| Title |
Behavior of Hollow Box Girder Using Unbonded Compressive Pre-stressing |
| Keywords |
PSC girder bridge;compressive prestressing;unbonded PS tendon;H-type compression reinforcements;girder repair and rehabilitation;PSC 거더 교량;압축 프리스트레스싱;비부착 PS 텐던;H형 압축 보강강재;거더 보수보강 |
| Abstract |
Generally, PSC girder bridge uses total gross cross section to resist applied loads unlike reinforced concrete member. Also, it is used as short and middle span (less than 30 m) bridges due to advantages such as ease of design and construction, reduction of cost, and convenience of maintenance. But, due to recent increased public interests for environmental friendly and appearance appealing bridges all over the world, the demands for longer span bridges have been continuously increasing. This trend is shown not only in ordinary long span bridge types such as cable supported bridges but also in PSC girder bridges. In order to meet the increasing demands for new type of long span bridges, PSC hollow box girder with H-type steel as compression reinforcements is developed for bridge with a single span of more than 50 m. The developed PSC girder applies compressive prestressing at H-type compression reinforcements using unbonded PS tendon. The purpose of compressive prestressing is to recover plastic displacement of PSC girder after long term service by releasing the prestressing. The static test composed of 4 different stages in 3-point bending test is performed to verify safety of the bridge. First stage loading is applied until tensile cracks form. Then in second stage, the load is removed and the girder is unloaded. In third stage, after removal of loading, recovery of remaining plastic deformation is verified as the compressive prestressing is removed at H-type reinforcements. Then, in fourth stage, loading is continued until the girder fails. The experimental results showed that the first crack occurs at 1,615 kN with a corresponding displacement of 187.0 ㎜. The introduction of the additional compressive stress in the lower part of the girder from the removal of unbonded compressive prestressing of the H-type steel showed a capacity improvement of about 60% (7.7 ㎜) recovery of the residual deformation (18.7 ㎜) that occurred from load increase. By using prestressed H-type steel as compression reinforcements in the upper part of cross section, repair and rehabilitation of PSC girders are relatively easy, and the cost of maintenance is expected to decrease. |