Reinforcing Hook Development Length Under Opening Moments in Tanks

[jjezmarlo3]

For water and wastewater treatment tank design, I have been determining the amount of hook development length available for horizontal or vertical wall reinforcing by calculating the distance from the face of the wall/slab to the back of the hook (i.e. available hook development length equals wall or slab thickness - cover). However, there is an figure in the 2011 Structures Congress that has me questioning this dimension (attached). The article states that as tanks are subjected to opening and closing moments which can create a diagonal crack from the corner of the joint to the first set of reinforcing, the actual development length is reduced to wall or slab thickness - 2x cover. The attached figure is for vertical reinforcing, but I would assume it would also apply to horizontal reinforcing at wall corners.

For a 12" wall with #5 horizontal reinforcing requiring an 8.3" hook development, this difference can make a significant impact. As the horizontal bars are located inside the vertical bars, the available length would change from 12" -2" cover -5/8" outside bar = 9.375" (fully developed) to 12" - 2x (2" + 5/8") = 81% developed.

I have researched this item a bit, and have not found any other sources that state to use the thickness - 2x the cover. However, it seems to make sense, as there would be a diagonal crack to the first set of reinforcing.

I would be curious to get everyone's thoughts.

 

[jjezmarlo3]

Attached File