JPH0337057B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a vibration isolator for structures, and more particularly to a cantilever type dynamic vibration absorber for minimizing wind-induced Karman vibrations in girders or main towers of long bridges. . [Prior art] Conventional technologies of this type include the type of pedestrian bridge (RIVER WHARFE) in which a weight is supported by a vertical spring and a hydraulic damper (see Figure 6), or the patent application 1983-
No. 216999 (plate spring type dynamic vibration absorber using a viscoelastic or viscous material as a damper, see Figure 7) was published. In Fig. 6, 3 is the weight 42 of this dynamic vibration absorber.
is a piston rod, and a weight 3 is attached by a nut 44.
An oil damper 6 is inserted into the oil 40 at the other end of the piston rod 42 . Oil 40 is confined within frame 17. A coil spring 18 is inserted between the frame 17 and the weight 3.
A slide plate 41 is loosely fitted to the lower end of the frame 17 by screws 45 so as to be able to slide around the outer periphery of the cylindrical portion of the frame 17. 43 is a hook, which is used when transporting the weight 3. The dynamic vibration absorber for a pedestrian bridge configured as described above is fixed to a bridge to be damped or the like with bolts 36. Now, if periodic vibrations act on the bridge to be damped, etc., the weight 3 resonates vertically, and the oil damper 6 stirs the oil 40, so it receives viscous resistance.
Although vibrations are damped, friction between the frame 17 and the slide plate 41 cannot be avoided. Figure 7 shows an example of a conventional dynamic vibration absorber according to Japanese Patent Application No. 57-21699, in which a is a side view, b is a plan view, and c is a side view.
is a front view and shows the case where two leaf springs are used. In the figure, reference numerals 1 and 1' denote leaf springs, which are arranged parallel to each other at intervals, and one end of which is fixed to a spring fixing fitting 2. Weights 3 and 3' are fixed to the other ends of the leaf springs 1 and 1', respectively. The weights 3, 3' are fitted with weight mounting bolts 5, 4' through elongated holes 4, 4' provided in the longitudinal direction of the leaf springs 1, 1', respectively.
5' can be moved and adjusted and fixed at a desired position. Reference numeral 6 denotes one or more viscoelastic dampers or viscous dampers (hereinafter simply referred to as viscoelastic dampers), which apply pressure to the leaf springs 1, 1' via metal plates 7, 7' bonded to the viscoelastic body. They are fixed by damper mounting bolts 8 and 8', respectively. This uses a method in which a viscoelastic body is sandwiched between leaf springs 1 and 1', and is used in a shear deformation type. As the viscoelastic material, one with clear damping ability characteristics is used. The dynamic vibration absorber configured as described above is fixed to the structure 9 to be damped by the spring fixing fitting 2, but in some cases it is directly fixed to the structure, and in other cases the dynamic vibration absorber fixing member is fixed to the structure. (not shown in FIG. 6). FIG. 8 is an explanatory diagram showing the basic specifications of a conventional dynamic vibration absorber. The relational expression of these basic specifications is shown in Table-1.

【table】

[Problem that the invention seeks to solve]

