huangyhg

older steel beam
while looking through a 1930 vintage building (two story), i came across a steel beam section with differing flange thicknesses. as best as i can tell with tape measure, the beam is 8" deep with 5-1/2" wide flanges. however, the top flange is 1/4" thick while the bottom flange is 7/16" thick. bottom flange appeared to be slightly tapered similar to s-beam shapes.
have never come across beam with differing flange thicknesses. can anyone direct me to info on this beam type?
never seen different flange thicknesses like that before. is it a rolled section or fabricated section?
there is a possibility that this is a fabricated section. your assertion that the bottom flange tapered may suggest that this is an upside down rolled tee beam with a top flange welded on. i assume you are confident that this is not simply an i beam with a welded bottom flange plate?
do you need to do any analyis on this beam or is the question simply for interest?
on the subject of logic - i can't see any point in having differing flanges unless there is something else (for instance a concrete slab) which provides greater stability to the thinner flange.
1930's engineers would have a good knowledge of structures so it may be that they have good reason for the beam being the way it is.
just to confuse things even more - cast iron beams would have a larger tension flange. although i've never seen a cast iron beam.
lppe,
yes you are right. cast iron was weaker in tension than compression so the tension flange could be bigger.
here in the uk cast iron was effectively obsolete by 1900. by 1930 we would definitely expect steel but we are a much smaller and more uniformly developed country. in the us i could imagine that cast iron would still be used in some circumstances much later.
if this beam is cast iron its load capacity will be significantly different to that of a similar steel component.
in my experience, you will not be able to tell by simply looking at the beam. material testing is needed.
there are a couple very useful publications for sale at very reasonable prices at aisc.org regarding dimensions, physical and material properties for a wide range of older years. you might look into that for future reference.

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