TechNotes – CMHC publishes Investigation Protocol for Evaluation of Post-Tensioned Buildings

Read Jones Christoffersen, consulting engineers, have helped to write a Canada Mortgage and Housing (CMHC) Investigation Protocol for the Evaluation of Post-Tensioned Buildings.

The publication is a research document to assest engineers in planning and conducting an approrpiate program for identifying factors contributing to the wide range of performance in unbonded post-tensioned systems.

Unbonded post-tensoned buildings perform well provided the tendons are kept free from moisture. However, problems became apparent in the 1980s in buildings built before that time with tendons corroding and breaking due to moisture penetration. High strength steel strands are particularly susceptible to corrosion.

The investigation program involves selective exposure and testing of strands to assess safety, predict the likelihood of future breakage and to decide if monitoring or repair is required. The Investigation Protocol does not specify minimum levels of testing or maintenance standards, but provides suggestions regarding the evaluation process.

Also note that the Protocol deals only with buildings constructed with unbonded, single-strand, post-tensioned tendons. Different procedures are involved in assessing grouted (bonded) sngle-and multi-strand post-tensioning systems and pretensoined (precast) building components.

John Harder of Read Jones Christoffersen helped write the report, with David Rogowsky of the University of Alberta and Anast Demitt of Adem Engineering.

Source: CMHC “Research Highlights,” November 2002. O2-129
Visit www.cmhc, or tel. 1-800 668-2642.