Analysis Of The Causes Of Cracks And Local Stress In The Anchorage Zone Of PC Box Girder Based On The Theory Of Strut-and-Tie

In the development of China's bridge,the prestressed concrete box girder bridge has become a major member.Thus in the operation and construction of the bridge,the box beam crack control is a great task,especially in the anchorage zone of crack.But there was no mature design calculation procedures.In this paper,a box girder bridge in the 1# block when web tension,the web anchor end crack phenomenon as engineering background.On the strut theory of anti collapse design further analysis,on how to build a web of anti collapse of Strut and Tie model to explore the research and analysis of the causes of cracks.The main contents are as follows:1.By reading a lot of documents,summarizes the mechanical structure characteristics of the prestressed concrete box girder and its development actuality,And the research results of some scholars on the crack problem.Summarize the development status at home and abroad and using the strut theory development2.The PC box girder D area is divided,the anchorage zone of box girder is a typical area D;Introduces the basic principle of the tension compression bar,describe the basic process of the design of the Strut and Tie model,criteria for the establishment of the Strut and Tie model.Comparison of the countries about the Strut and Tie model of strut strength,tie strength and node strength.Points out the problems that should be paid attention,when establishing the model,and the different norms of different countries.3.Using finite element analysis software(Midas FEA)on the anchorage zone of the finite element stress analysis.Obtain reasonable Strut and Tie model,the internal force of the tie in the model is calculated.According to the calculation of the internal force of the tie,the web plate reinforcement design.The model can accurately reflect the stress distribution of the anchorage zone of box girder web.The box girder crack is caused by the anchoring position spread from the anchorage of the principal stress cross-sectional stress shows: The main factor that causes the failure of concrete is the large tensile stress in the joint zone in the anchorage zone,in this paper,the engineering background in the anchorage zone of the main reason is the effect of web cracking radial lead.4.Summary of the types of cracks and the mechanism of the general prestressedconcrete beams.For the anchorage zone of box girder webs pull-pressure bar of the minimum angle between the impact parameter analysis,by many factors considered minimum tensile and compressive rod angle;from the vertical angle and horizontal angle consider tension webs of the anchorage zone of tension error,it is concluded that the angle deviation on in webs of the anchorage zone should force change of sensitive issues.Considering the influence of the overall design and construction of the bridge on the stress of the web anchorage zone,the prevention and repair measures for the anchorage zone are put forward from the aspects of design and construction.