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Garage loading?

Garage loading?

Garage loading?

(OP)
I have a project where a client would like to park a “one ton dump truck” and a “backhoe” on top of a suspended slab. I believe the building will be used for “industrial condos” which are basically spaces which can be rented and can possibly be used to house such equipment. So final loading from the client is not really feasible. As of right now the project is preliminary in nature.

I am considering using a 125 psf live load or an 8,000 lb point load on the slab. Does this loading seem appropriate for this requirement? Typical garage loading of 40psf seems low and sidewalk loading of 250psf seems high.

RE: Garage loading?

I'd likely be starting at 250 psf and see what came of it. I'd consider it a driveway over a basement (I'm assuming there is a basement, hence suspended slab)

Would there be the possibility of a vehicle over 18kips in there? Also drives me to 250psf and a 12kip point load.

RE: Garage loading?

Your logic seems sound to me. Not everything is a firetruck after all. I think that the key will be the management of client expectations. I'd prepare some kind of schematic report outlining what will and won't be able to be stored in the facility and what kind of signage etc you may recommend to express limitations.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Garage loading?

A 1 ton truck isn't particularly heavy. I think the loading you describe is reasonable for that. I do not have a feel for the weight of a backhoe, but the point load seem large enough to cover it. I would recommend the owner post the maximum permitted loads on the floor.

RE: Garage loading?

I believe a Ford F-350 is a 1-ton truck? so it cannot be that heavy. As for the backhoe, I'd get the model they have in mind or the class and then as Dcarr stated post the allowable load for 1.15% of the listed weight.

RE: Garage loading?

If this is going to be a type of "industrial storage area" like you are saying, I think you would fall under the storage warehouse live loading, which is 125 psf for light storage and 250 psf for heavy storage.

However, if they are only looking to store vehicles in this facility, I would suggest considering AASHTO's H20 or HS20 live loading. Depending on your requirements for the weights of the vehicles you are looking to accommodate, you may also be able to reduce these loads down to a H5 or H10 loading. Section 1607.6 of IBC 2009 discusses how to apply these loads.

RE: Garage loading?

I also agree with Dcarr, make sure the building is posted for an allowable. Also I would add clearance bars at the opens to restrict any oversized vehicles.

RE: Garage loading?

(OP)
Just an FYI. The client is looking to use a composite beam and deck system and I ended up having a hard time getting the slab to work with the 8,000# load, so for now, I decided to use a 6,000# load with beams spaced at about 6' o.c. If they need to increase the load I will do what I can if the client decides to go forward with the project.

Thanks for the help.

RE: Garage loading?

How thick of a slab are you using?

RE: Garage loading?

(OP)
7" overall on 2" from deck designed in accordance with the method found in the SDI manual.

RE: Garage loading?

Ok, keep in mind that most bridge decks are 8" thick and that is with a 0.5" integral wearing surface. Therefore, the actual structural depth of the deck is 7.5".

RE: Garage loading?

Find your max load - 20k, 40k, etc, then get worst case moments and shears. Work backwards to find what psf load gets you there. It will depend on the spans and how it is framed.

I've used 350 psf for fire trucks / trash trucks in the past. Whatever you do, put a max load sign on the building. No trucks over ####.

When I am working on a problem, I never think about beauty but when I have finished, if the solution is not beautiful, I know it is wrong.

-R. Buckminster Fuller

RE: Garage loading?

Not sure where this is located, but if you are in snow country don't forget about vehicles bringing in road salts. The snow melts and the water can penetrate the concrete and sit on the form deck. Wreaks havoc with the deck.

RE: Garage loading?

I'm not sure that it would be sufficient corrosion protection in this instance but you can get deck that is perforated with drainage holes to mitigate water build-up.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Garage loading?

(OP)
Yes, this will be in snow country however, the deck is going to be used as a form only, hence form deck. Part of the problem I was having related to composite deck and getting that to work. I settled on form deck with two layers of #4 bars in each direction. I was originally trying to get a heavy wwm to work but wasn't having much luck hence the thickness and heavier reinforcing than what was expected.

RE: Garage loading?

@Kootk: Typically when dealing with deicing chemicals you should avoid the use of perforated steel deck, because this provides a direct path for the chemicals to get to the beams. Instead you should consider sloping the floor and providing galvanized deck drains with long enough piping to get the run-off below/away from the beams.

Also, I would recommend using epoxy coated rebar in the deck and applying a penetrating sealer such as boiled linseed oil on the finished floor to help protect against the deicing chemicals.

RE: Garage loading?

