Building a Mansion…58 Stories Tall
In the rush to build and market condominium towers it was inevitable that the term “mansion” would be applied to one of these high rise structures. And where better than Atlanta, the home of southern style and stately mansions. Here is where AJ Concrete Pumping with headquarters in Atlanta is helping to build the Mansion on Peachtree, a 58-story condo/hotel project. AJ has elected to use a new Schwing model – the BP 4800 because of the high visibility and stature of the project.
“Schwing encouraged us to match the right pump to the project and we are using the Schwing BP 4800 and it is performing great,” according to Chad Barthlow, AJ General Manager. Getting maximum return on equipment investment is crucial in the competitive Atlanta market which explains the BP 4800 paired with the tried and true KVM 32 Schwing separate placing boom on a 39-foot mast supported in floor frames.
“This is the first time we have used the self-climbing feature and it is a lot easier,” Barthlow notes. As with conventional mounting, the mast extends through three pre-engineered floor openings with frames. Wedges and pins secure the mast in the frames. The difference with the optional self-climbing feature is that when it is time to raise the mast, the pins are removed from the frames, and a hydraulic cylinder raises the entire assembly. The lower frame is then transferred to the most recently completed floor. Barthlow adds, “Crane time is in short supply and we only need it to leapfrog the floor frame.”
A Schwing KVM 32 boom is atop the mast that is centrally located on the building. Its 93-feet of horizontal reach is sufficient to reach all of the corners of the eight-sided structure. All of the concrete has been placed to date with the separate placing boom and pump combination except for some lower level decks and columns. “Like most urban sites these days, this one has little room for truck pumps with booms so we have to get the separate placing boom up early to relieve congestion,” explains Barthlow.
Congestion doesn’t adequately describe Atlanta traffic jams, so in order to guarantee steady ready-mix supply, most of the pours have been scheduled for 3:00 a.m. and placed in about three to four hours. Post-tensioned decks consume between 250-300 yards of 5,000 psi concrete. Follow-up pours later in the day place columns and walls with a 10,000 psi mix. “Later this spring the morning pours will be good for placing the early strength material as the outside temperatures rise,” Barthlow notes.
“We have dedicated the same two operators to the entire job – one man with the pump and one man with the boom, “explains Barthlow, “They communicate directly with the general contractor to schedule the pour times and they ride together to work. They also handle the jumping of the mast without any assistance. The contractor is very comfortable with our personnel on the job.”
Holder Construction Company with offices in Atlanta and Virginia is the general contractor on the project. They have a long history with AJ and are dedicated to a “team approach” to project delivery.
As a community conscious contractor, AJ is sensitive to relations in the upscale Buckhead neighborhood where the Mansion is being built. “Because of the pour times, the Soft Start feature of the BP 4800 has been appreciated,” according to Barthlow. This standard feature allows the operator to control the speed at which the differential cylinders accelerate at the beginning of each stroke. By allowing the speed of the cylinder to ramp up gradually, Soft Start reduces surge in the pipeline for smooth pumping with an accompanying drop in noise.
The pump is placing through 80-feet of horizontal 5-inch pipeline before it turns 90-degrees to rise vertically. A diversion valve reroutes the concrete back into ready-mix trucks during pipeline cleanout. The BP 4800 is averaging 85-90 yards per hour at the 18th floor with “no problems” operating in the volume mode. The pump can be shifted to a high-pressure setting if needed. “The 4800 is meeting Holder’s expectations that were laid out before the project began,” states Bartlow.
Routine maintenance is performed by mechanics from AJ’s shop thirty miles away. “The Rock Valve requires very little attention,” according to Operations Manager Glen Grabowski, “Not only is it easy to clean out, if wear parts are required, we can do it easily in the field.” Another advantage of the Rock Valve is its patented, self-adjusting pressure spring which maintains pressure on the cutting ring to assure successful pumping.
The Mansion on Peachtree, designed by Robert A.M Stern Architects LLP, New York will be clad in light-colored limestone. Rosewood Hotels and Resorts, an ultra luxury hotel and resort provider with 11 locations in the US will manage the facility’s 124 hotel rooms, 43 condominiums restaurants and 15,000 square foot spa upon completion in 2008.