End Cracking in Prestressed Members during Detensioning.

摘要

This report is concerned with an investigation to determine analytically as well as experimentally the theory that end cracking observed during prestress transfer in pretensioned operations is caused by tensile stress induced by the restraining effect of relatively short length of unbonded cables. Production line prestressed members were monitored for strain increase during detensioning and the castings were measured for elastic shortening. Results were compared with an analytic model capable of furnishing cable strains during any detensioning scheme in a multiple casting operation. Full scale experimental members were designed such that during transfer tensile stress in concrete due to cable restraint would be maximized. Cracks were indeed caused as predicted by analytic calculations. Finally as an example problem,full scale production line girders were monitored for cable strain during detensioning and compared with analytically calculated values.