Speed of Construction
The most important advantage of using a sophisticated formwork system is the speed of construction. The speed of construction affects cost because it determines the time when the building will be available for use and also reduces the financial charges. The major factors that determine the speed of construction follow.
Floor Cycle. Faster floor cycle is always desirable for contractors and owners. For contractors, faster floor cycle allow the contractor to finish on schedule or earlier which reduces the overhead cost. For the owner, faster floor cycle reduces his/her shortterm financial charges and allows early utilization of the constructed facility.
The use of efficient vertical formwork systems such as slip formwork and self-raising formwork allow the contractor to complete the casting of one story every two to three days. Also, vertical formwork systems control the pace of progress for horizontal concrete work.
Rate of Placement. The speed at which concrete is placed in vertical formwork has the largest influence on the lateral pressure that is imposed on the formwork. The lateral pressure is increased by increasing the rate of placement, up to a limit equal to the full fluid pressure. Higher rates of placement influence the size, material, and tie pattern of the selected system.
Construction Sequence. Tall buildings typically have an inside core to resist lateral loads. One alternative is to completely construct the inside core in order to create a ‘‘closed’’ area for the other trades to start. This alternative has proven to be faster than constructing and finishing floor by floor. This can be accomplished by using slipforms or self-raising forms.