Prestressed concrete beams: controlled demolition and prestress loss assessment

This technical note 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. 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 then considered. The long-term losses of prestress in the pretensioned beams, and their overall load-carrying capacity, are then assessed using three independent methods. Some scatter in the results from the direct measurements and coring method was observed and it is recommended that further development and calibration work should be carried out in controlled laboratory tests