Yield Strength of Steel Joists
Yield Strength of Steel Joists
(OP)
I am checking an existing building for the addition of new equipment that will be suspended from open web joists. The drawings list a variety of 22H and 24H joists in the different locations. The added equipment will increase the moment in the steel joists beyond the published acceptable value and the customer wishes to suspend between the panel points of the joists in order to align with floor mounted equipment for the assembly line. We can add a new internal chord at the hanger location, but still need to check the joists, so we are analyzing them as trusses.
The issue I have is that the publication I am looking from Vulcraft lists a base yield strength of 50 ksi for the chords of H-series joists. The building was put up in the 70's and the chords are only 2x2 double angles. I find it hard to believe that they have a yield strength of 50 ksi, yet I can't find any publication to support me, or I overlooked it. My preference would be to assume A36 for all of the members. Does anyone have an alternate course of action?
The issue I have is that the publication I am looking from Vulcraft lists a base yield strength of 50 ksi for the chords of H-series joists. The building was put up in the 70's and the chords are only 2x2 double angles. I find it hard to believe that they have a yield strength of 50 ksi, yet I can't find any publication to support me, or I overlooked it. My preference would be to assume A36 for all of the members. Does anyone have an alternate course of action?






RE: Yield Strength of Steel Joists
RE: Yield Strength of Steel Joists
RE: Yield Strength of Steel Joists
I highly doubt there is much additional capacity in the joists. The manufacturer is in the business of making money not wasting material. Most of the modern designs I have seen have the members stressed to 98%-100% of their capacity. You could reverse engineer the joists to see if it is 50ksi or 36ksi.
RE: Yield Strength of Steel Joists
Antiquated Structural Systems Series - 9a - Open Web Steel Joists - June 2009
www.SlideRuleEra.net
www.VacuumTubeEra.net
RE: Yield Strength of Steel Joists
RE: Yield Strength of Steel Joists
RE: Yield Strength of Steel Joists
Based on the measured steel sizes, you should be able to determine allowable compression in the top chord, allowable tension in the bottom chord, an allowable moment, and the uniform load that corresponds with this moment.
Do this for 50 ksi and 36 ksi.
Then, calculation the moment of inertia (with 15% reduction per SJI), allowable deflection, and the uniform load that corresponds with this deflection.
Lastly, check the load tables. I expect you`ll find a good match for the 50ksi design. The 36ksi results may appear a little bizarre - like the allowable load for deflection is greater than the allowable load for strength.
The first time I ran into this situation I went through the above procedure, convinced myself it was 50ksi, and then pulled a coupon for tensile testing to confirm 50ksi. If I recall correctly, this building was from the late 70s.
RE: Yield Strength of Steel Joists
As you might or might not be able to tell, I'm not a fan of joists. Besides their inherent flimsiness, their customer service is HORRIBLE. How many posts do we have in these forums asking for data on some obsolete or non traceable joists? Vulcraft is one of the better ones and they're not great. Arguments about the way I specify them, about the loads, and about many things they won't do.
When I'm forced to use them, I never specify them by load. I pick a joist one or two sizes larger than I need. If a 18K7 works, I use an 18K10. That way I know the capacity and retain a little control.
Sorry about the soap box. But bad customer service irks me. In my small world, I won't tolerate it.
RE: Yield Strength of Steel Joists
@JedClampett, I couldn't agree more. Every time I see joists, I know it's not going to go well and I'll have to explain to a salesman that steel isn't adamantium, and we actually have to check to see if it can carry more loading.