Tri-axial motion decoupling periodic structure for shaking table container

Abstract

Provided is a three-directional motion decoupling periodic structure for a shaking table container. The periodic structure is formed by sequentially superimposing n periodic structure units, wherein each of the periodic structure units is formed by sequentially superimposing a first side-confining layer, a planar decoupling layer, a second side-confining layer and an elastic layer, wherein n is a positive integer greater than or equal to 2; the cross-sectional shapes of the first side-confining layer, the elastic layer, the second side-confining layer and the planar decoupling layer are the same; and the periodic structure is used for implementing three-directional motion decoupling in the operating condition of ground shaking. Further provided is a three-directional motion decoupling container for shaking table test, which is formed by combining the periodic structure, a container base plate and a position-limiting protection door-type frame (3). The container, which is light in weight and high in strength, is applicable to the shaking table tests at hypergravity and normal gravity. Multiple measures are taken to ensure the motion synchronization between the container and tested soil, the non-interference of the motions of the container and the tested soil in the three directions of X, Y and Z, no extra acting force being exerted on the tested soil by the container, and the avoidance of a boundary effect as much as possible, so as to fully realize the three-directional decoupling and reconstitute original site characteristics.

Claims

1. A tri-axial motion decoupling periodic structure for a shaking table container, comprising: n periodic structure units sequentially superimposed together, wherein n is a positive integer greater than or equal to 2; wherein the periodic structure unit comprises a first side-confining layer, a planar decoupling layer, a second side-confining layer, and an elastic layer sequentially stacked together; wherein the cross-sectional shapes of the first side-confining layer, the elastic layer, the second side-confining layer, and the planar decoupling layer are the same; wherein the planar decoupling layer comprises a plurality of symmetrically distributed decoupling units, the decoupling unit comprising a decoupling component, lubricating grease and a circular groove, wherein the circular groove is configured to allow a free motion of the decoupling unit and to limit maximum horizontal displacements of the decoupling unit; wherein the decoupling component and lubricating grease are configured to realize a synchronous motion between the container and a test soil, and the decoupling units are configured to realize non-interference between the periodic structure unit's horizontal motions; wherein the plurality of symmetrically distributed decoupling units is configured to implement horizontal vibration decoupling; wherein the planar decoupling layer connects the first side-confining layer and the second side-confining layer, on which there are a plurality of the circular grooves with symmetrical distributions; and wherein the elastic layer is used to change the vertical stiffness of the container and to realize a synchronous vertical motion between the container and the test soil.

2. The tri-axial motion decoupling periodic structure of claim 1, wherein the periodic structure is configured to realize the tri-axial motion decoupling of the container of a centrifuge shaking table.

3. The tri-axial motion decoupling periodic structure of claim 2, wherein a centrifugal acceleration factor N of the shaking table is greater than or equal to 20.

4. The tri-axial motion decoupling periodic structure of claim 1, wherein the material density of the side-confining layer is less than or equal to 7.85 g/cm.sup.3, and the elastic modulus is greater than or equal to 40 kN/mm.sup.2; the material of the side-confining layer is aluminum alloy.

5. The tri-axial motion decoupling periodic structure of claim 1, wherein a shape of the said side-confining layer is circular or regular polygon; the number of regular polygon's edges is greater than or equal to 2m, m is a positive integer and m is greater than or equal to 4.

