NCEES problem #119

[chess5329]

I would like to have some help to undestand this concept. Below I wrote the sum of Ad2 for each section, I want to check if I did the calcs well.

• A) sum Ad2=35.25 in4
  
• " " = 36.75 "
  
• C) " " = 54 "
  
• D) " " = 90.37 "
  

So, D is the strongest section, the solution in the book doesn't explain very much how to get to this result.

If I'm doing something wrong I would appreciate your help.

Thanks in advance.

 

[biofem2011]

My understanding of this question is that the section with the highest I provides the greatest flexural rigidity (EI). I don`t have my calc close by but when I did it, I calc the I about x-x (E is the same for all) and also got (D) as the highest.

Besides, I`m not a structural babe

 

[chess5329]

My understanding of this question is that the section with the highest I provides the greatest flexural rigidity (EI). I don`t have my calc close by but when I did it, I calc the I about x-x (E is the same for all) and also got (D) as the highest.

Besides, I`m not a structural babe

Well, could you provide your cals for each section, or any structural that want to help me?

Thanks

 

[Ble_PE]

I don't have the NCEES sample exam you are talking about, but it sounds to me that you are calculating the moment of inertia for various sections based on the parallel axis theorem. If you have the CERM (and you should!), page 42-4 has a section about this theorem. In terms of why the correct answer is the highest value, with all other things being equal, the section with the highest moment of inertia will always be the strongest section.