Do 24-inch (610-mm) No. 3 or No. 4 reinforcing bars at reentrant corners prevent cracking?

Do 24-inch (610-mm) No. 3 or No. 4 reinforcing bars at reentrant corners prevent cracking?

• A. Yes
• B. No, they hold cracks that do form tightly closed but do not prevent cracking
• C. They prevent other types of cracking
• D. They cause cracking

Answer: (B)

Crack control versus crack prevention at reentrant corners is the idea here. Reentrant corners concentrate tensile stresses from shrinkage and restrained movement, so cracks are likely to form there. The 24-inch No. 3 or No. 4 bars placed at these corners don’t stop cracks from forming, but they act as crack-bridging reinforcement. By spanning across potential cracks and providing a tensile path, the bars help keep any cracks tightly closed and limit crack width, which improves durability and serviceability. They don’t eliminate cracking because the shrinkage, temperature changes, and restraint forces will still induce cracking; this reinforcement simply reduces how wide those cracks open.

Crack control versus crack prevention at reentrant corners is the idea here. Reentrant corners concentrate tensile stresses from shrinkage and restrained movement, so cracks are likely to form there. The 24-inch No. 3 or No. 4 bars placed at these corners don’t stop cracks from forming, but they act as crack-bridging reinforcement. By spanning across potential cracks and providing a tensile path, the bars help keep any cracks tightly closed and limit crack width, which improves durability and serviceability. They don’t eliminate cracking because the shrinkage, temperature changes, and restraint forces will still induce cracking; this reinforcement simply reduces how wide those cracks open.