6. The tri-axial motion decoupling periodic structure of claim 1, wherein the said side-confining layer is a metal ring.

7. The tri-axial motion decoupling periodic structure of claim 1, wherein a strain of the periodic structure is equal to a strain of the test soil and satisfies the following formula: $\stackrel{\_}{{\mathrm{.Math.}}_{\mathrm{periodic}\mathrm{structure}}}={\int }_h^{h+h_1}\frac{\mathrm{kh}}{E_1}\mathrm{dh}+{\int }_{h+h_1}^{h+h_1+h_2}\frac{\mathrm{kh}}{E_2}\mathrm{dh}+{\int }_{h+h_1+h_2}^{h+h_1+h_2+h_3}\frac{\mathrm{kh}}{E_3}\mathrm{dh}+{\int }_{h+h_1+h_2+h_3}^{h+h_1+h_2+h_3+h_4}\frac{\mathrm{kh}}{E_4}\mathrm{dh}$ ${\mathrm{.Math.}}_{\mathrm{test}\mathrm{soil}}={\int }_h^{h+h_1+h_2+h_3+h_4}\frac{\mathrm{kh}}{E}\mathrm{dh}$ $\stackrel{\_}{{\mathrm{.Math.}}_{\mathrm{periodic}\mathrm{structure}}}={\mathrm{.Math.}}_{\mathrm{test}\mathrm{soil}}$ wherein ε.sub.periodic structure is the strain of the periodic structure, ε.sub.test soil is the strain of the test soil; an elastic modulus of the first side-confining layer is E.sub.1 and height of the first side-confining layer is h.sub.1, an elastic modulus of the planar decoupling layer is E.sub.2 and height of the planar decoupling layer is h.sub.2, an elastic modulus of the second side-confining layer is E.sub.3 and height of the second side-confining layer is h.sub.3, an elastic modulus of the elastic layer is E.sub.4 and height of the elastic layer is h.sub.3, a compressive modulus of the test soil is E, a distance between the upper boundary of the test soil and the elastic layer is h, a vertical stress linearly increases with the depth of the test soil, the vertical stress can be expressed as kh, wherein k is a linear coefficient.

8. The tri-axial motion decoupling periodic structure of claim 1, wherein the elastic layer's material is rubber.

9. The tri-axial motion decoupling periodic structure of claim 1, wherein an elastic modulus of decoupling component material is greater than or equal to 160 kN/mm.sup.2; the decoupling component material is steel or stainless steel.

10. The tri-axial motion decoupling periodic structure of claim 1, wherein a shape of the decoupling components is circular.

11. The tri-axial motion decoupling periodic structure of claim 1, wherein the decoupling components are ball bearings.

12. The tri-axial motion decoupling periodic structure of claim 10, wherein dimensions of the circular grooves and the decoupling components is determined according to the maximum shear deformation: Y.sub.max=(R−r)/ΔH, where R is a radius of the circular grooves, r is a radius of the decoupling components, and ΔH is a distance between centers of two adjacent periodic structure's elastic layers, Y.sub.max is the maximum shear deformation of the test soil at the periodic structure.

13. The tri-axial motion decoupling periodic structure of claim 1, wherein the quantity of the decoupling components is equal or more than one.

14. The tri-axial motion decoupling periodic structure of claim 1, wherein the quantity of the circular grooves is at least 3.

15. The tri-axial motion decoupling periodic structure of claim 1, wherein the cross-sectional shape of the periodic structure is a circle or regular polygon; the number of regular polygon's edges is greater than or equal to 2m, m is a positive integer greater than or equal to 4.

16. The tri-axial motion decoupling periodic structure of claim 1, wherein the periodic structure unit further comprises at least two limiting devices, wherein the limiting devices are configured to realize vertical limit protection for the planar decoupling layer, preventing the vertical relative displacements between the first side-confining layer and the second side-confining layer from being too large that causes separation.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is the three-dimensional schematic diagram of the tri-axial motion decoupling shaking table container.

(2) FIG. 2 is the elevation view of the tri-axial motion decoupling shaking table container.

(3) FIG. 3 is the vertical view of the tri-axial motion decoupling shaking table container.

(4) FIG. 4 is a schematic diagram of the periodic structure unit.

(5) FIG. 5 is the dimension diagram of the periodic structure unit.

(6) FIG. 6 is a plane schematic diagram of the planar decoupling layer of the periodic structure unit.

(7) FIG. 7 is a schematic diagram of ball bearings.

(8) FIG. 8 is a schematic diagram of periodic structure.

(9) As shown in FIGS. above, 1 indicates the container bottom plate, 2 indicates the regular polygon metal ring of twelve edges, 3 indicates limit protection door frame, 4 indicates double layer rubber films, 5 indicates ball bearings, 6 indicates circular grooves, 7 indicates lubricating grease, 8 indicates thin steel sheets, 9 indicates bolts, 10 indicates rubber layers, 11 indicates test soil.

