This paper describes the design and construction of unbonded post-tensioned slab and beam (PT) in building construction in the USA, with emphasize on details and techniques that have been overlooked. Suggestion and guideline to improve both the design and the construction are discussed and given.
The unbonded post-tensioned concrete system used in building design in the USA is described. It is the encapsulated monostrand system. Two slab forms have been used, a one-way slab and beam system and a flat slab system. They are a popular design choice for parking garages, residential condominium and office buildings.
Methods of design are described. Many designers make use of commercial computer programs. These are based on strip method and finite element method. The design, in fact, can simply be done using manual or hand calculation.
The paper highlights and discusses several design and construction issues. Methods for improvement are suggested. These issues include: hardware testing and approval, effective prestressing force specification, uniform placement of tendons versus bundled tendons, allowable number of broken tendons, snapping of tendons after taking up service loads for some period of time, prestressing force verification, anchorage zone reinforcement,tendon profile curved in plan, partial prestressing design, tendon pattern and shear reinforcement.