NCARB practice test question help
There is a question on the NCARB practice test about the best place to have a penetration for piping through a structural beam web. Can someone help me understand the answer? Why does the maximum shear dictate the location, rather than the moment? Where the shear is at zero, the moment is also at its maximum, so it didn't seem like the right answer to me. thanks in advance for any clarification! 
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In a simple support beam the shear force at the ends is the maximum, and minimum at the center. The tension and compression forces are 0 at the ends and max at center. The Tension in the mentioned part of the beam makes the stress in the BOTTOM FLANGE part of the I beam, the compression the TOP FLANGE part of the I beam. The shear forces generate the stress in the WEB PLATE part of the beam, so, if you are going to do a hole in the WEB of the beam, you want it to be in the middle of the beam where the shear force is 0. In other hand if you want to do like a hole in the BOTTOM FLANGE part of the beam it should never be closer to the Middle.
IN the second column you can see that shear forces are 0 at the center of the beam. In the third column you can see that the max Moment force (Compression/Tension) is at the center of the Beam.
You can find this generic information in the Building Construction Illustrated, but you should use Elif or Amber Book for better understanding. Also is important to use the FEMA book for more understanding regarding structures.
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Manuel. The new penetrations should never be located in the middle of the span. When making a penetration in a beam, it should ideally be located near the neutral axis (= in the middle of the WEB) and AWAY from the midspan of the beam (because the midspan is where the stresses are highest).
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Valerie for your clarification, the NCARB free exam is selecting the correct answer not me, I just provided the explanation. There are different stresses on beam shear, torsion and bending. Where the shear force is 0(ZERO) is where you put the whole on the web, if you put it AWAY from the midspan where the Shear force tends to increase, you will have more risk for having a failure.
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This is what I've read: "Areas of high stress should be avoided close to the supports where the shear force is at a maximum and also at mid-span where the bending stress is at a maximum. This leaves the zones along the neutral axis and a point of compromise between the mid-span and supports."
I think out of the answer choices given by NCARB, the "middle span" option is the most correct, whereas the other options are just BAD.
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Thanks all for the input! Farrah, your diagram above seems to suggest that a penetration from 1/4 - 1/3 span would be acceptable, but this may not be depicting a wide flange beam. What reference is that from? That is why I answered A. Valerie, I also understand your point about being in the middle axis of the web vs the top portion or bottom portion vertically. I think if the beam did not have flanges, the answer might be different, because yes as you say, the mid span of the beam would seem to be experiencing high stresses. I think Manuel explained it well that the flanges are taking up those compression and tension moment stresses, while the web is taking the shear stress and will be minimized at mid span, because shear stresses are higher near the supports, at the end.
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@Dianna I believe the diagram suggests that the first 1/4 of the span is NOT an acceptable penetration area...Looks like the best locations begin in the 1/3 section of the span. The source is from a university lecture:
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