Comparing Concrete Tilt-Up with Metal Building Systems

by Mark Robins | September 1, 2020 12:00 am

Today, one common concrete building application is tilt-up construction. It involves a building’s concrete elements (walls, columns, structural supports, etc.) being horizontally cast on a concrete slab. This normally requires the building floor to be a building form but may be a temporary concrete casting surface near the building footprint. After the concrete has cured, the elements are tilted to the vertical position and temporarily braced into position until the remaining building structural components (roofs, intermediate floors and walls) are secured.

Concrete tilt-up and metal building construction both have their advantages and each works best in different applications. Concrete is a rock; steel is a metal. Concrete has very high compressive strength. It can be compressed and squeezed, but it has very little tensile strength. Conversely, metal has enormous tensile strength and can resist forces trying to tear it apart. This article focuses on how concrete tilt-up and metal building construction compare, contrast and even work with each other.

CONSTRUCTION AND MATERIAL COSTS

Metal has the highest strength-to-weight ratio of any building material and that’s key to making it a more cost-efficient building material than concrete tilt-up. Steel produces a stronger building with far less material than concrete; less material equals less material costs. Using recycled materials also reduces material price and structural steel can contain up to 90% recycled steel.

Because metal buildings are prefabricated and engineered to be assembled easily, a pre-engineered metal building requires less specialized labor in its assembly and can be completed in less time than concrete tilt-up. Tilt-up construction requires a precise coordination of services between many different professionals, which can quickly add up in labor costs. Pre-fabricated metal buildings have the ability to work alongside other trades safely where concrete does not. All of this reduces cost and when working on large structures; time is money.

W. Scott Schellhase, AIA, NCARB, APA, LEED AP BD+C, vice president, SLS Partnership Inc[2]., Lubbock, Texas, asserts concrete tilt-up has considerably more construction costs than a metal building because, “With tilt wall you will have another internal structure and overhead structural systems (roof) that is normally a metal structural system. With a metal building, you get both at once.”

William L. Coulbourne, PE, F.SEI, ASCE, consulting specifying engineer and owner of Coulbourne Consulting[3], Rehoboth Beach, Del., explains that concrete will require more of a foundation than just the column footings used for metal buildings. “Cost of tilt-up per square foot for concrete would seem to be higher than metal depending on whether the tilt-up is formed and poured in a shop or field constructed.”

Concrete tilt-up uses many time-consuming steps, including creating and placing formwork, mixing and pouring concrete, waiting for the curing process to take place, and form removal. While metal buildings do require a concrete foundation, they can be faster to build overall because there are fewer steps involved. “Concrete is an inherently heavy material and its weight should be taken into consideration in the structural engineering of the building,” says Whitney Castro, marketing coordinator at Bunger Steel Inc[4]., Phoenix. “It’s common to see larger structural members such as beams, columns and footings in a concrete building. When the building is constructed out of steel, those elements will typically be lighter, comparatively smaller and often less expensive.”

SIZE AND APPLICATION

When choosing between the two options, Schellhase contends that for long and linear shapes, metal buildings are better due to their clear-span designs, uninterrupted space and tall overhead space. “[Metal is] very ideal for warehouse and storage facilities. We did a very long facility for FedEx in Lubbock; it was perfect for all their equipment, sorting systems, etc. [It had] complete unencumbered space, and a very efficient cost and time to install and obtain owner occupancy.”

In terms of application, Bruce Bortree, building engagement manager at Butler Manufacturing[5], Kansas City, Mo., asserts that metal buildings are far superior to tilt-up concrete. “Metal buildings can accommodate changes in function, ownership, equipment and regulations. The ease of expansion can be built into the original design. The flexibility extends to the cladding. Metal building systems can accommodate any cladding for much greater aesthetic appeal.”

Castro agrees that a concrete structure is usually built for a very specific end use such as an industrial warehouse and very rarely is a concrete building going to be easily adaptable for another use. “Metal buildings on the other hand are incredibly versatile and can be adapted to many different uses such as gyms, arenas, aircraft hangars, storage facilities, etc.”

At Heritage Building Systems[6], North Little Rock, Ark., metal buildings can be manufactured for a variety of uses, including the commercial, industrial, agricultural and recreational markets. “One attractive advantage to choosing steel as your building material is its versatility … nearly every aspect can be customized to desired specifications,” says Barry Clifton, sales manager at Heritage Building Systems. Select the framing, roofing and siding options that best fit your needs … in a variety of colors.”

