A free vibration test device for simulating nonlinear stiffness of a bridge rigid model

Abstract

The application belongs to the technical field of bridge wind tunnel test device, and provides a free vibration test device for simulating nonlinear stiffness of a bridge rigid model, which comprises a rigid model, a rigid rod, a rigid arc-shaped hanging arm, a bearing fixed pulley, a linear tensile spring and a light high-strength thin rope. By flexibly designing the shape and size of the rigid arc-shaped hanging arm, the spatial position of the bearing fixed pulley and the initial strain of the spring and other parameters, the device can realize various vertical and torsional coupling nonlinear stiffness modes, and can also realize only vertical nonlinear stiffness and constant torsional stiffness, so as to carry out large-amplitude vertical torsional coupling flutter and large-amplitude vertical galloping vibration test of the bridge structure under nonlinear stiffness. In the process of large-amplitude vibration of the model, the spring can always keep a vertical state and will not vibrate laterally, so that the test device has stable low damping, mass and stiffness.

Description

Technical Field

[0001] The invention belongs to the technical field of bridge wind tunnel test devices and relates to a free vibration test device for simulating the nonlinear stiffness of a bridge rigidity model. Background Art

[0002] Long-span bridge structures are delicate and have low damping, making them susceptible to large wind-induced vibrations, such as flutter and galloping. These large wind-induced vibrations exhibit dual nonlinear effects: the coupling of structural stiffness nonlinearity with aerodynamic nonlinearity. However, existing research and defense concepts for large wind-induced vibrations primarily assume linear structures, making it difficult to simulate the nonlinear behavior of large-amplitude stiffness. Free vibration wind tunnel tests of rigid models of bridge girder segments are an important tool for studying the wind resistance of long-span bridges. However, existing large-amplitude flutter wind tunnel tests of rigid models of bridge girder segments assume constant structural stiffness. The applicant's patent application (CN108414186B, a wind tunnel test apparatus for vertical and torsional coupled large-amplitude free vibration of bridges) utilizes a constant-diameter hub to convert the torsional displacement of the rigid model into the expansion and contraction of a vertical spring. This allows for the realization of large-amplitude free vibrations coupled with bending and torsional forces while maintaining highly ideal constant stiffness, enabling the study of nonlinear aerodynamic effects. However, this apparatus cannot accommodate test conditions where both vertical and torsional stiffness exhibit nonlinearity. In addition, there are currently few reports on nonlinear stiffness test devices for large-amplitude vertical galloping. Therefore, there is an urgent need to develop a large-amplitude, stable, low-damping free vibration wind tunnel test device that can achieve both vertical and torsional nonlinear stiffness, or only vertical nonlinear stiffness. Summary of the Invention

[0003] The technical problem addressed by this invention is to address the need for large-amplitude free vibration of segmented rigid models of bridge components, such as bridge main beams, under nonlinear stiffness during wind tunnel testing. By further modifying the applicant's previously authorized patent (CN108414186B, a wind tunnel test apparatus for bridge vertical and torsional coupled large-amplitude free vibration), the invention is able to simulate both vertical and torsional nonlinear stiffness, as well as vertical nonlinear stiffness alone while maintaining constant torsional stiffness. Furthermore, the invention maintains a vertical spring under varying amplitudes, achieving stable, low-damping performance. The apparatus comprises a rigid model, a rigid rod, a rigid curved boom, a bearing fixed pulley, a linear tension spring, and a lightweight, high-strength string.

[0004] The technical solution of the present invention:

