control joint spacing

[sme75]

Can anyone tell me where to find a recommended spacing for control or contraction joints in concrete walls? The walls will be below grade and have been designed for the lateral earth pressures to span vertically. I was looking in ACI 301 but have not found anything. The copy I have is old so I may need to get a current one. If that is the right source can anyone tell me whic section I should be looking in.

 

[CarlB]

I won't be able to cite ACI too well but have recently been exposed to a wall cracking problem. I believe ACI 224 has some general guidelines. One "general rule" is for vertical control joint spacing not to exceed 2 to 3 times the wall height.

Now you could go to ACI 350 for some stringent criteria, although this guide is for "environmental structures". It will lead you to greater reinforcing for crack control. As I recall the joint spacing is not to exceed 20 feet for "partial" joints (half the reinforcement discontinued), and 30 feet for "full" joints (all reinforcement discontinued). See that code for specific crack control reinforcement, joint spacing and joint detailing.

 

[boo1]

Expansion Joints - Vertical expansion joints or movement control jointsto account for expansion due mainly to temperature changes and moisture conditions. On changing from a saturated to a dry condition, average concrete will contract approximately 2/3 of an inch per 100 linear feet. Place Vertical expansion joints 1/2 inch in width at Max intervals of 90 feet throughout the length of retaining walls and fill with expansion joint material. All exposed edges shall be beveled 3/4 inch. The footings should incorporate an expansion joint too.

Construction Joints - These can be vertical or horizontal joints between successive pours of concrete. When it is not practical to pour the wall to full height in one operation, ensure construction joints are truly horizontal and provide a bond between the sections with keys formed by beveled timbers. Where necessary to provide construction joints in the length of the wall, ensure joints are truly vertical and provide a bond between the sections with shear and sliding resistance keys formed by beveled timbers. Spacing depends of project and crew.

Contraction Joints - Vertical joints cut (or formed)into the wall. Allows the concrete to shrink without showing the cracks. Place 24-inch long, 1/2-inch diameter, commercial grade steel dowels and 12-inch long, 5/8-inch inside diameter, commercial grade steel dowel sleeves across the joint. Provide caps on one end of the sleeves. Grease one end of the dowel and insert into the sleeve. Space dowels and sleeves at 12-inch intervals along the centerline of the wall stem. Do not pass reinforcing steel through either joint. Seal joints from top to bottom with waterstops. Provide contraction joints at 30-foot intervals


One area that can be commonly overlooked, or at least underestimated, is the necessity to drain the backfill of rainwater and/or groundwater. Hydrostatic pressure can cause or induce retaining wall failure, or at least damage
Provide 4-inch weephole drains at 8-foot intervals through standard gravity. Weepholes should have material between the wall and the backfill to prevent fines migration, and weephole clogging. If required drainage lines are required, consider perforated pipe and wrapped in geotextile or buried in a granular filter bed, and serve to carry water to the weepholes from areas deeper within the backfill.

 

[StructEng99]

I suggest a control joint every 16' or less in a straight walls without pilasters or obennings.
I would add a control joint at both exterior ends of a pilaster. Where you have any opennings i.e. loading dock pit openning I would add a control joint.
I have tried all the above and we did minimize shrinkage crack appearance in foundation walls.