| The cable-stayed cable is one of the main force components of the cable-stayed bridge,the force size and state of the stay cable are directly related to the safety of the construction and the health of the bridge during the operation,so it is necessary to measure the cable force.After completion of cable stays and during bridge operation,the cable force is generally measured by frequency method.Using Jialu River Bridge at Humanistic Road in Zhongmou Green Boyuan District as engineering background,measurement of cable tension of parallel steel stranded cables installed with shock absorbers by frequency method is studied,it mainly includes the following aspects:(1)The existing research on cable force measurement by frequency method is summarized,the basic theory of cable force measurement by frequency method is deduced;the influence of cable bending stiffness,sag,boundary condition,shock absorber and other factors on cable force measurement are analyzed;using the method of conversion length,the effective vibration length of the cable can be calculated to reflect the influence of the shock absorber on the cable force;the commonly used formula for calculating cable force is analyzed,and a practical formula for calculating cable force is obtained.(2)Using the finite element software ABAQUS,the parallel cable strands installed with shock absorbers are simulated by solid element and beam element respectively,the results obtained are in good agreement with the design,two types of unit model can well reflect the vibration characteristic.At the same time,it was also found that the shock absorber has a greater influence on the vibration modes at both ends of the cable,and it has an influence on the measured cable frequency,the influence of shock absorber should be taken into account when the cable force is measured by frequency method.(3)In practical engineering,a restraint ring is sometimes installed on the cable of the parallel steel strand to enhance the integrity of the cable body.In order to analyze the effect of spacing of constraint rings on cable force measured by frequency method,the effect of constraint rings on cable body is simulated by fully coupled constraints,the solid element model and beam element model with different coupling spacing are established,it is found that with the increase of coupling spacing,the cable force error measured is also increasing,so the spacing should not be too large when setting the constraint ring,and it is preferably 3 to 5 meters.(4)Aimed at the characteristics of parallel steel wire stay cables installed the shock absorber,namely steel wires contact in the middle of the rope and shock absorber,but mutually discrete in other locations,as well as the steel wire cable force in the rope is not uneven,three cable-stayed cables with long,medium and short length are selected,and the coupling model of the single steel strand,whole cable and 61 steel strands installed with a shock absorber is established by the solid element and beam element,the simulation results are compared and analyzed to verify the feasibility of measuring the cable tension of parallel steel strands installed with shock absorbers by frequency method.(5)When measuring the force of the cable by frequency method,generally the vibration pickup directly is installed on the lasso HDPE outer casing,the outer casing diameter is larger than the diameter of the steel wire rope body,and in the middle part of the casing will be in contact with the steel wire rope body,in response to these problems,a cable body-HDPE outer tube model considering shock absorber is established,by analyzing the simulation results,it is found that the influence of HDPE jacket tube on cable force is great,and the influence of cable force can not be ignored,the effect of the outer casing on the cable force can be reduced by correcting the linear density of the cable body.(6)The conclusion of this paper has been applied to the cable force test of the Jialu River Bridge at Humanistic Road in Zhongmou Green Boyuan District,and the measured force is in good agreement with the design. |
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