Behavior up to Ultimate State and Analysis of Unbonded Prestressed Simple and Continuous Beams

PPENT研究包括两个测试系列。A系列试验的目的是比较无粘结预应力筋梁和有粘结梁在极限状态下的结构性能，包括最大强度后的下落分支区。在B系列试验中，对两跨无粘结预应力混凝土连续梁的极限承载性能进行了试验和理论研究。A系列简支梁的研究表明：1)在给定的总跨长/有效高度比(L/d)下，无粘结梁的最大抗弯弯矩随着剪跨长度的增加而减小；2)与有粘结梁相比，无粘结梁的最大抗弯强度随L/d比的增大而显著降低。3)在L/d比值较低的情况下，加载点位置对无粘结预应力钢材最大极限弯矩时的可得应力影响较大。4)…在与后载相差极大的短剪跨处，即使预加荷载达到最大极限弯矩的75%，无粘结梁的最大抗弯强度也几乎没有降低。5)考虑无粘结钢筋和混凝土全跨伸长协调条件的分析方法，可以很好地估计无粘结梁的极限承载性能，特别是在包括下落分支的极限状态下。其次，连续跨度梁的B系列研究表明：1)无粘结梁的极限抗弯强度比有粘结的梁低10-20%；2)无粘结梁的构件刚度和预应力钢筋的应力增量比有粘结梁的小得多；3)有粘结梁在开裂后开始弯矩重分布，但无粘结梁和有粘结梁在加载点或中间支承处的荷载-弯矩关系没有显著差异；4)应用非线性分析可以很好地估计预应力混凝土连续梁开裂后的弯矩重分布、预应力钢筋应力和挠度等结构极限状态。其中，有粘结梁和无粘结梁的预应力钢筋协调系数分别为1.0和0.2。较少

The pesent study consists of two test series. The purpose of series A tests is to examine the structural behavior at the ultimate state including falling branch region after the maximum strength of unbonded beams without bond of prestressing steel in comparison with those of bonded beams. In series B tests, on the other hand, the load carrying behavior up to the ultimate state of two-span continuous unbonded prestressed concrete beams was studied experimentally and theoretically.It was shown from series A studies on simple beams that 1) maximum resisting flexural moment decreased with increasing shear span length at a given total span length/effective depth ratio (L/d) in unbonded beams, 2) reduction in the maximum flexural strength of unbonded beam in comparison with bonded beam became remarkable with increasing L/d ratio, 3) effect of location of load-points on attainable stress in unbonded prestressing steel at the maximum ultimate moment was significant in case of low L/d ratio. 4) … More maximum flexural strength of unbonded beam scarcely reduced even when subjected to pre-loading up to 75% of the maximum ultimate moment at a short shear span extremely different from post-loading, and then 5) load carrying behavior in particular at the ultimate state including falling branch of unbonded beams could be estimated well by an analitical method considering compatibility condition of elongation in unbonded steel and concrete over total span length.Nextly, series B studies on continuous-span beams showed that 1) ultimate flexural strength of unbonded beam was lower by 10-20% than that of comparable bonded beam, which could be estimated well by using appropriate value of compatibility factor for unbonded prestressing steel and applying limit analysis, 2) member rigidity and stress increase in prestresing steel after flexural cracking were considerably small in unbonded beam than bonded one, 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 and bonded beams, and 4) structural 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. Less