[0005] A free vibration test device for simulating the nonlinear stiffness of a bridge rigid model comprises a rigid model 1, a rigid rod 2, a rigid arc-shaped suspension arm 3, a first bearing fixed pulley 4, a first linear tension spring 5, a first lightweight high-strength thin rope 6, a second bearing fixed pulley 7, a second linear tension spring 8 and a second lightweight high-strength thin rope 9; the rigid rod 2 is fixed at both ends of the rigid model 1, and the torsion center line of the rigid model 1 is ensured to be collinear with the axis of the rigid rod 2, and the free end of the rigid rod 2 vertically passes through the center of the rigid arc-shaped suspension arm 3 and is fixed thereto; the rigid arc-shaped suspension arm 3 is a symmetrical structure, which is mainly composed of an arc-shaped rod connected at both ends of a straight rod, and the arc-shaped rod is fixed to the center of the rigid model 1. There is a groove on the outer wall; there are two first bearing fixed pulleys 4, first linear tension springs 5 ​​and first lightweight high-strength thin ropes 6 on one side of the rigid model 1, which are arranged in a symmetrical structure to ensure that the first bearing fixed pulley 4 is directly below the first linear tension spring 5; the upper end of the first linear tension spring 5 is fixed, and its lower end is connected to the upper end of the first lightweight high-strength thin rope 6; the first lightweight high-strength thin rope 6 passes vertically downward through the first bearing fixed pulley 4, and the inclined or vertical first lightweight high-strength thin rope 6 is tangent to the outer wall of the rigid arc-shaped boom 3 and is wound in its groove, and the lower end of the first lightweight high-strength thin rope 6 is fixed to the bottom of the rigid arc-shaped boom 3; the rigid There are two second bearing fixed pulleys 7, second linear tension springs 8 and second lightweight high-strength thin ropes 9 on one side of the model 1, which are symmetrical in structure, ensuring that the second bearing fixed pulley 7 is directly above the second linear tension spring 8; the lower end of the second linear tension spring 8 is fixed, and its upper end is connected to the lower end of the second lightweight high-strength thin rope 9, and the second lightweight high-strength thin rope 9 passes vertically upward through the second bearing fixed pulley 7, and the inclined or vertical second lightweight high-strength thin rope 9 is tangent to the outer wall surface of the rigid arc-shaped boom 3 and is wound in its groove, and the upper end of the second lightweight high-strength thin rope 9 is fixed to the top of the rigid arc-shaped boom 3; thereby ensuring that the rigid model 1 and the rigid arc During the vertical and torsional coupled free vibration of the boom 3, the first lightweight high-strength thin rope 6 above the first bearing fixed pulley 4 and the second lightweight high-strength thin rope 9 below the second bearing fixed pulley 7 remain in a vertical state, so that the first linear tension spring 5 and the second linear tension spring 8 only undergo vertical telescopic deformation; the inclination angle of the first lightweight high-strength thin rope 6 below the first bearing fixed pulley 4 and / or the second lightweight high-strength thin rope 9 above the second bearing fixed pulley 7 changes nonlinearly with the vertical displacement of the rigid model 1, so that the deformation of the first linear tension spring 5 and the second linear tension spring 8 has a nonlinear relationship with the vertical displacement of the rigid model 1.

[0006] When the outer shape of the rigid curved boom 3 is a variable diameter arc, the tangent distance between the first lightweight high-strength thin rope 6 and the second lightweight high-strength thin rope 9 and the variable diameter rigid curved boom 3 changes nonlinearly with the torsional displacement of the rigid model 1, so that the deformation of the first linear tension spring 5 and the second linear tension spring 8 is nonlinearly related to the torsional displacement of the rigid model 1; both the vertical displacement and the torsional displacement can change the inclination angle and the tangent distance, thereby realizing vertical and torsional coupled nonlinear stiffness; when the outer shape of the rigid curved boom 3 is a constant diameter circular arc, the tangent distance between the first lightweight high-strength thin rope 6 and the second lightweight high-strength thin rope 9 and the constant diameter rigid curved boom 3 is always constant, and the deformation of the first linear tension spring 5 and the second linear tension spring 8 is always linearly related to the torsional displacement of the rigid model 1, thereby realizing only vertical nonlinear stiffness while the torsional stiffness remains constant.

[0007] The nonlinear stiffness of the free vibration test device is related to the following parameters: the vertical displacement and torsional displacement of the rigid model 1, the original length, initial strain and stiffness coefficient of the first linear tension spring 5 and the second linear tension spring 8, the shape and size of the rigid curved boom 3, the spatial position of the two first bearing fixed pulleys 4, and the spatial position of the two second bearing fixed pulleys 7; the shape, size and spatial position of the rigid curved boom 3 and the first bearing fixed pulley 4 determine the initial inclination angle of the first lightweight high-strength string 6 and its initial tangent distance with the rigid curved boom 3; the shape, size and spatial position of the rigid curved boom 3 and the second bearing fixed pulley 7 determine the initial inclination angle of the second lightweight high-strength string 9 and its initial tangent distance with the rigid curved boom 3; the degree of nonlinear stiffness is improved by increasing the initial inclination angle of the first lightweight high-strength string 6 and the second lightweight high-strength string 9, increasing the degree of change in the inner diameter of the rigid curved boom 3, and reducing the initial strain of the first linear tension spring 5 and the second linear tension spring 8.

