Continuous reinforcing in tank walls

[rethornton]

A question has come up regarding the horizontal wall rienforcement in underground precast tanks. If the bars are bent 90 degrees at the corner, does this constitute a hook subject to the requirements of Art. 12.5 of ACI 318? I don't believe it does but I cannot find a definative reference that states otherwise.

 

[ishvaaag]

Normally horizontal rebar ias assumed to (between other things) help to the containment of rheological effects. Some of these ould require good anchor at ends, and so continuity is welcome if not required.

In Spain we have used without much though both "escuadras" (supplementary rebar in L about 1 m long in each side for splices, in both faces), the inner passing to the exterior face plus the exterior "escuadra", and the same but the inner reinforcement passing to the outer face to form 90 deg bent anchors, never there being a problem. Of course splice must be related to diameter, and it can be good shear reinforcement tien outer and inner walls in some cases at corners, or include colum-like reinforcement embeded in the corners.

 

[rethornton]

I agree with developing horizontal steel as you describe. We use either corner bars or, in the case of rectangular precast tanks, "U" bars around the ends and developed into the long wall with a proper splice. The questions is whether this bent bar is considered a "hook", if it is then you must maintain the proper hook development from the inside face of the wall, or lhd (ACI 12.5).

 

[JAE]

rethornton
We consider that the hook development length must be satisfied if you are transferring forces across the corner joints. This forces you to minimize the bar size so that the thickness of the slab doesn't get too big.

We have struggled with this philosophy on a number of projects because ACI does NOT let you reduce the hook length (As(req'd)/As(provided)) if you are trying to develop shear friction across the joint. See ACI 12.5.3.4 where it notes that it applies only where fy is not requried.

Specifically, at masonry/hollow core plank connections, ALL of the standard details that the masonry and precast industries show (with a rebar extending into chipped out hollow core cells) DO NOT meet ACI as the hook is never developed. Now they don't fall down but that's because they are never loaded to their design loads. But still, they don't meet code.