huangyhg

vertical wall reinforcment
i've got questions regarding an existing 12' tall 12" cip basement wall i've been asked to analyze. the wall is grossly under reinforced with #4 @ 24" e.w. located in the middle of the wall. the wall has a keyway at its base. the wall shouldn't be standing. the question i'm trying to answer is how is it. they used a "sand" for backfill material which i presume means a pit run river sand.
first, does anyone know of published literature or research on wet installed dowels (aci term from aci 332.1r-06 section 3.8.6)? this is when vertical reinforcing and/or dowels (no hooked ends) are stabbed into the footing after the concrete is place but before initial set as occurred.
second, any thought on the possibility of applying aci 318-05 section 14-8 alternate design of slender wall in this situation?
lastly another possibility is chapter 22 "structural plain concrete" which i haven't done yet.
safe to say there won't be a ductile failure. any shared thoughts will be greatly appreciated. thanks
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look at ibc table 1805.5(5) for foundation walls. for 10' tall walls, no reinforcement is required for an 11.5" thick wall with 30 psf/ft soil loading. it does not seem to me that this is necessarily "grossly under reinforced".
do the analysis. sand is a good backfill. if it was compacted properly, it can be great. if there are sumps and drain tile, there will not be hydrostatic pressure.
i definitely don't think this would be a slender wall. 12' tall, 12" thick is not slender.
the minimum reinforcement requirements for walls may be waived if an analysis shows adequate strength and stability (per aci). one layer of reinforcement is all that is required for walls up to 10" "except basement walls". there is a good chance this wall is standing because it has plenty of capacity to carry its loads.
if you are in a high seismic area, those requirements may govern...
it's still standing for a number of reasons-
is it a cantilever or is it restrained at the first floor level?
the load factor for soil is 1.6. the wall is likely not seeing that.
the location of max moment has compression on it (at the very least from self-weight) which is helping it out. did you account for that?
there is likely some small degree of fixity of the wall to the footing which further reduces the positive moment.
depending on the aspect ratio, it could be benefitting from spanning two ways - the way you're assuming, and horizontally to the perpendicular walls.
the concrete strength is probably higher than you are assuming.
the wall doesn't know that it has a phi factor of 0.9 applied to its capacity.
i agree, the wall is ignorant and doesn't know it's supposed to be over loaded. the wall looks good without apparent cracks or rotation. more information about the wall is its actual a "pit" wall so it aspect ratio (z/h) is very small and thus i have been ignoring bi-directional moment distribution. the wall has a longitudinal cold joint 8'-0 above the base and axial load is only from self weight and plus occasionally truck loads. i've checked it as a pinned top & bottom beam which means the top must be supported by grating or diamond checkered plate. without factored loads and strength reduction it works, so when i previously wrote it shouldn't be standing i was being a bit facetious. seismic won't govern; it's located in the upper midwest.
if there is "some" fixity at the bottom goes to the heart of my question about the wet installed dowels. i'd really like to distribute moment into the base, but is just shear being transferred. i can't find anything discussing this matter even though i recall reading something about it a few years ago.
again, i really appreciate any and all comments except for any that may contain "you stupid @#$% idiot", but heck i'd probably like those too.
would it be possible to reinforce the wall using steel straps and hilti anchors?
best regards,
ba
i would check moment capacity at the base without worrying about the "wet installed dowel" issue, to see where you are at.
in actuality, probably a lot of dowels are installed as you describe, and most engineers don't worry about it.
daveatkins

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