# Errors in NCEES practice exam



## rfehr613 (Oct 14, 2016)

'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!?


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## rfehr613 (Oct 14, 2016)

rfehr613 said:


> ...


Replying just because i forgot to subscribe to thread lol


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## ptatohed (Oct 15, 2016)

Can you list the problems you believe to be in error?


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## rfehr613 (Oct 15, 2016)

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## rfehr613 (Oct 15, 2016)

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## rfehr613 (Oct 15, 2016)

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## rfehr613 (Oct 15, 2016)

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## rfehr613 (Oct 15, 2016)

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## rfehr613 (Oct 15, 2016)

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## rfehr613 (Oct 16, 2016)

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## rfehr613 (Oct 16, 2016)

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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## kaf21 (Oct 18, 2016)

Does anyone have the Errata for the 2008 and 2011 Civil NCEES PE exams?  I am looking for the general civil morning and the structural afternoon.


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## kaf21 (Oct 18, 2016)

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.


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## rfehr613 (Oct 18, 2016)

kaf21 said:


> What codes are you referring to for 530?


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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## rfehr613 (Oct 18, 2016)

Here's another i just did. They emphasize that the downstream pipe must flow full, but their answer is a pipe that doesn't quite flow full lol

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## jijir83 (Oct 19, 2016)

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.


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## jijir83 (Oct 19, 2016)

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?


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## rfehr613 (Oct 19, 2016)

jijir83 said:


> 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.


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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## rfehr613 (Oct 19, 2016)

jijir83 said:


> 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.
> 
> ...


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 (Oct 19, 2016)

jijir83 said:


> 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 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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## gpoli111 (Oct 19, 2016)

rfehr613 said:


> 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.
> 
> Sent from my VS980 4G using Tapatalk


That's essentially what the solution does though. It takes the pressure over a reduced area


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## rfehr613 (Oct 19, 2016)

gpoli111 said:


> > 2 hours ago, rfehr613 said: 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. Sent from my VS980 4G using Tapatalk
> 
> 
> That's essentially what the solution does though. It takes the pressure over a reduced area


The solution assumes a triangular pressure distribution with a reduced footing area. The CERM, like other references I've seen, assumes a uniform pressure distribution over the reduced area.

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## geomane (Oct 19, 2016)

Here is the equation (eq. 3.38) from one of my geotech books. I get 2.72ksf.


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## geomane (Oct 19, 2016)

It didn't work last time. Try this one.

View attachment 20161019130324.pdf


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## ptatohed (Oct 19, 2016)

kaf21 said:


> Does anyone have the Errata for the 2008 and 2011 Civil NCEES PE exams?  I am looking for the general civil morning and the structural afternoon.


I have it.  I have the 2008 errata and 2011 but for 2011 I only have the AM and the Transpo PM.  Feel free to PM me your e-mail address.


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## kaf21 (Oct 19, 2016)

Jmcc06 said:


> It didn't work last time. Try this one.
> 
> View attachment 8723


This is the equation I was thinking of.


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## kaf21 (Oct 19, 2016)

rfehr613 said:


> The solution assumes a triangular pressure distribution with a reduced footing area. The CERM, like other references I've seen, assumes a uniform pressure distribution over the reduced area.
> 
> Sent from my VS980 4G using Tapatalk


What section of the CERM are you looking at for if located outside of B/6?  The CERM that I have does not go into detail about e greater than B/6?


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## kaf21 (Oct 19, 2016)

ptatohed said:


> I have it.  I have the 2008 errata and 2011 but for 2011 I only have the AM and the Transpo PM.  Feel free to PM me your e-mail address.


Just send you my email.  Thanks.


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## jijir83 (Oct 19, 2016)

rfehr613 said:


> 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.
> 
> Sent from my VS980 4G using Tapatalk


Mmm.... Ok. Yes, your markings reduce to the same. So you're bugged by being misled. You have to remember that this is about taking the test and passing and not about our OCD engineering tendencies. The pipe "must flow full" means and is an indication to "use the full pipe equation". The solution is "most nearly" means "We, test writers, are too lazy to give you an exact number so pick the closest value". It's just another way, if you don't know your stuff, to throw you off and make you think that you made a mistake. Next thing you know, you might use a different equation and might pick the wrong answer if you lack confidence.

