# M/Vd with Allowable Stress Design



## McEngr (May 25, 2010)

M/Vd will change if V is considered with an ASD 50% increase (per IBC chapt 21) when multi-story is considered. Has anyone dealt with this issue? The M/Vd is typically Vh/Vd which boils down to an aspect ratio issue for determining the Fv equation. However, when M/Vd has a multiplier of accumulated stories with a 50% V increase, all of this changes. Is the purpose of the M/Vd only for an aspect ratio of shearwall? Thanks in advance.


----------



## Hromis1 (May 25, 2010)

McEngr,

Oddly I just ran the same calc yesterday at work. It was the first time I have ever come accross the issue on a project. It was for a small masonry building that was both a SDC "D" and had to take 150 mph winds.

I came to the same conclusion as you for my simple project....(very heavy rigid roof on a small building with significant "e").

Do you have the SH Ghosh masonry design sheets? using these I take this calc is the first step in determining which equations from the MSJC are applicable for allowable shear. (2-21, 2-22, 2-24 or 2-25)

However as I look again at the equation....it only cites "M" in the shear wall. M being the maximum moment in the wall. Are you looking at this as the moment from the eq forces? or as the total moment from EQ and deadload counter acting the overturning moment?

...However, watch out for section 2107.5...the last full paragraph....all the splice lengths are also modified. Some of this is a dramatic difference...The splice lengths ended up driving the design.


----------



## McEngr (May 25, 2010)

Hromis1 said:


> However as I look again at the equation....it only cites "M" in the shear wall. M being the maximum moment in the wall. Are you looking at this as the moment from the eq forces? or as the total moment from EQ and deadload counter acting the overturning moment?


This is the main issue for me in my understanding. I should probably look at the commentary to make sure.


----------



## Hromis1 (May 26, 2010)

McEngr said:


> Hromis1 said:
> 
> 
> > However as I look again at the equation....it only cites "M" in the shear wall. M being the maximum moment in the wall. Are you looking at this as the moment from the eq forces? or as the total moment from EQ and deadload counter acting the overturning moment?
> ...


McEngr, I tend to design Masonry as ASD....I was looking for something else in the strength part of the MSJC...You might want to look at section 3.3.3.5.1 etc....The additional requirements here surpised me...much more than an aspect ratio...Hromis1


----------



## Hromis1 (May 27, 2010)

I'm having a Homer Simpson moment here. DUH!The title of your question was specific to ASD design. And yes, I am not clearly understanding the implications other than to determine the allowable stress levels.

This was a very good question. It made me look at the strength design portion of the code. Quite a difference in this case.

Thank You. I wish more people would ask questions like that. I learned a lot from it.


----------

