A free-vibration testing device for simulating nonlinear stiffness of a bridge rigid model, wherein the free-vibration testing device comprises a rigid model (1), rigid rods (2), rigid arc-shaped supporting arms (3), first fixed bearing pulleys (4), first linear tensile springs (5), first lightweight high-strength thin strings (6), second fixed bearing pulleys (7), second linear tensile springs (8), and second lightweight high-strength thin strings (9);
- the rigid rods (2) are fixed at both ends of the rigid model (1), the torsion center line of the rigid model (1) is ensured to be collinear with the axes of the rigid rods (2), and the free ends of the rigid rods (2) pass perpendicularly through and are fixed to the center of the rigid arc-shaped supporting arms (3);
- the rigid arc-shaped supporting arm (3) is of a symmetrical structure and is mainly composed of arc-shaped rods connected to both ends of a straight rod, and the outer wall surfaces of the arc-shaped rods are provided with grooves;
- two first fixed bearing pulleys (4), two first linear tensile springs (5), and two first lightweight high-strength thin strings (6) are provided at each upper side of the rigid model (1) and arranged in a symmetrical structure, and the first fixed bearing pulleys (4) are ensured to be directly below the first linear tensile springs (5);
- the upper ends of the first linear tensile springs (5) are fixed, and the lower ends are connected with the upper ends of the first lightweight high-strength thin strings (6);
- the first lightweight high-strength thin strings (6) pass vertically downward through the first fixed bearing pulleys (4), the first lightweight high-strength thin strings (6) that are inclined or vertical are tangent to the outer wall surfaces of the rigid arc-shaped supporting arms (3) and are wound in the grooves on the outer wall surfaces, and the lower ends of the first lightweight high-strength thin strings (6) are fixed to the bottom of the rigid arc-shaped supporting arms (3);
- two second fixed bearing pulleys (7), two second linear tensile springs (8), and two second lightweight high-strength thin strings (9) are provided at each lower side of the rigid model (1) and arranged in a symmetrical structure, and the second fixed bearing pulleys (7) are ensured to be directly above the second linear tensile springs (8);
- the lower ends of the second linear tensile springs (8) are fixed, the upper ends are connected with the lower ends of the second lightweight high-strength thin strings (9), the second lightweight high-strength thin strings (9) pass vertically upward through the second fixed bearing pulleys (7), the second lightweight high-strength thin strings (9) that are inclined or vertical are tangent to the outer wall surfaces of the rigid arc-shaped supporting arms (3) and are wound in the grooves on the outer wall surfaces, and the upper ends of the second lightweight high-strength thin strings (9) are fixed to the top of the rigid arc-shaped supporting arms (3);
- this design ensures that during the vertical-torsional coupled free-vibration process of the rigid model (1) and the rigid arc-shaped supporting arms (3), the first lightweight high-strength thin strings (6) above the first fixed bearing pulleys (4) and the second lightweight high-strength thin strings (9) below the second fixed bearing pulleys (7) remain in a vertical state, so that the first linear tensile springs (5) and the second linear tensile springs (8) only undergo vertical stretching and contracting deformation;
- and by taking advantage of the nonlinear variation of inclination angles of the first lightweight high-strength thin strings (6) below the first fixed bearing pulleys (4) and/or the second lightweight high-strength thin strings (9) above the second fixed bearing pulleys (7) with the vertical displacement of the rigid model (1), the deformations of the first linear tensile springs (5) and the second linear tensile springs (8) exhibit a nonlinear relationship with the vertical displacement of the rigid model (1);
- when the shape of the rigid arc-shaped supporting arm (3) is a variable-radius arc, by taking advantage of the nonlinear variation of tangential distances from the first lightweight high-strength thin strings (6) and the second lightweight high-strength thin strings (9) to the variable-radius rigid arc-shaped supporting arms (3) with the torsional displacement of the rigid model (1), the deformations of the first linear tensile springs (5) and the second linear tensile springs (8) exhibit a nonlinear relationship with the torsional displacement of the rigid model (1);
- both the vertical displacement and the torsional displacement of the rigid model (1) can change the inclination angles and the tangential distances, thereby achieving the vertical-torsional coupled nonlinear stiffness;
- and when the shape of the rigid arc-shaped supporting arm (3) is a constant-radius circular arc, the tangential distances from the first lightweight high-strength thin strings (6) and the second lightweight high-strength thin strings (9) to the constant-radius rigid arc-shaped supporting arms (3) are always constant, the deformations of the first linear tensile springs (5) and the second linear tensile springs (8) always have a linear relationship with the torsional displacement of the rigid model (1), thereby achieving nonlinear stiffness only in the vertical direction while maintaining constant torsional stiffness.