# Steel joists

• posted
Anyone here have knowlegde of steel joists? I am trying to ID a joist
that is made of a pair of 1.5 x 1.5 x 1/8 angles for the top and the
same for the bottom, 1/2" diameter rod is zig-zaged inbetween. It
measured about 11-1/4" tall. I have done a whole buch of googling
and I now think it is a K series joist. I have not been able to get
any further than that.
Help??
BTW, its used to construct a wrestling ring outer frame.
Thank You,
Randy
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• posted
You might try searching Bar Joists, and/or Bar Trusses, and see if a fabricator's website lists specifications for sizes and loads.
K series is very likely correct for what you described, some may just have Z bars, and others may have vertical bars within V bars.
• posted
Here is a radical idea: Assume it's A36 steel (for determining load capacity) and calculate the second moment of area (moment of inertia).
Wolfgang
Wolfgang
• posted
I believe the reason you're having trouble is that bar joists are designed to to meet specifications that dictate maximum stresses and deflections under specified load conditions and other functional requirements, not the details of the design. It's up to the manufacturer to choose the materials and construction to meet the spec.
• posted
It's a bar joist, i.e., a truss.
• posted
How much does it weigh per foot?
Dan
• posted
Ned,
The top (compression) flange consists of two legs of angle, ditto for the bottom tension flange.
For the first approximation simply use the equivalent of two flat bars spaced by the dimension separating the two "bars". Calculating "I" for this is simple, or can be looked up in a handbook.
For a better approximation take the total area of two angle sections for each the top and bottom flange, separated by the vertical distance between their neutral axes, and do the arithmetic. This would be close and ok for this application. Don't forget that the manufacturer designed the zig-zag bars and welds to carry the shear and vertical loads and would not need analysis for this purpose.
A heavily loaded roof or floor is another issue, and I would not condone the use of material with an unknown history of use in such an application. But for a wrestling rink where the danger of falling down or buckling is a distance of what? 3 feet or so I would not see a problem.
Wolfgang
• posted
Yup, I got distracted thinking about analyzing all those pin-jointed trusses 35 years ago and missed the analogy between the zig-zags and the web of rolled beam.
• posted
I did not weight it. it has a bunch of 4" channel welded to it, I'd need to subtract that, but I did find a bunch of specs that give #/ft so that might just be the best way to ID it.
Thanks.
Next time they disassemble the ring, I'll weight a peice.
Thank You, Randy
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• posted
I don't really care what the load capacity is, I just want to match it.
Thank You, Randy
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• posted
To match the strength of an existing beam or truss you have to know its section modulus "Z", or second moment of area "I", plus the material. You can also replicate the existing beam by using a 3" or 4" channel for the top and bottom flange, separated by the same dimension as the existing.
However, replacing an existing beam with one of similar strength but differing size or configuration is not so easy unless one has the information for "Z" or "I". Hence my encouragement to calculate it using the simplifying assumptions I described.
The reason nobody is jumping up and down and offering to do this for free are the liability laws for P.Eng.
Wolfgang

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