Shear Capacity of Dowels in Masonry Wall

[Qrs]

How do you determine the shear capacity of dowels in a masonry wall? Let's say I have a 10' cantilever wall in a seismic area (so i cannot rely on friction for shear resistance.) How do I determine the capacity of the rebar dowels at the interface between the masonry wall and the concrete slab? I cannot seem to find anything in the masonry code. A textbook I have says to conservatively use values for anchors. Is this typical?

Thanks.

 

[RFreund]

Which textbook?

It's interesting because the dowels are there to ensure there is contact between the two surfaces and ACI also states that additional reinforcement should be added if there is net tension across the surfaces. Also I don't believe ACI Chapter 21 prohibits its use but I don't think Chapter 21 comments on this at all. Having said that, I would have initially thought to use the dowels as anchors, as your textbook suggested, but EQ rarely 'controls' for me. I'm sure someone who does more seismic work can comment...

EIT

http://www.HowToEngineer.com

 

[DST148]

@Qrs>> I have an older version of Canadian Masonry Code(1994) which is based on Limit State Design.
Per section 11.5.6, Factored Sliding Shear resistance of Masonry walls:
Vr = (Phi) * (Coeff. of Friction) * C

C = Comp Force in the masonry normal to sliding plane; normally taken as axial load + yield strength
of vertical reinforcement.

Coeff. of friction = 1.0 for masonry to masonry or masonry to roughened concrete slide plane
= 0.7 otherwise

 

[Qrs]

RFreund: I am looking at the Reinforced Masonry Engineering Handbook by the Masonry Institute of America. It's only weird because it doesn't discuss dowel capacity at all, but quickly says "conservatively use anchor capacity" without much explanation. (Me asking myself, why is this conservative?)

DST: I agree with what you have said, but that is relying on the frictional forces between the masonry and the slab. If EQ controls, ASCE 07 states "component attachments shall be bolted, welded, or otherwise positively fastened without consideration of frictional resistance produced by the effects of gravity." Basically in case the wall jumps off the slab during the EQ? I am confident the rebar dowels can accomplish the attachment, I am just unsure as to how to gauge their capacity accurately.

 

[a2mfk]

Having designed a lot of high shear CMU walls I still can't imagine this every being a controlling factor, but that is for wind and not seismic codes. But say you ignore bonding of grout and mortar at the base to the foundation, and only rely on the rebar, then to check a shear failure I would agree with the recommendation to design it as you would an anchor bolt or headed stud at the top of a wall, assuming you have fully grouted CMU. I would probably put a bond beam in the first course to have a continuous piece of rebar along the interface.