@SteelPE: Are your considering the deck to be continuous over the beams?

RE: Garage loading?

If the backhoe is on a trailer, most of the weight may be at the trailers axles to keep the tongue weight down.

RE: Garage loading?

Can you elaborate on the corrosion mechanism that concerns you PittEng88? AISC specifically recommends perforated deck in their design guide on parking structures.

Quote (AISC Design Guide 18, pg 9)

At least a G-90 perforated galvanized deck is recommended(i.e., 0.90 ounces of galvanizing per ft2) for parking deck applications, as is welding or mechanical fastening of the side lap seams.

Certainly, I would recommend providing drains and drainage a as well.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Garage loading?

Steel deck is a bad system to use for this, because the relatively thin slabs that are used are not good at distributing concentrated wheel loads, are prone to cracking, and the steel deck is prone to corrosion. Galvanizing will protect the deck for a limited length of time against atmospheric corrosion, but not so well against reactive ion corrosion (like from calcium chloride deicing salts). Composite steel deck is not permitted by CSA Standard S413 "Parking Structures". Since you cannot control what enters the garage, my opinion is that 125 psf is not sufficient, but in any event the concentrated wheel loads may perhaps control the design for such short spans. In my opinion, no experienced parking structural engineer would choose steel deck for this application. Yes it is relatively cheap, but you tend to get what you pay for. No one will be thanking you for saving initial cost when they are faced with deterioration that is expensive and disruptive to repair. Steel deck might be ok if the garage is a temporary structure scheduled to be demolished in 5 to 10 years, and you can show that all the forces can be resisted properly and you don't mind leakage thru the deck. How many stories is the garage? Irrespective of what system you use, put a height restriction bar at the entrance, and post the load limit (although the signage may become obliterated in a snow storm). You have a difficult situation to deal with, but I would not use steel deck for this.

RE: Garage loading?

My concern is that any drainage from the perforated holes in the deck will have direct access to the beams. Which is why I would rather rely on a deck drains and pipes, corrosion inhibitors in the concrete, and sealers to keep the water out. However, I am looking at this from a bridge engineer's standpoint, so a parking structure may not see the amount of deicing chemicals that a bridge will (although I have seen a few that come pretty close).

RE: Garage loading?

(OP)
Pitt, yes I did consider the slab to be continuous over the beams, which was part of my problem.

So, using steel form deck as a form is not suggested because it may rust out in the future leaving a slab which has currently been designed to support the load w/o the deck? I don't understand the logic. Or maybe it will look bad.

Industrial condos should have a load of 250psf because the word industrial was used? The building is 100'x60'. The intent is to rent out 20'x60' spaces to landscapers, contractors, steel erectors and people who need spaces to store their work equipment. The client requested the slab to support a 1 ton dump truck which is a glorified pick up truck in line with what the occupancy is expected to be. Regular parking structures are 30psf with a 3,000# conc. load. I selected 125psf with a 6,000# conc. load.

FYI, this isn't a parking garage that will see thousands of cars per day drive in and out.

I get the point about drainage and we have the potential to slope the floor which will probably be the best most cost effective solution.

RE: Garage loading?

Thanks for indulging my curiosity PittEng. In the world of bridges, a plain concrete slab on composite beams would be acceptable, right? With respect to the corrosion of the steel beam, I'm still not clear on how the perforated deck makes things worse. I'm assuming that drains, slopes, and sealers would be common to both system.

@SteelPE: while flipping through AISC's parking structure design guide, I saw a lot of durability tips that might be useful here. I do realize, however, that this isn't a true parking structure and that you are treating your deck as sacrificial formwork.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Garage loading?

@Kootk: Yes you are correct. Typically when designing composite beams for bridges, it is assumed that the forms are not there and any structural benefits due to the forms are ignored. (i.e. a sacrificial form) However, we do take into account the additional weight of the forms and the extra concrete in the valleys for the design of the beams.
This is done for a number of reasons:
1.) It is more conservative. So when/if the forms do happen to corrode away, the bridge still has it's full design section (unless there are other issues)
2.) During the design phase of the bridge you don't know what type of deck pans the contractor is going to use, if he uses any.

Going back to the corrosion issue. They could make things worse because the perforated deck would allow water to drain directly onto the beams as opposed to a drainage system that would help to keep the water away from the beams entirely. Plus I'm pretty sure you wouldn't want to be walking through a parking garage (or industrial condo) and have water dripping on you bigsmile.

@SteelPE: If you have access to the 1992 AASHTO, you could consider using their distribution factors to help reduce your design forces.

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