California IDEX Practice Exam

Which type of slab cannot be penetrated for a stair opening?

1. Flat slab

2. Waffle slab

3. Post-tensioned slab

4. Prestressed slab

The correct answer is: Post-tensioned slab

A post-tensioned slab cannot be penetrated for a stair opening because it is specifically designed to carry loads through high-tensioned steel strands that are tensioned after the concrete has cured. These strands are placed in specific patterns to optimize structural performance and load distribution. Making an opening for a stair would compromise the structural integrity of the slab, as it could disrupt the continuity and effectiveness of the post-tensioning system. While other slab types, like flat slabs, waffle slabs, and prestressed slabs, can typically accommodate openings with careful design considerations and reinforcements, post-tensioned slabs prioritize their tensioned cables in their construction, making them highly sensitive to any modifications that would impact their performance.