Tilt-up concrete construction offers a lot of benefits. It’s a fast, efficient, and economical way to build, using the same series of panels to provide both structure and exterior cladding. The technique was originally developed for, and for years largely limited to, construction of utilitarian one- and two-story buildings like factories and warehouses.
As designers, builders, and developers began to recognize tilt-up’s advantages, they started adapting the technique to suit taller and more aesthetically complex projects. By the late 1970s, tilt-up was occasionally being used for three- and four-story buildings with large glass areas and a variety of decorative surface treatments. Today, tilt-up contractors build commercial, institutional, and multifamily residential projects, as well as industrial buildings and stores. Tilt-up buildings of five stories or more are becoming common.
As with any building system, successful results with tilt-up concrete depend on careful design and detailing, thoughtful construction planning, knowledgeable work crews, and suitable tools and equipment. Two recent multistory tilt-up projects can serve as examples.
University housing complex
Woodland Construction, based in Jupiter, Fla., is one tilt-up concrete contractor that has handled several multistory projects over the years, including several that have received awards from the Tilt-up Concrete Association (TCA). Woodland’s president Clay Fischer discussed one of these, the Innovation Village Apartments at Florida Atlantic University (FAU) in Boca Raton, which comprised seven- and eight-story buildings. One key to the success of that project was the designer’s decision to get Woodland involved in its early stages.
“With multistory projects like the apartments at FAU, we often have more opportunity to get involved earlier in the process,” Fischer says. “Because the work is more complicated, the architects and engineers will come to us as experts who can help make sure the design will work, the details are right, and construction will be cost-effective. Some perfectly good designs can be detailed to be more ‘construction-friendly’ and therefore less expensive to build.
“Anything we can do early on is a win-win for everybody involved, but owners and general contractors are sometimes reluctant to bring us in early, because then they can’t really go out for bids. They have to put a lot of trust in us in that case. We’ve occasionally suggested design changes after winning a bid, but then we have to show that it’s justified by potential cost savings. The savings have to be enough to cover the costs of redrawing the details,” Fischer says.
The FAU apartments were unusual because the tilt-up panels serve as cladding for the concrete structure, but aren’t load-bearing. They’re more like site-cast precast panels with embedded weld plates that were used to attach them to the floor slabs. Therefore, they didn’t need to be braced the way tilt-up panels typically do.
The tallest individual panels for the FAU apartments spanned the full eight stories and were more than 88 feet high. These panels served as the exterior walls of the apartment living rooms. They have the largest window openings and are 16 inches thick. This additional panel thickness allowed for them to be cast and installed full-height. The adjacent panels are 8 inches thick, producing a stepped effect on the façade. These panels were cast and installed in two sections, one enclosing the first four floors, and another cladding the upper three or four stories.
“We like to work with full-height panels whenever possible because it’s fast and efficient, but multistory panels present some challenges,” Fischer says. “You need to use cranes with the capacity to handle taller, heavier panels and you have to be careful to brace them safely and properly. You also need enough space on the site. For a warehouse or factory, you can usually cast the tilt-up panels on the floor slab. For large multistory panels, there may not be enough floor area to do that, so you need to form casting beds around the perimeter, and brace the panels from the exterior. That means you need a larger no-entry zone on the site to keep people safe.
“When you’re working with multistory panels, the layout has to be extremely accurate,” Fischer says. If a one-story panel is off by 1/16-inch, it’s not a big deal. If you’re going up eight floors, though, and the panel is off by a few inches, that’s a problem. Here in Florida we use some high-tech glazing systems designed to withstand hurricanes, and they require the openings to be accurately sized within 1/32-inch. That doesn’t give us much leeway.”