Will.I.Am PE
Well-known member
This information may be buried in this forum, somewhere. I couldn't find it, though.
I'm looking at the NCEES Sample Questions and Solutions, c.2008 and I'm wondering about two of the morning breadth sample problems that both focus on structures. (I'm taking the geotech depth, but I took a couple of structures classes in my bachelor's and master's degrees, so I'm somewhat versed in more complex details.)
Question 111 asks what the effect would be of changing the yield stress (Fy) of a steel beam from 50 to 36 ksi, while keeping all other factors the same. The answer choices are essentially, would the deflection increase, decrease, remain the same, or there isn't enough information given. I knew it had to be one of the latter two, given the available information. I'm under the impression that they implicitly assume the deflection must be elastic in the solution, because the "most correct" answer is that it remains the same. However, if you don't make that assumption and the stresses in the beam fall between 36 and 50 ksi, the beam would experience plastic deformation and defections would increase. No information is given about the loading or stress states, which leads me to believe that, in reality, not enough information is given. Is this problem slightly bogus, or am I missing something?
The very next problem, question 112, asks what the most efficient steel section would be for a beam with a span of 20 feet and an unbraced length of the compression flange of 20 feet. The answer choices are a square HSS, a channel, a wide flange, and a double-L/T section. When I read the question, I figured that it had to be alluding to a more complex concept, but had no idea what it might be. After I saw the solution, it was obvious that, unbraced length of the compression flange was the indicator that this was, indeed, a lateral torsional buckling problem. However, I really don't know how I would have recognized that from the outset. Are there any tips out there for recognizing the key words and phrases that indicate an implicit concept that's being tested?
This all ended up being kind of wordy, but I hope it's decipherable. Thanks!
I'm looking at the NCEES Sample Questions and Solutions, c.2008 and I'm wondering about two of the morning breadth sample problems that both focus on structures. (I'm taking the geotech depth, but I took a couple of structures classes in my bachelor's and master's degrees, so I'm somewhat versed in more complex details.)
Question 111 asks what the effect would be of changing the yield stress (Fy) of a steel beam from 50 to 36 ksi, while keeping all other factors the same. The answer choices are essentially, would the deflection increase, decrease, remain the same, or there isn't enough information given. I knew it had to be one of the latter two, given the available information. I'm under the impression that they implicitly assume the deflection must be elastic in the solution, because the "most correct" answer is that it remains the same. However, if you don't make that assumption and the stresses in the beam fall between 36 and 50 ksi, the beam would experience plastic deformation and defections would increase. No information is given about the loading or stress states, which leads me to believe that, in reality, not enough information is given. Is this problem slightly bogus, or am I missing something?
The very next problem, question 112, asks what the most efficient steel section would be for a beam with a span of 20 feet and an unbraced length of the compression flange of 20 feet. The answer choices are a square HSS, a channel, a wide flange, and a double-L/T section. When I read the question, I figured that it had to be alluding to a more complex concept, but had no idea what it might be. After I saw the solution, it was obvious that, unbraced length of the compression flange was the indicator that this was, indeed, a lateral torsional buckling problem. However, I really don't know how I would have recognized that from the outset. Are there any tips out there for recognizing the key words and phrases that indicate an implicit concept that's being tested?
This all ended up being kind of wordy, but I hope it's decipherable. Thanks!
