factored footing loads

[bhart192]

I have a prefab building, the metal bldg. manufacturer has given me the maximum column loads per UBC 2006,the loads are already combined(for example col 1 has a total load of 35 kips) these numbers do not break out the dead,live ,wind etc. since most footing design takes into consideration factored loads how should I address the footimg design using a single combined load that is the result of the load combinations. hope this makes sense.

 

[Lion06]

I would size the footings using the service load given to you, then design the reinforcing by factoring the loads by 1.6.

 

[par060]

I would get the loads individually from the bldg company...they should supply them

 

[BAretired]

I am surprised that the metal building manufacturer didn't give you a more detailed breakdown than that. Usually, they give both specified and factored loads for every conceivable combination of dead load, live load, crane load, wind load etc.

The answer depends on which code you are using. If the load is comprised of only dead and live loads, the NBC (Canada) uses a load factor of 1.25 for dead and 1.5 for live load. The major portion of load for a metal building is likely to be live load, so you would be safe to use 1.5 times specified load as your factored load.

The area of the footing will likely be determined on the basis of specified load, because geotechnical engineers deal in allowable bearing values, not factored.

BA

 

[kslee1000]

Reject the submittal, request break down loads with load factors/combinations clearly indicated, unless you want to take over the responsibility for theirs mistakes, if any.

 

[apsix]

"unless you want to take over the responsibility for theirs mistakes"

I don't think that's the issue at all.
Footing designers don't have to check the building calcs. for mistakes do they?

 

[kslee1000]

No, we don't check program (input/output) concerns building itself, its the manufacture's responsibility. But as a structural, we do check the loads, load cases, and load combinations specified by contract, and/or required by code. Ultimately, we cannot say "I just put whatever he gave to me, I didn't know how he got though, NOT MY FAULT".
Mistake is rare, but had occurred before, and will occur if we don't care to catch it.

 

[kslee1000]

Another confusion could arise, let me try an example, though I am not familar with the current building code.

Say you were provided with an uplift of 5k, horizontal load of 10k. On over turning, without knowing which load cases were involved, shall you use safety factor 1.0, or 1.5? Or even you know: vertical = wind + 0.6DL; H = earthquake + DL + LL, would these help?

Sure, you can alway check against 1.5 to be SAFE. Gosh, lucky there is a way out.

 

[apsix]

kslee1000

So you see that it's your responsibility to check the derivation and combination of the loads?
What happens when you are contracted to design the piling for a complex multi-storey building, how much load checking are you going to do?

I do agree that receiving the raw column load data is preferrable. At the very least an uplift case should be given.

 

[kslee1000]

On top of load and load cases, give me the prime reactions for each load case, that's ALL I NEED, period. Now I could make the combinations as I see fit, and question your assumptions, accuracy in certain areas that I have problem to have your numbers came close to mine. I am JUDGING, ACCEPTING, or REJECTING your design on something that I can work on to achieve required understanding, not just blindly follows. GOOD, GOOD, THERE IS SKETCH, HERE ARE THE NUMBERS. JOB DONE.

 

[2meterman]

I happen to have this exact problem with a project that I am currently working on.

The reason the building manufacturer isn't giving me the broken out design loads is due to the contractor/owner not paying for more than 5% of the building cost. The manufacturer states that they need 25% of the building cost before they will give the final design parameters.

If you have the column reactions for each location, look carefully on that sheet. Usually, the manufacturer will give you the different load combinations and assign them a load case. This load case is then assigned to a load calculation matrix on that sheet.

You will probably have "Prelimnary Calculations" stamped all over the drawings as well. There are a couple of ways you could approach this situation.

Try looking in the book "Metal Building Systems Design & Specifications, 2nd Editions" by Alexander Newman. In chapter 12 he explains how to approximate design loads for a building. As was said in a previous statement on this thread live load, specifically wind uplift will usually control the design. You can come up with your own loads and compare them to what was given you. On my building 0.5D + 1.0 Wind was the governing load case. The building manufacturer usually gives you the dead weight of the building so you could ferret out the wind load by subtracting the dead load.

Another option would be to take the load case given and multiply by the most conservation load case factor you are comfortable for using on a live load. The load will be conservative, but that is all you have to work with.

Either route you take, be sure and stamp on the drawings that they are 'preliminary only' or 'for bidding purposes only' or 'not for construction, review only'.
State on the drawings or in the submittal to the contractor/owner that a final design will not be available until the final column reactions have been submitted to the engineer of record (You).

Good Luck!

 

[vandede427]

It seems like every third thread on this webiste is about pre-engineered metal buildings. I've posted my share of them too.

You should be provided with not only the factored loads/reactions but also the break down for each service load. I rarely ever look at their factored loads and I just run my own load cases from the service loads provided.