[0008] The shape and size of the rigid arc-shaped boom 3 should be determined according to the target nonlinear stiffness of the free vibration test device, the vertical amplitude, torsional amplitude, mass, mass moment of inertia, the ratio of torsional frequency to vertical frequency of the rigid model 1 and other parameters; when the outer shape of the rigid arc-shaped boom 3 is a variable diameter arc, the rigid arc-shaped boom 3 is symmetrical about the central vertical line, symmetrical about the central horizontal line, or asymmetrical about the central horizontal line; for the working condition where the torsional stiffness decreases with the increase of the absolute value of the torsional displacement, the initial tangent distance of the first lightweight high-strength thin rope 6 and the second lightweight high-strength thin rope 9 is made as close as possible to the long axis of the rigid arc-shaped boom 3, so that when the rigid model 1 generates torsional During displacement, the tangent distance moves away from the major axis and decreases, thereby reducing the torsional stiffness. For the working condition where the torsional stiffness increases with the increase of the absolute value of the torsional displacement, the initial tangent distance of the first lightweight high-strength thin rope 6 and the second lightweight high-strength thin rope 9 is made as close as possible to the minor axis of the rigid arc-shaped boom 3, so that when the rigid model 1 produces torsional displacement, the tangent distance moves away from the minor axis and increases, thereby increasing the torsional stiffness. When the outer shape of the rigid arc-shaped boom 3 is an arc of equal diameter, while keeping the vertical nonlinear stiffness unchanged, the arc radius is increased as much as possible, thereby improving the torsional vertical frequency ratio, avoiding the interference of torsional vibration on vertical vibration that may occur under different working conditions, and ensuring the accuracy of the large-amplitude vertical galloping test.

[0009] The first bearing fixed pulley 4 and the second bearing fixed pulley 7 are arranged on the rigid frame outside the wind tunnel for suspending the rigid model 1, and the spatial position is adjusted according to the target nonlinear stiffness, while ensuring that there is no collision with the rigid arc-shaped boom 3 within the design amplitude; for the working condition that the vertical stiffness increases with the increase of the vertical downward displacement and decreases with the increase of the vertical upward displacement, the spatial position of the two first bearing fixed pulleys 4 is adjusted so that the first lightweight high-strength thin rope 6 at the lower part of the first bearing fixed pulley 4 has an appropriate initial inclination angle, and the spacing between the two second bearing fixed pulleys 7 is adjusted so that the second lightweight high-strength thin rope 9 is all in a vertical state; for the working condition that the vertical stiffness increases with the increase of the vertical downward displacement and decreases with the increase of the vertical upward displacement, the spatial position of the two first bearing fixed pulleys 4 is adjusted so that the first lightweight high-strength thin rope 6 at the lower part of the first bearing fixed pulley 4 has an appropriate initial inclination angle, and the spacing between the two second bearing fixed pulleys 7 is adjusted so that the second lightweight high-strength thin rope 9 is all in a vertical state; For the working condition where the vertical stiffness decreases with the increase of the downward displacement and increases with the increase of the vertical upward displacement, the spacing between the two first bearing fixed pulleys 4 is adjusted so that all the first lightweight high-strength strings 6 are in a vertical state, and the spatial positions of the two second bearing fixed pulleys 7 are adjusted so that the second lightweight high-strength strings 9 above the second bearing fixed pulleys 7 have an appropriate initial tilt angle. For the working condition where the vertical stiffness increases with the increase of the absolute value of the vertical displacement or decreases with the increase of the absolute value of the vertical displacement, the spatial positions of the two first bearing fixed pulleys 4 and the two second bearing fixed pulleys 7 are adjusted respectively so that the first lightweight high-strength strings 6 and the second lightweight high-strength strings 9 have an appropriate initial tilt angle. According to the actual situation, the first lightweight high-strength strings 6 and the second lightweight high-strength strings 9 are tilted toward the inside or outside of the model.

[0010] The first and second fixed pulleys 4 and 7 are lightweight and high-strength, with minimal friction coefficients during bearing rotation. During system vibration, the first and second lightweight, high-strength cords 6 and 9 compress and rotate the first and second fixed pulleys 4 and 7, respectively. The use of small-diameter bearings and large-diameter pulleys reduces bearing rotation distance, lowers system energy consumption, and reduces vibration system damping, even when the first and / or second lightweight, high-strength cords 6 and 9 experience the same displacement.

