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Span your options
3 ways to meet the demands of multi-story construction using long-span composite systems
Recent data about the structural steel industry builds a pretty clear case where the marketplace is headed: Up. Literally.
Multi-story construction, particularly the residential segment, is on the rise, according to the American Institute of Steel Construction white paper “Structural Steel: An Industry Overview.” Overall, steel was the top structural framing material for buildings in the U.S., with a 46% market share in 2017 for non-residential and multi-story residential construction. In the multi-story residential segment, which includes hotels and dormitories, steel has a market share of 37%—and that number has grown “significantly” over the past five years, the AISC reported in August 2018.
As demand for multi-story construction builds, so too do the structural steel framing options on the market. Long-span composite systems, however, stand out as superior solutions for project owners and design teams. But which long-span system is right for your multi-story application?
New Millennium Building Systems is the only provider to offer three long-span composite solutions under one roof, each with inherently unique characteristics and advantages. Depending on project needs, composite joists, Deep-Dek® Composite or Versa-Dek® Composite have the structural and aesthetic qualities required for mid- to high-rise applications.
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Meet the 3 systems
Although they have qualities and benefits all their own, the three long-span composite systems from New Millennium succeed because they blend the speed and versatility of steel with the performance and durability of concrete. Determining the appropriate long-span system for a multi-story project requires diligent analysis and comparison of the options, and those efforts will pay off in the end, says Sean Smith, Market Development Manager at New Millennium.
“Each of these systems can offer structural and aesthetic benefits for your building project,” he says. “From thin composite slabs to long clear-spans, our composite systems offer lighter, shallower and cheaper design solutions than concrete alone. Other benefits feature reduced building height, mechanical, electrical and plumbing (MEP) integration and large areas of column-free space.”
The longest spanning system capable of 20 feet to 60 feet and beyond, composite steel joists integrate steel joists and composite deck using shear studs that are attached through the composite steel deck to the joist top chord. Concrete is then poured on top of the decking, and the shear studs become embedded in the cured concrete, forming a unified load bearing system that deflects as a single unit. Floor-to-floor elevations can be narrowed due to the thinner floors. Longer spans mean fewer columns and a more space-efficient design. Lighter and fewer joists mean lower costs at every step, including joist erection and joist fireproofing. The combined time saved can often lead to earlier building occupancy.
“Composite joists offer a lighter, shallower and less costly solution than wide-flange beams,” Smith says. “MEP systems can run through the open webs of each joist rather than under a solid beam, which can contribute to a higher finished ceiling in the space below.”
Offering spans up to 36 feet with unshored pours up to 22 feet, Deep-Dek® Composite helps make steel frame solutions cost-effective. It is available in deck heights of 4.5”, 6” and 7.5”. Deep-Dek® features patented side-lap connections that enable it to achieve its composite bond.
Deep-Dek® Composite as a base system has comparable acoustics to standard construction methods. Sound transfer is a critical component in multi-story design. Measured in Sound Transmission Class (STC) and Impact Insulation Class (IIC), long-span composite floor systems bolster these criteria with floor and ceiling assemblies. For floors, these are as straightforward as sound mat underlayments. They can perform as the base layer for any finish floor type. Ceilings may be more elaborate assemblies. One of the most popular is using resilient channels to offset structure from the finish ceiling material.
In spaces that may require it, Deep-Dek® Composite can address ambient noise (NRC). A shop-welded liner panel, referred to as Cellular or Cellular Acoustical, creates a flat-bottom aesthetic. The latter utilizes the entire cavity of the Deep-Dek® for an acoustical batt, attaining impressive Noise Reduction Coefficient values. The application for this variation in Deep-Dek® is a mixed-use project that has a retail component at ground level. The system offers construction flexibility that cannot be replicated in standard multi-story structural systems. Deep-Dek® Composite may be pre-fabricated on-site, potentially saving time and money. This Panelized Delivery Method™ enables work crews to assemble floor panels on the ground before hoisting into place with a crane.
Deep-Dek® Composite is UL fire rated for up to 4 hours.
“With span-to-depth ratios equaling those of traditional cast-in-place concrete and hollow-core plank, a long-span system featuring Deep-Dek® Composite helps make steel frame solutions affordable and the design aspirations of architects possible,” says Marty Williams, Design Development Manager at New Millennium.
Available in 2” and 3.5” dovetail profiles, this system provides the thinnest total floor depth possible, reducing story height while maximizing ceiling height, with clear spans up to 28 feet. It is ideal for use in mid-rise residential and hotel structures and is well-suited to work with light gage structural steel, panelized wall systems as well as any beam or bearing-wall method.
With its prevalence in multi-story residential, Versa-Dek® Composite requires equally articulated acoustical consideration to Deep-Dek® Composite. Mitigating sound transfer in floor and wall assemblies is not only preferred by users, it is being codified by municipalities. Portland, Ore., for example, mandates 50 STC and 50 IIC for multi-family new builds. Similar to strategies with Deep-Dek® Composite, sound mats and secondary ceiling systems are the preferred paths to increasing acoustical performance. Even with the growing desire for an exposed aesthetic, there are designs that do not compromise STC and IIC.
Versa-Dek® Composite is UL fire rated for up to 3 hours. Its dovetail design also accommodates the Versa-Wedge® hanger system to suspend lighting or facilitate MEP integration.
