'm sitting for the PE (civil-structural) in two weeks. I've been running through NCEES official practice exams for preparation. Has anyone noticed the glaring errors in the "official" NCEES practice exams? Me and some friends have discovered quite a few. Some are corrected in the errata (which they should be plastering all over their website, not making us find [read: stumble upon] it!). But some have not been corrected to my knowledge. There are some really massive errors in fundamental engineering theory (using centroid instead of shear center) and there are some very misleading questions (uniformly distributed loads on stairs not acting on projected area of stairs). This is very unsettling given these are from THE official national testing agency for engineering. Even non-NCEES practice problems are riddled with errors. How am I even supposed to know if the actual test answers are correct!?
Errors in NCEES practice exam
- Thread starter rfehr613
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ptatohed
Licenced to Spell
Can you list the problems you believe to be in error?
Sorry to unload so many photos, but these are the issues I've discovered in just the 2011 NCEES Civil-Structural practice exam alone... And I'm not even done like half the afternoon problems yet.
Now i realize that it's always possible that I've made mistakes, but some of these are just plain wrong. The torsion in the spandrel beam problems? Those are incorrectly computed in the official solution manual. NCEES sort of acknowledged this by correcting problem 509 in an errata to use the shear center; however, these did not correct problem 513 which is nearly identical.
It also seems that we're left guessing which code to use, when each code offers different methodologies (see problem 530). Or the problem statement seemingly contradicts the requirements of the code (see problem 516).
This didn't exactly spur confidence that the true correct answers to the test problems I'll be solving on October 28th will be one of the 4 options. Or worse, they will be an option, but they'll be deemed an incorrect option by NCEES. It's not like there's any way to verify the actual tests. It also doesn't help to see stuff like "flexural rigidity" in reference to a beam's stiffness. Were these tests even written by engineers? Nobody uses that terminology.
I'm seeing stuff like this on other non-NCEES practice material too, but i suppose that should be more excusable. The test makers shouldn't be messing up. I've talked at length with a good friend of mine who is also taking the same test with me. We're in agreement that there are some pretty serious issues with many of these problems.
What do you think? Surely, we're not the first to raise this concern.
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Now i realize that it's always possible that I've made mistakes, but some of these are just plain wrong. The torsion in the spandrel beam problems? Those are incorrectly computed in the official solution manual. NCEES sort of acknowledged this by correcting problem 509 in an errata to use the shear center; however, these did not correct problem 513 which is nearly identical.
It also seems that we're left guessing which code to use, when each code offers different methodologies (see problem 530). Or the problem statement seemingly contradicts the requirements of the code (see problem 516).
This didn't exactly spur confidence that the true correct answers to the test problems I'll be solving on October 28th will be one of the 4 options. Or worse, they will be an option, but they'll be deemed an incorrect option by NCEES. It's not like there's any way to verify the actual tests. It also doesn't help to see stuff like "flexural rigidity" in reference to a beam's stiffness. Were these tests even written by engineers? Nobody uses that terminology.
I'm seeing stuff like this on other non-NCEES practice material too, but i suppose that should be more excusable. The test makers shouldn't be messing up. I've talked at length with a good friend of mine who is also taking the same test with me. We're in agreement that there are some pretty serious issues with many of these problems.
What do you think? Surely, we're not the first to raise this concern.
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rfehr613: I have noticed the same errors as you as well. I had the same concern for 516 and 521. How are we suppose to know that the test makers want us use a Cb = 1.0 rather than actually calculating it? I have seen similar things in other practice exams where they will ask for lightest member design of tension member and will assume worst case shear leg (U). If you consider allowable shear legs, then a lighter member can be used. What codes are you referring to for 530? I am getting the same answer as NCEES, but using different equations.
There are a few different theories for determining bearing pressure from a footing. If you look in the CERM, they reduce the footing bearing area. There's no mention of the 2/3 factor, so i wanted to know where it came from.
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jijir83
Expert in everything useless
Too late to do math but I think 530 is right. They're asking for the soil pressure right?
I remember deriving this equation in school. Haven't really used it since but it's a typical geotech problem. The load distribution is a triangular shape and with the 1/6B rule, it just works out that way in the end. The way they write their solution hides some things but I think the bottom of this page is what you're looking at: http://www.ce-ref.com/Foundation/Spread_footing/Size_footing/footing_size.html
A geotech reference might explain it better and might have to look it up for strip footings strip footings.
I remember deriving this equation in school. Haven't really used it since but it's a typical geotech problem. The load distribution is a triangular shape and with the 1/6B rule, it just works out that way in the end. The way they write their solution hides some things but I think the bottom of this page is what you're looking at: http://www.ce-ref.com/Foundation/Spread_footing/Size_footing/footing_size.html
A geotech reference might explain it better and might have to look it up for strip footings strip footings.
jijir83
Expert in everything useless
121... I don't know how they worked out their solution but the pencil marks is not what I would have done.
1) Using manning's for full pipe Q = (1.5/n) x ((π x D^2)/4) x (D/4)^(2/3) x S^(1/2).
2) The n value doesn't matter since the single pipe will be the same material, they will cancel out. The slopes S are also the same so they will cancel out as well. Only D terms and exponents will be left. But let's assume the whole equation is used. Answer should be the same. Units are in Imperial for this equation.
3) The flow from the 12 in pipes will be 2xQ then solving for D with the 2xQ value should result in 15.56 inches.
They ask for "most nearly" so 16 inches makes sense. Am I too rusty or am missing something?
1) Using manning's for full pipe Q = (1.5/n) x ((π x D^2)/4) x (D/4)^(2/3) x S^(1/2).
2) The n value doesn't matter since the single pipe will be the same material, they will cancel out. The slopes S are also the same so they will cancel out as well. Only D terms and exponents will be left. But let's assume the whole equation is used. Answer should be the same. Units are in Imperial for this equation.
3) The flow from the 12 in pipes will be 2xQ then solving for D with the 2xQ value should result in 15.56 inches.
They ask for "most nearly" so 16 inches makes sense. Am I too rusty or am missing something?
This is a different method though. In another method, like the one in the CERM, you reduce the footing area if the eccentricity is greater than B/6. My problem is that there's no way to tell which method we're supposed to be using.
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The pencil marking are mine, and they're exactly the method you describe lol. I only included the components of the equation that vary, as you are saying. The solution uses the full equation which is unnecessary. The solution is just below 16" like you say. But the fact that they state the pipe must flow full is the problem i have. They make it a point to state that, then none of the answers will actually flow full. Having "most nearly" in the problem statement means nothing if they have the qualifying condition that the pipe must flow full. If this were a question on the exam, I'd get hung up on it because I'd think i was doing something wrong. That's a problem.
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gpoli111
PE
I am also getting 2.72ksf.
M = 1000 k*ft
P = 120k a = 24'/2
e = 1000k-ft / 120k = 8.33'
a = 24'/2 - e = 3.67' (Distance from e to overturning toe)
x = 3*a = 11' (bearing length from overturning moment)
Increased bearing pressue, p = (2*P)/Width*x = (2*120kip)/(8ft*11ft) = 2.72 ksf
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