Floor Loading question

[ttuterry]

We have a modular trailer that was originally designed for a live load of 50 psf. There was no indication of the design load for dead load, but i am assuming 20 psf. This trailer is 1900 ft^2 but is in two halves, so each half is 950 ft^2. The floor is made of 2x8 joists (#2 H.F. can someone tell me what this means?) and on the west half of the trailer the spacing is 8" O.C. and on the east half of the trailer they are 16" O.C. The decking is 5/8" plywood.

The floor of the trailer is supported uniformly with piers that are rated at 4000 lbs. The issue is that file cabinets were placed inside this trailer. Each file cabinet's maximum weight is 700 lbs when completely full, according to the manufacturer. This comes out to be roughly 200 psf per file cabinet. Before these cabinets were placed, cinderblock supports were added underneath the trailer. We have no drawings or information as to why they were added, but im assuming for deflection purposes? The problem is that we must have a floor loading sign per 1910, General Industry Standards. When these cabinets were placed, there were no calculations or anything that gave a floor loading, and a floor loading sign was not placed. The engineer who oversaw that has since retired and we contacted him, but he said he did not remember why he had the cinderblocks placed...Currently there are 42 cabinets on the west side (the side with 8" O.C. joists) and 21 file cabinets on the east side (the side with 16" O.C. joists). We have a layout to where they are with respect to the piers and cinderblock supports underneath.

I am a young Civil engineer EIT at this company (and only Civil engineer) and I am working with a Mechanical Engineer trying to figure out how to figure out the current floor loading. Should we say the floor is only good for 70 psf (dead + live load) and have all the file cabinets removed?? Or since the joist spacing is half the distance on the west side, is it safe to say the west side can hold 140 psf ((dead+live)*2)? If somebody has some ideas to get us going in the right direction that would be greatly appreciated! Thanks..(sorry such a long OP)

 

[csd72]

Check out

http://www.awc.org/pdf/WSDD/C1.pdf

I imagine it is number 2 Hem Fir.

a 2 x 8 is smaller than 2" by 8" - read up on it.

The awc website is a good place to start reading up on timber.

csd

 

[COEngineeer]

H.F. is hem fir which is probably not my first choice to use as joist (weaker). I usually specify D.f. As far as the loading goes you have to analyze 2x10 H.F @16 and 8 for the spans you have. Usually the deflection controls on this scenario. You can figure out the how much load you can have per square foot based on the deflection you want (probably L/360). Good luck!

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Sea Water Intake and Jetty Construction

 

[wannabeSE]

The Western Wood Products Association is another resource for information on hem-fir properties.

http://www.wwpa.org

 

[UcfSE]

You should hire a consultant since this is out of your area of expertise, as well as that of your supervisor apparently.

 

[JAE]

So what I'm hearing is that you are an EIT in Civil Engineering, have little experience in structural design and wood engineering, and are tasked with providing a floor live load capacity with no structural PE participating?

I really think this is bordering on practicing outside your area of expertise and technically without a license. I know it is "only" a small modular trailer, but to be honest, an office worker inside, who falls through a failed floor and gets hurt can sue you very easily.

Respectfully, I'm just a bit worried that you are not doing the right thing here.

 

[COEngineeer]

Just call for an inspection from a local structural eng. firm. It will probably cost you $500.

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Sea Water Intake and Jetty Construction

 

[ttuterry]

JAE, yes what you are saying is correct. To make things even more interesting, my boss pulled the Mechanical Engineer off the project. I know he didn't have much civil experience but anything helps. So now i'm at it alone! And to make this situation even worse, my boss just calls and says I would like this done by the close of business tomorrow! I haven't asked my boss if maybe we should consult someone, but I personally think that would be the right thing to do. At this point, I don't think it is an option for my boss. As you were saying JAE, someone could fall through the floor and then I could be sued. So maybe this brings up another question of this being ethical of my boss for him to allow me, an EIT with little structural experience, to be the only person working on this project. And another question I just thought of; would a licensed engineer have to approve the floor loading since it is going to be posted on a sign in the trailer? Thanks for all your responses so far..

 

[COEngineeer]

I think putting a sign on the trailer is a little useless. You need to design it to anticipate what is going to be put there. Not tell people how much they can put in there. It is not a small bridge! The person whos going to put something in there will never know how many PSF he/she is adding. Design it for light storage room (125 psf) and call it good.

http://www.swijetty.com

Sea Water Intake and Jetty Construction