Study On The Prestressed Concrete Continuous Box Beam (Rigid Frame) Bridge With Straight Beam Reinforcement Mode

The method of straight beam reinforcement of prestressed concrete box girder bridge had ever been widely used due to its significant superiority. However, there are some serious problems such as web cracking and deflection of the main beam and so on among those bridges which were made by this way in years. No mat t er w h at ki nd of reinforcement programmes had been taken, there was still some web diagonal cracks and deflection of the main beam.In view of this phenomenon, many researches have indicated that the main causes of this phenomenon can be divided into design factors and construction factors. In the design aspect, the main reason is the lack of consideration of shear stress during the time of design; In the construction aspect, the main reason is the quality of vertical prestressing cannot be guaranteed. Under the condition of accurate calculation of shear stress of eccentric load coefficient and proclaimed "Standard for Detecting Tension Forces of Vertical prestressing Fine Rolling Steel Bars in Webs of PC Box Girder Bridge"(DB43/T 847-2013)as well as the premise of ensuring the construction quality of vertical prestress, this paper has done some researches about the applicability and superiority of prestressed concrete rigid frame bridge with straight beam reinforcement. The main work and research results are as follows.1.A large number of related literatures about Prestressed Concrete bridge with straight beam reinforcement have been read. Two main reasons about the serious diseases have been summarized which include the lack of consideration of shear stress during the time of design and the quality of vertical prestressing cannot be guaranteed during the time of construction. Different reinforcement programmes of prestressed concrete box girder bridges have been studied and the advantages and disadvantages of different reinforcement methods have been summarized.2.The eccentric load coefficient of Dagutan bridge has been calculated. The result shows that The eccentric load coefficient of the bridge is more than 2.0.1.05 as it often be used make a serious shortage of shear stresses.The accurate calculation of eccentric load coefficient of shear stress shuold be taken in the practical design of bridge.3.According to the disease reason of straight beam reinforcement and practical condition,the practicability of straight beam reinforcement has been demonstrated. In terms of the basic principle of straight beam reinforcement mode, "Standard for Detecting Tension Forces of Vertical prestressing Fine Rolling Steel Bars in Webs of PC Box Girder Bridge"(JTGD62 2012) and diffusion rule of precompression stress under vertical prestress, the formula about the design of vertical prestressed reinforcemen has been deduced and the design of Dagutan bridge in straight beam reinforcement mode has been redesigned. It further proves that straight beam reinforcement is practicable now.4.The contrastive analysis of the origin model and the redesign model has been completed. The result shows that the self- balance construction and long–term deflection,normal stress on the cross section and the lower edge controlling effects of Dagutan bridge are no obvious difference. The redesign model has a better performance on controlling the principal tensile stress,the principal tensile stress of original design is easy to be exceeded. It improves the utilization rate of material properties and makes the construction be more convenient and economical.