For years, the steel joist industry standard has been that loads either need to be applied at panel points, or a member brace (strut) must be added in the field. In response to inquiries from structural engineers and other members of the Building Team, the Steel Joist Institute recently issued a new rule for loads not exceeding 100 pounds within any given panel.
The full text of the SJI rule reads as follows: “For nominal concentrated loads between panel points, which have been accounted for in the specified uniform design loads, a strut to transfer the load to a panel point on the opposite chord shall not be required, provided the sum of the concentrated loads within a chord panel does not exceed 100 pounds and the attachments are concentric to the chord.”
Bruce Brothersen, engineering manager for Vulcraft-Utah, Brigham, Utah, says, “The rule is an attempt to better define what is acceptable and put some quantitative numbers to it.”
Tim Holtermann, corporate engineering manager for Canam Steel in Washington, Mo., says that even with the new rule, manufacturers remain concerned that “people may be hanging things in excess of 100 pounds away from panel points and not field-adding struts, as they’re required to do.”
Holtermann says one option for structural engineers is to ask the manufacturer to provide a specially designed joist that can take point loads over 100 pounds without the added members. “It’s not uncommon to have a design requirement for, say, 250 pounds or 400 pounds,” he says. “We can readily do that as long as the magnitude of the loads and this design requirement are specified on the contract drawings.”
DON’T WAIT FOR THE FINAL PUNCH LIST
Often the problem with the joist loads isn’t discovered until the project is completed and the final walkthrough is taking place, says Joe Pote, director of research and development for New Millennium Building Systems, Hope, Ark.
“The inspector notices ductwork or sprinkler lines or mechanicals hanging from the joists between panel points that aren’t called out on the contract drawings,” says Pote. “Then he comes back to us and asks if it’s okay.” Many times the loads are small (20-50 pounds), so additional reinforcement isn’t necessary. “But we never had a good rule that stated the maximum load,” he says. “I think it helps clear up some of the discrepancy between SJI requirements and actual field practice.”
The manner in which the loads are hung is a key element of the 100-pound rule, says Holtermann. “The rule presumes that the load will be placed concentrically,” he says.
As SJI managing director Ken Charles notes, some trade installers make the mistake of attaching beam clamps to only one bottom chord angle of the joist instead of both. On top of that, he says, “the load isn’t placed concentrically even to that one chord angle, so you’re inducing some torsion and bending of the horizontal leg of the angle.”
His advice: “By far the better way to do it is to make sure the attachment is always concentric and always attached to both chord angles.” (See diagram.)
Steel Joist Do’s and Don’ts
- Recognize how and when to specify total uniform load or factored load and/or net uplift load, and when loads need to be broken out by load category and combinations.
- Know the limits of a concentrated load applied between panel points before an additional web is needed on the joist. The Steel Joist Institute’s new “100-pound rule” clarifies these limits.
- Install bridging early and follow the proper procedures to avoid safety problems, such as a partial building collapse.
- Designate a field representative to inspect the joists during construction and ensure that components are being installed correctly.Ideally, a representative of the team should walk the job site before completion and look for situations where loads aren’t handled correctly.
“A lot of times there’s a disconnect between the design intent and the construction site personnel,” says Charles. “Some sites have representatives in the field to do inspections, but often that’s not the case. Those are the projects that are most likely to have problems down the road when the final punch list is done.”
GET YOUR SPECS STRAIGHT
Joists are designed to handle different types of loads, such as dead load, live load, and wind, snow, and seismic loads. A given joist might experience more than one type of load, so the joist manufacturer needs to know which loads apply and properly combine them according to parameters set by the International Building Code. Most jurisdictions use the 2006 version of the IBC or the 2009 version, which is similar with regard to steel joists.
Brothersen notes that the building code loading combinations are based on the probability of which loads will act simultaneously. “For instance, the probability of a seismic event occurring when the maximum snow load is on the joist is relatively small, so the building code reduces the loads in those cases,” he says. “This is more realistic and doesn’t require manufacturers to design for the maximum load in every category at the same time.”
Pote says manufacturers prefer, when it’s feasible, that loads be provided to them as either a total uniform load or a factored load. In other words, if all components of the joist can be designed for a single downward-acting load case and a single upward-acting load case, the easiest thing for engineers to do is provide the total uniform load and/or net uplift load (dead load minus wind load).
