| The prestressed anchor bolt connection of fan foundation can solve the deformation coordination problem between steel tower and concrete foundation,and has the advantages of continuous structure,no stiffness mutation,no foundation cracking and so on.Therefore,it has been popularized in China.When the connection system is widely used,the accidents such as the foundation concrete cracking,abnormal fracture of prestressed anchor bolt,local instability of tower and even collapse of the whole machine were caused by failure to reach design load.The main reason for the above accidents is that the prestress loss of the anchor bolt of the fan foundation is too large or even invalid in the tension construction and operation stage.The most direct and effective way to solve the above problems is to put forward a simple and fast nondestructive testing method for the prestress of fan anchor bolt,which is to identify the peak frequency of energy concentration of anchor bolt anchorage system and indirectly identify the effective tension of fan anchor bolt.Frequency method is a simple and efficient non-destructive testing method,which can quickly and effectively detect the effective tension of prestressed anchor bolt.It is widely used in the vertical prestressed testing of Prestressed Concrete（PC）box girder bridge.However,in the actual testing process,it is sensitive to the testing accuracy by the length of reinforcement in non-stressed section.Based on the anchoring mode of the prestressed anchor bolt of the wind turbine foundation is basically the same as the vertical prestressed reinforcement of the PC box girder bridge,this paper adopts the frequency method to study and analyze the effective tension detection of the prestressed anchor bolt of the wind turbine foundation: In view of the shortcomings of the method in the practical application（the influence of the reinforcement length on the test accuracy）,the characteristics of the prestressed anchor bolt of the fan foundation（the shorter length of reinforcement of the non-stressed section）and the stress characteristics（anchor bolt thread turns,height,width and nut height of anchor bolt）are studied.In order to eliminate the influence of the length of reinforcement in non-stressed section on the test accuracy,the range and method are obtained,and the non-destructive testing of the effective tension of prestressed anchor bolt in wind power foundation is realized.The main work and achievements are as follows:（1）The indoor test model is made to study the influence of the length of the non-stressed section and the tensile force of the prestressed anchor bolt on the test peak frequency,and to determine the detection range of the exposed end reinforcement length of two different types of prestressed anchor bolt of fan foundation;（2）Based on the reasonable hypothesis,four simplified mechanical models are proposed to obtain the frequency equation,Based on the previous indoor test database,the influence of the length of the exposed section of the non-stressed anchor bolt on the relationship between the stiffness parameters and the tension of the anchor bolt is studied,and the simplified mechanical model with the least influence of the length of the non-stressed section of the anchor bolt is obtained;（3）On the basis of the above model comparison results,the shear deformation of the exposed section,the force transfer characteristics of the anchor bolt anchorage section,and the non-uniform force transfer characteristics of the joint surface between the nut and the tower flange plate are considered.In order to obtain the non-destructive test method of effective tension of prestressed anchor bolt for fan foundation,the correction model is constructed by echelon,the influence degree and law of different factors on the relationship between stiffness parameters and anchor bolt tension are compared,and the correction method and correction formula are put forward. |
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