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Parapet out-of-plane seismic loads

ASCE 7-05 parapet seismic

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#1 McEngr

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Posted 29 February 2012 - 05:01 PM

OK - I'm going to go out on a limb here and ask a silly question: when is a parapet a non-structural element? I'm asking because chapter 13 seems to be for the anchorage of a seismic, non-structural element whereas the loading could easily be designed from ASCE section 12.11.

It seems a matter of judgement as to whether the parapet is non-structural or not. In practice, I would probably check both sections and design the parapet for the worst-case loading.

Thanks.

#2 kevo_55

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Posted 29 February 2012 - 06:04 PM

Unless the parapet isn't the actual shear wall, then it would be a component of the building.

#3 McEngr

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Posted 29 February 2012 - 06:17 PM

I guess I don't understand. There would be no shearwall action from a diaphragm load when a parapet is above the roof level. Therefore, (what I think you're saying is...) the shearwall needs detailed all the way to the top.

On another note: I was talking about oop loads. Shearwalls are in-plane, so I'm taking a big leap at assuming you knew my question. :)

#4 kevo_55

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Posted 29 February 2012 - 06:20 PM

Well, of course the shearwall needs to be detailed up to the top.

But then again... I just realized that the shearwall does nothing out of plane.

#5 dakota_79

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Posted 01 March 2012 - 04:16 AM

I make sense of it this way: a parapet serves no structural function - a building system is just as functional without one. Therefore, it's a non-structural (architectural) component. All it does is attract loads.

I think if you compare 12.11 to chapter 13 requirements, you'll quickly see the ch 13 puts a much larger seismic force on the parapet, so comparing to 12.11 is a waste of time.

I make sense of that this way: if the non-essential parapet does fail, it could severely (catastrophically?) affect the o.o.p. integrity of the structural wall panel below. Thus the amplified forces on the parapet to ensure an architect's doodling doesn't control the integrity of the important stuff.

#6 dakota_79

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Posted 01 March 2012 - 04:17 AM

Also, I think there's a couple examples in SEAOC V1 that lay this out pretty clearly.

#7 kevo_55

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Posted 01 March 2012 - 12:42 PM

Dakota,

You're right. SEAOC v1 does have an example or two on this.

I make sense of that this way: if the non-essential parapet does fail, it could severely (catastrophically?) affect the o.o.p. integrity of the structural wall panel below. Thus the amplified forces on the parapet to ensure an architect's doodling doesn't control the integrity of the important stuff.

This is a good way to think about this. It kind of put into words what I was thinking.

#8 McEngr

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Posted 01 March 2012 - 02:55 PM

Dakota and kevo: thank you for the help! Sometimes it takes more than the struggle alone.

#9 dakota_79

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Posted 03 March 2012 - 04:34 AM

No problem - I'll have plenty of ?? for you I'm sure once I get into seismic detailing. This studying has been my intro to parapets, too, since doing almost exclusively heavy industrial bldg's IRL, the extent of our architectural features starts and stops with a "flash as required" note on the eave details. Just the way it should be!

#10 teamspears2010

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Posted 19 March 2012 - 10:14 PM

ASCE 12.1.2 staes that a "nonstructural component is a part or an elemnet of an architectural, electrical or mechanical system. ASCE 7 13.5: A parapet is an architectural component.

If you're designing for out of plane forces, you would use the Rt=Fp=fp (hw/2+hp). hp=height of the parapet

#11 Dexman PE PMP

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Posted 19 March 2012 - 10:19 PM

Can the plane still take off from the conveyor belt during a seismic event? What if you're out of the plane?





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