TABLE OF CONTENTS Deterioration of post-tensioned concrete buildings is difficult to diagnose and repair. These proprietary structures often reveal very little about their true condition until failure is evident. In this chapter, we examine the issues involved in the study and evaluation of distressed concrete reinforced with post-tensioned tendons and the repair methods available. Expertise in this type of renovation is quite valuable and rare. We hope that this brief discussion of the history of post-tensioned structures, evaluation techniques, and basic procedures necessary to perform repairs to these structures will benefit both the experienced restoration engineer and the novice.
In essence, post-tensioning of concrete improves its flexural behavior by imposing additional stresses that counteract those from service loads. It involves applying large tension stresses to post-tensioning steel and anchoring the steel in a stretched condition at the ends of the member. A similar idea is used in prestressed concrete, except that there the tendons are tensioned before the concrete is cast.
Tendons can be tensioned from one end (the "live" end) or from both ends. Stressing anchors are placed in pockets and grouted for corrosion protection. The stressed post-tensioning steel transmits compressive forces to concrete by bearing of mechanical anchors. If the steel is properly placed, this compression reduces the applied stresses in the tension zones of the structural member. As a result, post-tensioned structures can be thinner and lighter, and can span longer distances; their deflections and porosity are reduced. Concrete cracking in them...
