Why are post-tensioned slabs so dangerous to core?
Post-tensioned slabs rely on high-strength steel tendons stressed after the concrete is cast. Cutting a tendon releases stored force and removes prestress, and in unbonded systems the loss can affect the tendon along its length rather than only at the cut. Engineers warn that a cut tendon cannot simply be left because the slab shows no immediate distress. That is why Singapore's slab-opening exemption excludes prestressed elements, and why tendon positions must be located before any drilling.
From the RRD Field Guide, checked against the sources cited in Hacking Walls and Slabs in Singapore: Structural Elements, PT Slabs and Household Shelters. General information, not advice for your project.
The fuller picture
In Singapore you may remove or open a wall without BCA submission only if it is genuinely non-load-bearing, meaning it carries nothing but its own weight. Openings in reinforced concrete walls, beams, columns or most slabs need a PE's structural plans and a BCA permit before work starts. Household and storey shelters must not be hacked; only limited drilling and finishes are allowed under SCDF's rules.
More questions on this topic
- How can I tell whether a wall is structural?
- Do I need BCA approval to hack a non-structural wall?
- Can I core a hole through a floor slab for a pipe?
- Can I hack or modify my household shelter?
- What happens if structural works are done without a permit?
- Does a condo need to approve hacking inside my unit?
- Is scanning the slab enough before coring?