When the preliminary plans for a possible tilt-up project hit your desk, you should immediately look at a number of areas, including site layout and topography, foundations (type, depth, and design, if any), the slab, panel design, and scheduling. These considerations are important especially when deciding whether to use tilt-up construction.
Site layout and topography
When looking at the site plan of a potential tilt-up project, it is important to know if all the panels can be cast on the proposed building's floor slab or if casting beds will need to be constructed. If casting beds are needed, is there enough room directly around the building? Now the combination of site topography and space both become critical. A flat area around the building will be needed for casting beds, along with an access path for the erecting crane. If casting beds are not required and all your panels can fit well on the slab, crane access and picking requirements still need to be evaluated. Determine how much grading is necessary to get a flat, graded path for your crane. Occasionally, this will require spending additional dollars for grading and maybe gravel roads for the crane.
Every tilt-up project requires a panel layout diagram to detail exactly where the panels will be cast on the slab. This is helpful in many ways because it will assist in determining if the panels do indeed fit on the slab and that casting beds are unnecessary. Also, it forces the contractor and panel erector to agree on what panels get picked when and from where.
On many projects, tilt-up may be an “option” you're considering over steel, precast, or masonry. Oftentimes, contractors are presented with a project the design team thinks may be a terrific candidate for tilt-up, but the initial review of the site and building layout may prove the contrary. For example, an architect thought a distribution warehouse would be perfect as a tilt-up project. However, it was a two-story building in the side of a hill with virtually no lay down area and excessive slope all around the building. To make matters worse, the panels would have to be designed to act as retaining walls and resist significant horizontal loads. Compared to other structural systems, tilt-up wasn't the best choice for this particular building.
Foundation types vary depending on soil conditions and climate. Panels can be erected on drilled piers, pad footings, continuous footings, grade beams, or stem walls. But what if you're comparing different building systems to tilt-up? Frequently, design/build teams fail to investigate the foundation system when comparing tilt-up, masonry, pre-cast, and steel with studs. Precast panels need to be transported, so they are limited in width, usually between 13 and 15 feet. Thus if you are working on a caisson foundation system, you'll have similar spacing for your piers. If looking at tilt-up, panels can be designed much wider, most often twice the width of its precast counterpart, thus saving money on caissons. Likewise, a masonry wall composed of concrete masonry units usually is built on a grade beam, whereas a tilt-up wall directly founded on caissons or footings acts as a grade beam itself. Therefore, the grade beam can be a differentiating factor with regard to cost. Be sure to consult the structural engineer to determine appropriate foundation design when doing these comparisons.