AISI Material Properties
AISI Material Properties
(OP)
I'm looking for some data on yield strength for Z purlins in this manufactured building the client wants to hang stuff from. It was built around the 1970's, and I don't know what kind of steel they were typically using for purlins at the time. Does anyone know offhand or know where I can find out? Of course the client doesn't have the original drawings of the building, or know who the manufacturer was.
Thanks,
Jay
Thanks,
Jay






RE: AISI Material Properties
Keep in mind that the AISI spec has changed over the years (what spec hasn't?) and capacities today for the same cross-section are probably going to show as lower than the original design capacities.
RE: AISI Material Properties
I hope that ajh1 is correct.
RE: AISI Material Properties
RE: AISI Material Properties
RE: AISI Material Properties
1) It appears my company moved to 55 ksi around 1971, although I find prints dated 1960 on some parts that show 55 ksi back then. Light gage material such as cold-formed purlins tends to run at higher yields than equivalent hot-rolled structural shapes and plates. Easier to push the strength levels on the thinner coils.
2) Purlins are generally controlled by lateral torsional buckling of the compression flange and/or compression lip. For gravity load, that would be the top flange, not the bottom. It is unlikely that bolting a C flat on the bottom is going to give you a lot of extra net capacity. I would agree with hokie66 that adding a vertical C attached to the web would work better. Keep it an inch or so shorter than the existing purlin and align the bottom edges. That keeps the top flange out of the way of things like projecting fasteners coming through the existing top flange. Analysis on a non-symmetric composite section like that is a bit of a pain, but programs like CFS do a good job generating the properties.
As I noted in my earlier response, the AISI spec has gotten stricter since the time in question. I would anticipate at least a 7-10% reduction in allowables from then to now.
RE: AISI Material Properties
RE: AISI Material Properties
Basically you need to decide how much of the loading remains in the existing member keeping in mind that any load present at the time of the reinforcement installation is going to remain in the current member. Design each of the two pieces for the desired percentage (plus a little). Design connections between the two to properly transfer the new member's load. Extend the new member a foot or two at each end beyond the minimum length necessary to insure a good transfer of forces near the ends. Keep in mind that the forces that are in the new piece will need to transfer back into the old piece for transfer to the frame supports unless the new piece spans the full length (undesirable but you are almost there anyway).