SE Practice Exam Problem Questions

[Br_Engr]

Good morning -

Full disclosure - I practice in the bridge field, so I am re-acquainting myself with some of the provisions of AISC. Forgive me if these seem 'basic', but rest assured that, if successful, I have no intention of dabbling in the "dark arts" of the building realm...

1. I was working a practice exam for the upcoming SE and had a question about the base plate design problem (AM Vertical; Problem 121)

First, NCEES did not provide the column section in the problem statement, but that is a QA issue. My question is in the solution. Did they omit the 'omega' factor for computing "X"? It seems that a 2.31 factor is missing and this would seem to blow the problem up.

2. Solved a wind problem (AM Lateral; Problem 102) using the "Directional" method. Solutions used the "Envelope" method. Same answer. Question is when to use one over the other? Logic says use directional when there are ground conditions differ depending on direction of wind (i.e. hills to the east, open ground north/south (like a valley).) I am assuming that if they want you to use the direction procedure on the exam, they will give you the varying conditions. If the problem is phrased "generically", envelope is the way to go.

Thank you in advance for any help you may provide.

 

[organix]

Full disclosure, I didn't do this practice exam... Also, it sounds like our versions of the practice exam are the same, but I actually think I have a previous version (2014 printing).  So maybe you have a newer one.

With that said:

1.  My problem statement does have the column size actually.  Verify you did not miss it.  It is in the design data next to the effective column length.  I am not sure where Pn/omega comes from in the solution.  It appears they incorrectly used a W12 instead of the W14 (well, I'm sure they did in my solution).  But this shouldn't be based on the nominal compressive strength of the column to begin with.  It should be the concrete bearing strength unless I am missing some exception in the code.  Anyway, lets just assume the value is correct, it already has omega in it and that's they didn't add it in the calculation of X.

2.  Problems will generally tell you what you need to use if it is critical information. At least they should tell you.  In this case, it doesn't matter what method you use because it's only asking for the wind velocity pressure which doesn't have any pressure coefficients.  Those coefficients are really what separate the methods.  Do note that the envelope procedure will produce a different Kz for exposure B at heights less than 30 ft.

 

[Br_Engr]

No section given.

Looking at other samples (AISC V15.1 - Design Examples and the Anchor Bolt and Base Plate Guide) they use Omega = 2.31 in the numerator of the X equation.

 

[Br_Engr]

I did find the "Errata" where they provide the column section in the problem statement.

But there was no correction for the "Omega" factor in the solution.  What am I missing?

 

[organix]

So what I am assuming happened is they deleted the column information because it was incorrect to use to calculate Pp. 

My version of the problem shows a W14x53 with an effective length of 12' instead of the concrete information you have.  The solution was incorrectly using the column compressive strength for Pp so they must have "corrected" it by replacing it with the concrete compressive strength.  They made two mistakes when they did that.

1. You still need the column size for the problem so they shouldn't have deleted that.
   
2. It sounds like they also didn't update the solution correctly to consider omega.  They previously used Pn/omega from the SCM Tables.
   

 

[EBAT75]

I wish to know whether anyone knows if the solution to problem 105 - Lateral SE Samples 2011 edition is correct or if an erratum was published. For the older sample exams errata are now not available on NCEES website.

 

[psustruct]

I have that 2011 sample exam, and I posted the errata. That problem was not part of the corrections.

 

[EBAT75]

I have that 2011 sample exam, and I posted the errata. That problem was not part of the corrections.

Thank you psustruct for the information. Much appreciated. I realized later this is a longitudinal case and is solved correctly.