[0011] The first lightweight, high-strength string 6 and the second lightweight, high-strength string 9 are lightweight, high-strength, have a high elastic modulus, and are free of bending and torsion resistance, and can be made of any material. The first lightweight, high-strength string 6 and the second lightweight, high-strength string 9 should be of sufficient length to ensure that the first linear tension spring 5 does not collide with the first bearing fixed pulley 4, and the second linear tension spring 8 does not collide with the second bearing fixed pulley 7, within the designed amplitude.

[0012] The beneficial effects of the present invention are as follows: (1) it can achieve the vertical and torsional coupling nonlinear stiffness and the vertical nonlinear stiffness alone while the torsional stiffness remains constant, so as to carry out large-amplitude vertical torsional coupling flutter and large-amplitude vertical gallop vibration measurement tests under the nonlinear stiffness of the bridge structure; (2) by flexibly designing the shape and size of the rigid arc-shaped boom, the spatial position of the bearing fixed pulley and the initial strain of the spring and other parameters, it can realize a variety of complex nonlinear stiffness change modes with displacement; (3) during the large-amplitude vibration process of the model, the spring can always remain in a vertical state and will not vibrate laterally, thereby ensuring that the test device has stable low damping, stable quality and stiffness characteristics; (4) the device is low-cost, easy to process, efficient and feasible. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a structural diagram of the wind tunnel test device for nonlinear stiffness free vibration when the thin rope is tilted outward.

[0014] Figure 2 These are the external structural diagrams of the boom with different rigidity arcs; among them, (a) is the external structural diagram of the boom with an elliptical arc (major axis), (b) is the external structural diagram of the boom with an elliptical arc (minor axis), (c) is the external structural diagram of the boom with an involute, and (d) is the external structural diagram of the boom with an equal-diameter circular arc.

[0015] Figure 3 This is the structural diagram of the first wind tunnel test device for the free vibration of nonlinear stiffness of lightweight and high-strength thin ropes when tilted.

[0016] Figure 4 This is the structural diagram of the second wind tunnel test device for the nonlinear stiffness free vibration of lightweight and high-strength thin ropes when tilted.

[0017] Figure 5This is a structural diagram of the wind tunnel test device for nonlinear stiffness free vibration when the thin rope is tilted inward.

[0018] In the figure: 1 rigid model; 2 rigid rod; 3 rigid arc-shaped boom; 4 first bearing fixed pulley; 5 first linear tension spring; 6 first lightweight high-strength thin rope; 7 second bearing fixed pulley; 8 second linear tension spring; 9 second lightweight high-strength thin rope. DETAILED DESCRIPTION

[0019] The specific implementation of the present invention is described in detail below in conjunction with the technical solutions and drawings.

[0020] like Figure 1As shown, a free vibration test device for simulating the nonlinear stiffness of a bridge rigid model comprises a rigid model 1, a rigid rod 2, a rigid arc-shaped suspension arm 3, a first bearing fixed pulley 4, a first linear tension spring 5, a first lightweight high-strength thin rope 6, a second bearing fixed pulley 7, a second linear tension spring 8 and a second lightweight high-strength thin rope 9; the rigid rod 2 is fixed at both ends of the rigid model 1, and the torsion center line of the rigid model 1 is ensured to be collinear with the axis of the rigid rod 2, and the free end of the rigid rod 2 vertically passes through the center of the rigid arc-shaped suspension arm 3 and is fixed thereto; the rigid arc-shaped suspension arm 3 is a symmetrical structure, which is mainly composed of arc-shaped rods connected at both ends of a straight rod, and the arc The outer wall of the shaped rod is provided with a groove; there are two first bearing fixed pulleys 4, first linear tension springs 5 ​​and first lightweight high-strength thin ropes 6 on one side of the rigid model 1, which are arranged in a symmetrical structure to ensure that the first bearing fixed pulley 4 is directly below the first linear tension spring 5; the upper end of the first linear tension spring 5 is fixed, and its lower end is connected to the upper end of the first lightweight high-strength thin rope 6; the first lightweight high-strength thin rope 6 passes vertically downward through the first bearing fixed pulley 4, and the inclined or vertical first lightweight high-strength thin rope 6 is tangent to the outer wall of the rigid curved boom 3 and is wound in its groove, and the lower end of the first lightweight high-strength thin rope 6 is fixed to the bottom of the rigid curved boom 3; There are two second bearing fixed pulleys 7, second linear tension springs 8 and second lightweight high-strength thin ropes 9 on one side of the rigid model 1, which are symmetrical in structure, ensuring that the second bearing fixed pulley 7 is directly above the second linear tension spring 8; the lower end of the second linear tension spring 8 is fixed, and its upper end is connected to the lower end of the second lightweight high-strength thin rope 9, and the second lightweight high-strength thin rope 9 passes vertically upward through the second bearing fixed pulley 7, and the inclined or vertical second lightweight high-strength thin rope 9 is tangent to the outer wall surface of the rigid arc-shaped boom 3 and is wound in its groove, and the upper end of the second lightweight high-strength thin rope 9 is fixed to the top of the rigid arc-shaped boom 3; in this way, the rigid model 1 and the rigid arc are ensured to be stable. During the vertical and torsional coupled free vibration of the shaped boom 3, the first lightweight high-strength thin rope 6 above the first bearing fixed pulley 4 and the second lightweight high-strength thin rope 9 below the second bearing fixed pulley 7 remain in a vertical state, so that the first linear tension spring 5 and the second linear tension spring 8 only undergo vertical telescopic deformation; the inclination angle of the first lightweight high-strength thin rope 6 below the first bearing fixed pulley 4 and / or the second lightweight high-strength thin rope 9 above the second bearing fixed pulley 7 changes nonlinearly with the vertical displacement of the rigid model 1, so that the deformation of the first linear tension spring 5 and the second linear tension spring 8 has a nonlinear relationship with the vertical displacement of the rigid model 1.

