NCEES SE II, EXAMPLE PROBLEM 260

[Hromis1]

Hi all, I am trying to work the NCEES, SE II example problem number 260. Have any of you worked this problem? There is quite a lengthy errata given on the NCEES web site.

The difficultly I am having is that I am agreeing more with the original solution than the errata. The problem (part a) has could calculating the moments in a beam that carries a slab on both sides. (I cannot located anywhere in the problem statement information as to if the slab is continous or simple spans).

No beam sizes are given, so you only have the center line to center line spans to work with. The original solution does the math in manner as if the slabs are continous. (adding 15% to the shear/reaction bearing on the center beam).

The errata treats the problem using the center to center spans, but does not add the extra 15%. (Big difference)

Granted both solutions never give you the beam dimensions, so both solutions start off in a some what conservative manner as you never have Ln.

The solution in the errata simply has the statement "since no member sizes are provided, use span lengths in lieu of clear spans".

The end result is a significantly lower moment the the beam being designed. (45 ft-kips)

I am having a hard time "swallowing" the errata solution. Any of you worked this problem yet?

 

[McEngr]

Hi hromis,

To answer your question: the moments are approximations for one-way slabs, which is already implied to be continuous throughout supports in the problem statement. Adding the 15% is not practical since the face of the beam would not be anywhere near it would be if the slab negative moment were to be at the center of the beam... afterall, the equation squares the length and make a huge difference for this condition. The errata was necessary for me because the original makes no sense at all.

 

[Hromis1]

McEngineer,

I do see your point, however it depends on the dimension of the supporting beam. If the beams were 18" wide, then comparing the two "methods" gives (Wx1.15x23.5), versus (Wx25) . 27.03W versus 25W....not much of a difference. (This is for the shear from both sides of the slab over the center beam)

I would have failed that question on an exam...I would have used (Wx1.15x25) = 28.75, and marked it down as a conservative approach since the beam dimension was not given.

In the real world, I would have already had a reasonable beam dimension in mind.

It is all about passing the exam though....

I am not sure the people grading the exam would understand this enough to give credit for the. problem.

Or am I thinking too hard about this, being stuck in the the SE 1 micro engineering approach?

Hromis

 

[Hromis1]

To anyone using the NCEES SE-II practice book......be careful!!!!....after careful examination of the building problems there are some real problems in the original solutions and the Errata....

Even in example building problem 450- the errata contains basic errors such as load combinations, or using the incorrect formula for forces under a footing with moments...

Shameful! ....This makes me afraid of the grading...If they can't get the example problems correct. How can they grade the exam fairly?

 

[McEngr]

To anyone using the NCEES SE-II practice book......be careful!!!!....after careful examination of the building problems there are some real problems in the original solutions and the Errata....
Even in example building problem 450- the errata contains basic errors such as load combinations, or using the incorrect formula for forces under a footing with moments...

Shameful! ....This makes me afraid of the grading...If they can't get the example problems correct. How can they grade the exam fairly?

hromis1, if you can handle the SE II problems, then you should do fine. I didn't study and I passed it. However, the SE III is a whole new ball of wax. I think I'll have to treat it like I'm craming for a college graduate exam because there are so many nuances to the ASCE that I now know I overlooked. Not to mention all of the seismic detailing/compactness/special equations pertaining to seismic, and overall lateral force resisting system problems in that test. I get overwhelmed thinking about it. Oh yeah... and all of the horizontal/vertical irregularities, the calculation of indeterminate structures, the ability to design by 2nd order seismic analysis, dynamic analysis, etc etc etc... Yes, the SE II practice exam has problems, but if you have found the flaws, you are better than most.

 

[Hromis1]

McEngr. My hat's off to you....I am trying to go through some of those higher level seismic design class problems now. My head hurts. I don't think they could have come up with a more contorted set of load equations if they tried. Good luck to you.

I can do most these problems, the issue is TIME!

I am going to have to open up my computer models and see how they handle this. No way can you do all this by hand and still be in buisness.

 

[McEngr]

I am going to have to open up my computer models and see how they handle this. No way can you do all this by hand and still be in buisness.

Agreed!