Ballast Question

Structural Layout Vignette and Multiple Choice

Ballast Question

Postby k4dm0nky » Sat Sep 14, 2013 8:18 pm

Image

I can't figure these things out to save my life. Ugh. I just hope I won't get one of these on the exam.

Anyone know any shortcuts on figuring something like this out?

Thanks!!!
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Re: Ballast Question

Postby Mike-SE » Sun Sep 15, 2013 7:00 pm

the force is 12 kips.
For everybody, this could be on the test. You MUST be able to solve this problem in 30 seconds or less.
Loading is symmetrical (As will almost all truss problems on the exam)
Reaction each end is 15 kips.
Vertical component of member FD is 15 kips
Triangle CDF has ratio of V:H of 15:12. Vertical is 15, therefore horizontal is 12 kips
Look at joint F, only member EF has a horizontal force. Therefore, force in EF MUST equal 12 kips.
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Re: Ballast Question

Postby AKK_VT » Sun Sep 15, 2013 8:13 pm

Thanks Mike-SE ... been looking at this too long, how does FD = 15k?
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Re: Ballast Question

Postby kbrsnow » Tue Sep 17, 2013 2:58 pm

I might need to figure this one out so that I would know how to solve it if I have to retake the exam.....
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Re: Ballast Question

Postby k4dm0nky » Tue Sep 17, 2013 7:35 pm

Ugh I still can't figure this out. I was able to figure out the reactions... and thats about it.

I can tell if there is a zero force member, but solving forces in web or chord members I am going in blind folded on this... It's just one of those things that just hasn't clicked for me... ugh :x i feel so stupid! :oops:
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Re: Ballast Question

Postby acadia » Tue Sep 17, 2013 8:47 pm

Watch the videos on trusses in this series http://www.khatrinternational.com/AIAexam.html. It was the only way I could comprehend truss questions. Good luck, you will get it.
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