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.

摘要

预应力预应力混凝土 (PC) 梁是串联预制的，以降低成本并提高制造效率。然而，尚未就偏转器处预应力摩擦损失的计算达成共识。现有的计算方法假设预应力筋与偏斜器之间存在完美接触，这与现实生活中观察到的不完美接触是不一致的。本研究通过理论分析和实验，在研究摩擦损失时考虑了不完全接触。研究了三种代表性类型的偏转器，并在摩擦损失的大小方面进行了比较。通过理论研究提出了计算摩擦力的修正方程，并通过实验验证，并应用于研究串联梁中摩擦损失的分布和影响。结果表明，由于接触缺陷造成的摩擦损失占总摩擦损失的很大比例 (61%)。不考虑接触缺陷的方程低估了摩擦损失达 54 MPa，高估了钢筋束的伸长率达 77 mm，高估了串联梁的拱度和抗裂性达 6.6%。这项研究提供了对预应力预应力摩擦损失的新见解，修改后的方程有助于改进 PC 梁的设计、制造和评估。不考虑接触缺陷的方程低估了摩擦损失达 54 MPa，高估了钢筋束的伸长率达 77 mm，高估了串联梁的拱度和抗裂性达 6.6%。这项研究提供了对预应力预应力摩擦损失的新见解，修改后的方程有助于改进 PC 梁的设计、制造和评估。不考虑接触缺陷的方程低估了摩擦损失达 54 MPa，高估了钢筋束的伸长率达 77 mm，高估了串联梁的拱度和抗裂性达 6.6%。这项研究提供了对预应力预应力摩擦损失的新见解，修改后的方程有助于改进 PC 梁的设计、制造和评估。