The conventional device configured as described above has the following problems. (1) In the conventional example shown in Fig. 7, when used for construction work such as large-scale bridge girders, the leaf spring became large and had manufacturing difficulties. (2) In the conventional example shown in FIG. 6, there was a frictional part in the structure, which affected the initial operation. (3) In the conventional example shown in FIG. 7, moving the weights 3 and 3' is troublesome. (4) In the conventional example shown in FIG. 7, when used as a vertical vibration device, "initial deflection" occurs in the leaf spring due to the weights 3 and 3', and it is difficult to compensate for this. [Means for Solving the Problems] The present invention uses the following means to solve the above problems. In other words, a substantially horizontal shaft fixed to the frame, a main rod having one end pivotally supported on the shaft, a weight attached to the main rod, and a spring that holds the main rod so that it can vibrate relative to the frame. In a cantilever type dynamic vibration absorber consisting of a member and a damper provided between the main rod and the frame to damp vibrations of the main rod, the spring member is a torsion type spring arranged approximately coaxially with the axis. And so. Here, if a mounting position adjustment mechanism for changing the position of the weight with respect to the main rod is provided, the resonant frequency of the main rod can be easily adjusted by the mechanism, and the mounting position of the torsion spring on the frame side can be adjusted as described above. If a torsion angle adjustment mechanism that rotates around the axis is provided, the resting position of the main rod can be easily adjusted by the mechanism. Furthermore, the damper may be a rubber viscoelastic body arranged so as to receive shearing force due to the vibration of the main rod. [Function] When the dynamic vibration absorber of the present invention is installed and vibration occurs in the structure, the vibration is transmitted to the main rod via the base, frame, main rotating shaft, and spring, but the vibration of the main rod and structure is It is absorbed by the viscoelastic body and dampens the vibrations of the structure as much as possible. [Embodiment] FIGS. 1a and 1b are a plan view and a side view showing an embodiment of the present invention, and FIG. 2 is a diagram of its principle. first second
The principle of the present invention will be explained with reference to the drawings. One end is slidably fitted to the main rotating shaft 12 fitted into a bearing of the frame 17,
Main rod 1 with a weight 3 attached to the other end so that it can slide
0 is coupled to a coil torsion spring 18 mounted on the outside of the main rotating shaft 12, and this coil torsion spring 18
is connected to the frame 17 and supported elastically. On the other hand, the auxiliary rod 25 rotates around the auxiliary rotating shaft 23 provided on the frame 17, and rotates around the viscoelastic body 6.
It is connected to the main rod 10 via. Now, suppose that the apparatus shown in FIG. 2 is attached to a structure that requires vibration damping and has a mass m ₁ and a spring constant R ₁ . The mass of the weight 3 is m ₂ , the spring constant is R ₂ , the viscous damping coefficient of the viscoelastic body 6 is C, and a periodic external force F=
When Fosinpt works, the displacements of m ₁ and m ₂ are converted to X ₁ and X ₂
If it is shown using symbols, it can be expressed as shown in Fig. 4. Here, F ₀ is the initial force applied to spring R ₁ ,
P is the angular frequency of the external force. By the way, one of the problems that the present invention attempts to solve is
The first is to suppress the amplitude X ₁ of the structure to a minimum and damp the vibration. It is known that the theoretical formula regarding X ₁ of the system according to the present invention shown in FIG. 4 can be expressed as follows. (X ₁ /Xst) ² = 4μ ² γ ² + (γ ² − δ ² ) ² /4μ ² γ
² (γ ² −1−βγ ² ) ² + [βδ ² γ ² −(γ ² −1) (γ ²
−δ ² )] ² … [1] However, Xst=F ₀ /k ₁ is the static deflection of the main vibration system due to force F ₀ ω ₂ =√ _{2 2} is the natural angular frequency of the dynamic vibration absorber β = m ₂ / m ₁ is the mass ratio between the dynamic vibration absorber and the main mass (mass
ratio) δ＝ω ₂ /ω _o is the ratio of the natural angular frequency of the dynamic vibration reducer and the main vibration system γ=P/ω _o is the ratio of the frequency of the external force and the natural angular frequency of the main vibration system. Here, the damping is It is determined by μ=c/2m ₂ ω _o . That is, if parameters such as δ, β, μ, etc. are given, the forced amplitude X ₁ can be determined using equation [1] for various frequency ratios γ. From Figure 5, C _c = 2m ₂ ω _o = critical damping, and C/C _c = 0.
= μ, and it can be seen that the best condition for a dynamic vibration absorber is when μ = 0.10. The foregoing has provided a summary of the principles of the invention and the theory behind these principles. FIG. 1 shows a specific example of this, and it was actually developed taking into consideration conditions at the site of use, ease of handling, manufacturing cost, etc. In FIG. 1, reference numeral 10 denotes a main rod which is configured to fit smoothly with the main rotating shaft 12 and allow the weights 3, 3' to slide thereon. A coil torsion spring 1 is attached to the main rod 10.
8 and 18' are fixed on one side, and the other ends are fixed on the main rotating shaft 12 while being wound left-handed or right-handed, respectively.
If the main rotating shaft 12 is now fixed, the main rod 10 will rotate the coil torsion springs 18, 18' with the main rotating shaft 12 as a fulcrum.
It can vibrate elastically in a fan shape by applying the force of . On the other hand, one end of the auxiliary rod 25 is fitted into an auxiliary rotating shaft 23 which is rotatably mounted on the bases 22, 22' fixed on the upper plate 19 via bearings 24, 24'.
Since the other end is connected to the main rod 10 via the viscoelastic body 6, it moves in conjunction with the vertical vibration of the weights 3, 3'. At this time, the viscoelastic body 6 absorbs the kinetic energy of the weights 3 and 3', converts it into thermal energy, and radiates it, so that the swing width is stabilized without being expanded. Further, the viscoelastic body 6 is connected to the parallel rods 30, 30', 31, 3 which are engaged with the auxiliary rod by pins 26, 27 and with the main rod 10 by pins 28, 29.
Since the main rod 10 is attached in a sandwich-like manner between 1', when it vibrates up and down, it is sheared into a parallelogram shape and converts kinetic energy into thermal energy. The coiled torsion springs 18 and 18' are compactly attached to both sides of the main rod 10 in such a way that one end is wrapped around the main rod 10 and the other end is wrapped around the main rotating shaft 12. As described, the strength of the coil torsion springs 18, 18' and the weights 3,
3' and its fixed position and viscoelastic body 6
By adjusting parameters such as the viscosity coefficient of the structure, it is possible to exert a damping effect in accordance with the natural frequency of the structure to be damped. However, usually a weight 3, 3' that can slide on the main rod 10
The position is selected to maximize the effect, and it is fixed with the fixing bolt 36 for use. Moreover, when the horizontal bar 32 is removed in the state shown in FIG. 1b, the main rod 10 tilts downward to the right. This would result in poor balance and the ability to function to its full potential. Therefore, for example, the main rotating shaft 12 inserted into the left end of the main rod 10
A fan-shaped worm wheel 14 is engaged with a worm 15 supported by a bearing provided on a frame 17 through a key 13 on one side of the worm 1.
5 counterclockwise, the torque will be applied to the main rod 10 tilted downward to the right as described above, from the worm 15 to the worm wheel 14 to the key 13 to the main rotating shaft 12 to the coil torsion springs 18 and 18. ' → is transmitted to the main rod 10, and the main rod 10 can be returned to the horizontal position. In this case, other drive mechanisms may be provided. 35 is a base, which is integrated with the frame 17 and the support frames 33, 33'. Then, the bolt 36, which is an accessory, is attached to the structure to be damped.
Match the direction of the vibration force with the direction of vibration of the weights 3 and 3',
In the case of a horizontal bridge girder, the base 35 is fixed downward as shown in FIG. 1b, for example. The mounting direction should be selected in a position that can dampen vibrations while considering the shape of the target structure, the direction of vibration, and its environment. If it is known that the direction of forced vibration changes each time the wind direction changes, a device whose mounting position is linked to the wind direction may be used. FIG. 3 is another principle diagram that can be created by applying the principle of the present invention. Figure a shows an example in which a piston having viscous resistance is installed obliquely between the main rod 10 and the auxiliary rod 25 instead of a viscoelastic body. Figure b shows an example in which the coiled torsion spring 18'' is mounted downward in the center of the main rod. Figure c shows an example in which the viscoelastic body 6 is installed between the main rod 10 and the base 35. Figure d is an example showing that the viscoelastic body 6 may be provided between the main rod extending to the left of the main rotating shaft 12 and the auxiliary rod. The mass ratio of the weight and the structure to be damped is about 1/200. [Effects of the Invention] As is clear from the above description, the cantilever type dynamic vibration absorber according to the present invention can Not only can it prevent resonance destruction due to Karman vortices caused by wind hitting bridge girders and main towers during or after construction, or forced vibrations caused by other causes, it can also respond to a wide range of changes in natural frequencies, and it can further reduce worker fear. Since the feeling can be removed, construction can be carried out with peace of mind,
In addition, since the coil torsion spring and the viscoelastic body are installed compactly, the overall size is reduced, so it can be installed in a pinched place. Furthermore, this invention can be applied not only to large-scale structures but also to small-scale construction work. Also, if used in buildings etc. whose natural frequencies are known, damage caused by other forced vibrations can be prevented.

