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

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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