Attendees at World of Concrete 90 were shown a fast and efficient method of constructing the concrete core of high-rise building. The technique is to make the forms self-lifting by building a system including jacks to raise the forms without crane assistance. The core form consists of a two-way grid of intersecting steel beams that support a work deck and safety railings on top. Gang form panels made with aluminum framing members and three-quarter-inch plywood face hang from the grid, as do the hydraulic rams that move the system up the building. Inside the building core, the work platform is suspended at the proper elevation for workers to release form support brackets.
The process works best when a starter wall about 6 feet high has been cast first, with all the necessary anchorages in place ready to support the wall forms and hydraulic rams. Once the cycle is under way, the sequence calls for: setting the inner form, steel, and embedments; setting the outer form and installing ties; placing the concrete and allowing it to cure; stripping and raising the forms. When the core form reaches the building top it is normally disassembled in units and lowered by tower crane. Speed of core construction with this forming system is potentially one floor every 2 or 3 days.