new block wall on top of existing 4' footing

[marc.rogue]

I am working on a small project in which i have to put a block wall on top of an existing footing 4' deep.
The lead engineer in my firm recommended doweling in #5 8 in every 16" along the block wall.

My question is: Is there really a need for this? i was thinking doweling in every 4' (for every fill cell) for a depth of 14" and extend the doweled bar out 18.75" lets stay 20"
to lap with the filled cell reinforcement. I just don't see why this can't be treated as a regular footing/block wall?

Thank you

 

[HouseBoy]

I can see doweling every 16" if the wall is doing a lot of work (like it's a RETAINING WALL). Otherwise something between 16" and 48" would be my "starting point".

Are there ANY lateral loads on the wall?
Seems like that (loading) is the critical consideration for making the decision on spacing.

 

[marc.rogue]

Definitely not a retaining wall. It's in the Florida area so high speed winds of 175 miles/hour but at the mean roof height.
we are talking about 19 lb/ft2. My thinking is that it's just like any other block wall, why do I need to drill more holes to an existing slab?

 

[SWComposites]

Well, did you discuss the logic or analysis with your lead engineer?

 

[XR250]

Sounds like the boss is being overly conservative. Might want to ask him why the need for rebar so often. Probably what you are suggesting is fine. I would lap 24" not 20" though.

 

[marc.rogue]

Most times on an iffy subject the answers are not real answer just something along the lines of, we have always dont it that way.
After checking the lap length for bars in compression .0005*Fy*db its 18.75" so i bumped it up to 20

 

[BridgeSmith]

If you're lapping the bars to resist bending loads on the wall (lateral loads on the structure above), the tension lap length would be the proper one to use. However, if you're only going up 4', it seems like a waste to lap them at all, instead of just extending the dowels an extra couple of feet.

Sometimes, there's wisdom in doing what's been successful in the past, but ultimately the decision on spacing comes down to who's sealing the design. If it's you, I'd recommend you make darn sure you understand why your lead engineer thinks you need the tighter spacing before you go a different direction and take responsibility for it. If the lead engineer is sealing it, you'll need to use the closer spacing, unless you can show him or her that it's not necessary, and get agreement on that.

Rod Smith, P.E., The artist formerly known as HotRod10