As new residents of Charlotte, N.C., are seeking to make a connection with the rapidly growing Southeastern hot spot, Atlanta-based general contractor Batson-Cook Construction last month completed a connection of its own with the city. This one provides some of those residents and workers downtown with a pedestrian and retail pathway that ties together an existing 32-story high-rise to a new residential mixed-use development and a green park.
Until May, this "retail connector" was the fifth level of an existing eight-level, 900-space parking deck built by Batson-Cook three years ago. Now it provides a 100-ft.-long corridor connecting Three Wachovia Center and The Ratcliffe Condominiums residential, retail and office development adjacent to its south side.
Both structures and the park, which sits atop a new five-level underground parking garage, are part of a phased downtown redevelopment project being conducted by owner First Union Corp., which is headquartered in Charlotte, known as the financial capital of the Southeast. Batson-Cook is the contractor for all these structures.
Code calls for added deck support
Because the connector now supports pedestrian traffic and retail space instead of automobiles, the deck's poured-in-place, post-tensioned concrete slab and double-T beams required strengthening to meet code. "The parking deck was designed at 50 pounds-per-sq.-ft. capacity for parking loads. To accommodate the pedestrian corridor and retail shops, we had to upgrade the capacity of the structure to 100 pounds per square foot," says Chuck Gaston, Batson-Cook project superintendent.
In addition, 10,000 square feet of the parking deck's sixth level was removed to provide 16-ft. ceiling heights for the retail space.
In preparation for the removal of the sixth-level deck and because the 12 columns would now support two stories instead of one, Engineered Restorations, Lawrenceville, Ga., shored the columns with an added 6 inches of concrete. "In order to handle the load being transmitted into the sixth-level slab, we had to transfer the loads to slabs above it and below," says Randy Hall, Batson-Cook's project executive.
"The columns were beefed up on four levels — three levels below the sixth floor and one level above it — to transfer the loads," says Gaston.
Beams and slab post-tensioned
Once the columns were shored, crews strengthened the 100-by-100-ft. bay section of deck five, which supports the connector and retail shops. Led by George Prieto, Batson-Cook's post-tensioning expert, crews strung post-tensioning cables along each side of each bay's north- and south-running double-T beams. Engineered Restorations then formed and pressure grouted the beams, adding 6 inches of concrete reinforcement to each beam.
Attention then turned to the post tensioning of the slab in an east-west direction. Crews strung the cables every 3 feet through slots cut into the underside of the slab. Where beams were encountered, the cables were run through slots over the top of the beam and on through the slot on the underside of the slab continuing on to the next bay, says Gaston. The cables were then anchored at both ends.
To protect the cables from fire, 2-by-2-in. steel angles were installed back to back 3 inches apart on either side of the cables and bolted to the underside of the slab. The space between the angles was then grout filled with concrete.
The retail connector continues a tradition of building corridors in Charlotte, according to Hall. "People downtown can get from one building to the next almost without ever having to go outside," he says, noting the typically humid 90-plus-degree day in late May.