Part 4 — More Types of Beams You Are Likely to Encounter Welcome back to the "Behold the Beam" series of articles. In part three ( Firehouse ®, September 2010) of the series, we discussed the first five of the 13 common types of beams that firefighters can expect to encounter: 1. Solid...
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As with all structural steel, rule-of-thumb elongation is one inch for each 10 feet in length when the steel (not the ambient temperature) is heated to 1,000 degrees Fahrenheit. The rule-of-thumb for structural steel failure is between 1,200°F and 1,300°F. Structural steel is unable to support its own weight when heated to 1,500°F. The cooling of super-heated structural steel should be a tactical priority. What's interesting is that structural steel gets stronger as it heats. The compressive strength of structural steel increases until heated to around 300°F; its tensile strength increases until heated to around 600°F.
11. LiteSteelbeam (LSB)
New (to me anyway) is the "LiteSteelbeam," or LSB. Note that the LSB manufacturer borrowed the "lite" moniker from the beer industry; not only are Lite Steelbeams strong and efficient, apparently they are low calorie as well. On average, LSB is 40% lighter than a hot rolled steel beam or an engineered wood I-beam. Because carpenters can manipulate an LSB without a crane or other special handling equipment, LSB in installation is comparable with lumber. LSB can be assembled by carpenters using a circular saw equipped with a special blade and traditional nailing. LSB can also be assembled using self-drilling screws and can be welded.
The good news is that steel is inherently non-combustible and thus will not contribute fuel to a fire. That said, it should be expected that Lite Steel products can fail quickly when exposed to high temperature — with or without direct fire exposure. Comparing the fire performance of unprotected Lite Steel to that of structural steel is similar to comparing the performance of a wood I-joist to a solid sawn timber.
12. Pre-Cast Concrete
When you gaze upon a large concrete beam, you can be certain that it is a composite of concrete and steel. A concrete beam without reinforcement does not exist. For concrete to function as a beam, it must be a composite of concrete to resist compression and steel to resist tension. This reinforcement can be steel reinforcing bars ("rebar"), steel cables or a combination.
13. Faux Beam
Don't be fooled by contemporary buildings that feature what appear to be conventional timber beams. Faux timbers look impressive but they are charlatans; faux beams are decorative and non-structural. (Faux, pronounced "foe," is an adjective that means artificial, imitation or fake; not genuine or real.) Faux beams are not part of the building construction structural hierarchy, add no additional strength or fire resistance, and should not be relied on to support firefighters. I've seen buildings that feature impressive faux timber trusses. Be careful not to classify a building featuring faux timber as Type IV, heavy timber.
Faux beams are featured in both residential and commercial applications. Common commercial applications include restaurants, hotels, offices and places of worship. Often made of extruded polyurethane or high-density Styrofoam, faux beams are molded and painted to mimic wood timbers — right down to hand-painted faux knots. Occasionally, gypsum board is finished and painted to look like a timber beam; although gypsum sheetrock will not burn it is not load bearing and should not be considered an operating platform for firefighters. (Just to clarify, no faux beam should be considered as an operating platform for firefighters.)
Faux timber beams typically are not fire rated; however, depending on the type of occupancy and your local code, they can be manufactured to provide a Class A fire rating or finished with a fire-retardant coating.
MARK EMERY, EFO, is a shift battalion chief with the Woodinville, WA, Fire & Life Safety District. He is a graduate of the National Fire Academy's Executive Fire Officer program and an NFA instructor specialist. Emery received a bachelor of arts degree from California State University at Long Beach and is a partner with Fire Command Seattle LLC in King County, WA. He is in no way affiliated with or an advocate for the truss manufacturing or building construction industries. He may be contacted at firstname.lastname@example.org or access his website www.competentcommand.com.