Advantages, Usage, and Limitations of the Column-Mounted Shoring Systems
1. Height-independent Systems. The system can form slabs at higher elevation [15 ft (4.57 m) and above]. Traditional formwork systems are limited to story heights between 10 and 12 ft (3.05 and 3.66 m). Buildings with story height more than 12 ft (3.66 m) require several splices for shores; this slows the erection of formwork. In addition, construction workers are at risk because they are forming slabs at high elevation. Column-mounted shoring systems can be placed at higher elevation without the need for vertical posts. The fact that the system is height independent is of particular importance in the first few floors, where story height can reach 25 to 30 ft (7.6 to 9.1 m).
2. Because the system requires no shoring or reshoring, other construction activities are allowed to proceed simultaneously with the construction of concrete slabs. In conventional construction, shores that support the first slab are typically supported by mud sills that rest on the ground. Frequently, ground conditions are sloped,
rough, and/or irregular, causing concentration of loads on mud sills that might cause failure. Also, in the fall and spring seasons, day and night temperature vary substantially. Night temperatures cause a frozen ground condition, while high day temperatures in addition to excess water from construction activities make the frozen ground muddy, causing substantial settlement to mud sills. This may cause a serious safety problem. It should be noted that mud sills and/or slabs on grade are not required when column-mounted shoring systems are used.
3. Cost of the system is competitive with traditional systems if 8 to 10 reuses or more are available. The system requires a smaller crew size. Table 4.1 shows labor requirements for traditional systems and column-mounted shoring systems. The system can be assembled on the site at the ground level; this increases labor productivity. It should be noted that, on an average-size job, a four – person crew can strip, fly, and reset in approximately 20 minutes.
4. The system requires large capital investment (initial cost). However, if enough reuses are available, the final cost per square foot or square meter of contact area is competitive with traditional formwork systems.
5. The system requires adequate crane service in terms of adequate carrying capacity at maximum and minimum radii, adequate space around the building being con-
Table 4.1 Labor Requirements for Traditional Formwork Systems and Column-Mounted Shoring System
structed, and nonexistence of power lines or any other obstructions that might limit crane movement and swing of the boom. Standard deck panel dimensions are 20 ft (6.1 m) wide by 40 ft (12.2 m) long and weigh approximately between 10 and 25 lb/ft2 (48.8 and 122.1 kg/m2). Total weight of the average panel is between 10,000 and 12,000 lb (4540 and 5440 kg), which is within the capacity of most construction cranes. Larger panels can reach 30 ft (9.1 m) in width, 75 ft (22.9 m) in length, and 25 lb/ ft2 (122.1 kg/m2) in weight, requiring special cranes for handling.
6. The deck panel has an indefinite number of reuses as long as the plywood sheathing is of high quality and the panel is handled with care.
7. Electrical and plumbing connections can be installed on the ground on the deck panels. This results in substantial productivity improvement because there is no need for scaffolding or work performed at high elevations.