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

 

[rb1957]

euler ? about the weak axis

Quando Omni Flunkus Moritati

 

[JedClampett]

In my 9th edition of AISC, there's allowable axial loads for W6 x 12's and W8 x 24's. I'm sure they're in the 13th Edition, too, but I don't feel like reaching for it.
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.

 

[fegenbush]

AISC Steel Construction Manual. The current edition is 14th, but it would be acceptable to use the 9th for rating an old structure. Be sure to check for corrosion of the members and connections.

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.

 

[steris]

As you may be able to tell I'm not a structural engineer and while I would love to enlist one for this project, my boss doesn't want to spend the money. As such, I'm left doing what I can. Thanks for the references!

 

[fegenbush]

I like to go back to a saying I've heard: "If we don't have time to do it right, when are we going to have time to do it again?"

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?

 

[msquared48]

Your boss is dangerous.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[rb1957]

what building/country should we avoid ? what country permits this type of work not to be stamped by an engineer ?

Quando Omni Flunkus Moritati

 

[GearsNsparks]

omg the sky is falling.

 

[JAE]

Not the sky - just perhaps the mezzanine someday.

 

[MiketheEngineer]

This is basic Structures 101 - I would do it for like $250-$500. Find one and have him/her do it!!

 

[BAretired]

You may have just got yourself a job, Mike.

BA

 

[steris]

Hi All,

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

 

[rb1957]

"have been used for well over 60 years" ... often a statement made after a failure occurs in the 61st year.

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

 

[JedClampett]

As far as a copy of AISC, you're not going to find one on line. But it's very likely that someone in your office, even if they're all pump jockeys, has a copy. Ask around. The 9th Edition is green, with capital ASD on the binding. The 13th Edition is black with "Steel Construction Manual" on the binding. There's indented tabs in the pages with column design on them.
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.

 

[bookowski]

Steris,

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.

 

[Archie264]

The only reason I can think of for a boss wanting to know the loading capacity of a mezzanine is so he will have an idea how heavily he can load it. After all, if he was planing to leave a 60 year old structure unloaded there wouldn't be a need to check it's capacity. It's therefore worth getting right. Remember, nothing fails until it does.

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.

 

[Archie264]

Bookowski, good for you; great response, in my opinion. That is, you suggested the best way to approach the issue, but, in the interest of safety of others, you also provided a means for a reality/sanity check.

Still, though, Steris, proceed with caution.

 

[GearsNsparks]

Good resources would be:
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).

 

[steris]

Hi All,

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