Industry perceptions can at times shield the obvious upsides of a particular steel building product. When it comes to designing high-performance floor systems, using wide-flange beams has been the norm. Take a deeper look and you’ll see using steel floor joists with Flush-Frame Connections from New Millennium is often a better way to go.
In the past, floor joists were often specified for economy and constructability, with 2- to 4-foot joist spacing, 20- to 30-foot span, shallow steel form deck, and a thin slab. That design approach led to bouncy floors compared to using wide-flange beams with thicker slabs, longer spans, and wider beam spacing. However, using today’s designs for high performance floors—with 8- to 10-foot spacing and 30+ foot spans—the vibration performance of floor joists is comparable to wide-flange beams and offers the other added benefits of steel joists.
You can achieve even better vibration results than wide-flange beam floors with steel joists by utilizing deeper joists than your wide-flange beam design option. You may already have space to increase the joist depth as compared to your wide-flange beam design, or you may want to increase your joist depth to take advantage of MEP integration. For more on that topic, see the MEP section of this article.
Finally, you can utilize flush-frame connections to take the vibration performance of a steel joist to the next level by bringing the steel deck into direct contact with the girder. This allows the girder to act composite with the slab for vibration characteristics and it “ties in” the adjacent bay—which significantly increases the joist effective panel weight, thereby improving system damping
Achieve up to 35% weight savings using steel joists as compared to wide-flange beams. Whether using composite or non-composite members, steel joists provide serious cost-saving opportunities in floors without sacrificing performance.
The average recycled content in steel joists across the six fabrication facilities of New Millennium is 80%, thanks in large part to Steel Dynamics, our parent company, and its Electric Arc Furnace (EAF) lower-carbon emitting steel making process. Additionally, steel joist floor systems can save up to 35% in steel usage as compared to wide-flange beam floor systems. As our Sustainability Practices outline in more detail, the option to use less carbon intensive products allows for an opportunity to reduce the overall greenhouse gas emissions associated with your building, helping achieve goals to decarbonize.
Specifying professionals utilize steel joists in steel-framed buildings across the country because they’re economical, versatile, and easy to specify utilizing industry standards. New Millennium has published a set of standard flush-frame connections which allows specifying professionals to easily specify flush-frame connections for floor joists. These connections are simple and predetermined based on the joist reaction and wide-flange girder sizes, simplifying specification and coordination amongst the steel design and fabrication team. The tried-and-true ease of specifying steel joists, combined with the simple New Millennium standard flush-frame connections, make a win-win option for your next steel-framed floor system design.
Not only are steel joists simple to specify, but they also provide more flexibility in optimizing the design of your floor system as compared to wide-flange beams. The open-web system of a steel joist, and its inherently custom design, enables an array of load, span, and depth options—allowing you to investigate weight and performance modifications that aren’t as plentiful with wide-flange beams. With as little information as column spacing, clear height requirements, and loading, the sales specialists at New Millennium can assist you in finding the right solution for your project.
Additionally, the Steel Joist Institute Floor Bay Comparison Tool is a free resource that assists specifying professionals in comparing many variations of wide-flange and steel joist floor bays, and includes parameters such as cost of material, cost of installation, weight of framing, floor vibration, and floor depth.
If panelizing multiple members at a time during erection, extended-tab flush-frame connections on joists are preferred by erectors because the joists can be placed without having to be rotated into place, and handling joists with open-web systems are easier than wide-flange beams. Further adding to the speed of construction, light MEP systems are easy to hang from joists and route through webs, as compared to needing to cut holes or use beam clamps on wide-flange members. Joist bridging does add time to install as compared to wide-flange beams. However, it’s insignificant when considering the installation as a whole and in context with the other steel joist benefits. Use the SJI Floor Bay Comparison Tool, input your costs to install bridging, and see for yourself today!
Locating the flush-frame joist working-point directly over the center line of the girder makes best use of system strengths. Since steel joists are so efficient at supporting in-plane flexural loads, New Millennium designs the joist components—including the joist end plate for shear and moment—and by relying on the moment resistive bolt group, makes the connection an integral part of the joist. This design ensures that the joist reaction aligns directly over the girder’s center line, effectively eliminating any torsion effects on the girder.
Many designers indicate a standard 18- to 24-inch MEP clear-height allowance beneath a wide-flange floor system. If a portion of this allowance is utilized in increasing the joist depth—which is not an option with wide-flange beams—it will provide substantial increases in floor stiffness, weight savings, and cost savings, plus will provide significant pass-through space in the steel joist. Additionally, steel joists with flush-frame connections eliminate the need for standard joist seats. These options reduce the overall story height of your building and streamline the integration of MEP systems.
Steel joist camber is built into the standard manufacturing process. Therefore, it’s either no additional cost (standard SJI camber) or very little additional cost (non-standard camber) compared to cambering wide-flange beams. Additionally, steel joist camber is consistent and repeatable, providing a flat finished floor across the span of the joist. By comparison, wide-flange beams are relatively expensive to camber and tend to have substantial variance in the resulting camber magnitudes.
There are occasions where wide-flange beams are specified with a span/depth ratio greater than 24, the maximum for standard steel joists. Thus, in contemplating a comparison of steel joists to the wide-flange systems, one may think the floor depth would have to increase. This is not the case with SJI CJ-Series joists, whose composite action allows a span/depth ratio up to 30. This provides an option for an apples-to-apples comparison of steel floor systems of the same depth, if routing MEP through the open-web system of deeper steel joists isn’t an option.
Turn to us as your guide to steel floor systems with better performance at less weight, reduced costs, and a lower carbon footprint, and make the move to steel floor joists with Flush-Frame Connections from New Millennium.
The refined engineering connections from New Millennium have a more efficient design to eliminate wide-flange girder torsion concerns and make it easier for structural engineers.
An innovative design from the engineers at New Millennium, our connections feature a joist reaction point designed to occur at the center line of the wide-flange girder.
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