Part of the exam is learning to take the exam. One of the first things that a review course instructor, like the ASCE ones will do, is bring your attention to these "most nearly" and things (i.e. assumptions to make unless otherwise stated) that are strictly for exam sake. For all intended purposes, that 16-in pipe is flowing full. If they gave you 14, 15.56, 16 and 17, you better pick 15.56. If they give you 14, 15, 16, 16.7, you better pick 16 and not 15 or 16.7. Your goal is to pass within the confines of this test.



rfehr613 said:


> The solution assumes a triangular pressure distribution with a reduced footing area. The CERM, like other references I've seen, assumes a uniform pressure distribution over the reduced area.
> 
> Sent from my VS980 4G using Tapatalk


I don't know what the CERM is doing but my instinct would say to use the method that I mentioned. Seems like others have worked it out the same way. I don't do foundation design anymore  but, in determining dimensions of combined rectangular footings (one strip with two columns as is shown), uniform soil pressure is used. In making structural design of the combined footing, non-uniform soil pressure is considered. In this question, the footing is not being designed. So, part of the clue of what to use is in the question itself. If there are multiple ways of doing something, the methods have to be ones that give the same solution, or they either have to tell you what to use, or it is an inherent known fact which assumption to make. If you're not well versed in the topic, you won't know which way to go.

I hope you figure out those quirks. The exam in April was loaded with things like that and the afternoon geotech was all about these quirks that could through you off. If it's like that again this cycle, everyone needs to be sure to study with and have a good foundation/geotech reference. They were sneaky at linking structural (became foundation design) and water (became seepage) back to geotech in the morning.

Good luck on the test!


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## rfehr613 (Oct 19, 2016)

Jmcc06 said:


> It didn't work last time. Try this one.20161019130324.pdf


Do you need some kind of special access to view this? It is telling me it's blocked.

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## rfehr613 (Oct 19, 2016)

kaf21 said:


> > 38 minutes ago, rfehr613 said: The solution assumes a triangular pressure distribution with a reduced footing area. The CERM, like other references I've seen, assumes a uniform pressure distribution over the reduced area. Sent from my VS980 4G using Tapatalk
> 
> 
> What section of the CERM are you looking at for if located outside of B/6?  The CERM that I have does not go into detail about e greater than B/6?


Perhaps I'm misunderstanding what the CERM is saying, but it sounds like there are two different methods described: one for eL/6 which is uniform and reduced footing dimensions. It's on page 36-9 in the 2013.

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## geomane (Oct 19, 2016)

rfehr613 said:


> Do you need some kind of special access to view this? It is telling me it's blocked.
> 
> Sent from my VS980 4G using Tapatalk


Not that I am aware of.


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## rfehr613 (Oct 19, 2016)

jijir83 said:


> > 5 hours ago, rfehr613 said: 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. Sent from my VS980 4G using Tapatalk
> 
> 
> Mmm.... Ok. Yes, your markings reduce to the same. So you're bugged by being misled. You have to remember that this is about taking the test and passing and not about our OCD engineering tendencies. The pipe "must flow full" means and is an indication to "use the full pipe equation". The solution is "most nearly" means "We, test writers, are too lazy to give you an exact number so pick the closest value". It's just another way, if you don't know your stuff, to throw you off and make you think that you made a mistake. Next thing you know, you might use a different equation and might pick the wrong answer if you lack confidence.Part of the exam is learning to take the exam. One of the first things that a review course instructor, like the ASCE ones will do, is bring your attention to these "most nearly" and things (i.e. assumptions to make unless otherwise stated) that are strictly for exam sake. For all intended purposes, that 16-in pipe is flowing full. If they gave you 14, 15.56, 16 and 17, you better pick 15.56. If they give you 14, 15, 16, 16.7, you better pick 16 and not 15 or 16.7. Your goal is to pass within the confines of this test.
> ...


This isn't about being OCD. This is about them being wrong. There's a difference between making a problem tricky and making a problem intentionally misleading and contradictory. I admit i am not well versed in water resources, but this isn't something that should ever be on a test (probably why it's not anymore). It's designed to get people stuck even when they have the right answer. And on that, i think a question like this is more likely to confuse someone who actually knows this stuff well, rather than someone like me who doesn't. I can do the structures problems in my sleep, but when i run into the structures equivalent to problems like this, which there are plenty of, i still sit there and question myself because i know what I'm doing, but my answer doesn't make sense. I've come to realize this test has nothing to do with technical knowledge. It's like a series of riddles with a timer. How does that prove anyone is a qualified engineer? It doesn't. I know plenty of people with PEs that i don't think should ever have been given a license. But whatever, I'm willing to play this game to get my license. Its not exactly news to me that this test is all about tricks and time management. But in order to make sure i can beat it, i need to understand it. It's hard to do that when the questions and solutions are contradictory or flat out wrong. Look at my other examples. These mistakes shouldn't happen.

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## rfehr613 (Oct 19, 2016)

rfehr613 said:


> > > 38 minutes ago, rfehr613 said: The solution assumes a triangular pressure distribution with a reduced footing area. The CERM, like other references I've seen, assumes a uniform pressure distribution over the reduced area. Sent from my VS980 4G using Tapatalk
> >
> >
> > What section of the CERM are you looking at for if located outside of B/6?  The CERM that I have does not go into detail about e greater than B/6?
> ...


Sorry, the board seems to have cut off my post. Maybe they don't like the greater than and less than signs? Or greater than or equal to? Anyway, what i was trying to say is that there appears to be two different cases in the CERM.