[0021] like Figure 1As shown, when the outer shape of the rigid curved boom 3 is a variable diameter arc, the tangent distance between the first lightweight high-strength thin rope 6 and the second lightweight high-strength thin rope 9 and the variable diameter rigid curved boom 3 changes nonlinearly with the torsional displacement of the rigid model 1, so that the deformation of the first linear tension spring 5 and the second linear tension spring 8 is nonlinearly related to the torsional displacement of the rigid model 1; both the vertical displacement and the torsional displacement can change the inclination angle and the tangent distance, thereby realizing vertical and torsional coupled nonlinear stiffness; when the outer shape of the rigid curved boom 3 is a constant diameter circular arc, the tangent distance between the first lightweight high-strength thin rope 6 and the second lightweight high-strength thin rope 9 and the constant diameter rigid curved boom 3 is always constant, and the deformation of the first linear tension spring 5 and the second linear tension spring 8 is always linearly related to the torsional displacement of the rigid model 1, thereby realizing only vertical nonlinear stiffness while the torsional stiffness remains constant.

[0022] The nonlinear stiffness of the free vibration test device is related to the following parameters: the vertical displacement and torsional displacement of the rigid model 1, the original length, initial strain and stiffness coefficient of the first linear tension spring 5 and the second linear tension spring 8, the shape and size of the rigid curved boom 3, the spatial position of the two first bearing fixed pulleys 4, and the spatial position of the two second bearing fixed pulleys 7; the shape, size and spatial position of the rigid curved boom 3 and the first bearing fixed pulley 4 determine the initial inclination angle of the first lightweight high-strength string 6 and its initial tangent distance with the rigid curved boom 3; the shape, size and spatial position of the rigid curved boom 3 and the second bearing fixed pulley 7 determine the initial inclination angle of the second lightweight high-strength string 9 and its initial tangent distance with the rigid curved boom 3; the degree of nonlinear stiffness is improved by increasing the initial inclination angle of the first lightweight high-strength string 6 and the second lightweight high-strength string 9, increasing the degree of change in the inner diameter of the rigid curved boom 3, and reducing the initial strain of the first linear tension spring 5 and the second linear tension spring 8.