(10) The meanings of each parameters in FIGS. are as follows: Δh is gap distance between regular polygon metal rings of adjacent periodic structures with twelve edges, Δh′ is the distance between upper surface of the circular grooves on the first side-confining layer and lower surface of the circular groove on the second side-confining layer, R is the radius of circular grooves, r is the radius of decoupling components, l.sub.0 is the distance between bolt fixed points, l.sub.0+l is the length of thin steel sheet, elastic modulus of the first side-confining layer is E.sub.1 and height is h.sub.1, elastic modulus of the planar decoupling layer is E.sub.2 and height is h.sub.2, elastic modulus of the second side-confining layer is E.sub.3 and height is h.sub.3, elastic modulus is E.sub.4 and height is h.sub.4, compressive modulus of the soil is E and the distance between upper boundary of the test soil and elastic layer is h.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(11) The following implementation is only used to illustrate the present disclosure while isn't used to restrict the range of the present disclosure. Besides it should be understood that after reading the content which the present disclosure has proposed, this field's technicians can make various changes or modifications to the present disclosure. These equivalent forms are also included in the range that the present application's attached claims have restricted.

(12) A tri-axial motion decoupling periodic structure in this the disclosure for shaking table containers is characterized in that the periodic structure is stacked (superimposed) together by n periodic structure units, and the periodic structure unit is formed orderly by superposition of the first side-confining layer, the planar decoupling layer, the second side-confining layer and the elastic layer, and n is a positive integer greater than or equal to 2. The first side-confining layer's cross-sectional shape is same as elastic layer, second side-confining layer and planar decoupling layer, while the material of first side-confining layer and the second side-confining layer can be same or different. So the periodic structure can be used to realize the tri-axial motion decoupling under earthquake motion conditions.

(13) The planar decoupling layer comprises a plurality of symmetric distributed decoupling units, and a decoupling unit comprises decoupling components, lubricating grease and a circular groove, wherein the circular groove is used to realize free motion of decoupling components and limit maximum horizontal displacements. The decoupling components and lubricating grease can realize synchronous motion between the container and the test soil, and the decoupling unit can realize non-interference of the periodic structure unit's horizontal motions. The plurality of symmetric distributed decoupling units can realize horizontal vibration decoupling and ensure consistency of the interlayer shear strain between periodic structure units.

(14) The planar decoupling layer connects the first side-confining layer and the second side-confining layer, on which there are a plurality of circular grooves with symmetrical distributions.

(15) The elastic layer is used to change vertical stiffness of the container and to realize synchronous vertical motion between the container and the test soil.

(16) The planar decoupling layer and the elastic layer are combined to realize decoupling of vertical and horizontal motions of the container and the test soil.

(17) The decoupling units of each periodic structure unit's planar decoupling layer can be same or different.

(18) In some embodiments, the lateral limit layers are regular polygon aluminum alloy rings of twelve edges, the decoupling component are steel ball bearings, the elastic layers are rubber layers, and the door frames function as limit protection. The abovementioned parts form the basic components of a tri-axial motion decoupling container for shaking table test.

(19) A tri-axial motion decoupling container for shaking table test comprises the follows: container bottom plate 1, regular polygon metal ring of twelve edges 2, limit protection door frames 3, double layer rubber films 4, ball bearings 5, circular grooves 6, lubricating grease 7, thin steel sheets 8, bolts 9, rubber layers 10, and test soil 11. The periodic structure can be formed by orderly stacking regular polygon metal rings of twelve edges 2, ball bearings 5, the regular polygon metal rings of twelve edges 2, and rubber layers 10. The periodic structures are protected by thin steel sheets 8 with excess length, which are fixed by bolts 9. The container is formed by stacking periodic structure onto container bottom plate 1 from bottom to top. By setting ball bearings 5 between regular polygon metal rings of twelve edges 2, the container can deform freely along horizontal directions. Ball bearings 5 are placed in circular grooves 6 and lubricated with lubricating grease 7, the circular grooves 6 can limit horizontal displacements of the container. Vertical stiffness of the container can be changed by putting the selected rubber layer 10 in regular polygon metal rings of twelve edges 2. The container's vertical displacements can be limited by thin steel sheets 8 with excess length, which are fixed by bolts 9 onto adjacent regular polygon metal rings of twelve edges 2. The combination of plane decoupling layers and rubber layers can realize coordinate motions of the container and the test soil. The interaction between the container and the test soil can be eliminated tri-axially, including the container's shear deformation excited along two horizontal directions and tensile or compression deformation excited along vertical direction. The container does not produce additional force to the test soil and realizes motion decoupling of tri-axial vibration.

