Dowel Bar Placement

[abusementpark]

A lot of times when we have L-shaped slab-to-grade beam dowel bars, the contractors prefer to "wet-stick" them during the grade beam pour, instead of the tying them to the grade beam rebar before the pour.

Is there any reduction in dowel capacity that should be taken if the dowel bars are placed in this manner? Does ACI comment on the matter? Any help would be greatly appreciated. Thanks.

 

[BAretired]

Yes, I would say there is a problem with that.

BA

 

[TXStructural]

The bars need to be tied into place. The reasons this is frequently done are:
1) ability to strike a flat surface with the screed, then insert dowels - just to make it easy.
2) the dowels do not have intersecting bars which can provide proper support to the free-floating dowels.

The solution is the addition of carrier bars to hold the dowels, and a bit more work at the screed. Otherwise, you have to use a have a piece of formwork to support the exposed portion of the dowels.

Tolerance on embedded length is -1 or -2 inches, depending upon bar diameter. If the bar is intended to develop tensile capacity, bond and development is critical, and this is only assured by proper embedded length and proper consolidation around the bars. Bars need to be placed and tied to prevent movement prior to concrete placement to assure depth of placement and that vibration can be carried out in fresh concrete with the bar inserted in its final position.

John Turner CSP PE
CRSI Greater Southwestern Regional Manager

 

[JAE]

doka1 - yes I'd have a problem with wet sticking bars. The issues you present (as roadblocks to pre-tied bars) are overcome in thousands of projects by competent contractors.

If you have proper slump concrete (not soup) then stabbing a bar into properly placed concrete creates voids around the bars, limiting the pull-out strength. For a structural slab/beam system, these bars may be critical - taking stress and providing strength/stability in the assembly.

If so, then as an engineer, I cannot allow wet-stabbing as I KNOW that this creates uncertainty in my structure.

Contractually the contractor is required to bid and build the job per the drawings and specs - the drawings and specs will refer to "in accordance with ACI...". ACI requires pre-tied bars.

 

[asixth]

I had a builder ask me on Thursday whether they can "wet-stick" the starter bars for the blockwork walls into the footing which I disallowed.

If the footing is 20" deep and the starter bars for the cmu wall extends 24" out of the footing, then the total fall of the concrete is 3'8" which shouldn't be a problem for placement of the concrete. Likewise if the starter bars are required at 16" crs then wouldn't it be easy to provide ties at 16" crs so the wall starter bars can be tied to the cage.