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Parking Structure Subjected To: Roof Party - "Gangnam Style"
4

Parking Structure Subjected To: Roof Party - "Gangnam Style"

RE: Parking Structure Subjected To: Roof Party - "Gangnam Style"

Perfect example of the spring action of prestressed members.

I feel similar movements in my car as I sit on an overpass (constructed of pretensioned concrete I beams) waiting for the light to change while traffic is passing to either side of me. I don't even have to play music to rock out!

Mike McCann
MMC Engineering
http://mmcengineering.tripod.com

RE: Parking Structure Subjected To: Roof Party - "Gangnam Style"

It is a little scary, especially when there are comments as follows:

"The average passenger vehicle weighs approximately 4,000 pounds, which is equivalent to 26 people that weigh around 150 pounds each. For clarity, that's 26 people per parking stall. If the parking garage can withstand the weight of hundreds of parked and moving vehicles (and their passengers), I don't think that people dancing on the top floor will cause a structural problem."

This guy would be shocked to find that parking garages are designed for 40psf which was recently reduced from 50psf.

Years ago my now wife was living in an apartment next to a major university in a large metropolitan area. She lived on the first floor with a bunch of college kids living above. They used to have dance parties above and you could literally see the floor deflect up and down as they would jumped in unison. Plaster was falling from the ceiling. Had something happened I'm sure their parents would have sued the building owner, city inspector, contractor and anyone else involved. Our future leaders hard at work.... ugh.

RE: Parking Structure Subjected To: Roof Party - "Gangnam Style"

So it didn't fall down so the load test worked!

Figure 5 people in a 5 ft. x 5 ft. area each weighing 160 lbs. each.
That is 800 lbs in a 25 s.f. area = 32 psf.

Assume a dynamic impact factor of 2.0. That equates to 64 psf. (don't know if the 2.0 is accurate or not - I pulled it out of the er, air.)

If the garage was designed for 40 psf. Using LRFD that would be an ultimate capacity of 40 x 1.6 / 0.9 = 71 psf.

So perhaps it was almost at collapse.

RE: Parking Structure Subjected To: Roof Party - "Gangnam Style"

And also - now that I think about it - perhaps the failure mode would be ductile (flexural limit state where the tendons went inelastic)...it would be interesting to know the before and after camber in the floor.

RE: Parking Structure Subjected To: Roof Party - "Gangnam Style"

Alternatively, look at SteelPE's 26 people/4000 lb per stall. A very tight stall is 9'X20', or 180 sq. ft., & if it's designed at 50 psf (ours is still that) it's 9000 lbs. Live load is live load, whether cars or people, so according to the design you can't put enough people on it to overload it.

Of course, we don't know what the design really was, do we??? Was the designer competent?

RE: Parking Structure Subjected To: Roof Party - "Gangnam Style"

Probably popped a few embed welds! Harmonics could bring it down!

RE: Parking Structure Subjected To: Roof Party - "Gangnam Style"

(OP)
I agree regarding the harmonics. The live load can be inconsequential when you are oscillating near the natural frequency in the absence of damping.

There is a pretty substantial cable suspension pedestrian bridge near me. Just from shaking the cables lightly I am pretty convinced that one or two people could bring it down if they wanted to.

RE: Parking Structure Subjected To: Roof Party - "Gangnam Style"

So, Ron.....perhaps my impact factor of 2.0 should be 20? Harmonics are a many splendorous thing!

RE: Parking Structure Subjected To: Roof Party - "Gangnam Style"

Nah! Impact factor of 2 is good...just tune the cables to play something good....maybe something from the 60's or 70's...Clapton, the Byrds...trick is to get a 12-string sound from it.

RE: Parking Structure Subjected To: Roof Party - "Gangnam Style"

Shobroco

Just so that we are clear, that wasn't my load of 26 people per stall. That was a comment made in the video by someone who said that the structure should easily be able to take the load of the people because the structure is designed to support vehicles.

RE: Parking Structure Subjected To: Roof Party - "Gangnam Style"

[shameless school rivalry]
How many ASU girls does it take to bring down a parking garage?
[/shameless school rivalry]

Also saw this in the comments:
"Just FYI, we did this last year too. After the intensive bouncing, the facilities manager double-checked with a few engineers and people who had been responsible for the construction of the parking structure and got the OK to do it again this year."

Now can we consider fatigue too?

RE: Parking Structure Subjected To: Roof Party - "Gangnam Style"

Those engineers are "braver" than me; I would never sanction such a thing. For those who haven't seen it this video of a wedding party in Israel a few years back ought to be a wake-up call.

http://www.youtube.com/watch?v=CMCXjZ3xuEc

RE: Parking Structure Subjected To: Roof Party - "Gangnam Style"

(OP)
HAHAHA! That's rich azcats.

So a student said a facility manager said that he/she double-checked with a few engineers, and people (contractor's apparently), who said that the original design was fine for anything a mob of inebriated teens could dish out. How about a sealed report?



Seriously tho to Ron or Mike or some of you guys with experience in PT component manufacture/testing/approval...Are these panels ever tested to failure under heavy dynamic loads (light load at high amplitude near the natural frequency)? My initial thought was that this type of loading was obviously damaging, but it may not be as bad as it looks if the load never exceeds the cracking moment or causes a stress reversal of the pretensioned member.

Thanks all.





RE: Parking Structure Subjected To: Roof Party - "Gangnam Style"

Great, now I have to add the "Gangnam Style" load case to my calcs. It's bad enough that the stupid song will be in my head for the next 4 hours.....

