Car Park Floor Loading

[NIO85]

I am at the initial stage of designing a multi-storey car park but have doubts on floor loading. I have been using imposed loading 2,5kN/m2 for vehicles not exceeding 2.500Kg gross mass as provided in BS 6399 Part 1 but some one is advising me to increase the loading by 25% to cater for dynamic effect induced on the structure during braking and acceleration. I thought the dynamic effect is already catered for by 2,5kN/m2. Am I wrong? Please advise.

 

[asixth]

I have used both those values you have used without an additional 25% for dynamic loading.

 

[ajk1]

Here in Canada, we do not use an additional 25%. Never heard of that. However, I do give consideration to whether the clear height entrance barrier bar allows trucks to enter; if it does, then I design for greater live load, although I think that is often (usually?) overlooked, although I don't know why. I could not justify overlooking it. For rooftop car parking, we design for the greater of 2.4 kPa or the design snow loading as per the National Building Code of Canada. I design rooftop parking for greater than 2.4 kPa (generally 3.6 kPa to account for the snow plough weight and the pile of heavy snow in front of the blade). Designated snow piling areas on the rooftop parking must be designed for much higher loads, depending on the height limitation for the pile. I have generally designed snow piling areas for > 10 or 12 kPa based on maximum wet snow density of about 35 to 40 pounds per cubic foot. Hope this helps a bit.

 

[hetgen]

NIO85 BS6399 is Withdrawn, the current code is BS EN 1991-1-4:2005+A1:2010

No dynamic effect is need , 2.5kN/m[sup]2[/sup] as you have it is applicable. Your natianl annex may dictate a specific value but according to EN a range value 1,5 to 2,5 kN/m[sup]2[/sup] and point load of 10 to 20 kN is specifed for:

Traffic and parking areas for light vehicles ( < 30 kN gross vehicle weight and  8 seats not including driver)

-Access to areas should be limited by physical means built into the structure & posted with the appropriate warning signs.

 

[manstrom]

The US code uses 40 psf for garages (1.9kN/m^2), this is down from 50 psf (2.4kN/m^2) in the old codes because it was considered too high. In reality, the load can be reduced down to 32 psf for precast double tees (1.5 kN/m^2). I'd say you are OK using the base value.

 

[briancpotter]

Agreed, I've designed a fair number of parking garages in the US and have never had to consider dynamic effects. Any acceleration/braking loads should be taken into account by using the design wheel load (3000 lbs in the US).

Brian C Potter, PE

http://simplesupports.wordpress.com

 

[Archie264]

>>>...the load can be reduced down to 32 psf for precast double tees<<<

Wow, that makes me nervous. While that may, perhaps, be justifiable if the garage is never loaded beyond it's design load, it's tough to ensure that at some point someone won't drive something onto the garage that doesn't belong there. To wit, see this video:

http://www.youtube.com/watch?v=EKRz2WThyf0

Unfortunately that type of thing happens more that people realize because snow removal is a serious logistical undertaking. People such as ajk1, who have to deal with this regularly (in Canada), design for this with that heavy loading in the staging area he referenced. But, ironically, areas where there is less snow fall might be more susceptible to such problems because they don't have to have as rigorous a snow removal program in place and the maintenance personnel may not be aware of the dangers involved.

And then there's the issue of corrosion and periodic maintenance...

 

[briancpotter]

Archie264-

The reduction is only permitted for vertical members (columns, walls) supporting 2 or more floors. So it'd take quite a few rogue vehicles before the loading became dangerous.

However, I tend to agree - the loading for garages skirts a lot closer to the max a garage is likely to see than I'm comfortable with. A fully loaded pickup truck or SUV will weigh a lot more than 40 psf, so it's only by taking into account the drive aisles won't be full and that people will obey the striping that the design works.

Brian C Potter, PE

http://simplesupports.wordpress.com

 

[Archie264]

>>>The reduction is only permitted for vertical members (columns, walls) supporting 2 or more floors.<<<

Oh. Thanks for the clarification.

And those things do bounce a lot...

 

[NIO85]

Thank you all for your advise.

 

[dik]

In reality, you're unlikely to see 20 or 25 psf in a parkade will all the stalls and isles loaded with vehicles... Big SUV's put a bit of a wrinkle in that... We still design for 2.4kPa, (50psf) here... pluss snow piling...

Corrosion is a bigger issue, and we have a separate standard for parkade design.

Dik

 

[JacksPanic]

I do not know of the additional 25% you mention. 2.5kPa is ok. Remember to allow for suspended services and construction loads...

 

[NIO85]

hetgen, I think even if BS 6399 has been withdrawn in the UK, it does not necessarily mean it is unsafe to refer to them in the design. Aren't Eurocodes just meant to eliminate trade barriers among the EU countries?

 

[hetgen]

@ NIO85 there could be some risk when using withdrawn standards; pls see link below

http://webarchive.nationalarchives....documents/planningandbuilding/pdf/1454859.pdf

http://webarchive.nationalarchives....documents/planningandbuilding/pdf/1454859.pdf

 

[msquared48]

My Suburban is 6000# bare bones (10,000# with gas ). Extrapolated over an 8X15 parking stall, that's 50 psf...

Mike McCann
MMC Engineering

 

[dik]

A really well designed parking garage will have 300 sq.ft. per vehicle. 10000/300 is 33 psf, and the guy next to you is half empty. You will not likely find an entire parkade filled with Suburbans... and, I noted that big vehicles put a wrinkle in that... May be the reason for going to 40 psf.

Dik

 

[EngineerofSteel]

I think the recommendation for 25% comes from ASCE7 Section 4.10- which applies to crane loads in buildings.

Realistically, a stopping vehicle, esp. one stopping suddenly, will exert a (small) lateral force into the structure, via the horizontal diaphragm- which will surely distribute it into the MFRS.

More interesting than this stopping force, would be an impact force- 10,000 pounds at 18" above grade. No ABS action to attenuate a bumper crashing into the parapet or spandrel.

The Steel Deck Institute does say 35 psf is more realistic. However, the ASCE 7 lists 40 psf, and calls it irreducable.

Curiously, however, reducing the 2.5 kN by 25% is about 41 psf, very close to the ASCE 7 live load. Perhaps there is a 25% increase. But, more likely, the Canadian code uses the same sources as the US codes, and has not (yet) decreased the design value.