Nonshored Formwork System for Top-Down Construction

Recently, the top-down construction method has been applied to building construction to secure excavation safety by providing rigid diaphragm walls. Usually, proper and economical formwork systems need to be selected for successful top-down construction. This paper proposes a nonshored top-down formwork system (referred to as NSTD) as a modified formwork system for top-down construction. The NSTD method provides sufficient workspace for excavating under the suspended forms. Upon completion of concrete placement and curing on the ground level slab, the formwork system is lowered to the next floor, and the process is repeated down to the lowest underground floor. The advantages of the NSTD method include a reduction in the excavation duration and an improvement in the quality of the underground concrete work by the hanging-type formwork. A case study was performed to verify the validity of the NSTD by comparing its schedule and cost effectiveness with those of traditional top-down methods.