Architect: Rule Joy Trammell Rubio, Atlanta, GA
Engineer: SDL Structural Engineer, Atlanta, GA
General Contractor: Brasfield & Gorrie, Atlanta, GA
Reinforcing Bar Fabricator: Gerdau Ameristeel, Duluth, GA
Total Project Cost: $265 million
Total Project Size: 2,116,500 sq ft
STRUCTURAL FRAMING SYSTEM AND UNIQUE STRUCTURAL DESIGN FEATURES
The 1075 Peachtree project consists of three primary components: office, hotel/condominium with parking, and retail space which is integrated into each of these. The project basically consists of two main structures. The first being an office building and the second is the hotel/condominium with parking structure. The two structures are separated by an expansion joint.
The office structure is a 36 story building that consists predominantly of a 25 inch deep reinforced concrete space frame with shear walls at the core for the first five levels of the building. The building is 524 feet tall from the slab on grade elevation to the top of the screen wall at the roof. At this height a typical reinforced concrete frame system would not work on its own so it was supplemented with an inner core tube wall and frame system. The tube wall and space frame system started with five levels of shear walls. A tight spacing of columns starting off the top of the shear wall carried up the remainder of the building. The columns were linked together to form the inner tube lateral system by 36 inch deep beams within the core. This system allowed for the speed of traditional beam and column construction (as compared to the speed of shear wall construction) while still providing a substantial lateral system capable of supporting this height of building.
HOTEL/CONDO AND PARKING STRUCTURE
The hotel/condo structure is a 34 story building that consists predominantly of two-way mild and two-way post-tensioned reinforced concrete slabs with a shear-wall lateral system. The building is approximately 425 feet tall from the lowest slab on grade to the top of the screen wall at the roof. Because the elevator cores were only two elevators wide, the aspect ratio of the building height to shear-wall width to was approximately 18. This aspect ratio for the lateral system would be prone to problems with motion. Because the upper floor of the hotel/condo tower were condos it was necessary to stiffen the lateral system by building a reinforced concrete outrigger system at the 28th floor and at the roof. This outrigger system allowed additional building columns to become engaged into the lateral system thereby effectively increasing the width of the lateral system that that the effective aspect ratio and the subsequent building motions were within acceptable limits.
The parking structure is part of the hotel/condominium and consists predominantly of two-way mild and two-way post-tensioned reinforced concrete slabs with shear-walls similar to the hotel/condominium. Because shear walls were not allowed on the East side of the structure, a 15-story moment frame was utilized along this side of the building to provide for the lateral resisting system. The building’s loading dock is located under the parking structure at “Level S” of the building. A 72 foot long one-story high concrete transfer girder was used to just above the loading dock to allow for truck turning clearance under the building.
MAIN REASONS FOR CHOOSING REINFORCED CONCRETE
The lowest levels of the building are as much as 45 feet below exterior grades around the building. To keep wall construction as efficient as possible is was necessary to integrate the floor structures with the building retaining walls. This coupled with the fact that several of the lower levels of both building structures serve as parking floors led the design team to choose reinforced concrete for these levels. Once that decision had been made, the office was a natural to keep going with the reinforced concrete frame because the floor framing patterns could be replicated again and again thus allowing a very efficient forming system and cost effective structure. To keep the hotel/condominium to minimum floor to floor heights and to allow the floor to be the ceiling of the hotel or condo below, cast-in-place plate flat plate concrete floors were an obvious answer. Finally, by using cast-in-place concrete framing systems, the design was able to continue at the same time as construction because small changes in the design could be accommodated rapidly in the field by relatively easy modifications to formwork and reinforcing that could be made on a floor by floor basis as needed.