Masonry Clarification

[VAStrEngr]

I am working through a reinforced running-bond masonry wall design for wing pressure coupled with a vertical load component and I am having trouble understanding one aspect of the MSJC codes.

In section 2.3.3.3.1, it specifies a width of compression area used in stress calculations. Is this the "b" term used when determining Axial, Shear, and Flexural Compression? If so, then you are not supposed to design the wall based on a 12" section?

If you design for the "b" term width, then I am guessing you would use the pressure over that width in determining your forces and/or moments?

If you design for 12", then I am assuming you have to ensure you use a proportionate area of steel reinforcing in that section?

To me, it seems as though these would result in the same stresses...one based on a larger section with larger loads and consequently larger area of steel...the other on a smaller section with smaller loads and a percentage of the reinforcment area.

Am I correct?

 

[Lion06]

That is limiting your effective section properties. Don't calc them by hand, just use the section properties from NCMA based on your reinforcement spacing with a 12" wide section of wall.

 

[VAStrEngr]

Makes sense...so what then is the 'b' term in the code book referring too?

 

[Lion06]

"b" in 2.3.3.3.1 or at another location?

 

[steellion]

Similar to concrete, it can be either. Set b=12" to get your As/ft or set b= total or effective width to get the As required for that section.

For in-plane flexure and shear of a partially grouted wall, you need to determine your effective width of the wall "b" based on the effective section properties.

 

[Lion06]

NCMA gives the net section properties per foot of width, so you should always use b=12" for a wall.

 

[steellion]

SEIT, I agree, for out-of-plane loading.

For in-plane loading, the equations are similar, but b= wall thickness. b=full wall thickness if grouted solid, average wall thickness if partially grouted.

 

[Lion06]

I assumed we were only talking about out of plane loading. For shearwalls, I would always makes sure the ends are grouted such that all cells within the kd distance are fully grouted and use the thickness
as b.

 

[VAStrEngr]

Yes, out of plane loading is what I was referring to.

StructuralEIT, I see your responses everywhere on this board and you are usually spot on...how come your still an EIT?!

 

[Lion06]

Thanks for the compliment. I am taking the PE for the first time on Friday - I only have 4 years under my belt.