50 ksi beams, when

huangyhg

50 ksi beams, when?
i am checking an existing (25-year old) seed corn tower supporting (4) surge bins.  the problem i have is that i cannot get the existing support beams to check out.  they fail under flexure at 150% using 36ksi steel.  if i check with 50ksi they just barley work 103%.  however, i do not believe (no drawings) 50ksi was that readily available 25-years ago...  
these beams also support the 4" thick concrete surge bin roofs/upper floor.  i typically design these floors for 100 to 125psf (ibc - light manufacturing).  they are typically only used for equipment access.  we typically classify these seed toweres upper floors as equipment access to keep overall structure sq footage down trying to avoid sprinklers.
does anyone else work on the these seed towers, if so what do you use for your upper floor live loads?  125psf seams heavy, 60psf seams light.  i would prefer 100psf and use that for a minimum.  however, the code has no good classification for seed towers.
thanks,
jeff  
check out our whitepaper library.
50 ksi was common in late seventies and 103% calculated would get a ok from me when checking someone else's work.  50 psf is a standard loading for walkways and access.  what density are you using for corn volume loading?
was "barley" a pun or a typo ?
we used 50 ksi material in the late 70's when constructing a 26 story high rise.  yes, it was very available 25 years ago.   
mike mccann
mmc engineering
re  
as i re  
i've always wondered what field tests we have at our disposal to determine the in-situ yield stess of steel beams.
is there anything reasonable??
hardness testing would be appliciable as a field test
i think you would have a hard time using hardness testing to determine between 36 ksi and 50 ksi steel.  hardness testing works much better on the high strength steels where there is a much greater difference in strengths.  when i took the asce class on condition assessment of existing buildings, the instructor confirmed this statement and said the only way that you could usually tell the difference was cutting out a coupon and testing it.  as has been pointed out, there is a lot of overlap between 36 ksi and 50 ksi steels.  many beams in that time period came with dual certs.
we had a client who bought an old railcar to be used for a bridge.  railcar was used by the military during the 1940's.  we had a sample cut out and testing lab determined that the steel would comply with 50 ksi steel.
you can cut out a coupon of steel (say at the bottom flange of a beam right next to a simple shear connection) and have it tensile and metalurgically tested.  they can then tell you what grade of steel the piece would comply with.  the tests are cheap.  both test for under $200 around here (chicago).  why mess around?  just have it tested.
i don't trust any of the in-situ testing methods yet.  hardness tests would not make me confident enough to use more than 36 ksi...  i need to see better research on in-situ methods that proves they are reliable.