Experimental Study On Test Of Cable Force Of Hangers Of Arch Bridge By Frequency Method

The frequency method is an indirect method to measure the cable force of the hanger of an arch bridge.The natural vibration frequency of hangers is measured on site,and then the cable force of them is calculated according to the theoretical formula between frequency and cable force.It is mostly used to detect the cable force of hangers after the completion of bridge.In fact,there are a lot of theoretical formulas for calculating the cable force at home and abroad,but in practical engineering applications,especially in short hanger cable force test,the error is large.Aiming at the above situation,in order to improve the accuracy of the calculation formula of short hanger cable force of arch bridge,this paper carries out the indoor similar test research of hanger frequency test and cable force calculation.Based on the analytical solution of the hinge boundary condition of beam vibration theory,this paper puts forward the applicable empirical formula of hanger cable force calculation under different slenderness ratio,and verifies the accuracy of formula through the existing short hanger cable force test of arch bridge.The main research contents and results are as follows:(1)The Basic Principle of Frequency Method to Calculate the Hanger Cable ForceBased on the analysis of the analytical solutions of the string model and the beam model,the beam model considering the influence of stiffness should be adopted in the calculation of the cable force of the short hanger of the practical arch bridge.But the anchoring boundary conditions at both ends of the hanger are between the hinge and the rigid connection.(2)Numerical Analysis of Vibration Characteristics of Hanger on Arch BridgesThe effects of slenderness ratio and boundary conditions on the natural frequency of the hanger were studied by numerical analysis of 14 ANSYS models.The results show that the smaller the slenderness ratio of the hanger is,the greater the influence of the boundary conditions on the natural frequency of the hanger and the larger the error of the cable force calculation resultswill be.(3)The Development of Indoor Test Device for Cable Force Test of HangerBased on practical engineering investigation,a set of indoor test device for testing the cable force by frequency method is designed.The frequency of the device is close to that of arch bridge,and so are the slenderness ratio.The indoor test conditions meet the practical engineering requirements.(4)The Indoor Test of the Hanger Cable Force with Frequency MethodThe vibration tests of hangers of three arch bridges with different lengths were carried out.Based on beam vibration theory,the empirical formulas for calculating hanger force were proposed,and the accuracy of the formulas for calculating hanger force in three groups of literatures was compared.The results show that when the slenderness ratio of the hanger is close to 102 to 167,the calculation formula of the cable force proposed in this paper is closer to the actual value than the classical beam theory formula.At the same time,based on the calculation results of indoor test data,the applicable scope of different cable force calculation formulas is put forward.(5)The Engineering Validation of the Test for the Hanger Cable Force with Frequency MethodTaking Xujiadu Bridge in Fenghua as an example,through the vibration test of seven hangers on the bridge,the accuracy of the formulas in this paper and three groups of formulas in literature are studied.The results show that when the slenderness ratio of the hanger is close to 123 to 150,the formula proposed in this paper is more accurate.At the same time,the engineering verification results are consistent with the indoor test results,which shows that the indoor test research method and the revision of cable force calculation formula have certain engineering application value.