“Versa-Dek® Composite is ideal for reducing building height and the square footage of exterior cladding systems,” Smith says.
These three long-span composite systems are engineered for a wide range of multi-story structural applications, including healthcare, office buildings, retail/commercial buildings, schools, prisons, hotels, residential and parking garages. Each system also is available in a variety of configurations. That makes selecting the right system for a project a critically important decision.
Multiple choice questions
Multi-story projects have a set of interdependent factors that long-span composite systems must address, including span, depth, performance, aesthetics and cost. Furthermore, each of these factors is made up of deeper criteria that will influence the choice of system for a multi-story project.
Span?
Span: Achieving wide-open spans uninterrupted by support columns, long-span composite systems can open the door to a wide range of building design possibilities. Multi-story projects typically utilize floor systems spanning 20 feet or longer, sometimes reaching 60 feet. “Span is one of the first project demands considered when selecting a long-span system,” says Smith, Market Development Manager at New Millennium.
Depth?
Depth: The total composite floor depth is directly affected by required span and loads, but also by the system selected. You may have heard the expression that “deeper is cheaper,” but when considering overall building height and the costs associated, this may not be true. Depending on project requirements, some long-span floor systems can be used to minimize floor depth to optimize floor-to-floor height.
Performance?
Performance: Factors related to performance include load, fire, vibration and sound ratings. What are the dead-load and live-load requirements? Which system will achieve the proper protected and unprotected fire-resistance ratings? Does the design require vibration analysis studies and control? What ambient noise and sound transmission management options are available?
Aesthetics?
Aesthetics: What is the desired finished look and feel? Does the design call for an exposed structural appearance with finish coatings or for the addition of ancillary ceiling systems? How will the mechanical, electrical and plumbing systems integrate?
Costs?
Costs: Above and beyond the composite system material costs, what labor costs are associated with the system of choice? What additional costs will be incurred to achieve the finished look and performance? Will the selected system help optimize the overall height of the finished structure and contribute to greater occupancy and owner profitability? Which system will achieve project results quickly and efficiently?
A short story about multi-story
So how do you select the right system for a multi-story project? The following compares three solutions for one hypothetical project.
Project details A 30-story hotel project with open spans of 26 feet with one row of shoring preferred. New Millennium and two competitors can meet the span conditions, but additional acoustic and vibration testing is required. Vibration analysis sets New Millennium apart from the market.
Project solutions: Based on preliminary study, New Millennium presented three solutions: Versa-Dek® Composite 3.5” and Deep-Dek® Composite 4.5” or 6.0”. Depth of profile, total slab depth, bearing strategies, closed ends, shoring and side lap attachments can differ for each system. All three New Millennium systems are the only options that account for long-term deflection.
Partners in production
Determining the right long-span composite system for a project doesn’t have to be a solitary endeavor. New Millennium experts are available for consultation and design assistance to help you choose the system that best meets project demands.
When a firm asks New Millennium what long-span composite system is best for their multi-story project, several questions come to mind, Smith says. What is the project’s budget? What is the project type? What is the size of the project? How many stories is it? What are the spans desired? What are the floor plan dimensions? Where is the project located? What is the structural system? Can shoring be used? What are the acoustical and fire-rating requirements? The list goes on.
As those questions are answered, the long-span composite system of choice will come into focus. No matter the system, it is the mission of New Millennium to optimize your project application, accelerate the construction timeline and reduce project costs.
Learn more about our long-span composite systems.
Case studies
- Cauley Ferrari dealership
- West Bloomfield, Mich.
- Architect: inFORM Studio
- Facility: 51,000 square feet
- Composite joist and deck
This dealership has a unique live load to support on the second floor of the stunning showroom and storage area: cars. The flooring system is composed of a 3-inch concrete slab on 2-inch composite 20-gage floor decking supported by composite joists.
“The 20-gage, 2-inch composite deck chosen for the mezzanine and second floor was selected because it could span 50 feet unshored and still support both the enormous dead loads as well as the moveable live loads [292,000 pounds],” says Kurt Voigt, Engineering Manager for New Millennium Building Systems.
- University of Arizona Health Sciences Innovation Building
- Tucson, Ariz.
- Architect: CO Architects
- Facility: 220,000 square feet
- Deep-Dek® Composite Cellular Acoustical 6.0
The floor system of University of Arizona’s new state-of-the-art educational facility had to have visual appeal—since it would be left architecturally exposed—and the strength to support heavy superimposed loads. The 85-foot-by-25-foot bays (2,125 square feet total) had to control floor vibration below the threshold suitable for research environments. It also had to possess a 2-hour self-performing fire-endurance rating.
“To meet all these requirements, Deep-Dek® Composite Cellular Acoustical 6.0 was chosen. The floor system could span 24.5-feet between 80-foot-long plate girders,” says Trent Fowler, Specialty Deck Project Manager for New Millennium Building Systems.
- Elan Heights apartments
- Architect: Houston
- Meeks + Partners
- Facility: 11 floors, 326 units
- Versa-Dek® Composite 2.0
This project’s long-span composite floor system created narrow floors that extend unsupported up to 28’ wall-to-wall. Living spaces were freed up by open spans and more space-efficient floor-to-ceiling heights. Versa-Dek® Composite systems are UL fire-endurance rated for 2 hours without additional spray-on or gypsum materials. Unlike traditional steel decking, fireproofing met code without special drywall work or filling the deck flutes with fire retardant material.
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