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

本研究包括两个试验系列。A系列试验的目的是检验无粘结预应力钢筋梁与有粘结预应力钢筋梁在达到最大强度后的极限状态下的结构性能，包括落分支区域。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研究和理论分析，A系列简支梁的试验研究表明：（1）在总跨长/有效高度比（L/d）一定的情况下，无粘结梁的最大抗弯弯矩随剪跨长的增加而减小;（2）无粘结梁的最大抗弯承载力随长径比的增大而显著降低;（3）在低长径比情况下，荷载点位置对无粘结预应力筋最大极限弯矩时的可达应力影响显著。四、 ...更多信息 无粘结梁的最大抗弯强度几乎没有降低，即使在短剪跨处承受高达最大极限弯矩的75%的预加载时，（5）考虑无粘结钢筋和混凝土总伸长协调条件的分析方法，可以很好地估计无粘结梁的承载性能，特别是包括落分支的极限状态对连续梁的B系列试验研究表明：1）无粘结梁的极限抗弯强度比有粘结梁低10-20%，采用合适的无粘结预应力筋协调系数和极限分析方法可以较好地估算出无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明显小于有粘结梁; 3）受弯开裂后弯矩重分布开始;但无粘结与有粘结梁在加载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结构性能，如弯矩重分布、预应力筋应力和挠度等，非线性分析可以很好地估计，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。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