Formwork for Concrete Structures by R.L.Peurifoy and G.D- By EasyEngineering.net

392 Chapter Thirteen
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FIGURE 13-5 Formwork for a circular shell roof supported by tubular-steel-frame
scaffolds. (Source: Safway Steel Products)
with wood shores, as discussed in Chapter 6. Using shores with screwtype
adjustments facilitates setting the heights. Also, lowering the
forms for removal can be accomplished easily and quickly. Patented
shores should be also be adequately braced.
Figure 13-5 illustrates the use of tubular scaffolding as centering
for a shell roof. Where these frames are interconnected with both horizontal
and diagonal braces, they form a rigid system that is capable
of supporting substantial loads. The top frames should be equipped
with adjustable U-heads to support the stringers or ribs under the
decking at the exact elevations required.
In the event that the forms are to be lowered and moved to a new
location for reuse, the bottom legs of the forms can be equipped with
casters onto which the frames may be lowered during the moving
operation only. This will permit an entire assembly of forms and centering
to be moved and reset for additional use within a relatively
short time period.
Use of Trusses as Centering
Wood or steel bowstring trusses have been used as centering for forms
for circular shell roofs. Each end of a truss is supported by a post or
column whose length may be adjusted for exact height. Wood joists,
extending from truss to truss, support the decking. An entire form
assembly may be constructed and erected in such a way that it can be
lowered and moved to a new location for reuse within a short time.
Figure 13-6 shows the seven trusses required for one section of
forms in position for the installation of joists and decking. Figure 13-7
shows two sections of the forms lowered for moving.
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