[0023] like Figure 2As shown, the shape and size of the rigid arc-shaped boom 3 should be determined according to the target nonlinear stiffness of the free vibration test device, the vertical amplitude, torsional amplitude, mass, mass moment of inertia, the ratio of torsional frequency to vertical frequency of the rigid model 1 and other parameters; when the outer shape of the rigid arc-shaped boom 3 is a variable diameter arc, the rigid arc-shaped boom 3 is symmetrical about the central vertical line, symmetrical about the central horizontal line, or asymmetrical about the central horizontal line; for the working condition where the torsional stiffness decreases with the increase of the absolute value of the torsional displacement, the initial tangent distance of the first lightweight high-strength thin rope 6 and the second lightweight high-strength thin rope 9 is made as close as possible to the long axis of the rigid arc-shaped boom 3, so that when the rigid model 1 generates torsional During displacement, the tangent distance moves away from the major axis and decreases, thereby reducing the torsional stiffness. For the working condition where the torsional stiffness increases with the increase of the absolute value of the torsional displacement, the initial tangent distance of the first lightweight high-strength thin rope 6 and the second lightweight high-strength thin rope 9 is made as close as possible to the minor axis of the rigid arc-shaped boom 3, so that when the rigid model 1 produces torsional displacement, the tangent distance moves away from the minor axis and increases, thereby increasing the torsional stiffness. When the outer shape of the rigid arc-shaped boom 3 is an arc of equal diameter, while keeping the vertical nonlinear stiffness unchanged, the arc radius is increased as much as possible, thereby improving the torsional vertical frequency ratio, avoiding the interference of torsional vibration on vertical vibration that may occur under different working conditions, and ensuring the accuracy of the large-amplitude vertical galloping test.

[0024] The first bearing fixed pulley 4 and the second bearing fixed pulley 7 are arranged on a rigid frame outside the wind tunnel for suspending the rigid model 1. Their spatial positions are adjusted according to the target nonlinear stiffness, while ensuring that they do not collide with the rigid arc-shaped boom 3 within the designed amplitude.

[0025] like Figure 3 As shown, for the working condition where the vertical stiffness increases with the increase of vertical downward displacement and decreases with the increase of vertical upward displacement, the spatial positions of the two first bearing fixed pulleys 4 are adjusted so that the first lightweight high-strength thin rope 6 at the lower part of the first bearing fixed pulley 4 has an appropriate initial inclination angle, and the spacing between the two second bearing fixed pulleys 7 is adjusted so that all the second lightweight high-strength thin ropes 9 are in a vertical state.

[0026] like Figure 4 As shown, for the working condition where the vertical stiffness decreases with the increase of vertical downward displacement and increases with the increase of vertical upward displacement, the spacing between the two first bearing fixed pulleys 4 is adjusted so that all the first lightweight high-strength thin ropes 6 are in a vertical state, and the spatial positions of the two second bearing fixed pulleys 7 are adjusted so that the second lightweight high-strength thin rope 9 on the upper part of the second bearing fixed pulley 7 has an appropriate initial inclination angle.

[0027] like Figure 1 and Figure 5As shown, for the working condition where the vertical stiffness increases or decreases with the increase of the absolute value of the vertical displacement, the spatial positions of the two first bearing fixed pulleys 4 and the two second bearing fixed pulleys 7 are adjusted respectively to make the first lightweight high-strength string 6 and the second lightweight high-strength string 9 have appropriate initial tilt angles. Depending on the actual situation, the first lightweight high-strength string 6 and the second lightweight high-strength string 9 are tilted toward the inside or outside of the model.

[0028] The first bearing fixed pulley 4 and the second bearing fixed pulley 7 are lightweight and high-strength, and the bearing rotational friction coefficient is minimized. The use of small-diameter bearings and large-diameter pulleys reduces the bearing rotation distance, lowering system energy consumption and reducing vibration system damping, even when the first lightweight, high-strength string 6 and / or the second lightweight, high-strength string 9 experience the same displacement.

[0029] The first lightweight, high-strength string 6 and the second lightweight, high-strength string 9 are lightweight, high-strength, have a high elastic modulus, and are free of bending and torsion resistance. The first lightweight, high-strength string 6 and the second lightweight, high-strength string 9 should be of sufficient length to prevent collision between the first linear tension spring 5 and the first bearing fixed pulley 4, and between the second linear tension spring 8 and the second bearing fixed pulley 7, within the designed amplitude.

[0030] The above description is merely an example of a preferred embodiment of the present invention and does not constitute any limitation on the present invention. Any equivalent changes, modifications, or variations made by a person skilled in the art using the technical solution of the present invention to the above examples shall still fall within the scope of the technical solution of the present invention.

