Pretensioned prestress friction losses considering contact imperfection at deviators in prestressed concrete girders

Abstract

Pretensioned prestressed concrete (PC) girders are prefabricated in series to reduce cost and facilitate fabrication efficiency. However, a consensus of the calculation of prestress friction losses at deviators is not achieved yet. The existing calculation methods assume a perfect contact between prestressing tendon and deviator, which is inconsistent with observed imperfect contact in real-life practices. This research considers imperfect contact in the investigation of the friction loss through theoretical analysis and experimentation. Three representative types of deviators are investigated and compared in terms of the magnitude of the friction loss. Modified equations for calculating the friction are proposed through the theoretical study, validated against experiment, and applied to investigate the distribution and effects of friction loss in series girders. The results show that the friction loss due to contact imperfection accounts for a significant percentage (61%) of the total friction loss. The equations without considering contact imperfection underestimated friction loss by up to 54 MPa, overestimated the elongation of tendons by up to 77 mm, and overestimated the camber and crack resistance of series girders by up to 6.6%. This study provides new insights into pretensioned prestress friction loss, and the modified equations are useful to improve the design, fabrication, and evaluation of PC girders.