# EARTHQUASKE-PROOF BARRIER USING BURIED RESONANT CYLINDERS

Disclosed are an earthquake-proof barrier for protecting a building against an earthquake, and more particularly, an earthquake-proof barrier using buried resonant cylinders capable of weakening seismic waves outside a building, instead of installing an earthquake-proof apparatus in a building. According to the earthquake-proof barrier using the buried resonant cylinders, buildings are not independently protected, but one district beyond the earthquake-proof barrier is protected. Thereby, magnitude of an earthquake can be reduced to a desired level without altering the building.

**Description**

**TECHNICAL FIELD**

The present invention relates, in general, an earthquake-roof apparatus for protecting a building against an earthquake, and more particularly, to technology for protecting a building beyond an earthquake-proof barrier or a seismic shadow zone that stops seismic waves from being propagated by burying plurality of resonant cylinders outside the building so as to function as the earthquake-proof barrier or the seismic shadow zone, instead of installing an earthquake-proof apparatus in the building itself.

**BACKGROUND ART**

An earthquake is one of inevitable typical natural disasters, and is a great threat to property, and above all, for inhabitants who live in or near earthquake zones. To minimize damage caused by earthquakes, much study has been done on earthquake-proof designs for buildings including early earthquake warning systems. As a result, inhabitants who live in or near earthquake zones are considerably effectively protected from earthquakes.

However, due to earthquakes, tens of thousands to hundreds of thousands of people are still killed or hurt all over the world every year. An earthquake, which recently occurred on Mar. 11, 2011 on the east coast of Sendai, Honshu, Japan, shows that, no matter how good an earthquake-proof design may be, a building can never be entirely safe from the dangers of an earthquake.

Existing earthquake-proof construction methods have generally employed earthquake-proof techniques such as vibration resistance, vibration isolation, vibration damping, etc. for a building itself when the building is initially constructed. However, these earthquake-proof construction methods should independently provide to each building, and thereby costing a great deal.

Thus, a separate method capable of protecting buildings in a group or significantly improving an earthquake-proof protection even for previously built buildings should be provided.

The present invention is directed to a method of reducing damage from an earthquake, which is based on a new design completely different from an existing traditional earthquake-proof design. Existing methods are point protection of independently protecting each building after seismic waves reach the building, whereas the method of the present invention is an area protection method of previously interrupting seismic waves and protecting an area before the seismic waves reach a building or buildings. To this end, resonant cylinders corresponding to seismic wave frequencies are buried on seismic wave paths. The structure absorbs seismic waves when the seismic waves pass through the resonant cylinders, and prevent strong seismic waves from reaching the building. This effect of the present invention is to use a principle of acoustic metamaterials that has recently been actively studied in academic circles.

Seismic waves are basically a sort of acoustic wave. After all acoustic waves pass through resonant cylinders waves near a resonant frequency are absorbed, and fail to pass through the structures. This principle comes from the acoustic metamaterials. However, there is so far no example of applying the principle of the acoustic metamaterial to a technique for preventing damage to an earthquake.

**DISCLOSURE**

**Technical Problem**

Existing earthquake-proof design protects the building itself. The design is associated with a basic structure of the building, and thus many expenses are incurred in applying an earthquake-proof design to a previously built building to increase its earthquake resistance. Especially, once existing buildings such as an atomic power station or a steelworks are completed and operated, it is difficult to change the earthquake-proof design to increase its earthquake resistance.

Accordingly, the present invention has been made keeping in mind the above problems occurring in the related art, and is intended to install an vibration-proof barrier in such a manner that resonant cylinders are buried around a building, and collectively protect all the buildings around which the earthquake-proof barrier capable of weakening seismic waves are buried before the seismic waves reach the buildings.

**Technical Solution**

The present invention provides an earthquake-proof barrier **150** formed by burying and stacking a plurality of resonant cylinders **100** underground, in which each resonant cylinder is enclosed to form an internal cavity by planar barrier parts **1** and a curved barrier part **2**, and at least one of the planar barrier part and the curved barrier part has at least one through parts **10** communicating with the cavity from an outside thereof. A shape of the earthquake-proof barrier may be a circular shape, a semi-circular shape, a rod shape, or the like, and is fitted to an area to be protected.