Claims

1. A free vibration test device for simulating the nonlinear stiffness of a bridge rigidity model, characterized in that: The free vibration test device comprises a rigid model (1), a rigid rod (2), a rigid arc-shaped suspension arm (3), a first bearing fixed pulley (4), a first linear tension spring (5), a first light high-strength string (6), a second bearing fixed pulley (7), a second linear tension spring (8) and a second light high-strength string (9); The rigid model (1) is fixed with rigid rods (2) at both ends, and the torsion center line of the rigid model (1) is ensured to be colinear with the axis of the rigid rod (2). The free end of the rigid rod (2) vertically passes through the center of the rigid arc-shaped boom (3) and is fixed thereto. The rigid arc-shaped boom (3) is a symmetrical structure, which is mainly composed of arc-shaped rods connected at both ends of a straight rod, and the outer wall surface of the arc-shaped rod is provided with a groove. The first bearing fixed pulley (4), the first linear tension spring (5) and the first light high-strength thin rope (6) on one side of the rigid model (1) are all two and are arranged in a symmetrical structure, ensuring that the first bearing fixed pulley (4) is in the first linear tension spring (5). Directly below; the upper end of the first linear tension spring (5) is fixed, and its lower end is connected to the upper end of the first light high-strength thin rope (6); the first light high-strength thin rope (6) passes vertically downward through the first bearing fixed pulley (4), the inclined or vertical first light high-strength thin rope (6) is tangent to the outer wall surface of the rigid arc-shaped suspension arm (3) and is wound in its groove, and the lower end of the first light high-strength thin rope (6) is fixed to the bottom of the rigid arc-shaped suspension arm (3); the second bearing fixed pulley (7), the second linear tension spring (8) and the second light high-strength thin rope (9) on one side of the rigid model (1) are all two, forming a symmetrical structure, ensuring that the second bearing fixed pulley The wheel (7) is directly above the second linear tension spring (8); the lower end of the second linear tension spring (8) is fixed, and the upper end thereof is connected to the lower end of the second light high-strength string (9); the second light high-strength string (9) passes vertically upward through the second bearing fixed pulley (7); the inclined or vertical second light high-strength string (9) is tangential to the outer wall surface of the rigid arc-shaped boom (3) and is wound in its groove; the upper end of the second light high-strength string (9) is fixed to the top of the rigid arc-shaped boom (3); thereby ensuring that the rigid model (1) and the rigid arc-shaped boom (3) are in the process of vertical and torsional coupled free vibration, the first bearing fixed pulley (4 ) above the first light high-strength string (6) and the second light high-strength string (9) below the second bearing fixed pulley (7) are kept in a vertical state, so that the first linear tension spring (5) and the second linear tension spring (8) only undergo vertical expansion and contraction deformation; the inclination angle of the first light high-strength string (6) below the first bearing fixed pulley (4) and / or the second light high-strength string (9) above the second bearing fixed pulley (7) changes nonlinearly with the vertical displacement of the rigid model (1), so that the deformation of the first linear tension spring (5) and the second linear tension spring (8) shows a nonlinear relationship with the vertical displacement of the rigid model (1); When the outer shape of the rigid arc-shaped suspension arm (3) is a variable diameter arc, the tangent distance between the first lightweight high-strength thin rope (6) and the second lightweight high-strength thin rope (9) and the variable diameter rigid arc-shaped suspension arm (3) is nonlinearly changed with the torsional displacement of the rigid model (1), so that the deformation of the first linear tension spring (5) and the second linear tension spring (8) is nonlinearly related to the torsional displacement of the rigid model (1); both the vertical displacement and the torsional displacement can change the inclination angle and the tangent distance, thereby realizing vertical and torsional coupled nonlinear stiffness; when the outer shape of the rigid arc-shaped suspension arm (3) is a constant diameter circular arc, the tangent distance between the first lightweight high-strength thin rope (6) and the second lightweight high-strength thin rope (9) and the constant diameter rigid arc-shaped suspension arm (3) is always constant, and the deformation of the first linear tension spring (5) and the second linear tension spring (8) is always linearly related to the torsional displacement of the rigid model (1), thereby realizing only vertical nonlinear stiffness and constant torsional stiffness.

2. The free vibration test device according to claim 1, characterized in that: The nonlinear stiffness of the free vibration test device is related to the following parameters: the vertical displacement and torsional displacement of the rigid model (1), the original length, initial strain and stiffness coefficient of the first linear tension spring (5) and the second linear tension spring (8), the shape and size of the rigid arc-shaped suspension arm (3), the spatial position of the two first bearing fixed pulleys (4), and the spatial position of the two second bearing fixed pulleys (7); the shape and size of the rigid arc-shaped suspension arm (3) and the spatial position of the first bearing fixed pulley (4) determine the initial inclination angle of the first lightweight high-strength thin rope (6). and the initial tangent distance between the rigid curved boom (3); the shape and size of the rigid curved boom (3) and the spatial position of the second bearing fixed pulley (7) determine the initial tilt angle of the second light high-strength thin rope (9) and the initial tangent distance between the second light high-strength thin rope (9) and the rigid curved boom (3); the nonlinear degree of stiffness is improved by increasing the initial tilt angle of the first light high-strength thin rope (6) and the second light high-strength thin rope (9), increasing the degree of change of the inner diameter of the rigid curved boom (3), and reducing the initial strain of the first linear tension spring (5) and the second linear tension spring (8).

