Masonry Reference Question

[Titleistguy]

Anyone who is using the following reference, "2015 Design of Reinforced Masonry Structures" (Concrete Masonry Association of California and Nevada), I have a question for you:

Page 146, 2nd column, has the final steps of example 4.4.3, (Min & Max reinforcement in a concrete masonry shear wall) -- My question is this, the problem statement goes out of its way to state it is SDC D, which automatically puts in you special reinforced masonry shear wall category (SRMSW).  The problem concludes that 2-#4's @ 24" are required for horizontal shear reinforcement, ok fine.  And it goes on to discuss the final checks for the overall steel reinf. ratios, and the one check that reads as follows is where my question is:

"For the sum of the horizontal and vertical reinforcement: 0.0014 + 0.0047 < 0.002, therefore ok …"

My issue isn't where those numbers came from , its the fact that the check is only considering a total of 2 #4 bars, and for a wall of this height (14'-0"), and given the SRMSW requirements for horizontal steel at no more than 48" OC, then there would need to be at least a couple more rows of bars to complete the reinforcement requirement.  However, the check, the 0.0014 number only accounts for two total bars for all the horizonal steel, while the 0.0047 accounts for ALL OF THE VERTICAL steel as one would expect.  So my issue is this:

Are they not complying with the SRMSW min. steel detailing requirements?  If not, that is ok, it would just be nice if that problem stated as such, or is it because its an example problem, and not necessarily germane to the example to provide all the detailing that they didn't -- which doesn't make sense as those numbers are required for the final steel ratio checks.

Do anyone have any thoughts on this?

Thanks,

TG.

 

[AlexPE]

Think of a cmu wall like a cantilevered beam. Height of the wall is like the span length of the beam. Cross section is always length of the wall x thickness. Vertical bars are your long reinf and horiz bars are like your stirrups.

As in a beam, your horiz reinf is calculated over a spacing required to resist shear. In a cmu wall this is usually found as an area of steel per foot of height.

Sorry if thats not it, I dont have the TMS in front of me and thats the best reason I can think of right now. If it were a textbook, Id say most likely its an error, but youd think theyd make sure to get code manual examples right.

 

[ChaosMuppetPE]

Anyone who is using the following reference, "2015 Design of Reinforced Masonry Structures" (Concrete Masonry Association of California and Nevada), I have a question for you:

Page 146, 2nd column, has the final steps of example 4.4.3, (Min & Max reinforcement in a concrete masonry shear wall) -- My question is this, the problem statement goes out of its way to state it is SDC D, which automatically puts in you special reinforced masonry shear wall category (SRMSW).  The problem concludes that 2-#4's @ 24" are required for horizontal shear reinforcement, ok fine.  And it goes on to discuss the final checks for the overall steel reinf. ratios, and the one check that reads as follows is where my question is:

"For the sum of the horizontal and vertical reinforcement: 0.0014 + 0.0047 < 0.002, therefore ok …"

My issue isn't where those numbers came from , its the fact that the check is only considering a total of 2 #4 bars, and for a wall of this height (14'-0"), and given the SRMSW requirements for horizontal steel at no more than 48" OC, then there would need to be at least a couple more rows of bars to complete the reinforcement requirement.  However, the check, the 0.0014 number only accounts for two total bars for all the horizonal steel, while the 0.0047 accounts for ALL OF THE VERTICAL steel as one would expect.  So my issue is this:

Are they not complying with the SRMSW min. steel detailing requirements?  If not, that is ok, it would just be nice if that problem stated as such, or is it because its an example problem, and not necessarily germane to the example to provide all the detailing that they didn't -- which doesn't make sense as those numbers are required for the final steel ratio checks.

Do anyone have any thoughts on this?

Thanks,

TG.

TG, I think what is confusing you is the fact that it is a ratio. As a ratio As/bd, it does not change whether you take it over spacing or the whole wall as long as you are consistent in your calculation. I don’t have the problem or the book, so maybe I could be wrong. Just my 2 cents. I was also thinking that the sum of those two ratios had to be greater than 0.002 from memory of the TMS. But again, it’s not in front of me.

 

[Titleistguy]

First off, thanks all for the responses.

FutureSE, I agree, and yes 0.002 is the check on this.  I went through and did it by hand and verified that it works.  What is confusing is the way they calculate it, they use the WHOLE wall and ALL the steel for the vertical roe, and just the typ horiz bars at the typ spacing for the horizonal roe, and that is what confused me.  From a teaching stand point, I'd show one formulation, or the other, and not mix them.  But anyways thanks again for the reply.

 

[ChaosMuppetPE]

First off, thanks all for the responses.

FutureSE, I agree, and yes 0.002 is the check on this.  I went through and did it by hand and verified that it works.  What is confusing is the way they calculate it, they use the WHOLE wall and ALL the steel for the vertical roe, and just the typ horiz bars at the typ spacing for the horizonal roe, and that is what confused me.  From a teaching stand point, I'd show one formulation, or the other, and not mix them.  But anyways thanks again for the reply.

So just another random thought late into a night of insomnia, but I'd say the vertical steel is over the whole wall so as to place the minimum number of bars. The SRMSW requires one third the roe of the horizontal steel for the vertical steel. It makes some semblance of sense to me at this moment.