Development Length of Footing Dowels

[EngrJS1]

Hi,

I am providing footing dowels to my design. However, I computed that the bearing strengths of both the footing and column are larger than the compressive loads. With that, do I still need to provide sufficient compressive development lengths?

 

[KootK]

With that, do I still need to provide sufficient compressive development lengths?

I believe that most engineers would say "no".

I have a slight concern with this in that creep tends to migrate much of your column axial stress out of the concrete and into the rebar, whether you want that or not. This is one of the reasons that we have the minimum 1% reinforcing requirement. As a result, much of your compression may arrive at your joint interface via your reinforcing eve if the interface works in bearing as you say. So the only way for the bearing mechanism to truly kick in fully is for the rebar dowel embedment to fail in bond stress. Maybe you care about that, maybe you don't. It kind of depends on the situation and whether or not you hope to use the dowel in tension for other load cases etc.

 

[JoshPlumSE]

This is one of the reasons that we have the minimum 1% reinforcing requirement

0.5% for pedestals, right? Or, am I behind the times.

 

[KootK]

0.5% for pedestals, right? Or, am I behind the times.

That's still what I'm doing for most pedestals based on:

1) Somewhere there used to be an "architectural column" provision and;

2) There is a reference somewhere to 0.5% being the minimum crossing the pour joint I think.

I mentioned the 1% in reference to things more accurately envisioned as true "columns"/

 

[milkshakelake]

We call such rebar and anchor bolts "decoration." If I had to think of a technical way of doing it though, I'd get the compression forces based on strain compatibility and reduce the compression development length using the ratio As/As[sub]req[/sub].

I think 0.5% is the provision is for "compression members with a cross section larger than required by considerations of loading" per ACI 318-08 10.8.4, it lets you reduce it by half. So half of 1% is 0.5%. A pedestal can be taken as the size of the column above it in the ACI 318 section about footings so theoretically, we can go way lower than 0.5% by considering only the area with column above and pour a ton of concrete around it.