The proposed High Point Pittsburgh elevator system consists of four glass-walled elevator cars that rise in an open shaftway structure fitted into the recessed area of the building’s northeast corner (7th Street side).
Although they are grouped in pairs back to back, each car is individually lifted and lowered by an electric motor equipped with a regenerative power system for maximum efficiency and mounted at the top of that car’s shaftway.
Measuring 8 ft. x 8 ft. (64 sq.ft. of floor space) each car is capable of carrying 25 people to the top in 90 seconds, and with loading and unloading time, making a round trip every 10 minutes. Thus, the four-car system has the potential of conveying 600 passengers up and down every hour.
Many issues arose in the design of this structure.
Since the shaftway occupies the entire indented corner of the existing structure, we wanted to preserve as much as possible the views from offices along that corner. We also wanted a structure that would be appropriate to the building’s distinctive architecture and image.
These considerations led us to design an unenclosed elevator shaft as well as to minimize the size and number of structural elements involved.
The primary purpose of an enclosed shaft is to protect the elevator’s cables, wiring, and other machinery from the weather. To protect this equipment without an enclosure, we developed a system where only the guardrails and the cables are enclosed in columns. These columns would then be filled with insulation and a membrane of a gel-like insulating material so the elevator could glide through them during motion without exposing anything.
The footprint of the structure’s primary support is a series of Cor-ten steel girders that extend approximately 30 feet beyond the ends of the building’s existing horizontal girdering between every three floors. These two horizontal members will meet at a common lateral beam 16 feet long, creating a stable shape that can be welded to the building’s existing girdering.
Primary support for this series of structures is provided by a single large vertical column that rises midway along the lateral beams, paralleling in placement and dimension the vertical column that rises in the vertex of the building’s corner, creating a space of 25 feet between the the two columns.
Finally a pair of smaller beams will connect the two vertical columns at each three story level, creating open cages that define the four individual shaftways. Since the building’s existing columns are filled with water for fire protection, these beams must be welded to the horizontal girders.
In addition to this geometric framework, smaller vertical columns at the two rear corners of each elevator car provide added support and stability. The horizontal beams connecting the two primary columns will also keep the shaft way from swaying under its own weight or wind loads.
Finally, each car is fitted at the back onto to a pair of vertical rails that it follows to the top, with an anti-sway bar on each side.
The safety features of the elevator system are the minimum in order to avoid visual disruptions for the corner offices in the building. These safety features include a caged access/escape ladder in the spine of the hoist way with a landing at every floor.
Given a rated load of 12,000 pounds and a speed of 850 ft/min (meaning that the elevator would reach the top of the Steel Tower in under a minute), the square footage of each elevator car was found to be well within the maximum allowable area of 103 square feet (Rule 202.1). The guide rails, which are mounted along the sides of each elevator and prevent the elevators from swaying, must be made of #15 steel (15 lb/ft, Rule 200.3), with a fishplate thickness of 11/16″ and a bolt diameter of 5/8″ (Rule 200.7b). Finally, each elevator car can be sufficiently supported by four suspension wires of 3/4″ diameter (Rule 212.3). The preceding specifications were taken from ASME A17-1978.