FACTORS AFFECTING THE SELECTION OF VERTICAL FORMWORK SYSTEM
Vertical supporting structures such as buildings’ cores in high-rise construction, towers, or silos are typically a critical activity that control the pace of the project progress. Consequently, when selecting a core forming system, time is a critical factor. Duration that must be considered are the movement of the form from floor to floor, original assembly, time to set rebar and inserts within the form, stripping time, close-in time, and final disassembly.
Other factors to consider in formwork selection are the amount of labor required to strip, set, pour, and control the system; the amount of precision needed as far as plumbness and corner tolerances, ease of lifting, and the designer’s intent when developing the structural system. Other methods substitute the manual labor with valuable crane time. The decision between labor or crane time requires careful financial analysis. As explained in Chapter 8, crane-independent systems have been developed that
do not require crane time and require considerably less labor than other systems. However, these systems are generally proprietary and require a significant investment.
Precision requirements make some systems better than others. On huge towers, cores must remain very plumb due to elevator tolerance requirements. The formwork must have a method of remaining plumb and level. If the formwork is moved piece by piece, each piece must be checked for being plumb and level, which leads to a gross amount of field engineering. Most systems become increasingly more difficult to keep plumb and level as wear and tear loosens corners and the form deteriorates in general. Also, wind loads at higher elevations tend to deform the system.
The architect usually doesn’t design a building with any particular form system in mind. In some cases, such as slipforming, the design must reflect the method of forming. However, it is usually assumed the building will be conventionally formed.
Many other factors that affect the selection of vertical formwork systems for buildings are similar to those factors affecting the selection of horizontal formwork systems. However, there are some factors that are particularly important to the selection of vertical formwork systems. Among these are:
1. Factors related to building architectural and structural design, including lateral supporting system(s) and building shape and size
2. Factors related to project (job) specification, including concrete appearance and speed of construction
3. Factors related to local conditions, including area practices, weather conditions, and site characteristics
4. Factors related to the supporting organizations, including available capital, hoisting equipment, home-office support, and availability of local or regional yard supporting facilities
An overview of all the factors affecting the selection of vertical formwork systems is shown in Figure 5.1 that included the factors
that are critical to selection of both horizontal and vertical formwork systems. The following sections are focused on those factors that are related solely to the selection of vertical formwork systems.