Development Length of Vertical Rebar at Construction Joint

[bumbler]

Hi all,

In ACI318-14 Table 25.4.2.2, "clear cover at least db" is required to avoid using the more conservative development length equations. Without this clear cover, the equations yield a 50% higher development length. Does this apply at a construction joint? For example, at a concrete wall over a grade beam/footing, are we required to offset a vertical wall bar that is lapping with a vertical dowel to provide cover to the construction joint? We had a contractor request to use dowels from the grade beams and lap vertically. See attached sketch for details.

Thanks!

 

[bugbus]

The cover used to calculate the development length is only perpendicular to the bar, not what is happening at the end.

A strict interpretation of some codes might warrant lifting these bars up to get concrete flowing below the bar, but I would not see a problem with having the wall bars just resting on the pile cap. You see this pretty often.

 

[bumbler]

The cover used to calculate the development length is only perpendicular to the bar, not what is happening at the end.

Do you have a code reference for that? I can't find anything in ACI318-14 Chapter 25 specifying that. I have always thought that clear cover was all sides of the bar, and top/bottom/side cover is explicitly perpendicular to the bar.

As far as having the bars rest on top of the concrete below, would you be concerned about water intrusion?

 

[slickdeals]

The cover is measured to outside surface of concrete, not to a construction joint. Read "cover, concrete" in definitions. Outside surface of concrete is anything other than concrete.
If you're concerned about water intrusion (from the sides), raising this bar isn't going to solve that problem. You still have the bar you're trying to lap. Typically construction joints in situations where water can creep in either have waterproofing on the positive side (i.e., side exposed to water) or a expansive material (clay bar) etc. placed on the exterior side of the vertical rebar.