Time-dependent losses in post-tensioned prestressed concrete

An investigation has been undertaken into the factors
affecting the time-dependent deformations, prestress losses and deflections of Class 1 uncracked prestressed concrete beams. The main influencing factors considered were environmental conditions, loading conditions,size and shape of members and concrete mix composition. Twenty seven beams consisting of both I- and rectangular sections with different concrete mixes, and tested under different environmental and loading conditions, were monitored for a
period of one year. Tests were also conducted on short I- and rectangular beams and cylindrical control specimens to determine the shrinkage and creep properties of various concrete mixes including some with PFA and admixtures.

A comprehensive assessment has been undertaken to determine
the reliability of various methods of predicting deformations, prestress losses and deflections by comparing current prediction methods with experimental results obtained during this research programme. The use of experimentally determined material parameters for creep and shrinkageq is also considered in the prediction methods. Proposals are made for improving prediction by the current
British Code: BS8110: 1985.