(20) The double layer rubber films 4 are composed by two rubber films, which are filled with 7—lubricating grease such as silicone oil, and the unlubricated faces of rubber films are contacted with the container and 11—test soil respectively, so the boundary effects and horizontal motion's influence on vertical motion can both be reduced by relative free deformation of both rubber films. The tri-axial motion decoupling of shaking table containers can be better realized by the combination of periodic structures and double layer rubber films.

(21) The top of the container is provided with cross shaped limit protection door frames 3, which are connected with the container bottom plate 1, so the vertical deformation of the container is limited.

(22) The choice of material for the rubber layer 10 should be such as to satisfy the same vertical strain between the periodic structure and the test soil, that is ε.sub.periodic structure=ε.sub.test soil, the following formulas can be used to calculate the rubber layer's elastic modulus and then the rubber layer material can be chosen.

(23) $\stackrel{\_}{{\mathrm{.Math.}}_{\mathrm{periodic}\mathrm{structure}}}={\int }_h^{h+h_1}\frac{\mathrm{kh}}{E_1}\mathrm{dh}+{\int }_{h+h_1}^{h+h_1+h_2}\frac{\mathrm{kh}}{E_2}\mathrm{dh}+{\int }_{h+h_1+h_2}^{h+h_1+h_2+h_3}\frac{\mathrm{kh}}{E_3}\mathrm{dh}+{\int }_{h+h_1+h_2+h_3}^{h+h_1+h_2+h_3+h_4}\frac{\mathrm{kh}}{E_4}\mathrm{dh}$${\mathrm{.Math.}}_{\mathrm{test}\mathrm{soil}}={\int }_h^{h+h_1+h_2+h_3+h_4}\frac{\mathrm{kh}}{E}\mathrm{dh}$$\stackrel{\_}{{\mathrm{.Math.}}_{\mathrm{periodic}\mathrm{structure}}}={\mathrm{.Math.}}_{\mathrm{test}\mathrm{soil}}$

(24) Wherein, elastic modulus of the first side-confining layer is E.sub.1 and height is h.sub.1, elastic modulus of the planar decoupling layer is E.sub.2 and height is h.sub.2, elastic modulus of the second side-confining layer is E.sub.3 and height is h.sub.3, elastic modulus is E.sub.4 and height is h.sub.4, compressive modulus of the soil is E and the distance between upper boundary of the test soil and elastic layer is h. The vertical stress linearly increases with the test soil's depth, which can be expressed as kh, where k is a linear coefficient. Based on the aforementioned simple integral operations and the deformation equality of the container and the test soil, vertical elastic modulus of the elastic layer can be calculated according to the following parameters: the soil's compressive modulus, the elastic moduli and heights of two the regular polygon metal rings of twelve edges, the elastic modulus and height the plane decoupling layer, and the height of rubber layer. So the specific elastic layer material can be selected according to calculated elastic modulus.

(25) The dimension of circular grooves can be determined according to maximum shear deformation: γ.sub.max=(R−r)/ΔH, wherein R is the radius of circular grooves, r is the radius of decoupling components, and ΔH is the distance between the centers of two adjacent periodic structure's elastic layers, γ.sub.max is the maximum shear deformation of the test soil at the periodic structure. A preliminary estimate of γ.sub.max can be obtained based on test soil's properties, then the dimension of circular groove can be reversed according to the dimension of selected ball bearings.

(26) For thin steel sheets, excess length l can be determined by:
l=max{(R−r),(Δh′−Δh)}

(27) Wherein, Δh′ is the distance between upper surface of circular grooves on the first side-confining layer and the lower surface of the circular grooves on the second side-confining layer, the Δh is gap distance between the first side-confining layer and the second side-confining layer, R is the radius of circular grooves, r is the radius of decoupling components. In order to be safer, excess length l of thin steel sheets can be multiplied by certain safety factor for the actual application, for example, take 1.1 for the safety factor.

(28) The upper and lower limits of distance Δm from the container's top to door frames can be determined by following methods:

(29) Lower limit can be determined according to vertical deformation ranges of general test soil, which can be obtained by multiplying the test soil's height value by test soil's vertical seismic strain ranges by centrifugal accelerations.

(30) Upper limit can be determined by considering maximum deformation of the elastic layer and the plane decoupling layer, wherein the elastic layer is limited by the irreversible deformation of the material, that is, the elastic material exceeds elastic boundary, and the planar decoupling layer is limited by separation of decoupling components from the circular grooves.

