PE exam steel beam Cb value

[13bob1313]

This should be simple, but there seems to be different ways to go about it. On the latest practice exam there is a question asking you the allowable capacity of a steel beam, braced at midspan, with a point load. The solution provided determines the LTB capacity of the beam to get the answer. However, it assumes cb=1.o, which it is not if you calculated it out. If you use the correct Cb value, yielding actually governs. But you would get the wrong answer. Does anyone know if this is standard on the exam to assume Cb=1.0? You know there will be one steel beam question, and it should be free points, but this is bothering me. Thanks.

 

[KootK]

I'd stick with the technically correct answer. I believe that,
when they score the exams, they look for instances where many candidates make the same "error" and reevaluate. Trying to game the system in the direction of less technically correct answers seems clumsy and more risky to me.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[13bob1313]

Thanks for the reply. I would hope it will be more clear on the actual exam. Just concerning because this is the NCEES practice exam, which is supposed to be based on actual exam questions. The fact that they give you a load diagram would make me think they expect you to determine the Cb value....Oh well, can't fret over something like this I guess. Thanks.

 

[TehMightyEngineer]

Agree with KootK. The sample exams are problems that were not used on the exam for a reason (or at least, that's what I've been told).

If a bunch of engineers show that the "correct" answer isn't really correct then they will likely reevaluate the question. And they do make mistakes, I've seen it on at least one SE exam that had a typo where dimensions didn't add up.

Just try to solve it the "most correct" way. By "most correct" I mean that if they specifically ask for the lightest beam that can support a load then you better be using Cb.

Maine Professional and Structural Engineer.

http://www.fepc.us

(Just passed the 16-hour SE exam, woohoo!)

 

[KootK]

Oh well, can't fret over something like this I guess.

Exactly. The most important thing to do with ambiguous questions will be to get through them as fast as possible so that you can focus your efforts on questions where the ROI is better.

When I wrote the PE, I did take a few shortcuts where I felt that the technically correct answer would have just taken way too much time to be reasonable.

One example that sticks out in my mind is a question where I was asked to determine the axial force in a diaphragm chord splice connection. The question pointed to a location at the 1/4 point of the diaphragm. Most engineers would just use wL^2/8d everywhere and be done with it.

WL^2/8d was one of the available answers. However, the more accurate 1/4 pt answer was not. I spent 15 minutes on that when I only had five budgeted for it. It was poor execution on my part regardless of whether or not I got the point.

On the flip side, there was a question that I saw in a practice exam where you had to calculate the soil bearing pressure beneath an I-shaped footing connecting two columns. Two pads and a strip footing. Any sane engineer would tackle this ignoring the strip footing. The correct answer on the exam required one to use the Sx of the the entire I-shape however.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[racookpe1978]

If something similar occurs on the exam question, TELL THEM.

Obviously, and first ofall, re-check your own assumptions and constants and process.
Then, if you still find a difference (or discrpanacy between a value they assign (or assume) and what you find is correct, write the problem up in your answer.
List your variables and your references (including page nbr and table ID or formula) and the version of the references you are using. Write what your answer was, what other things might be correct - or might be incorrect - and where you'd go to look up more data.
Write up what their answer was, and why you disagree with it.

Happened on my exam for nuke engineer. Came up with a heat transfer answer basically calling for a pool of ice around the reactor to remove the heat they claimed was present some-and-so many minutes after shutdown. Listed the problem, their statements on vessel diameter and concrete thickness, what I looked up for concrete thermal properties, what I used for earth and air heat transfer values, core power factors and the like, etc.

Wrote what I thought was wrong with the problem statement, the assumed dimensions, and why the calculated answer could not be valid. Worked backwards from the probable answer to a more likely diameter, and showed why this problem needed to be reviewed and checked.

Passed the exam.

Passed.

 

[SLTA]

I found several problems in the sample tests. Those aren't perfect. Call NCEES or get online and see if there's an updated version.

Please remember: we're not all guys!

 

[13bob1313]

Thanks for the responses. Feel much better knowing they review these questions after the fact, and people can write in to tell them of any issues. If anyone feels like responding to another question: in general is the NCEES provided practice exam a pretty good indicator of the test difficulty? I felt the morning portion was much easier than the afternoon. Again, thanks.

 

[KootK]

in general is the NCEES provided practice exam a pretty good indicator of the test difficulty?

I thought so.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[TehMightyEngineer]

In general is the NCEES provided practice exam a pretty good indicator of the test difficulty?

Yes, it is quite accurate to the actual exam.

Except the sample exam fails to convey that the topics you may see are limited only by the NCEES syllabus. Thus, you may find that you know the topics well that the sample exam covers but the actual exam has a problem you're not as skilled at solving. This can create a disparity in difficulty between the real and sample exams. For example; I found the lateral afternoon problem of last years exam to be what I expected but the other test takers expressed that they thought them harder than they expected.

Maine Professional and Structural Engineer.

http://www.fepc.us

(Just passed the 16-hour SE exam, woohoo!)

 

[NOLAENG]

in general is the NCEES provided practice exam a pretty good indicator of the test difficulty?

I just passed the PE/Structural exam. The sample exam is a good indicator and the design problems were pretty comparable to the actual exam. But one piece of advice I would give is to know NCEES can/will ask anything from the design codes. It might be some small clause in the fine print too. This really bugged me during the exam since I didn't feel it tested whether I was a capable engineer. What's the point in asking a code specific question that maybe 5% of the examinees use on a regular basis? Anyway, just make sure you know all the code sections even if you don't use them during your studying and good luck.