huangyhg

cmu/concrete foundation dowels
our office typically does not show reinforcing dowels between a concrete foundation wall and a reinforced cmu wall. this is for low seismic areas a or b.
we use the grout on top of the concrete wall to resist shear at the bottom of the wall. the rebar in the cmu wall is usually just there for bending strength mid-height in the wall. the cmu walls start at the floor height and are completely above grade.
i'm asking what other people think because i've gotten a lot of calls recently from contractors wondering if we missed something on our drawings. i assume everyone else must be using a dowel at the bottom and maybe they have a good reason for doing so.
we dowel all our vertical wall reinforcement to the foundation including additional jamb reinforcement.
aci 530-99 2.1.8.3.2 requires 25% positive reinforcement be carried into the support. although 2.1.8.3.1.3 says that it need not extend beyond the point it is needed at supports of simple spans.
i do not want the joint at the base of the wall opening under lateral load.
we add dowels. how do you resist the lateral wind forces on your wall? using friction isn't always a good idea.

we use dowels.
personally, i usually match the dowels size and spacing to the size and spacing of the cmu vertical bars. think this is just good practice.
i've always seen and shown dowels.
how do you tie down the ends of the shear walls without dowels?
dowels are required in our area. allowing for friction is disallowed.
i have aci 530-05 in front of me and i see the section jike is referring too. it says the 25% requirement is for walls that are part of the -lateral- load system.
i understand the positive moment reinforcing needs a certain development length beyond where it is needed. i think for a lot of walls the vertical rebar probably isn't needed at the ends of the span for flexure.
does anyone have a reference where dowel anchorage is needed if the wall is not a shearwall?
there is definitely some shear capacity in the mortar to concrete wall interface, right? mortar holds cmu to cmu, so it must hold cmu to concrete, right? otherwise how do unreinforced walls function?
i'm not saying i'm right. i'm just trying to figure out the code requirements, and why other engineers design the way they do.
thanks
using your same logic, i guess there's no need to extend concrete beam bars into the support. you should always use dowels for reinforced masonry. you can't design for bending as reinforced masonry, and shear as unreinforced masonry. you are definitely out of the mainstream on this one!
see aci 530 1.14.2.2.2 and 1.14.3.3. it seems that the intent of the code is to provide a mechanical connection between the wall and all locations of lateral support. you may be able avoid foundation dowels if you provide connection to a slab, but foundation dowels would be easier.
now the question is, how many of you use dowels into the foundation wall for unreinforced cmu walls?
when wind causes net uplift and horizontal shear, what shear strength remains at the junction of wall and footing if you are using grout with a horizontal surface?

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