Parking Garage LL

[JoeBaseplate]

Just wanted to confirm that LL for a parking garage is 40 psf (ASCE-7). Seems kinda low, so wanted to double check.

Also, in a multistory parking structure, would you impose full or partial snow load over this 40 psf at the roof level?

 

[dcarr82775]

It is 40psf, but there is a point load requirement as well. There are also some restrictions on how it can be reduced.

 

[RFreund]

I can't remember what IBC or ASCE7 requires but in Chicago you are required to add snow load to vehicle live load. Makes sense to do so.

EIT

 

[hawkaz]

40 psf is a good number. 4000# car over a 9'X18' space = 25 psf.

I would put the full snow load on the roof in addition to the 40 psf load (both can be there at the same time).

 

[msquared48]

6000# (Suburban)over 9X18 is 37. Hummer H2 is more (8600# curb) at 53 psf over same parking area. Old code for parking was 50 psf and you can see why.

May want to restrict the GVW to 6500# or so, or limit the vertical clearance. Just a thought.

Mike McCann
MMC Engineering

 

[JAE]

Keep in mind that for the top decks, the added snow load is one possibility, while the snow removal method may impose even higher loads on portions of the top deck.

In many cases, the owner will have the snow pushed off to one side and then eventually dumped down to the ground adjacent to the garage. I've seen cases where the snow piles up to 10 feet or more. In one case the precast IT girder cracked the supporting corbel at the column.

Having a snow removal plan in place - and perhaps a snow pile area designated is something to talk over with the owner.

 

[hokie66]

All loading codes should be considered by design engineers as representing minimum conditions.

Not applicable to the US, but for comparison, the Australian loading code gives 2.5 kPa, about 50 psf and 13 kN concentrated, for light vehicle traffic areas (restricted to vehicles with gross mass not exceeding 2500 kg. We don't need to add snow except in a very small area of the country.

 

[slickdeals]

If memory serves me right, the 50 psf load in the older code was reducible. But I think the 40 psf is not reducible, except a 20% reduction if column is supporting more than 2 floors.

 

[Teguci]

Lr = 40 psf - or one 3,00lb point load for the jack load replacing a tire (I've seen this control at the corner of a double tee that was not connected to a spandrel - btw this never happens).
S = 20 psf+ depending on your site - don't forget snow pile up at the spandrels (usually adds another 300 lbs + linearly along walls)
ASCE Combo 3, 4, or 6 use either Snow or Roof Live Load (not both - check local codes and client requirements for trip ups).

Don't forget to back off the 8 psf for your column load and foundations (except for the roof loading - new provision).

Its all good. I've designed garages for 30 psf (max LL reduction from previous codes) and they are still standing. You will need a head knocker to exclude large trucks from the garage (7'-0" height +/- , make sure you have clearance for the ADA vans though).

 

[SteelPE]

You guys mention about designated snow areas. We have been asked to look at similar parking garages but never have designed one. This is a question that has come up numerous times but since we have never been asked to finalize the design it has never been an issue.

How do you figure the load in this area? Is there a code or a paper that would give some guidance for these areas? Is this something you just place on the drawings as a note?

 

[Teguci]

Snow plow to have rubber edge.
Meet with client and designate an area for snow to be pushed off of the roof.
Design snow gate for that location.
Instruct owner to instruct contractor the requirements in snow removal - Such as no piling up snow above spandrel height and remove snow in small quantities.

Showing the client pictures and explaining to him the cost for not following these instructions may help too. I believe there is a maintenance guide for garages which should be required to follow.

 

[JoeBaseplate]

Thanks for the input. The designated area for snow removal sounds like a great contingency plan and could win us some points with the client.

I think for the prelim design/cost opinion I'll use 45 psf non-reducible for all floors and at roof level I'll throw in 30 psf (Chicagoland) snow on top of this load.

 

[dik]

and to confuse matters... a well designed parking garage will use about 300 sq. ft. per car... and with a 6000 lb vehicle, this will amount to about 20 psf...

Dik

 

[a2mfk]

Garage LL vs Office Live loads is one of the most non-intuitive loading scenarios I have ever encountered. I remember when I first saw that in a building code early on in my career and thinking, WHAT?? Then you crunch some numbers, and it all starts making sense. In terms of PSF, stacks of files can EASILY weigh more than a Hummer! Go to where your office keeps boxes of paper and pick it up, or weigh a stack of 4-5, or move a full single filing cabinet, and then you realize that maybe our office live loads are even a little on the light side. Well, not really, since there is also a lot of empty space, but you get my drift....

I remember an SE story involving a parking garage that at some point was converted, not sure how exactly, to office space or storage maybe. And sure enough they started having deflection issues, and the SE who reviewed the structure quickly came to the same conclusion we all just did.

 

[RacingAZ]

Check the building jurisdiction if there is a specific requirement for fire truck access to the upper floors. This will screw with your design loads, if it's required.

 

[hetgen]

Considering conventional flat slab parking deck, the concentrated live load doesn’t dictate ultimate design. Right? But if we are checking edge span deflection at what spacing do we place the point load? Do we consider the narrowest wheel line spacing?

H2 hammer weigh 30kN (6600lb) and it has 2.0m (~81 in) wheel line spacing.