Technical Note TN 129 Prestressed concrete beams: controlled demolition and prestress loss assessment

Publication Year

1987

Document Status

Current

Abstract

Reports on two aspects of prestressed concrete of interest to designers: the performance of different methods of cutting or breaking up prestressed sections, and the long-term prestress losses, both of which may be assessed during controlled demolition. Firstly, the use of traditional and specialist demolition techniques are compared for the controlled cutting and demolition of a series of 29m-long pretensioned concrete box beams. The efficiency, safety and environmental implications of each method are considered. The traditional demolition technique of impact breaking and burning with an oxy-acetylene torch is concluded to be the most effective method, but recent advances in water-jetting technology have created a technique suitable for the precise cutting of prestressed concrete structures. Further tests are considered necessary to develop the full potential of explosive techniques. Secondly, the long term losses of prestress in the pretensioned beams, and their overall load-carrying capacity, are assessed by three independent methods. Direct measurements of prestress forces were obtained from residual strain measurements on individual strands and the overall prestress losses were deduced from residual strains on concrete cores and from a full-scale cracking moment test.

ISBN

9780860172772

Publisher Information