Flexural and Shear Behaviors of Unbonded Prestressed Continuous Beams and Analysis

本文首先对无粘结预应力钢的无粘结预应力两跨连续梁的抗弯性能进行了试验研究，并与粘结预应力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，研究了无粘结梁和粘结梁在剪切作用下的承载性能。并对类似无粘结预应力的外预应力的发展趋势进行了探讨。结果表明：1)无粘结预应力梁的极限抗弯强度比有粘结预应力梁的极限抗弯强度低10-20%，采用适当的无粘结预应力钢协调系数值并应用极限分析可以较好地估算出无粘结预应力梁的极限抗弯强度；2)无粘结预应力梁的构件刚度和抗弯开裂后预应力钢的应力增加明显小于有粘结预应力梁；采用高强混凝土（f′c=85N/mm^2）或侧向加筋对改善无粘结梁的性能非常有效。3)无粘结梁和有粘结梁在受弯开裂后产生弯矩重分布，但在荷载点和中间支承处的荷载-弯矩关系没有明显差异；4)预应力混凝土连续梁在受弯开裂后直至极限状态的弯矩重分布、预应力钢的应力和挠度等受弯性能，应用非线性分析可以很好地估计。其中，粘结梁和非粘结梁预应力钢的协调系数分别为1.0和0.2。结果表明：1)无粘结梁和有粘结梁沿梁跨弯曲裂纹分布有明显差异，有粘结梁比无粘结梁更容易发生广泛的弯曲剪切开裂；2)无粘结梁和粘结梁的实测强度均大大超过计算抗剪强度，日本土木工程师学会标准将设计方程中的所有安全系数设为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