Behold the beam, an amazing structural element that bends when loaded — but one that must not bend too much. A fallen tree spanning the banks of a river was perhaps the first beam used by primitive man for a specific purpose: to see what's on the other side. That fallen tree was an...
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Within the hierarchy of a building, unprotected steel exposed to high heat is not a winning combination. Hot-rolled steel rods and reinforcing bars (rebar) retain much of their strength until heated to about 800°F; cold-drawn steel cables (and pre-stressing strands) begin to lose strength at around 500°F.
There can also be structural cables on the exterior of a building. Photo 6 and Photo 7 show a dormitory building (now demolished) at Central Washington University in Ellensburg, WA. Note the unprotected steel cables running up the face of the building. Much like a suspension bridge transfers the bridge deck load to the towers, these cables transfer the live and dead floor loads to towers on the roof. Each floor is suspended by cables that stretch in front of the windows and behind the wall panels between windows.
To Be Continued
In the first two parts of this article, we discussed basic beam behavior and six basic beam configurations. Next time, we will "behold" (and discuss) the 12 beam types:
- Sawn wood
- Laminated-strand lumber (LSL)
- Parallel-strand lumber (PSL)
- Laminated-veneer lumber (LVL)
- Glue laminated lumber (Glulam)
- Lite-steel (LSB)
- Pre-stressed, pre-cast concrete
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. Part 1 was published in the July 2010 issue.