Crack Propagation And Failure Law In The Anchorage Zones Of Soldering Bearing Plates

The post-tensioned prestressed anchorage system is composed of anchorage,bearing plate,bellows,clip and spiral reinforcement.Anchorage distribution plate is an important load-bearing member which transfers tensile stress evenly to concrete under anchor.Compared with the foundry bearing plate,the solder bearing plate produced by Q345 steel has the advantages of light weight,high strength,high reliability,low cost,and can be widely used.Welded bearing plate is a kind of metal welded component,the temperature gradient is large in the welding process,the local residual stress up to yield strength will be generated,which will affect the fatigue performance of welded bearing plate.In order to avoid the possible fatigue failure of welded bearing plate which can affect its utilities,the crack propagation in the welding process of welded bearing plate is studied in this paper.As a metal welding component,the welding anchor pad has a large temperature gradient during the welding process,which can generate residual stresses that can reach yield strength locally,which affects the fatigue performance of the welding anchor pad.On the other hand,the prestressed anchorage zone is a typical stress disturbance zone,and the local stress of the concrete under the anchor is complex,often requiring the configuration of steel bars.Different combinations of steel bars have an impact on the stress distribution in the anchorage zone.In order to avoid the possible fatigue damage of the welded anchor backing plate from affecting the practical application and provide guidance for the anti crack design of the anchorage zone,the welding process of the welded anchor backing plate was studied by using the theory of fracture mechanics of metal materials;Based on the cohesive force model in fracture mechanics of concrete,the process of crack propagation in the anchorage zone is studied.Combined with different reinforcement,the crack initiation and propagation of concrete under anchorage are studied.Specifically,it includes the following content.1.After read relevant literature,checked specifications and conducted field research in the factories,engineering drawings were drawn,12-hole circular welded anchorage distribution plates for 1960 MPa grade steel bar were designed.Combined with the design size,the section size and local ultimate bearing capacity are checked.2.The distribution of residual stress and the effect of residual stress on crack growth rate of welded bearing plate in the welding process are obtained.Based on ABAQUS software,the finite element simulation of the welding process of bearing plate was carried out by using the heat source subroutine written in FORTRAN language and the secondary development program written in PYTHON language.The temperature distribution and residual stress distribution of two welded components are obtained.Combined with the extended finite element method,the residual stress distribution in the form of pre-defined field was modeled with the same grid distribution,and the crack growth of welded bearing plate was simulated,and the influence of residual stress on crack growth of welded bearing plate was obtained.3.After designing 1960 MPa 12-hole circular welded bearing plate,a small amount of plates were produced by the factories.According to the requirements of national standard GB/T 14370-2015 on the force transfer performance test of post-tensioned prestressed anchorage area,three concrete specimens and six concrete strength verification test blocks were made,and the force transfer performance test was carried out.During the observation cycle,the surface strain,crack width,crack propagation state and final failure mode of the specimen and the state of the bearing plate were investigated.The test results show that there is no brittle failure in the 1960 MPa class 12-hole round welded bearing plate in the force transfer performance test,and the failure form,strain and crack of the specimen are all in line with the standard requirements.4.Combined with the crack development forms of test specimens,a finite model of prefabricated cracks was established for the prestressed anchorage area,and the crack growth analysis was carried out based on the cohesion model.The crack growth in the anchorage zone equipped with different reinforcement was compared to explore the influence of different reinforcement on the crack growth in the anchorage zone.