NCEES Practice Exam Problem 801

[lhpriest]

In this problem, the out of plane shear stress is checked at the base of the parapet for wind load perpendicular to the wall.

I am a bit confused on the correct calculation for the shear area. In the solution the shear area includes the face shell plus the half the area of the grouted cell (since the rebar is centered in the wall.) This seems to make sense since only the face shells are mortared.

I referenced an example in the Masonry Designers guide that had a similar check for out of plane shear. In this case, the shear area was taken as "bd." Where 'b' is taken as a 1'-0" strip and d is taken as 3.81" since the reinforcement is centered. This example was almost identical to the practice exam question except that #5's are spaced at 32" o.c. It seems that the full depth could only be used if the webs were also mortared however this was not specified.

Another example in the Masonry Designers Guide has reinforcement at 16" o.c. and uses "bd" as the shear area. The difference in this case is that 'b' is taken as a 1'-0" strip and d is taken as 2 x face shell thickness.

Thanks in Advance!

 

[colostructural]

The NCEES solution to that problem confused the hell out of me and I think it is incorrect (though I did include their methodology in my notes). Masonry TEK-4 states that the net area should be used in the calculation of unreinforced masonry. (BTW - for anyone reading this...Make sure to download TEK-14-1B it will make life somewhat easier). In my line of work, we typically use solid grouted CMU everywhere so I am always just using beff*d. But after an hour of googling I found the link below.

See page 5 of the pdf below for the figure - which shows the grouted cell, inside and exterior web, and both face shells included:

http://www.emcoblock.com/pdf/divisions/bri...-properties.pdf

Either way, why would it just be one face shell and not both??

 

[lhpriest]

The NCEES solution to that problem confused the hell out of me and I think it is incorrect (though I did include their methodology in my notes). Masonry TEK-4 states that the net area should be used in the calculation of unreinforced masonry. (BTW - for anyone reading this...Make sure to download TEK-14-1B it will make life somewhat easier). In my line of work, we typically use solid grouted CMU everywhere so I am always just using beff*d. But after an hour of googling I found the link below.
See page 5 of the pdf below for the figure - which shows the grouted cell, inside and exterior web, and both face shells included:

http://www.emcoblock.com/pdf/divisions/bri...-properties.pdf

Either way, why would it just be one face shell and not both??

Thank you very much for the input and the .pdf. If given this type of problem in an exam situation, would you stick to the NCEES methodology or the more correct methodology? I would be nervous that full credit may not be awarded for approaches other than what is shown by NCEES.

 

[colostructural]

I will most likely use their methodology and write in my book something along the lines of "this is what you jerks did, so I am doing the same - please don't fail me!"

 

[lhpriest]

I will most likely use their methodology and write in my book something along the lines of "this is what you jerks did, so I am doing the same - please don't fail me!"

I like it.