John Koury, architect, A M King[7], Charlotte, N.C., contends building usage is where metal buildings offer some advantages to concrete tilt. “Concrete tilt-up is an attractive option for larger buildings due to economy of using slab as casting bed and using the perimeter walls as the structure in both bearing and shear. However, metal is the more appropriate material in the following scenarios: when the desired building is below 40,000 square feet; if there is a specialty slab; if sacrificial casting beds need to be utilized for the tilt panels; or if specific thermal environments, such as cold/freezing, or sanitation performance is required.

If the warehouse is temperature controlled and includes refrigerator, freezer or cold processing area, or needs wash down—hands down insulted metal panels are the superior product. In colder climates, tilt is not as prevalent as in the south or west. Cold weather demands additives to the concrete for cold weather curing, and results of pours can be more varied in these conditions. Sometimes an owner must live with less than ideal results with superficial cracks on structural tilt panels.”

DURABILITY AND OCCUPANT SAFETY

Steel is a sturdy and long-lasting material that is often warrantied for decades and—if installed and maintained correctly—can last for generations. Metal buildings are resistant to man-made and natural damage. Concerned about building safety? Metal’s inherent ductility and strength make it a preferred blast-resistant structural material over concrete.

Metal’s strength makes it a popular choice when building in regions prone to earthquakes, wild fires and even snow. Metal buildings are designed to meet specific county/city/state and national building codes. Resilience has become a popular buzzword in the building design industry. Bortree contends metal building systems can support project resilience because all parts are manufactured remotely, so working in difficult weather conditions can be easier.

“If you’re in an area that is prone to earthquakes, a concrete structure will need to be designed with extra measures in order to stay standing when seismic activity occurs,” says Castro. “Concrete structures often crumble and fall which can be disastrous for occupants. In contrast, steel buildings can easily be designed to be prepared for the dynamic loading conditions imposed by earthquake activity. An inadequately reinforced concrete tilt-up structure can result in serious construction accidents. Metal buildings are designed to be assembled in the most efficient way possible, reducing the chance for accidents.”

Schellhase feels a responsibility to design any structure to meet or exceed building and life safety code requirements for the building’s occupants. “Either structure [concrete or metal] can provide life safety for its users, on occasions, possibly due to the building location on the property (near the property line) and adjacency to other buildings that would require exterior walls to be fire rated,” he says. “Concrete might appear to be the winner here, but our firm has done a fire-rated wall on a metal building before, no reason it can’t be done today.

As we approach any project that would require a possible analysis of either type of structure, we always hire a structural engineer. In my opinion, an engineer is going to design the same code compliant/structurally safe building using either of the two systems. I would prefer to allow our client to decide on which they feel their budget can withstand.”

In terms of impact resistance, Koury says concrete tilt-up construction is more apt to resist impacts with no appreciable damage. “Metal buildings can be dented and prone to corrosion once the surface is compromised. Some of this risk can be mitigated though with knee walls, curbs or other armoring around potential impacts.” Coulbourne agrees that metal has a tendency to corrode at some atmospheres, whereas concrete is not corrodible as long as the metal reinforcing is adequately protected from the weather.

ENVIRONMENTAL FRIENDLINESS

Metal buildings have the lowest environmental impact of any construction method. Bortree cites a whole building life cycle analysis by Walter Moore & Associates (MBMA 2015) that shows metal buildings outperform wood, concrete, masonry and tilt-up construction. “Because the metal systems begin their life with a large percentage of post-consumer recycled steel and can be recycled at the end of their useful life, they represent an exceptional sustainable choice,” he says.

Castro notes that steel is not likely to break or warp when it’s being taken down or moved, and can typically be used again in a new location. “Metal buildings are often repurposed as they easily can fit many types of end uses. Steel is a great insulator for both heat and cold often reducing heating and cooling costs.” Koury notes that concrete tilt-up has good environmental qualities, one of which is low transportation costs since they are cast on-site, as well as the potential to use fly ash in the concrete mixture.

Ultimately, the choice between using a metal building versus a tilt-up comes down to basics. Construction location, building size, envisioned design, end use and budget should all be considered when making the decision. An alternative option could be a hybrid building using both concrete and steel, which is often seen in industrial uses, and Castro recommends consulting with a metal building provider to discuss specific requirements.

Source URL: https://www.metalarchitecture.com/articles/comparing-concrete-tilt-up-with-metal-building-systems/

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