Introduction

Post-tensioning of concrete requires the introduction of large, concentrated tendon forces into structures. To appreciate the magnitude of these forces, consider a typical bridge tendon with 19-15.2 mm (0.6 in.) strands The jacking force for such a tendon may reach close to 4.000 kN (900 kips). This is equivalent to the weight of twelve HS 20-44 trucks.

Often several long tendons arc anchored in a closely spaced group (Fig. V1II-2). A significant amount of spring energy is stored in such tendon groups which would be released suddenly in case of tendon anchorage failure. As an example, the spring energy stored in four 19-15.2 mm strand tendons of 200 m length is theoretically sufficient to launch an HS 20-44 truck over a seven-story building.

The above examples make it obvious that the transfer of such large tendon forces into structures requires careful attention to the design and testing of anchorage devices and to design, detailing, and construction of tendon anchorage zones.

Throughout this chapter reference will be made to the AASHTO Standard Specifications for Highway Bridges and to the PTI Acceptance Standards for Post-Tensioning Systems, They will be referred to as "AASHTO" and "PTI", respectively. Additional information on design and behavior of tendon anchorage zones and background information for the AASHTO tendon anchorage zone specifications can be found in NCHRP Report 356.