Hangers on bar joists
Kudos to Gregory Havel for an excellent “back-to-basics” article (“Lightweight Steel Contruction,” November 2005). I have a question for the author: Should the hangers for fire sprinkler pipe be attached to the top chord of the steel joists, the bottom chord of the steel joists, or the web assembly of the steel joists? I have seen each of these situations in existing buildings. Does it matter?
Oscar Wiltse
EMT-P
West Palm Beach, Florida
Gregory Havel responds: Photo 18 in the article shows a roof drainpipe supported from the top chord of the bar joist. Photo 19 in the article shows a fire sprinkler pipe supported from the top chord of the bar joist. These photos show the accepted method for supporting any load from a steel bar joist or a wood truss joist, according to the standards used in the design of these girder and truss systems.
Most steel girder and joist systems are designed to carry the load on the top chord, which is in compression. A load suspended from the bottom chord of a bar joist designed for top loading could only cause the failure of that joist, since the tension in the bottom chord with the additional load would no longer balance the compression in the top chord. Suspension of pipes, ducts, and other equipment from the bottom chords of girders and joists usually requires the approval of the design engineer. This is true whether the girders and joists are steel or wood.
Most bundles of steel bar joists and wood truss joists delivered to construction sites today will be tagged or labeled “Approved for top loading only.” This accounts for most of the installations we have seen with loads supported from the top chord. If they have been designed to have loads supported from the bottom chord, the tag or label will state this and perhaps refer the contractor to specification sheets or shop drawings that detail the location and amount of weight that can be so supported.
During new construction or major remodeling, an observant and well-trained building inspector will notice loads suspended from other than the top chord of a truss and will question the practice. This same building inspector will make a note in his file if the designer approved loading the bottom chord or a cross member. This accounts for some of the loads we have seen that are not supported from the top chord. Our model building inspector will require the load to be reinstalled if the designer did not approve that type of installation.
Unfortunately, not all building inspectors are as described above. Also unfortunately, a lot of remodeling is done by the owner or tenant without permits, inspectors, or any knowledge of structural engineering. This accounts for the rest of the installations where loads are not supported from the top chords.
If your local building inspectors are anything like the model inspector described above, they may be willing to pass on to you and your department information on this type of construction that could be valuable in preparing and updating your preplans and your standard operating guidelines or standard operating procedures.
Thank you for your interest in this subject and for your question. If you have additional questions or need more information, please e-mail me ([email protected]). Also, thank you for your kind comment about my article.
In support of industrial fire brigades
As I returned from one of our annual refresher burns, I was surprised to see “Industrial Firefighters Are Firefighters, Too!” (Fire Commentary, November 2005) by Robert E. Zapatka.
The author really brought to light some of the differences and similarities between municipal firefighters and industrial firefighters. I volunteer with a local municipality but am also the emergency services coordinator for Oconee Nuclear Station in Seneca, South Carolina, responsible for our nuclear fire brigade. Industrial firefighters face a huge task of protecting their industry and some of the same issues a municipal fire department may face, from training hours to budget items to equipment issues and terrorist threats. Our firefighters train hard and take their jobs just as seriously as municipal firefighters do and, at least in our situation, have a great working relationship with our local fire departments.
Without a well-trained industrial firefighting organization, a local fire department may have to enter the industrial site with little or no knowledge of the types of hazards that may be encountered. A well-trained industrial firefighting team, however, not only can recognize the hazards because it is familiar with them but also can extinguish the fire in most cases so the local fire department doesn’t have to respond.
Let’s face it-there are 103 nuclear reactors in the United States. I’ll take a show of hands from the fire departments that want to run in and put out [a fire in] one. Here’s to all our industrial fire brigade firefighters!
Scott Boggs
Emergency Services Coordinator
Oconee (SC) Nuclear Station
