A 28-story office building, Colorado Tower is being constructed on the site of an existing surface parking lot in downtown Austin, Texas. Duda/Paine Architects/topsidefront
A 28-story office and retail tower is designed to maximize a tight site in downtown Austin, Texas.
August 20, 2013—A surface parking lot in downtown Austin, Texas, will soon be transformed into a 28-story office and retail tower. Although the site is essentially a clean slate, integrating the tower into the city’s existing fabric is no simple task. Challenges include positioning the tower without affecting an adjacent building of historical importance and ensuring that the tower is distinctive but does not detract from its low-rise neighbors. In overcoming the challenges, the building’s designers have realized a tower that rises from an unconventional foundation to be as recognizable at its street level as it is at its crown.
Colorado Tower is being constructed at the corner of Colorado and Third streets, next to the Nelson Davis Warehouse, a historically important structure in Austin’s Warehouse District. Cousins Properties, Inc., a real estate development, acquisition, and management firm based in Atlanta, is developing the project. The structure will be the first office tower of its size constructed in Austin since the Frost Bank Tower, another Cousins development, which opened in 2003. The design team includes two firms that have a long-standing relationship with Cousins and worked with the developer on the Frost Bank Tower and other large-scale projects in the past. Duda/Paine Architects, based in Durham, North Carolina, is the design architect, and Brockette/Davis/Drake, Inc., an engineering consulting firm based in Dallas, is the structural engineer on the project.
The tower will be a class A office tower as defined by Building Owners and Managers Association International. Because of soil conditions at the site, all of its 28 stories will be above grade. At ground level, the tower will have an approximately 5,000 sq ft lobby and two retail spaces, one approximately 2,000 sq ft and the other roughly 4,000 sq ft. Each space will have its own street access. Rising from there, the tower—which will include a 12-level parking garage topped by 16 levels of office space—will appear to be two interlocking forms.
The project is expected to fill a need for office space in the city. “The Frost Bank Tower really was the last office building of this size to be built in Austin,” says Jay Smith, AIA, LEED AP, a senior associate for Duda/Paine Architects. “Over that 10-year period of time, Austin has experienced a shortage of office space.”
The primary challenge of the project was fitting the tower on the relatively small site. Located just a few blocks from the Colorado River, the site is bordered by an alley to the east, the historically important warehouse to the north, Third Street to the south, and Colorado Street to the west. In addition to meeting the stringent setback requirements for the corner site, the designers had to ensure that the tower’s foundation would not damage the adjacent warehouse, a brick structure built in 1902. The tower will be founded on drilled concrete piers that will range in diameter from 72 to 78 in. and in length from 12 to 50 ft. To protect the warehouse, the piers on the tower’s north side will be farther inside the frame than will be the case with the columns, says Chris Borchers, P.E., a senior project manager for Brockette/Davis/Drake. This configuration produces a significant moment, requiring large-diameter piers and additional reinforcing in that area. “We have strap beams that go back inside of the building to help take that moment out,” Borchers explains.
The tower will be framed in concrete, a material widely used in Texas for its efficiency and affordability there. The framing system will have several unconventional components, including posttensioned joists to accommodate longer spans and reduce the number of joists overall. Moreover, some of the columns will turn 90 degrees at the tower’s base to accommodate the lobby and retail spaces.
The tower’s east and west sides will feature 15 ft cantilevers at the garage levels, and the south face will have a cantilever that extends as much as 15 ft to help reinforce the design concept of the tower’s two interlocking forms. These cantilevers will be achieved using traditional concrete beams without the need for transfer columns, Borchers says. To limit the number of transfer beams between the tower’s garage and office levels and reduce the amount of structural framing overall, several columns at those locations will lean to span as many as four floors. “We have lots of areas where columns move, essentially, and rather than doing a transfer column at each one with a big transfer beam, we’ve leaned the columns,” Borchers explains. “We do have a couple of transfers, but mainly the columns lean from the garage to the office space.”
The tower’s street level is designed to complement the surrounding
low-rise masonry buildings. Duda/Paine Architects/topsidefront
Another significant challenge was designing the tower to complement the surrounding neighborhood, which has many low-rise brick buildings like the Nelson Davis Warehouse. To that end, a canopy will extend over the tower’s lobby level, forming an intimate connection with the street while also protecting pedestrians from the weather. The underside of the canopy will be wood while the top will be zinc, materials selected to add warmth to the building and further connect it with the nearby structures. “We were really trying to find a way to respect the surrounding context and provide a connection back to the street,” Smith says. “Sometimes the street level is really ignored on towers in favor of the height or the presence of the tower, and I think we were particularly sensitive to designing the street level for the pedestrian experience.”
The tower will be clad with a high-performance glass curtain wall in which aluminum mullions will create distinctive horizontal and vertical patterns. Glass was selected to admit natural daylight and give occupants views of the river and nearby parks. Horizontal fins on the south facade and vertical fins on the west facade will prevent solar gain and reduce glare, while louvers on the east and west sides of the building will allow air to circulate through the garage without detracting from the overall look of the tower. “Even though we have an open-air component to the garage, we’ve come up with a patterning of louvers and perforations on both sides that blends in with the glass curtain wall that we’re using for the primary parts of the office building,” Smith explains. “And on the south side, we’re using glass to mask the facade that comes down [over the garage], which gives the south elevation a real presence.” At night, lighting along the tower’s curved glass top will provide a soft glow against the dark sky.
Construction of the tower is under way and will be completed in the fall of 2014. The designers say they hope that the building will be attractive to tenants as well as to the city at large. “We have designed a building for the client and city that will be recognizable in the skyline of Austin and one that we hope the city will be proud of,” Smith says.