RE: Parking Structure Subjected To: Roof Party - "Gangnam Style"

U = 1.2D + 1.6L + 4.5GM

RE: Parking Structure Subjected To: Roof Party - "Gangnam Style"

JAE, good one! Let me record that in my ASCE-7 book before I forget it.jester

RE: Parking Structure Subjected To: Roof Party - "Gangnam Style"

Wow, this is crazy.

In our city there are two parking structures in the downtown area. Every fourth of July the top floors are filled with people watching the fire works. This of course is on top of all the parking spots full. I am hoping that the structures are designed for 100 psf at that level. Perhaps the codes should consider a change to top floor parking.

RE: Parking Structure Subjected To: Roof Party - "Gangnam Style"

Honestly, this is one of the loadings that's always worried me. The problem is that "cars are heavier than people" is a thing that's in people's heads, so the layman is always going to think that something designed for cars is going to be strong enough for however many people you can stuff in there. Parking areas are also large open areas that could lend themselves fairly easily to being cheap places to host large gatherings.

However, we don't get a lot of parking structures that fall down because of occupancy loading, so I can't really argue that this is a real problem, but I've spent a bit of time worrying about this on several occasions.

RE: Parking Structure Subjected To: Roof Party - "Gangnam Style"

I received the following comments from a nationally-known parking garage consulting engineer:

With respect to allowing people load on the top garage level: Normally, the roof top of the garage is not designed for such a live load. The owner should not allow such an event to take place and the fire marshal would be very upset.

With respect to designing garages for a greater people load on the top floor: You really can't because that would be considered a different use (mixed use) and you will be unable to get a building permit as a garage. It would require more stairs, fire sprinklers, etc.

www.PeirceEngineering.com

RE: Parking Structure Subjected To: Roof Party - "Gangnam Style"

The additional loading isn't a code requirement, nor it is standard practice, nor is there a history of failures despite it not being included in current structures. It'd be pretty hard to justify the extra cost.

RE: Parking Structure Subjected To: Roof Party - "Gangnam Style"

Sometimes precast parking garages collapse under snow loads. That is, a snow plough operator piles up snow in a concentrated area exceeding the capacity of an individual double-T or even a whole bay.

RE: Parking Structure Subjected To: Roof Party - "Gangnam Style"

I am in complete agreement with PEinc's comment. I think it is unconscionable that the roof of a parking garage is being used for dancing if it has not been designed for it in all respects and to all requirements of the Code. As I have been involved with design of parking garages for a number of decades, I have always asked myself before each design whether the roof might be used as a viewing area by the public (to watch a parade, or the like) in which case it should be designed for 100 psf minimum live load. In any event the roof should be designed to accommodate the weight of snow piling (usually >> 100 psf) in selected locations, and the weight of the snow plough and pile of snow it is pushing in front of it, I think. The old Toronto Code (in effect until 1975 when the provincial Code superseded it) required parking garage floors to be designed for a live load of 75 psf - more than needed for a typical floor of a garage, but perhaps a good idea for the minimum live load of a roof.

RE: Parking Structure Subjected To: Roof Party - "Gangnam Style"

I was in San Francisco recently and heard the tale of how they closed the bridge to traffic and allowed 300,000 pedestrians to walk on the bridge at once during the bridge's 50th anniversary. It deflected by about 13 feet in the middle and experienced stresses likely beyond anything it had experience before.

http://www.standard.net/stories/2012/05/24/25-year...

The moral: densely packed people are much heavier than cars, though the majority of the general public would think otherwise.

RE: Parking Structure Subjected To: Roof Party - "Gangnam Style"

Yes, densely packed people are heavier than cars, but 100 psf is pretty hard to achieve in any case. Look in the mirror & tell me you can imagine being in a 1000 sq. ft room with 499 people getting the same 1'X2' space as you. It ain't gonna happen & you know it. The 100 psf is to allow for the effects of dancing, stomping, whatever, without introducing yet another factor, because face it: if there are enough people to make 100 psf they sure aren't going to be able to produce an impact of 2 or 20 or anything. They'll be happy to breathe.

RE: Parking Structure Subjected To: Roof Party - "Gangnam Style"

ajk1

Since this was in Arizona the most likely snow load is 0psf. I am interested is seeing how you figure out how much snow load would be piled in the the designated areas? I have always wondered how this was done. I have been asked to look into this before but the projects have always fell through.

RE: Parking Structure Subjected To: Roof Party - "Gangnam Style"

to SteelPe;

We have detremined the density of ploughed piled dense wet snow by actual measurements on site in downtown Toronto.

We limit the pile height and design the designated area for the corresponding load. Usually > 200 psf.

This is certainly not ideal for a number of reasons, including enforcement of pile area and pile height (say 5 feet), but we have seen garages where no snow load piling was designed for and yet we saw large snow pile with no visible distress.

In most garages the snow is removed by ploughing it into a snow melter (for larger garages like the 10,000 car garage we designed), or for smaller garages it is ploughed over the edge at barriers that open to allow the snow to be ploughed over the side Or down a shaft), or other snow removal methods.


Too bad that Arizona gets no snow. There is nothing more beautiful than to watch a raging snow storm (while looking out the living room window) or out walking thru a blinding storm.

RE: Parking Structure Subjected To: Roof Party - "Gangnam Style"

That part (Phoenix Metro area) of Arizona gets no snow. Other parts can get considerable snowfall. I've worked on projects in the Flagstaff area where snow load was certainly a consideration. Lots of climatic differences in our state. I'll agree that snowstorms are gorgeous, but as my father-in-law always says, "You don't have to shovel sunshine." ;)

RE: Parking Structure Subjected To: Roof Party - "Gangnam Style"

Has someone contacted the school yet? We can actually do something about this one before it ends very, very badly.

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