[Brief explanation of the drawing]

Figures 1 a and b are plan and side views showing the structure of the present invention, Figure 2 is a conceptual diagram showing the operating principle of the present invention, and Figures 3 a, b, c, and d are the operating principles of the present invention. Other applied conceptual diagrams, Figure 4 is a symbol diagram of the two-degree-of-freedom system dynamic vibration absorber according to the present invention, Figure 5 is a line diagram when parameters are changed in Figure 4, Figure 6 is a conventional pedestrian bridge. Figures 7a, b, and c are side views, plan views, and front views of other conventional dynamic vibration absorbers, and Figure 8 is the basic specifications of the conventional dynamic vibration absorber. FIG. In the figure, 3 and 3' are weights, 6 is a viscoelastic body,
10 is the main rod, 12 is the main rotating shaft, 14 is the worm wheel, 15 is the worm, 17 is the frame, 1
8, 18' are coil torsion springs, 19 is the upper plate, 23
is the auxiliary rotating shaft, 25 is the auxiliary rod, 30, 30', 3
1 and 31' are parallel rods, and 35 is a base.

Claims (1)

[Scope of Claims] 1. A substantially horizontal shaft fixed to a frame, a main rod having one end pivotally supported on the shaft, a weight attached to the main rod, and a main rod with respect to the frame. A cantilever type dynamic vibration absorber comprising: a spring member that is held so as to be able to vibrate; and a damper provided between the main rod and the frame to damp vibrations of the main rod; , A cantilever type dynamic vibration absorber characterized by having a torsion type spring disposed substantially coaxially with the axis. 2. The cantilever type dynamic vibration absorber according to claim 1, wherein a torsion coil spring or a torsion bar is adopted as the torsion type spring. 3. The device according to claim 1 or 2, further comprising an attachment position adjustment mechanism for changing the position of the weight with respect to the main rod, and the mechanism makes it possible to adjust the resonance frequency of the main rod. Cantilever type dynamic vibration absorber. 4. Claim 1, further comprising a torsion angle adjustment mechanism that rotates the mounting position of the torsion spring on the frame side around the axis, and the resting position of the main rod can be adjusted by the mechanism. The cantilever type dynamic vibration absorber according to any one of . 5. The cantilever type dynamic vibration absorber according to any one of claims 1 to 4, wherein the attenuator is a rubber viscoelastic body arranged to receive shearing force due to the vibration of the main rod. vessel.