Strength of tapered steel roof beam

[ivanga7]

I have to analyze a tapered steel roof beam but have no drawings of existing conditions. Is it usual for these tapered beams to be made of A36 steel or are they normally made out of stronger steel?

 

[structSU10]

that will depend on the age of the structure. up to the 50's it could be A9 (33 ksi yield), to about 2000 A36, and after 2000 it might be A992.

 

[ivanga7]

Was it ever common to use A529 steel?

 

[ajh1]

A529 is typical these days for the beam flanges. The webs are going to typically be A1011 for thinner webs or A572 for 1/4" and thicker webs. Current strength is typically either Grade 50 or Grade 55. A529 bars flats are generally dual certified for both grades. A992 would be unusual as that is a shape-only grade. Tapered beams are typically 3-plate fabrication rather than slicing a hot-rolled shape diagonally and rewelding.

 

[ivanga7]

ajh1, the building I'm dealing with was built around 1956. Pretty much what I want to know is if it's safe to assume a 50 ksi yield strength or should I just be conservative and use 36 ksi?

 

[BridgeSmith]

For bridge girders of that age (thru 1963), we would assume 33ksi yield if we don't have documentation of the steel strength. If it was important to know for sure, we would take a coupon from a non-critical area of the web and have it tested.

 

[structSU10]

Per AISC design guide 15 they note plate steel (A7) at 33 ksi yield. A36 showed up in 1962 according to the guide.

 

[ivanga7]

Well that's a bummer. Thanks guys for the help!