Dowel bars in foundation 2

[Saedhalteh]

Hello all,
I have question regarding Dowel bars and Development length that I hope you can help me with :
If the bearing capacity of the concrete is not sufficient to transfer loads from column to foundation then we need to put dowel bars.
My question is, does placing dowel bars means that we don't have to check development length for concrete reinforcement and that the column reinforcement should stop at the face of the foundation.?
or it is a must to check the development length in all cases ?
Additionally, Do we check the Compression development length and the Tension development length and then apply the larger ?

 

[Lomarandil]

In order for the dowels to develop the column bars, the dowels must:
[ul]
[li]lap with the column bars for an adequate length (inside the column)[/li]
[li]themselves be developed (by hooked or straight development length) and anchored within the foundation element (e.g. below the bottoms of the column) [/li]
[/ul]

If these two are met, the column bars can stop at the face of the foundation.
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just call me Lo.

 

[KootK]

Additionally, Do we check the Compression development length and the Tension development length and then apply the larger?

This depends on your load resistance requirements:

1) If your bars will experience compression, as most column bars do, they will have to be compression developed for the compression demand using only the straight portion of of the embedded length. Hooks don't count for this application although they are still a good idea for constructability.

2) If your bars will experience tension, usually in the form of flexural tension, they will have to be tension developed for the tension demand. In this case, the development can make use of any hooks present.

3) If you have a shear demand and the joint that would require the mobilization of shear reinforcement, that reinforcement will need to be fully developed for it's yield strength on both sides of the joint. No partial development is permitted. Many columns will either:

a) possess enough reliable axial load applied in concert with the shear demand that explicit shear friction reinforcement is unnecessary and/or;

b) be able to transfer shear into adjacent slabs on grade etc where designers are comfortable with that approach.