Self-lifting forms offer a way to expedite construction of columns, spandrels, shear walls, and core walls of high-rise buildings. The reasons for choosing such formwork are largely economic. Freeing the cranes from form handling work leaves more time for setting steel, stocking building materials, and placing concrete. The self-raising forms are supported on the concrete structure independent from all other operations.
PLANNING A PROJECT WITH SELF-LIFTING FORMS
Self-lifting forms are typically used on fast-track work, and more extensive planning is required at the outset. Items to be considered include: load imposed on the building by the forms and lifters; capacity of other hoisting equipment on site; wind load on the forms; crew size; cycle time; debris nets or guards on the outside of forms; jib boom or hoist mounted on top of post lifters for lifting form parts or setting rebar; mechanical parts that must be received, assembled, or maintained to keep the lifters working.
ROLL-AROUND FORM LIFTERS
On composite buildings, where slabs are poured ahead of the columns and spandrels, roll-around lifters work well. Mounted on wheels, these lifters can be rolled around the deck by hand. They are equipped with a hydraulic-powered winch for lifting and a hydraulically operated boom for in and out movement.
Post-type lifters are mounted on the structure from outside the building. They are powered by an electric motor driving a threaded rod, by hydraulic cylinders, or by cable grippers that climb a cable. The post lifter is more versatile than the roll-around lifter because it works on all types of vertical construction; it does not depend on having the slabs placed ahead of columns and spandrels.