3. The free vibration test device according to claim 2, characterized in that: The shape and size of the rigid arc-shaped boom (3) are determined according to the target nonlinear stiffness of the free vibration test device, the vertical amplitude, the torsional amplitude, the mass, the mass moment of inertia, and the ratio of the torsional frequency to the vertical frequency of the rigid model (1); when the outer shape of the rigid arc-shaped boom (3) is a variable diameter arc, the rigid arc-shaped boom (3) is symmetrical about the central vertical line, symmetrical about the central horizontal line, or asymmetrical about the central horizontal line; for the working condition where the torsional stiffness decreases with the increase of the absolute value of the torsional displacement, the initial tangent distance of the first light high-strength thin rope (6) and the second light high-strength thin rope (9) is as close as possible to the long axis of the rigid arc-shaped boom (3), so that when the rigid model (1) generates torsional When the torsional displacement occurs, the tangent distance moves away from the long axis and decreases, thereby reducing the torsional stiffness. For the working condition where the torsional stiffness increases with the increase of the absolute value of the torsional displacement, the initial tangent distances of the first lightweight high-strength thin rope (6) and the second lightweight high-strength thin rope (9) are made as close as possible to the short axis of the rigid arc-shaped boom (3), so that when the rigid model (1) produces torsional displacement, the tangent distance moves away from the short axis and increases, thereby increasing the torsional stiffness. When the outer shape of the rigid arc-shaped boom (3) is a constant diameter circular arc, the arc radius is increased as much as possible while keeping the vertical nonlinear stiffness unchanged, thereby improving the torsional vertical frequency ratio, avoiding the interference of torsional vibration on vertical vibration that may occur under different working conditions, and ensuring the accuracy of the large-amplitude vertical galloping test.

4. The free vibration test device according to claim 3, characterized in that: The first bearing fixed pulley (4) and the second bearing fixed pulley (7) are arranged on a rigid frame outside the wind tunnel for suspending the rigid model (1), and their spatial positions are adjusted according to the target nonlinear stiffness, while ensuring that they do not collide with the rigid arc-shaped boom (3) within the design amplitude; for the working condition in which the vertical stiffness increases with the increase of the vertical downward displacement and decreases with the increase of the vertical upward displacement, the spatial positions of the two first bearing fixed pulleys (4) are adjusted so that the first light high-strength thin rope (6) at the lower part of the first bearing fixed pulley (4) generates an initial tilt angle, and the spacing between the two second bearing fixed pulleys (7) is adjusted so that all the second light high-strength thin ropes (9) are in a vertical state; for the working condition in which the vertical stiffness increases with the increase of the vertical downward displacement and decreases with the increase of the vertical upward displacement, the spatial positions of the two first bearing fixed pulleys (4) are adjusted so that the first light high-strength thin rope (6) at the lower part of the first bearing fixed pulley (4) generates an initial tilt angle, and the spacing between the two second bearing fixed pulleys (7) is adjusted so that all the second light high-strength thin ropes (9) are in a vertical state; For the working condition where the vertical stiffness decreases with the increase of the vertical downward displacement and increases with the increase of the vertical upward displacement, the spacing between the two first bearing fixed pulleys (4) is adjusted so that all the first light high-strength thin ropes (6) are in a vertical state, and the spatial positions of the two second bearing fixed pulleys (7) are adjusted so that the second light high-strength thin rope (9) above the second bearing fixed pulleys (7) generates an initial tilt angle; for the working condition where the vertical stiffness increases with the increase of the absolute value of the vertical displacement or decreases with the increase of the absolute value of the vertical displacement, the spatial positions of the two first bearing fixed pulleys (4) and the two second bearing fixed pulleys (7) are adjusted respectively so that both the first light high-strength thin rope (6) and the second light high-strength thin rope (9) generate an initial tilt angle.

5. The free vibration test device according to claim 4, characterized in that: The first light-weight high-strength string (6) and the second light-weight high-strength string (9) are tilted toward the inside or outside of the model according to actual conditions.

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