Tension test method for stay cable steel strand of partially cable-stayed bridge

[0015] The test method provided by the present invention uses a section of the steel strand in a part of the cable-stayed bridge cable steel strand as the test section of the steel strand to test the fundamental frequency and bending rigidity of the section of the steel strand. Fundamental frequency, bending stiffness, length, quality parameters, according to the calculation theory of free vibration of cable considering the influence of bending stiffness, calculate the tension of some cable-stayed bridge cables; the test process of the fundamental frequency includes the following steps:

[0016] (1) Select any length of the steel strand in the cable-stayed bridge cable as the test section steel strand, and fix the two ends of the test section steel strand by connecting rigid bodies between the two ends;

[0017] (2) Use an acceleration sensor and a matching acquisition instrument to measure the fundamental frequency of the steel strand in the test section.

[0018] The bending stiffness test process includes the following steps:

[0019] (1) Select a section of steel strand without tension action, and fix its two ends with artificial boundaries, and its length, cross-sectional area and material are the same as the test section steel strand;

[0020] (2) Measure the fundamental frequency of this section of steel strand by using an acceleration sensor and a matching acquisition instrument;

[0021] (3) According to the known tension conditions (such as zero tension), calculate the bending stiffness of the steel strand in the test section.

[0022] Reference figure 1 In this embodiment, the following device is used to fix the two ends 11 and 12 of the steel strand 1 of the test section.

[0023] The device includes a strip rigid body 2 and steel stranded wire connectors 31, 32. The steel stranded wire connectors 31, 32 are fixed on the strip rigid body 2 and respectively used to connect to the two ends of the steel strand of the test section. Fix both ends of the steel strand in the test section.

[0024] The strip rigid body 2 can be a steel beam, and the symbol 4 is a vibration sensor. It uses an acceleration sensor, such as the DH301 capacitive three-way sensor produced by Donghua Electronic Instrument Factory, and is collected by a DH5901 handheld dynamic signal test analyzer 5 And analysis. According to the calculated length l between the two constrained boundaries of the steel strand and the section parameters (mass per unit length m, section bending stiffness EI and cross-sectional area A), the tension T of the steel strand is calculated from the measured frequency f.

[0025] According to the calculated length l between the two constrained boundaries of the steel strand and the section parameters (mass per unit length m, section bending stiffness EI and cross-sectional area A), the tension T of the steel strand is calculated from the measured frequency f.

[0026] The following describes the calculation theory of estimating tension based on frequency.

[0027] The free vibration equation of steel strand considering the effect of bending stiffness is:

[0028] EI ∂ 4 w ∂ x 4 - T ∂ 2 w ∂ x 2 + m ∂ 2 w ∂ t 2 = 0 - - - ( 1 )

[0029] In the formula, w is the lateral vibration displacement of the steel strand, EI is the bending stiffness, that is, the product of the elastic modulus E and the section moment of inertia I, T is the tension, and m is the mass per unit length of the boom. Here, it is assumed that the vibration of the boom is a small deformation, and the change in tension during the vibration can be ignored.

[0030] The natural frequency of the steel strand can be obtained according to the non-zero solution condition of equation (1). The natural frequency of the i-th mode is:

[0031] f i 2 = π 2 EI 4 ml 4 ( i - φ π ) 4 + T 4 ml 2 ( i - φ π ) 2 - - - ( 2 )

[0032] Where

[0033] tan φ = - 2 ω T mEI - - - ( 3 )

[0034] Where ω is the circular frequency.

[0035] Fix a steel strand under the condition of zero tension, test the vibration frequency, obtain the bending stiffness EI by formula (2), and then substitute formula (2) to obtain the steel strand of the cable-stayed bridge under any force Line tension.

[0036] In order to verify the effectiveness of the method and device of the present invention, it was verified in the inspection of a certain part of the cable-stayed bridge in Hangzhou, and several cables were selected for measurement. For easy operation, select a section of steel strand on the side close to the main beam and use both ends figure 1 The device shown is fixed, and the length of the fixed section is measured. The fundamental frequency of the steel strand is measured by an acceleration sensor and a matching acquisition instrument. Then test the bending stiffness of the steel strand. According to the steel strand of the same material, cross-sectional area and length, the two ends of the steel strand are fixed in the same way, and the fundamental frequency of the steel strand under environmental vibration is measured under zero tension. The tension is zero and the inverse calculation obtains the bending stiffness of the steel strand. In this way, under the premise that the boundary conditions and bending stiffness of the steel strand are known, the vibration frequency method is used to obtain the tension from the fundamental frequency of the steel strand according to formula (2).

[0037] The cable force of a partially cable-stayed bridge is measured, and any steel strand of the cable is selected, its tension calibration value T=129.0kN, the measured vibration frequency f=228.44Hz, the tension calculated by the method of the present invention T * =130.2kN, the ratio δ to the calibration value * =1.01; the tension T calculated according to the string theory without considering the bending stiffness 0 =171.02kN, the ratio δ to the calibration value 0 = 1.33. It can be seen that the algorithm of the present invention is more accurate than the tension calculated by traditional string theory.

[0038] According to the same test method, the tensions of the other 6 steel strands were tested, which are listed in Table 1. It can be seen from the data in the table that using the test method of the present invention, there are three sets of tension test accuracy of about 100%, and the remaining accuracy also exceeds 90%, while the traditional string theory test results are about 30% larger than the calibration value on average. It can be seen that the tension results obtained by using the testing method and device of the present invention have high accuracy.

[0039] Table 1 Tension test accuracy of cable steel strand

[0040]