EXPERIMENTAL AND THEORETICAL STUDY OF IMPACT OF FATIGUE LOADS ON LONG-TERM PRESTRESS LOSS

Unlike bonded prestressing tendons, there is no strain compatibility between tendons and concrete. The stress in the tendon is member-dependent rather than section-dependent, which makes the calculation of long-term loss of unbonded prestressing more complicated. For unbonded prestressed concrete beams subjected to fatigue loading, the interaction between concrete creep, shrinkage and relaxation of prestressed tendons is considered, as well as the constraint effect of non-prestressed tendons, and a model for the calculation of long-term prestress loss of unbonded prestressing tendons is established, which incorporates the creep strain constitutive under fatigue loading and relaxation of prestressing tendons considering fatigue damage. The model was verified by the 28-day prestress loss test of four unbonded prestressed concrete beams, and compared with the calculated values upon the current codes. The results show that the model proposed can accurately reflect the influence of fatigue loading characteristics on the long-term loss of unbonded prestress.