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Tilt-Up Concrete Construction
Engineering
Engineering is a critical phase of
Tilt-Up projects. Consult an engineer
with experience or familiarity with
Tilt-Up construction and current design
methods. Current recommendations for
many aspects of Tilt-Up, particularly
engineering, are presented in ACI 551R
(Ref. 1).
Engineering Tilt-Up panels to withstand
service and lifting loads is critical.
But using a design that is too
conservative could produce panels that
are thicker and heavier than required.
The net result could be larger footings,
bigger cranes, more panels, and more
joints-- all of which can increase the
cost of the project to the point where
it is not cost-competitive.
The thickness of a concrete panel
usually is determined by a quantity
called the slenderness ratio. This is
the ratio of the unsupported panel
height (usually the distance between the
floor slab and the roof structure
attachment) to the panel thickness. The
generally accepted slenderness ratio on
Tilt-Up walls is 50. However, a
qualified engineer should make the final
determination.
Floor slabs must be designed to support
crane loads during erection. These loads
may exceed building occupancy loads in
some cases, so select the crane early in
the project. Most contractors use at
least a 5- or 6-inch-thick slab, unless
structural requirements dictate a
thicker one.
Panel connections to the footings, floor
system, roof, and between panels also
are details designed by an engineer, and
must be determined before construction.
The loads applied during lifting
generally have the greatest affect on
the panels. Locations of openings,
lifting inserts, and other parameters
must be considered. Additional
reinforcement usually is needed to
accommodate these loads. Tilt-Up
accessory suppliers can be helpful in
this aspect of design. Most will provide
panel layouts indicating locations of
lifting inserts and other information
critical for erecting the panel.
A product of the design phase should be
a drawing of each panel, preferably
showing both the front and back, and
insert and embed locations. The
contractor or engineer should produce a
building floor plan showing the layout
of every panel on the slab and the
erection sequence.
Several other items must be considered
during the planning and engineering
phases of the project. These include
surface treatment, anticipated weather
conditions, and material and equipment
availability. For example, if the panels
are to have deep reveals, a thicker
panel might be required since the cross
section of the panel could be reduced at
a critical point by the reveal.
Careful consideration should be given to
the size, location, and attachment of
temporary wall braces. Here, again,
Tilt-Up accessory suppliers can be
helpful. Experienced Tilt-Up engineers
also can offer economical bracing
schedules.
>> Next:
Footings and Floor
Slabs
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