SouthTrust Bank of Charleston

Location:

Charleston, SC
 

Owner:

SouthTrust Bank, Birmingham, AL
 

Architect:

Liollio Architecture, Charleston, SC
 

Precast Specialty Engineer:

Structural Integrity, Nashville, TN
 

Contractor:

B.L. Harbert International Inc., Birmingham, AL
 

Precast Erector:

Gate Precast Company, Oxford, NC
 

Project Scope

Sq. Footage:

30,000
 

Levels/Floors:

4
 

Architectural Precast Elements:

286 total pieces including column covers,
spandrel panels, cap pieces, wall panels
and cornices.
 
 
 
 
 
 
 
SouthTrust Bank of Charleston
SouthTrust Bank of Charleston
SouthTrust Bank of Charleston
SouthTrust Bank of Charleston
SouthTrust Bank of Charleston
 
 
 
 
 
 
 
 
 
 
 
 
 

Precast Panels Achieve Historic Appearance

In the 17th and early 18th centuries, the Carteret Bastion served as a fortification for the city of Charleston, South Carolina. The bastion defended the city at what is now the corner of Meeting and Cumberland streets. So when SouthTrust Bank officials decided to locate an office building on the site, it was natural that they wanted to respect the historic character of the neighborhood. A façade composed of architectural precast concrete panels helped achieve that look while providing a contemporary flair.

“The owners wanted a building that was sensitive and responsive to its historic setting,” says C. Dinos Liollio, president of the bank’s architectural firm, Liollio Architecture in Charleston, S.C. That setting was dictated by nearby buildings such as the adjacent Circular Congregational Church, a Romanesque structure built in the 19th century. “But they didn’t want to confuse a 21st-century building with historicism. So they asked us to do a contemporary design sensitive to its historic context.”

Contemporary and Historic
That directive required the designers to take the historic architectural language and translate it into contemporary language. “That’s where precast was a tremendous asset,” says Liollio. “Precast allows the contemporary adoption of the structure to its historic setting. And it gave us a timeless language because it is so constant.”

The building’s footprint is approxi-mately square and about 7,500 square feet in size. Precast spandrels, column covers and cornices wrap the building on all four sides, with the panels extending up through the cornices on the third level. The fourth level is recessed and was designed purposely not to be ornate, to visually reduce the height of the structure, Liollio explains. The curve around the street corner acknowledges that there was a bastion at that location.

The 30,000-square-foot building’s façade is organized into three layers. The precast panels and cornices comprise one layer, which cooperates with the etched-bronze window frames of the second layer to create a “painting” on the backdrop of the third layer, comprising the stucco that clads the top floor and flanks the precast portion. The large precast cornice caps the ornate portion of the façade.

“The stucco is analogous to the canvas of a painting, and the precast and etched bronze are the painting itself,” he explains. “That theme is constant throughout the project.” The exteriors on the office’s conference rooms and corner entry stairway are clad in precast, and the more utilitarian functions of the building are sheathed in stucco. Liollio credits Gate Precast, the precast manufacturer, and general contractor B.L. Harbert International, with serving vital roles in bringing all of these aspects together.

“Precast gave us the option of providing the deep recesses that were so important in translating the façade in terms of light, shadow and materials,” says Liollio. The precast is purposely separated from the stucco, which provides us shadow. Only the precast could provide us the ability to achieve that finite detailing that we’re looking for in that intersection of stucco and precast.”

The exterior colors were defined by the manner in which the precast, bronze, and stucco work together, he says. “We knew we wanted the stucco to be white, and we knew the panels and windows would be bronze. So with the precast, we were trying to interpolate a color that would age with the bronze and site nicely against the stucco.”

The precast creates the look of buff-colored limestone with a light sandblasted finish, says Chris Galde, sales manager for Gate Precast, the manufacturer and erector. The color resulted from a discussion of alternatives among the architect and the Architectural Review Board of Charleston. “They chose the limestone with a light sandblast to complement the historic downtown architecture,” says Galde.

