Kaplan q&a n.16

Structural Layout Vignette and Multiple Choice

Kaplan q&a n.16

Postby pig » Tue Feb 06, 2018 3:32 am

please refer to attached.
can someone please help explain why the answer is:
0.3(30k) * 18ft
and can complete disregard the V=15k?
if 0.3W is working at either axis of the frame, then wouldn't it also work along the same axis as the V=15, therefore:
(0.3*30k)*18' + 15k*18' =. total OTM?
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Re: Kaplan q&a n.16

Postby Siege109 » Tue Feb 06, 2018 7:10 am

Hi,

I am the same as you. Just a struggling ARE taker trying to stay alive so take what I am saying with a grain of salt....

You can not disregard the V=15k (it is Y). That is your overturning moment in the clockwise direction.

The 30 Kip vertical load will give you a stabilizing moment of resistance in the counter-clockwise direction. I tried to do the math very quickly and failed miserably but will give it another shot later when by boss is not lurking but I think if you can start to evaluate stabilizing moment vs overturning moment the solution will start to surface. If you figure it out please post.
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Re: Kaplan q&a n.16

Postby pig » Tue Feb 06, 2018 8:45 am

hi Siege109,
thanks so much for your reply and your comment on Stablising moment!!...!!.
i found the same question in a newer version of kaplan that looks slightly different.
give me a minute and i will post it here again so you can use the updated version.
the other one was fro 2006 later force and i suspect the original answer was just wrong.
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Re: Kaplan q&a n.16

Postby Siege109 » Tue Feb 06, 2018 9:01 am

Awesome that would be great. Please post. And yes, not unlikely its just a mistake. I am glad to see some activity on here. I have SS exam in 3 weeks and studying hard until then. I would like to flip through your other post later on and see if maybe we can help each other out or at least share some info.
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Re: Kaplan q&a n.16

Postby pig » Thu Feb 08, 2018 7:31 am

so sorry...
i am a bit slow in responding,...
i just took my exam and am in a post exam trauma and depression.
it was sooooooo bad that i am quite sure it was a 99% fail attempt.
but please give me a few days to recover and i will try to write and share more in a bit....
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Re: Kaplan q&a n.16

Postby lali » Fri Feb 09, 2018 3:10 pm

This graphic was used several times in Kaplan for different questions.
The Y=15K is in the drawing, but it is not mentioned in the question. (I think it is a left over from a different question)
In other hand the seismic force is 0.3x30 = 9kips applied to the top of the whole tower (34') In seismic forces we assume that the force is applied at the top because the earth (below the bottom of the building)moves back and forth and the building tends to stay where is was because of inertia... so the effect is similar to applying the force to the top.
The weight of the water tank is vertical (centered on the tower) making a rotation moment with and arm of 6' (half of the structure width).

Added the two forces make an overturning moment of 126 ft-kips.

lali
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Re: Kaplan q&a n.16

Postby Siege109 » Mon Feb 12, 2018 11:59 am

Excellent. Thanks so much Lali!
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