Using I-Beams as a Columns
Using I-Beams as a Columns
(OP)
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
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






RE: Using I-Beams as a Columns
Quando Omni Flunkus Moritati
RE: Using I-Beams as a Columns
The fact that you don't know where to go to get column allowables for a simple case like this makes me think you need to get in touch with a structural engineer.
RE: Using I-Beams as a Columns
Another option is to enlist the services of a structural engineer in your area. This may be the best option for you to ensure the safest conditions at your workplace.
RE: Using I-Beams as a Columns
RE: Using I-Beams as a Columns
If your boss doesn't want to spend the money to do it right, how is he going to spend it to replace the structure after a failure?
RE: Using I-Beams as a Columns
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
RE: Using I-Beams as a Columns
Quando Omni Flunkus Moritati
RE: Using I-Beams as a Columns
RE: Using I-Beams as a Columns
RE: Using I-Beams as a Columns
RE: Using I-Beams as a Columns
BA
RE: Using I-Beams as a Columns
Thanks for the replies and concerns. The mezzanines have been used for well over 60 years with it's current loading so we're not afraid of any imminent failure - with the current loading. We're just looking to have some calcs on it. I don't have a copy of the AISC. If anyone can point me towards an online reference, that would be much appreciated. If not, thanks anyway.
Best,
Steris
RE: Using I-Beams as a Columns
i think we all feel your pain at undertaking something which you're not qualified to do, possibly under some duress,
but i think we feel that you're putting lives at risk and i'm quite sure that, if trouble happens, it'll be you defending your actions (and not your boss).
Quando Omni Flunkus Moritati
RE: Using I-Beams as a Columns
What myself and the others are trying to impress upon you is that there are nuances to structural engineering that need to be respected, like connection design, lateral bracing, or maybe misalignments that can greatly reduce a capacity. Everything is fine until a mezzanine falls down.
RE: Using I-Beams as a Columns
While I agree with the others that you should have a struct. eng. do this my guess is that you're going to end up doing it yourself so:
- The AISC 2010 specification is downloadable for free from AISC. You can't get the column tables or full manual, just the spec. but that will give you the design requirements. Go to chapter E, design of compression members. You can find the spec. for free at http://www.aisc.org/content.aspx?id=2884#spec You'll have to actually calc. the capacities, no tables there - it's not too difficult though.
- Section properties are available in a free downloadable excel sheet from AISC, just google it.
The black book (13th edit) which I have here doesn't have W6x12 for in the column tables, but if you want to see if you are doing the calcs right a W8x35 at 10' unbraced length should have an allowable load of 238 kips. That will give you a sense of the calcs and if you're on the right path.
RE: Using I-Beams as a Columns
Steris, I feel for you on this one. You're trying to conscientiously perform your job, which is why you're asking for help on this forum. Good for you. I know some people who would have just plowed ahead without asking for help.
In my opinion the best course of action would be if you could convince your boss to hire a local structural engineer who could do it for a modest fee. In addition to solving this issue you would thereby establish a relationship with someone you could call on for particularly tricky issues, as they arise. But, only you know the dynamics of your work place. There are people out there who might be too unreasonable to allow you to bring someone in and only you know if asking for that would put your job in jeopardy. On the other hand, if that's his position on the matter then it might be worth knowing that sooner rather than later.
The bottom line, though, is that you don't want to be the one who signs his name to something that might be outside of your direct field of expertise. I know a company that did that very thing and what they "blessed" later collapsed and killed someone. My understanding is that they were able to finagle their way out of culpability by claiming that the connection that failed was hidden. But, knowing some of the details of the case I believe that an experienced structural engineer could have caught it. Again, knowing some of the players involved in that it was a non-structural firm blessing the structural components (along with the other disciplines' components) of a historical building.
So, my suggestion is to use your best judgement on how to handle the workplace dynamics of this, but, whichever course of action you choose to take, proceed with caution.
RE: Using I-Beams as a Columns
Still, though, Steris, proceed with caution.
RE: Using I-Beams as a Columns
ASCE7-05/ASCE7-10 for loads on buildings and other structures
AISC 9th/13th/14th for hot rolled steel capacities and connections
AISC 9th will probably make more sense to ME's.
AISC offers some boot camps/courses that cover the latest edition of their manuals and connection design.
Do check with the local governing board for professional engineers in your area to explain what you intend to do. You'll figure out whether you need a licensed SE or PE to create & stamp the design and calcs. You might also find that its not applicable/required for what you intend to do.
Side note, a course or two in strength of materials and machine design from any undergrad mechanical engineering curriculum that I've seen does not qualify an individual to practice in a structural engineering capacity. (I don't know your background, I'm just guessing from your mechanical tag).
RE: Using I-Beams as a Columns
Thanks again for all the help, pointers, general advise and concerns. My boss is well aware that I am not qualified to sign off on any calcs of this type and is not asking me to. I fully understand that I am not a structural engineer. Regardless, this task is in my lap and I'm just trying to do it to the best of my ability. Jhake - your comment about a course or two from ugrad doesn't mean I'm qualified is amusing b/c that's basically what I said to my boss when I was assigned this task.
Bookowski (great handle btw) - you hit the nail on the head and your reply is very helpful. Thank you.
Best,
Steris
RE: Using I-Beams as a Columns
RE: Using I-Beams as a Columns
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.
RE: Using I-Beams as a Columns
RE: Using I-Beams as a Columns
If you want to do it right, get a structural engineer out there, otherwise you are just guessing.
RE: Using I-Beams as a Columns
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
RE: Using I-Beams as a Columns
CANEIT - there you went and did it - contributed to the demise of engineering as a profession!!
RE: Using I-Beams as a Columns
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.
RE: Using I-Beams as a Columns
Tell your boss thats your safety factor your use in your code. He can then change it if he wants.
RE: Using I-Beams as a Columns
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.