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. Panels must be designed with reinforcing to
support in-place loads including dead and live gravity loads, out-of-plane
wind and seismic loads, and in-plane shear loads as determined according
to the governing building code. Forces induced from thermal effects
and shrinkage effects should also be considered. In addition, panels
must also be designed for temporary construction loads, most notably
the forces experienced during lifting. Appropriate factors of safety
should be included to account for dynamic impact and suction forces.
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, as well as 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
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. Tilt-Up accessory suppliers
can be helpful with this. Experienced Tilt-Up engineers also can
offer economical bracing schedules.