|主題||Loss of Tendon's Eccentricity in Externally Prestressed Concrete Beam|
|筆頭著者||Songkiat Matupayont（Saitama University）|
|連名者1||Hiroshi Mmutsuyoshi（Saitama University）|
|連名者2||Kazuteru Tsuchida（Saitama University）|
|連名者3||Atsuhiko Machida（Saitama University）|
In external prestressing system, tendons are arranged outside the cross-section of a prestressed concrete beam. The externally prestressed concrete (PC) beam, in previous studies, can be treated as an unbonded prestressing member because no bonding between concrete and tendons exists. However, unlike internal unbonded tendons, external tendons are formed the profile by deviating at the deviators. When the externally PC beam subjects to bending, the tendon would not follow the concrete deflection, except at deviator point. The large deflection of PC beam, particularly when the beam is close to failure, could induce the secondary effect on flexural strength of PC beam, namely "loss of tendon's eccentricity". The loss of eccentricity would be influenced by the location and arrangement of the deviators. Fig.1 shows a typical deflection and loss of tendon's eccentricity in the externally PC beam.
In this study, to investigate the effect of loss of tendon's eccentricity on ultimate flexural strength of externally PC beams, 1)tests of externally PC beams having different arrangement of deviator points, and internally unbonded PC beam were carried out, 2)an analytical program considering the effect of loss of tendon's eccentricity was developed, 3)by using the analytical program, the parametric study changing the variables on the influenced parameters were investigated.
The experimental investigations of externally PC beam and internal unbonded PC beams were comparatively made to study the effect of loss of tendon's eccentricity on ultimate flexural strength. To accurately predict such a flexural behavior of externally PC beam considering the effect of loss of eccentricity, the analytical approach was developed, and compared with the test results. In this study, the conclusions can be drawn as the followings;
・ In comparison to an internal unbonded PC beam which has no loss of eccentricity , the externally PC beam with large distance between deviators (No.2) gives a remarkable lower flexural strength than that of internal unbonded PC beam.
・ It is found that the externally PC beam possessing a proper arrangement of deviator to eliminate the loss of tendon's eccentricity (No.3) shows the same flexural behavior as that of the internal unbonded PC beam.
・ The analytical approach using the concept of deformation compatibility and bond reduction coefficient gives an acceptable agreement with the test results.
・ By using the analytical program, parametric study on the influenced parameters was carried out as a guidance to propose the equation for design purposes of externally PC beam in the further study.