“It’s just easier to communicate,” says Charles. “However, if we have to consider multiple load combinations, we need the breakdown—dead load, live load, snow load, and so forth.”
Holtermann adds that if the structure might be affected by downward-acting winds, the total uniform load should assume the worst-case scenario.
DON’T FORGET THE BRIDGING
Once the joists arrive on site, it’s important that bridging be installed early and correctly, says Brothersen. “If the joists are put up but the bridging isn’t installed, it can become a safety issue.” For example, lack of bridging can result in a partial building collapse when the crew begins stacking bundles of deck material on the joists.
Charles agrees. “The best-laid plans of the engineer and manufacturer can go out the window when the product arrives at the job site and the erector doesn’t follow proper safety regulations and the manufacturer’s advice.” BD+C
--
Editor’s note: To order SJI’s “43rd Edition Catalog of Standard Specifications and Load and Weight Tables for Steel Joists and Joist Girders,” go to: http://steeljoist.org/free-download-form.
Related Stories
Multifamily Housing | Feb 11, 2023
8 Gold and Platinum multifamily projects from the NAHB's BALA Awards
This year's top BALA multifamily winners showcase leading design trends, judged by eight industry professionals from across the country.
Multifamily Housing | Feb 10, 2023
Dallas to get a 19-story, 351-unit residential high-rise
In Dallas, work has begun on a new multifamily high-rise called The Oliver. The 19-story, 351-unit apartment building will be located within The Central, a 27-acre mixed-use development near the Knox/Henderson neighborhood north of downtown Dallas.
Sustainability | Feb 9, 2023
New guide for planning, designing, and operating onsite water reuse systems
The Pacific Institute, a global nonpartisan water think tank, has released guidance for developers to plan, design, and operate onsite water reuse systems. The Guide for Developing Onsite Water Systems to Support Regional Water Resilience advances circular, localized approaches to managing water that reduce a site’s water footprint, improve its resilience to water shortage or other disruptions, and provide benefits for local communities and regional water systems.
Office Buildings | Feb 9, 2023
Post-Covid Manhattan office market rebound gaining momentum
Office workers in Manhattan continue to return to their workplaces in sufficient numbers for many of their employers to maintain or expand their footprint in the city, according to a survey of more than 140 major Manhattan office employers conducted in January by The Partnership for New York City.
Giants 400 | Feb 9, 2023
New Giants 400 download: Get the complete at-a-glance 2022 Giants 400 rankings in Excel
See how your architecture, engineering, or construction firm stacks up against the nation's AEC Giants. For more than 45 years, the editors of Building Design+Construction have surveyed the largest AEC firms in the U.S./Canada to create the annual Giants 400 report. This year, a record 519 firms participated in the Giants 400 report. The final report includes 137 rankings across 25 building sectors and specialty categories.
University Buildings | Feb 8, 2023
STEM-focused Kettering University opens Stantec-designed Learning Commons
In Flint, Mich., Kettering University opened its new $63 million Learning Commons, designed by Stantec. The new facility will support collaboration, ideation, and digital technology for the STEM-focused higher learning institution.
Sustainability | Feb 8, 2023
A wind energy system—without the blades—can be placed on commercial building rooftops
Aeromine Technologies’ bladeless system captures and amplifies a building’s airflow like airfoils on a race car.
Codes and Standards | Feb 8, 2023
GSA releases draft of federal low embodied carbon material standards
The General Services Administration recently released a document that outlines standards for low embodied carbon materials and products to be used on federal construction projects.
University Buildings | Feb 7, 2023
Kansas City University's Center for Medical Education Innovation can adapt to changes in medical curriculum
The Center for Medical Education Innovation (CMEI) at Kansas City University was designed to adapt to changes in medical curriculum and pedagogy. The project program supported the mission of training leaders in osteopathic medicine with a state-of-the-art facility that leverages active-learning and simulation-based training.
Multifamily Housing | Feb 7, 2023
Multifamily housing rents flat in January, developers remain optimistic
Multifamily rents were flat in January 2023 as a strong jobs report indicated that fears of a significant economic recession may be overblown. U.S. asking rents averaged $1,701, unchanged from the prior month, according to the latest Yardi Matrix National Multifamily Report.