Slabtec has developed proven epoxy-based, retrofitted Tendon Truncations procedures that ensure PT tendon forces can be safely transferred into the remaining structure.

TENDON TRUNCATIONS

What are Truncations?

Tendon truncations are epoxy-based, retrofitted tendon anchorages that provide alternate end anchorage locations in existing post-tensioning tendons.

Normally, this requirement is driven by alterations to existing slabs, which require the tendons to be reduced in length, but this can also be necessary due to damage to an existing anchorage.

A fully grouted tendon in a smooth galvanised duct should never be considered an anchorage in itself.

Bond relationships between strand/grout/duct/concrete are typically only required to transfer incremental stresses in strength events between long-term residual stresses in the tendon and the stresses at yield (proof stress).

Without an anchorage or truncation, if a tendon were cut, that same bond relationship would be required to transfer the full load at yield.

This could be 2 to 3 times that which would be required had an anchorage or truncation be used.

Slabtec has proven truncation procedures that we have load-tested to ensure anchorage forces can be safely transferred.

Our advice to stakeholders typically includes:

Where truncations will be required
What methodologies should be used
Structural considerations for the Engineer in the temporary construction stage
Safe and unsafe areas to use truncations
Alternatives to truncation in unfavourable locations

The Tendon Truncations Process on Site

Excavation of concrete around stressed tendons is a process that needs to be carefully understood and appropriately managed to ensure there is no damage to the tendon and, more importantly, the process is conducted in a safe manner.

The assumption cannot be made that the tendons are fully grouted and set out exactly as per the drawings or a third-party unverified scanning report.

Ungrouted tendons are, unfortunately, not particularly uncommon. The condition of the tendon grout must be assessed by experienced operatives during the excavation process, particularly in poorly grouted tendons.

This is a major safety issue and completely changes the approach to how the truncations are undertaken and whether remedial grouting must take place prior to the demolition of the floor slabs.

Slabtec provides documented reporting for the as-built condition of the tendon as a part of our standard QA procedure for the Design Engineers’ review.