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Discussion on the Measures for Guaranteeing Effective Prestress of Vertical Prestressed Reinforcement of Box Girder Bridge |
XU Hua-xuan |
China Railway 16th Group Co. Ltd., Beijing 100018, China |
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Abstract Research purposes:Based on the theoretic analysis, test and practice, the research is done on the reasons for the big pretress loss and poor effect of prestressed reinforcement of the web plate of concrete box girder, and the measures for them are presented to guarantee the effect of the vertical prestress and avoid the appearance of stress crack on the web plate.
Research conclusions:In design, the ratio between the stress and yield degree of vertical reinforcement should be controlled. The rebound value of 1.65 mm should be adopted when calculating the stress loss caused by anchor deformation and gap compression. The stress loss caused by installation error of anchor backer should be added and the rebound of 3.3 mm should be used. The stress loss caused by water thermalization of concrete and cement grout should be considered and the attention should be paid to improvement of the construction technique in construction. The error of incline angle should be controlled to make two flat and one straight and make the included angle within 1o when installing the anchor backer. The anchor torque of 1 200 N·m and 600 N·m with torque spanner should be used to φ32 reinforcement and φ25 reinforcement. The tension and super tension techniques should be used. The four groups of vertical reinforcements on the joint place of the front part and the rear part of the girder and the reinforcements on the rear part of the girder should be tensed at the same time.
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Received: 29 August 2009
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