NCEES Civil Morning Problem #116

[chotovec]

I went through the new Civil Construction sample exam booklet and I can't figure out why problem #116 multiplies a triagular area by 2/3rds. To clarify the problem is a gravity retaining wall where you are asked to calculate the FOS against Overturning.

Can anyone tell me why they multiply the value of the traingular section by 2/3rds? By doing so they are reducing the moment arm of that force to 2/3rds of half the base.

Thanks,

 

[jrf500]

I don't have this problem in front of me, but I worked it yesterday and know the one you're referring to. First of all, check the NCEES website for ERRATA.....this problem had a typo on it. If you didn't have the errata, go get it and I think it'll make sense.

If you already had the errata and are posting the question....They are breaking down the resisting moment (weight of the wall) into 2 parts. One is the square part of the retaining wall and one is the triangular. The triangular part needs to be multiplied by 2/3's of the triangle base to correspond with where that force is acting. Then the square part of the wall weight will be multiplied by the triangle base+1/2 the square base.

Hope this helps. I was beating my head against the wall forever on this one, so I was relieved when I found there was an errata correcting this problem.

Good luck.

 

[chotovec]

I don't have this problem in front of me, but I worked it yesterday and know the one you're referring to. First of all, check the NCEES website for ERRATA.....this problem had a typo on it. If you didn't have the errata, go get it and I think it'll make sense.
If you already had the errata and are posting the question....They are breaking down the resisting moment (weight of the wall) into 2 parts. One is the square part of the retaining wall and one is the triangular. The triangular part needs to be multiplied by 2/3's of the triangle base to correspond with where that force is acting. Then the square part of the wall weight will be multiplied by the triangle base+1/2 the square base.

Hope this helps. I was beating my head against the wall forever on this one, so I was relieved when I found there was an errata correcting this problem.

Good luck.

Thank you for the info. I didn't know about the Errata, but i have downloaded it and it matches my solution.... :woot: