Flexural and Shear Behaviors of Unbonded Prestressed Continuous Beams and Analysis

本文首先对无粘结预应力两跨连续梁的抗弯性能进行了试验研究，并与有粘结梁的抗弯性能进行了比较，然后将试验结果与非线性分析的理论结果进行了比较。其次，研究了无粘结和有粘结梁在剪切作用下的承载性能。在抗弯性能方面，研究表明：1）无粘结梁的极限抗弯强度比有粘结梁的极限抗弯强度低10-20%，采用合适的无粘结预应力筋协调系数并进行极限分析，可以较好地估算出有粘结梁的极限抗弯强度; 2）无粘结梁受弯开裂后构件刚度和预应力筋应力增量均比有粘结梁小得多，采用高强混凝土（f ′ c = 85 N/mm ^2）或侧向预应力筋加固， ...更多信息 对无粘结梁的加固效果明显。3)无粘结梁和有粘结梁在荷载作用点或中间支座处的荷载-弯矩关系无显著差异; 4）预应力混凝土连续梁开裂后的弯矩重分布、预应力筋应力和挠度等受弯性能可以通过非线性分析得到较好的估计。其中有粘结梁和无粘结梁预应力筋协调系数分别取1.0和0.2。在抗剪性能方面，试验结果表明：（1）有粘结梁和无粘结梁的抗弯裂缝沿着梁跨的分布规律有很大差异，有粘结梁比无粘结梁更容易发生剪切破坏，和2）无粘结梁和有粘结梁的实测抗剪强度都大大超过了通过设定所有安全系数估算的计算抗剪强度日本土木工程师协会标准的设计公式为1.0。少

In this study, firstly the flexural behavior of unbonded prestressed two-span continuous beams without bond of prestressing steel was examined in comparison with that of bonded beams, and then the results of those tests were compared with theoretical ones obtained from the nonlinear analysis. Secondly, the load carrying behavior of unbonded and bonded beams under shear were studied. And the recent trends on externally prestressing similar to unbonded prestressing were also investigated.It was shown on flexural behavior that 1)ultimate flexural strength of unbonded beam was lower by 10-20% than that of comparable bonded beam, and that of former beam could be estimated well by using appropriate value of compatibility factor for unbonded prestressing steel and applying limit analysis, 2)member ridity and stress increase in prestresing steel after flexural cracking were considerably small in unbonded beam than bonded one, and application of high strength concrete (f'c=85N/mm^2)or lateral c … More onfining reinforcenment was very efective for improving of unbonded beam. 3)moment redistribution initiated after flexural cracking, but no significant difference could be recongnized in load-moment relations at loading point or intermediate support between unbonded beam and bonded beam, and 4)flexural behavior up to the ultimate state after cracking of prestressed concrete continuous beams such as moment redistribution, prestressing steel stress and deflection could be estimated well applying nonlinear analysis, in which compatibility factor for prestressng steel was set to be 1.0 and 0.2 for bonded beam and unbonded beam, respectively. As for the shear behavior, it was indicated that 1)distribution of flexural cracks along beam span differed markedly between unbonded and bonded beams, and shear failure was liable to occur due to extensive flexural shear cracking in bonded beam rather than unbonded one, and 2)measured strength of unbonded beam as well as bonded beam was fairly in excess of calculated shear strength which was estimated by setting all of safety factors in design equations by Japan Society of Civil Engineers Standards to be 1.0. Less