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## kaf21 (Oct 20, 2016)

rfehr613 said:


> Sorry, the board seems to have cut off my post. Maybe they don't like the greater than and less than signs? Or greater than or equal to? Anyway, what i was trying to say is that there appears to be two different cases in the CERM.
> 
> Sent from my VS980 4G using Tapatalk


That is the same section and page I was looking at.  To me it does appear to go into detail about the method for e greater than B/6 other than stating negative soil pressure will result.  Either way, I believe eccentric loading of a footing like this would always have a triangular load.


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## geomane (Oct 22, 2016)

rfehr613 said:


> Sent from my VS980 4G using Tapatalk


I get B, 98 feet. You are using an equation that doesn't take into account the downhill gradient.

Thinking about this problem logically, do you think you can stop your car on steep slope as fast as you can on level ground?


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## JHW 3d (Oct 22, 2016)

Jmcc06 said:


> > On 10/15/2016 at 10:19 PM, rfehr613 said:
> >
> > Sent from my VS980 4G using Tapatalk



I haven't done the math, but agree the approach in pencil marks is wrong. The problem statement only shows decel rate for downhill portion, not for level portion.

_Update:_

I calculate *70ft (A). *

a_flat = 11.2 + 32.2*.06 = 13.13 ft/s^2

s_flat = 10,540/(2*13.13) = 401.4 ft

s_downhill is 470.5 ft (your calculation)

Diff = 69.1 ft (70 ft)

What's the solution list as the answer?


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## geomane (Oct 22, 2016)

The NCEES solution is B.


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## rfehr613 (Oct 22, 2016)

JHW 3d said:


> > > On 10/15/2016 at 10:19 PM, rfehr613 said:
> > >
> > > Sent from my VS980 4G using Tapatalk
> 
> ...


Ok, well that is a horribly worded question then. It reads as both having said deceleration rate, not one of them. I hope the real test isn't this much of a disaster.

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## JHW 3d (Oct 22, 2016)

rfehr613 said:


> > > > On 10/15/2016 at 10:19 PM, rfehr613 said:
> > > >
> > > > Sent from my VS980 4G using Tapatalk
> >
> ...


What is their reported answer?


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## geomane (Oct 23, 2016)

Can someone post a picture of the NCEES solution for problem #132?


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## rfehr613 (Oct 23, 2016)

Jmcc06 said:


> Can someone post a picture of the NCEES solution for problem #132?


I got out of bed just to take a picture of this for you. I haven't even reviewed it myself.






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## geomane (Oct 23, 2016)

rfehr613 said:


> I got out of bed just to take a picture of this for you. I haven't even reviewed it myself.
> 
> 
> 
> Sent from my VS980 4G using Tapatalk


Lol thanks @rfehr613.


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## JHW 3d (Oct 23, 2016)

rfehr613 said:


> > Can someone post a picture of the NCEES solution for problem #132?
> 
> 
> I got out of bed just to take a picture of this for you. I haven't even reviewed it myself.
> ...


Thanks for the solution. Agree that the wording is confusing. I associated the decel rate given with the downhill condition. Oh well.


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## ptatohed (Oct 26, 2016)

You know what's scary about errors in the NCEES Sample Exams?  These are supposedly (not supposebly, but supposedly) real questions taken from actual exams.  So, some poor saps at some point in time had errors in their exam's questions/answers and NCEES did not know about it.


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## rfehr613 (Oct 26, 2016)

ptatohed said:


> You know what's scary about errors in the NCEES Sample Exams?  These are supposedly (not supposebly, but supposedly) real questions taken from actual exams.  So, some poor saps at some point in time had errors in their exam's questions/answers and NCEES did not know about it.


This is what I'm saying. Look at these examples... they're terrible. I don't have a lot of faith in the real test being much better.

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## ptatohed (Oct 27, 2016)

rfehr613 said:


> This is what I'm saying. Look at these examples... they're terrible. I don't have a lot of faith in the real test being much better.
> 
> Sent from my VS980 4G using Tapatalk


That's ok.  All you have to do is pass.


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## rfehr613 (Oct 27, 2016)

ptatohed said:


> > On ‎10‎/‎26‎/‎2016 at 9:39 AM, rfehr613 said: This is what I'm saying. Look at these examples... they're terrible. I don't have a lot of faith in the real test being much better. Sent from my VS980 4G using Tapatalk
> 
> 
> That's ok.  All you have to do is pass.  [emoji6]


We'll see how it goes tomorrow

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## gpoli111 (Apr 11, 2017)

I'm bumping this thread. So NCEES posted an errata to #509 addressing that the correct torsion is obtained through the shear center but they don't show how to calculate the SC. They just give the location as 15.5 in from the left end. Can anyone direct me on how they got 15.5"?


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## gpoli111 (Apr 12, 2017)

Nevermind, I realized that the shear center of the section is a given for the problem in the errata.


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