formwork would be flying, so we utilized the pumping system all the way to the top," McManus said. "On average for the total project, we would lay about 100 cu. yds. per hour on the deck. We pumped twice a week on the tower and three times each week on the parking garage until topping out. We turned a floor on a tower about every 4½ to 5 days on the tower and then every about seven days on the parking structure."

Austin-based CTR installed 7,100 tons of reinforcing steel for the project, and Houston-based Suncoast Post-Tension handled the more than 400 tons of PT cable that are contained in all beams and girders throughout the building.

Crowning Achievement

Atop the Frost Bank Tower is an architectural feature that should redefine Austin's cityscape.

A unique 99-ft. crown of structural steel and glass curtainwall serves as the exterior focal point for the tower, capturing and reflecting sunlight during the day and emanating a glow throughout the nighttime sky via a high-intensity lighting system.

And while the tower crown will be the signature of the new structure, there were some major obstacles to overcome to complete it.

Before beginning construction of the crown, Constructors project manager Robert Salgo built a scale model to determine how erection of the more than 250 steel pieces could be achieved. The model also yielded other valuable information.

"What we discovered through creation of the model was that certain things needed to be modified to yield a more constructable envelope," Salgo said. "Additionally, the purpose of the model was to establish a close working relationship between the erector and the fabricator because we also adjusted some of the fabrication of the pieces to yield a more effective erection sequence."

Myrex Industries of Houston fabricated the steel for the crown and Austin-based C. Young & Co. handled the elaborate erection process. The pieces were hoisted to the top of the structure by tower cranes supplied by Texas Crane of San Antonio. The four jack frames that form the crest of the crown are the largest pieces and weigh approximately 10,000 lbs. each.

Movement of the crown also factored into the equation. "All high rises move to a certain degree and you just have to make your calculations based upon that fact," Eason said.
"How the structural steel is erected, how the curtainwall is installed … you have to make sure to include everything in those calculations."

Once all of the structural steel pieces were erected atop the 25,000-sq.-ft. footprint of the crown, painters applied two coats of cream-colored paint to the steel followed by installation of more than 40,000 sq. ft. of curtainwall by Dallas-based Haley-Greer Inc.

An impressive array of lighting will begin on the back of each of the crown's four sides and massive steel hip tubes will serve as raceways. The high-intensity light will enter at the bottom and exit through holes cut in the tubes, crisscrossing one another to leave the top of the building with a dramatic glow at night.

Impressive Top To Bottom

People entering the building on ground level will be treated to an impressive display of architectural features inside and out.

A variety of retail space and outdoor seating areas will be available in the more than 5,000 sq. ft. of plaza space opening onto Fourth and Congress. A unique glass water feature will also greet visitors as they make their way toward the lobby.

The lobby floor features a unique Indian blanket pattern with an intricate design of stars melding into one another. There are four different colors in the lobby floor - gold, beige, cream and black - utilizing a combination of marbles and granites imported from Spain, France and Italy. The 5,000-sq.-ft. lobby area will also boast other unusual features such as imported eucalyptus wood wall treatments, courtesy of Durham, N.C.-based project design architect Duda/Paine Architects.

A combination of EFIS material, Texas white limestone-colored precast panels, Italian white limestone and nearly 240,000 sq. ft. of glass curtainwall will comprise the exterior. The curtainwall will feature vision glass as well as fritted glass, which is manufactured from particles of glass that are fused, or sintered, into a solid but porous body that can be sealed into glass tubing for an entirely glass filter.

As of mid-June, approximately 50 percent of the building's office space had been leased. The first tenants are expected to begin inhabiting the structure by early next year.