Determining capacity of steel bar joists from 1955
Determining capacity of steel bar joists from 1955
(OP)
I'm working on a project evaluating the capacity of a partially collapsed roof. The steel bar joists are from 1955. I have the dimensions and am looking for some resources to evaluate this. I was thinking of going to the Nucor catalog and using current capacities, assuming the materials and capacities haven't changed too much over the years? Any other suggestions? Thanks






RE: Determining capacity of steel bar joists from 1955
I suggest that there are many differing configurations that have evolved and changed over the years. I would NOT depend on a current catalog other than for an approximate guide.
In many cases, without the tag, i've had to take measurements and calc all necessary physical properties and "do the math..."
RE: Determining capacity of steel bar joists from 1955
You typically have to contact the manufacturer (if they are still in business) and see if they can dredge up their old calculations.
Otherwise, you can estimate the originally intended joist capacity based on span, spacing, original roof dead load, and original code snow load.
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RE: Determining capacity of steel bar joists from 1955
However and fortunately, from my experience, close to 50/50, i have found the tag WITH joist size which has also been found in the manual. Please see attached...
Therefore, do not give up on the quest for a tag and the usefulness of the manual. I've had success on many more than one occasion!
RE: Determining capacity of steel bar joists from 1955
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RE: Determining capacity of steel bar joists from 1955
I suppose this is obvious, but might mention it just in case ....
OP: "I was thinking of going to the Nucor catalog and using current capacities, assuming the materials and capacities haven't changed too much over the years? "
Steel grades utilized in 1955 were, generally if not universally, significantly lower than they are for the current joist industry catalogues.
Look also at slideruleera's .com site. He may have catalogues there matching what you have discovered in the field.
What precipitated the partial collapse? Was it a joist? or something else?
Good luck!
RE: Determining capacity of steel bar joists from 1955
I do not recommend going today's joist catalog and obtaining a capacity as they used different materials back then. The 75 year joist manual will help with that (they should have a spec for that year). I highly suggest picking up the resource if you are ever going to do this again as it can tend to be quite valuable. In my instance above, it saved me 4 hours of analysis.
RE: Determining capacity of steel bar joists from 1955
https://steeljoist.org/joist-investigation-form/
RE: Determining capacity of steel bar joists from 1955
RE: Determining capacity of steel bar joists from 1955
RE: Determining capacity of steel bar joists from 1955
RE: Determining capacity of steel bar joists from 1955
RE: Determining capacity of steel bar joists from 1955
Richard A. Cornelius, P.E.
WWW.amlinereast.com
RE: Determining capacity of steel bar joists from 1955
BA
RE: Determining capacity of steel bar joists from 1955
RE: Determining capacity of steel bar joists from 1955
RE: Determining capacity of steel bar joists from 1955
BA
RE: Determining capacity of steel bar joists from 1955
Available steel had long been good enough to justify a somewhat higher value; for example AISC had raised allowable tensile stress for structural steel from 18 KSI to 20 KSI in 1936. During World War II, AISC increased it to 24 KSI, then returned to 20 KSI in 1946.
You may find that an original shop welded connection failed somewhere in one of the heavily loaded (but not overloaded) joists. Lack of lateral support from the corroded steel deck could have contributed to the weld failure.
Bar joist allowable tensile stress increased from 18 KSI to 20 KSI in 1959.
In 1961, it was increased again, from 20 KSI to 22 KSI.
Steel didn't just suddenly improve, but both bar joist fabrication methods and weld reliability did.
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RE: Determining capacity of steel bar joists from 1955