Using I-Beams as a Columns 4

[steris]

Hi All,

I'm working on a project where we have to create load ratings for some really old mezzanines that exist in our facility. The load on the mezzanine is really low (~25lb/sqft) but we want to put a number to the max allowable load. I found all sorts of sample calculations that I can follow for the decking and the beams. The hard part is that these mezzanines use I-beam as the columns (W6x12) and beams (W8x24). Can anyone help point me towards a resource for calculating allowable loads for I-beams used as columns? Thanks for the help!

Best,
Steris

 

[strucguy]

I know how much my boss checked my drawings when I was an EIT (sarcasm). In any case proceed with caution...and feel free to double check your answers with this forum.

 

[concretemasonry]

structguy -

Nothing is wrong with tiles, but responsibility is different. When I was a EIT in CA, I had a CA S.E. working for me and made sure he signed his name an number in blood when required (rare situation because it was a very large private company in the aerospace industry).

I used him as reference (working with him) to take my C.E. and S.E. registration requirements because he was good.

You learn a lot in private industry working with good engineers and unique problems plus flexibility.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[CANPRO]

you could always contact this guy for some advice on column strength....

http://www.virtualengineer.com/

 

[XR250]

There may be other issues at work other than just axial load. The columns may be providing lateral stability for the mezzanine as well - although an I-beam is not ideal for this. The connections from the beams to the columns should be evaluated as well.
If you want to do it right, get a structural engineer out there, otherwise you are just guessing.

 

[mtu1972]

Steris - I have had to rate "old floors" for allowable live loads where posting was being required by Building Officials or even OSHA. Especially storage areas.

Your work in back calculating the allowable load in all the components, including their connections, is the right way. In addition all of the members should be reviewed to make sure that they do not have much corrosion, etc.

What hasn't been said is that the steel for 60+ year old buildings was probably ASTM A6, not the A992 in the present codes.

I would use Fy = 33,000 psi and Fa = 20,000 psi for that era. If older it could be even less.

gjc

 

[JAE]

Fa could be less depending on column length and properties.

CANEIT - there you went and did it - contributed to the demise of engineering as a profession!!

 

[DCBII]

It's pretty clear from the original post that you shouldn't tackle this type of problem yourself until you've gained more experience working directly under a structural engineer. There could be more to this mezzanine than you think.

Are these gravity columns or are they part of the lateral force resisting system? You may have some braced frames or moment frames on your hands, which will complicate matters. Wide flange "I-Beams" are often used in braced frames or moment frames. How are the beams connected to these columns? Your simple column assumption may have just gone out the window. What grade of steel do you have? If it's 60 years old it's not A992.

A qualified engineer must look at the ENTIRE load path, not just one piece of it (e.g. the columns). What about the flooring, the beams, the beam to girder connections, the girder to column connections, the base plates, and the foundations? Are there eccentricities in any of the connections? The columns may have a lot of capacity, but what if there is not an adequate load path to or from the columns? The whole system needs to be evaluated because your giving a rating for the whole system.

 

[ztengguy]

Whatever capacity you come up with (if within reasonable sense), divide by 4, thus your covered right??

Tell your boss thats your safety factor your use in your code. He can then change it if he wants.

 

[TXStructural]

ztengguy, you sound like a geotech...

One consideration that I ran into on a similar structure was that it was all welded (not tabs or angles) and those beam-to-column moments made floor loads geometrically worse for the columns. It was also impossible to evaluate the welds.