(31) The followings are three examples of shaking table containers:

Embodiment 1

(32) The first container is formed by stacking regular polygon periodic structures of twelve edges, of which the side length is 13.1 cm and the inscribed circle's radius is 50 cm. The periodic structures are made of light-weight and high-strength aluminum-magnesium alloy, and the container's overall height is 61 cm. The tri-axial shaking table container has a total of 10 periodic structures, and the height of each regular polygon aluminum-magnesium alloy ring of twelve edges is 25 mm. The adjacent periodic structures are connected by 10 mm thick special rubber and reinforced with pressure to form a whole, meanwhile the gap distance of adjacent regular polygon aluminum-magnesium alloy rings is 1 mm. There are 12 circular grooves forming at each side center of the regular polygon aluminum-magnesium alloy ring of twelve edges, and each circular groove is arranged with a steel ball bearing. The maximum displacement 2.5 mm is allowed between adjacent rings. The excess length of the thin steel sheet is 2 mm. The top of the container is provided with cross shaped door frames, whose bottom are connected with the container bottom plate to form limit protection. Besides, the double layer rubber films are used as a supplementary measure of vertical and horizontal decoupling.

Embodiment 2

(33) The second container is formed by stacking circular periodic structures, of which the inner radius is 60 cm and outer radius is 62 cm. The periodic structures are made of light-weight high-strength boron-aluminum alloy, and the container's overall height is 51 cm. The tri-axial shaking table container has a total of 10 periodic structures, and the height of each circular boron-aluminum alloy ring is 20 mm. The adjacent periodic structures are connected by 10 mm thick special rubber and reinforced with pressure to form a whole, meanwhile the gap distance of adjacent circular boron-aluminum alloy rings is 1 mm. There are 16 circular grooves evenly forming at the center of the circular boron-aluminum alloy ring, and each circular groove is arranged with a steel ball bearing. The maximum displacement 2.5 mm is allowed between adjacent rings. The excess length of the thin steel sheet is 2 mm. The top of the container is provided with cross shaped door frames, whose bottom are connected with the container bottom plate to form limit protection. Besides, the double layer rubber films are used as a supplementary measure of vertical and horizontal decoupling.

Embodiment 3

(34) The third container is formed by stacking regular polygon periodic structures of eight edges, of which the side length is 14.2 cm and the inscribed circle's radius is 45 cm. The periodic structures are made of high-strength carbon fiber filled with epoxy resin, and the container's overall height is 71 cm. The tri-axial shaking table container has a total of 10 periodic structure, and the height of high-strength carbon fiber ring of eight edges is 30 mm. The adjacent periodic structures are connected by 10 mm thick special rubber and reinforced with pressure to form a whole, meantime the gap distance of adjacent high-strength carbon fiber ring of eight edges is 1 mm. There are 8 circular grooves forming at each side center of the high-strength carbon fiber ring of eight edges, and each circular groove is arranged with a steel ball bearing. The maximum displacement 2.5 mm is allowed between adjacent rings. The excess length of the thin steel sheet is 1 mm. The top of the container is provided with cross shaped door frames, whose bottom are connected with the container bottom plate to form limit protection. Besides, the double layer rubber films are used as a supplementary measure of vertical and horizontal decoupling.

(35) Motion coordination between the container and the test soil can be reflected by the deformations of the container and the test soil, which are monitored by sensors; in other words, tri-axial motion decoupling properties of the periodic structures can be detected. In particular, vertical deformation synchronization is reflected by deformations of the test soil and the container, which are measured by laser displacement sensors. Horizontal deformation synchronization is reflected by accelerations in middle of the test soil and along soil boundaries, which are measured by tri-axial accelerometers. If the container does not have good decoupling properties, the deviations in synchronous displacements and accelerations would be very big, namely the tri-axial vibration has caused serious mutual interference.

(36) The tri-axial motion decoupling properties of the container are detected in centrifuge test with centrifugal accelerations of 20 g, 50 g and 100 g respectively. The test results show that during the environment of centrifuge tri-axial vibration, the vertical displacement deviations can be controlled within 10%, and the tri-axial acceleration deviations in the test soil between the model middle position and the interface with the container can be controlled within 10%. All the deviations are within allowable ranges, which shows good tri-axial decoupling effects. In the environment of constant gravity tri-axial vibration, the container has better decoupling characteristics, with deviations of displacements and tri-axial accelerations can be controlled within 5%.