be up up

Tilt up

[tilt-uhp]

Tilt up or tilt-slab is a type of building, and a construction technique using concrete. The process resembles barn raising specifically and wood platform framing generally. It is cost-effective for low buildings.

In this method modular concrete elements (i.e. walls, columns, structural supports, etc.) are formed on a concrete slab; usually the building floor, but sometimes a temporary concrete casting surface near the building footprint. After the concrete has cured, the elements are tilted from horizontal to vertical with a crane and braced into position until the remaining building structural components (roofs, intermediate floors and walls) are secured.

Tilt up construction is a dominant method of construction throughout North America, Australia, and New Zealand. It is not significantly used in the UK, Ireland, and other regions, although popularity is increasing.

Concrete elements can also be formed at factories away from the building site. Tilt up differs from prefabrication in that the moulds are designed for a specific building and usually not reused.

Construction

Tilt up construction requires significant organization and collaboration on the building site. This increases project complexity but also gives designers more control.

Forming walls

Once the pad (casting surface or floor slab) has cured, forms are built on top. A high quality plywood or fiber board that has at least one smooth face is typically used, although aluminum or steel forms are also frequently used. Carpenters work off engineered drawings for each panel or element to design and construct the forms on site. They incorporate all door and window openings, as well as style accents (known as "reveals") and any other desired shapes that can be molded into the concrete. Studs, gussets and attachment plates are located within the form for embedding in the concrete. The forms are usually anchored to the casting surface with masonry nails, or otherwise adhered to prevent damage to the floor slab.

Next, a chemically reactive bondbreaker is sprayed on the form's surfaces to prevent the cast concrete from bonding with the form or slab, allowing the cast element to separate from the casting surface once it has cured. This is a critical step, as improper chemical selection or application will prevent the lifting of the panels, and will entail costly demolition and rework.

A rebar grid is constructed inside the forms, after the form release is applied, spaced off the casting surface the desired distance with plastic "chairs" or dobe blocks. The rebar size and spacing is generally specified by the engineer of record.

Concrete is then poured into the forms, filling the desired thickness and surrounding all steel inserts, embedded features and rebar. The forms are removed when the concrete is cured, and the element is tilted into place.

Stack Casting

Where space is at a premium on many sites the concrete slabs are cast one on top of the other, or stack cast. Quite often a separate casting pad is poured for this purpose and is removed when the panels are erected.

Erection

Cranes are used to hoist the wall slabs to a vertical position. (Previously, tilt tables were used instead.) The slabs are set into a foundation and propped up with braces until the roof is added.

Structure

Concrete walls are very heavy (over 150,000 kg is the record) and are most often engineered to work with the roof structure and/or floor structures to resist all forces (load-bearing walls). The connections to the roof and floors are usually steel angles and studs that were secured into the forms prior to concrete placement. These attachment points are bolted or welded. The upper attachment points are made to the roof trusses. Interior walls may be present for additional stiffness in the building structure as necessary, known as shear walls.

Insulation can be applied to either side of the panels or cast inside sandwich panels. Concrete has high mass, which regulates interior temperature (thermal mass) and provides soundproofing.

Collapse

Some engineers believe that older tilt up buildings are susceptible to collapse in earthquakes.

Like all concrete construction, tilt up buildings are fire-resistant. In addition, wall panels can be designed to sag inward when damaged, which minimizes collapse (this can also be done with prefabricated panels).

Gallery

Uses

Some authors believe that tilt up was one of the concrete construction methods used in Ancient Rome or the ancient Middle East. Modern tilt up, made with reinforced concrete, was first used in America circa 1905. Early erection was done using tilt tables, but the development of the mobile crane and truck mixers allowed tilt up construction to grow. Tilt up gained widespread popularity in the post World War II construction boom. Tilt up was not used successfully in Australia until 1969.

Most early tilt up buildings were warehouses. Today the method is used in nearly every type of building from schools to office structures, houses to hotels. They range from single story to more than seven and can be up to 30 metres in height.

An early example of this method is found in the innovative Schindler House, built in 1922 in West Hollywood, California. Architect Rudolf Schindler claimed that with the assistance of a small hand-operated crane, just two workmen were needed to raise and attach the tilt-up walls.

Appearance

Early tilt up architecture was very minimalist and boxy. Recent techniques have expanded the range of appearance and shape.

Many finish options are available to the tilt up contractor, from paints and stains to pigmented concrete, cast-in features like brick and stone to aggressive erosion finishes like sandblasting and acid-etching. Shapes are also a feature that have become dominant in the tilt up market, with many panels configured with circular or elliptical openings, panel tops that are pedimented or curved, facades that are curved or segmented and featured with significant areas of glazing or other materials.

Association

The Tilt-Up Concrete Association (TCA) is the international trade association for tilt up concrete construction. TCA is a membership-based association, with nearly 500 members world-wide. TCA members can be contractors (general contractors or tilt up subcontractors), engineers, architects, developers, consultants, suppliers, specialty trade firms, educators and students.

TCA offers primarily educational, networking and exposure benefits to its members. TCA also offers an Achievement Awards program annually, recognizing the best examples of tilt up construction over a variety of end uses.