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. 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 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. Tilt-Up accessory suppliers can be helpful with this. Experienced Tilt-Up engineers also can offer economical bracing schedules.

 

 

Several items must be considered during the planning and engineering phases of the project to include surface treatment, anticipated weather conditions, and material and equipment availability.

 

 

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