“The real issue with the precast is that neither the city nor the owner wanted a superficial material,” says Liollio. “They wanted a material of substance. Each material is designed to age with the building itself. Precast emulated a timeless material and provided us with the ability to do these large cornices and overhangs — and we know it will age gracefully in conjunction with the other two materials. The building could have been built in natural stone but that would have been prohibitively expensive.”

Non-Repetitive Pieces
The building required a total of 286 precast pieces: column covers, spandrel panels, cap pieces, wall panels and cornices. Of the total, 156 were erected by Gate Precast, with the remaining 130 cap pieces provided to the job site, where B.L. Harbert International erected them. “The biggest challenge we experienced was that the project required a lot of non-repetitive pieces,” says Galde. “We needed to make a number of various precast molds to produce the product.”

The structure’s frame consists of lightweight steel, which resists lateral loads. The precast features a stacked-exterior system, with each piece bearing on a vertical member. The cornice pieces provided a special challenge, Galde says. “There were many different exterior cornice molds that were either radiused or not radiused, which had to be placed at the parapet of the building.”

The complete erection process took a little more than two months. All steel framing was in place and the concrete floors were poured when erection began. Logically, erection of the stacked pieces began at the lowest level and worked upward. Column covers came first, followed by “water-table” pieces atop the first level. These pieces resembled the upper cornice, but they’re smaller. Next, more column covers were erected, then more spandrels at the top, followed by the large cornice pieces.

The heaviest column cover weighed 16,000 pounds. The heaviest piece of all was a cornice component weighing 32,000 pounds. Each cornice piece was 14 to 16 feet long and had scalloped cut-outs on the back to remove weight. Gate could use only one 300-ton crane, which had access to the site from two sides; structures on the other two sides precluded their use for access. “If the cornice pieces had been solid concrete, the crane could not have lifted them,” says Galde.

Another challenge resulted from the fact that the site was not precisely square, and the building’s footprint followed the property line. “That presented some challenges in corner conditions,” says Galde. “From a production standpoint you’re not dealing with 90-degree corners.”

To flank the main-stair entry, the architect designed two large precast spheres that rest on pedestals. The spheres consist of precast cladding cast around large Styrofoam balls, each 36 inches in diameter. The spheres are derived from two large lion-like sculptures that are used at the entrance of a nearby historic building, says Jay White, an architect with Liollio.

All stakeholders are pleased with the building. “Precast is a highly durable material that gave the architect the flexibility to construct a building that meets his expectations,” concludes Galde.

Key Engineering Concerns
William Edd Mitchell Jr., principal at Structural Integrity, the Nashville, Tenn.-based precast specialty engineering firm, singled out these key engineering challenges on the SouthTrust Bank of Charleston project:

The difficult site due to a variety of factors inherent to the Charleston area. “Hurricane wind loads, high seismic requirements and very poor soils are typical of the area,” he says.

No gravity loads could be applied to the structure. The basic precast system featured two-piece stacked column covers for gravity support of the floor and roof spandrels. The panels only could be tied back to the building structure. “While the column covers had large returns making flexure and axial loading design less difficult, the transition of loads from the upper to lower column cover created a meeting of two very different cross sections,” he says.

A notched bearing pocket was created for the spandrels due to the cornice profile of the typical floor spandrel, combined with the requirement for the spandrel to bear off the column covers. The pocket allowed column covers to be erected, after which spandrels were moved horizontally into place by bearing on tube bearings cast into the column covers. The roof spandrels were gravity supported on top of the upper column covers. “Due to the weight of the roof spandrels and the location of their bearing on the upper column cover, careful consideration had to be given to the eccentric gravity moment induced into the upper column cover.”

Transferring seismic loads to the structure was challenging due to the variety of structural elements. Because the precast components’ center of mass was nearer the panel faces than the return features, substantial connection elements were used to “reach out” to the precast. This allowed the majority of the work to be done by the connections rather than the return features of the precast. As a result, some creative connections were developed to ensure the elements could expand and contract. This flexibility eliminated the need to “stitch” the elements together in a restrained manner that would eventually lead to expansion cracking.

SouthTrust Bank creates a harmonious look in a historic setting for less than the cost of stone, thanks to the use of architectural precast concrete panels.

 
Back to