The resonant cylinder embodies an inductor-capacitor (LC) oscillator of electric engineering into that of mechanical engineering. Energy of the seismic waves travels through the resonant cylinders, and is converted into sound and heat energy. Thus, amplitude of the seismic waves is abruptly exponentially reduced while the seismic waves pass through the plurality of resonant cylinders.

As a width of a seismic barrier increases, an effect of reducing the amplitude of the seismic waves increases. When the magnitude of the seismic waves is to be fitted to 3 on the basis of a Richter scale, the width of the seismic barrier should be similar to a wavelength of the seismic waves as in Equation 10. The wavelength of the seismic waves is not constant, but can be usually approximated to 100 m.

The number of resonant cylinders is determined according to a length of the seismic barrier. As shown in

The resonant cylinders **100** may have a cylindrical shape, a hexahedral shape, an octahedral shape, or a spherical shape. A resonant frequency of the resonant cylinder is fitted to that of the seismic waves, and is determined by three factors, i.e. an internal volume of the resonant cylinder, an area of the through part of an inlet of the resonant cylinder, and a length of the through parts, regardless of the shape of the resonant cylinder. As the area of the inlet becomes larger, the internal volume becomes smaller, and the length of the through part becomes shorter, a high frequency is isolated. When there is a plurality of through parts, the resonant cylinder follows a combination of series and parallel connections of an electric circuit.

When the resonant cylinders are buried and stacked four by four as in

Since the seismic waves are waves mixed with various frequencies, the plurality of resonant cylinders having different resonant frequencies are mixed and stacked such that the through parts thereof are interconnected as if elements of an electric circuit are connected in vertical and horizontal directions.

Considering that five through parts having a diameter of about 50 cm are bored in the resonant cylinder having a thickness of about 30 cm, a volume of one resonant cylinder **100** may range from 1.0 to 100 m^{3 }according to the wavelength of the seismic waves.

The resonant cylinders **100** may be buried within a range from 1 to 100 m, which is a depth of foundation work or the frequency of the seismic waves, below the ground from a height of one resonant cylinder.

**Advantageous Effects**

According to the earthquake-proof barrier using the buried resonant cylinders, the buildings are not independently protected, but the earthquake-proof barrier is installed on a predicted path of the seismic waves to isolate the seismic waves. As such, one district is protected en bloc. Strength of an earthquake transmitted to a building can be reduced to a desired level by adjusting the refractive index and width of the earthquake-proof barrier.

Unlike a change in design of the building itself, the earthquake-proof barrier is installed around the building. Thereby, before the seismic waves reach the building, the seismic waves are weakened. As such, the earthquake-proof barrier can be effectively applied to a previously built building. Thus, a measure for changing an earthquake-proof design of the building itself is not required.

**DESCRIPTION OF DRAWINGS**

_{eff}(w) is changed into a negative according to a frequency (w) when sound waves travel through the resonant cylinder, wherein an imaginary number part (dotted line) becomes negative on this region, and energy is absorbed.

_{c }is a depth of the earthquake-proof barrier and at least corresponds to a depth of foundation work, and X_{c }is a width of the earthquake-proof barrier, and thus the wider the width of the earthquake-proof barrier, the lower the magnitude of the seismic waves.

**MODE FOR INVENTION**

Hereinbelow, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the following embodiments are provided to allow the present invention to be sufficiently understood to those skilled in the art, and can be variously modified. The scope of the present invention is not limited to the embodiments described herein. Throughout the drawings, the same reference numbers are used to refer to the same or like parts.

Seismic waves are a sort of acoustic wave, and are made up of a primary (P) wave and a secondary (S) wave that are body waves and a Rayleigh (R) wave and a Love (L) wave that are surface waves. Further, various wavelengths of waves are non-uniformly mixed. Among these waves, the R wave and the L wave do damage to buildings.

The reason the R wave and the L wave are called surface waves is that these waves exist only to a depth corresponding to about a wavelength from the surface, and abruptly diminish exponentially when exceeding the depth corresponding to about the wavelength. The surface waves have a much slower velocity than the body waves, are more non-uniform than the body waves, and have a speed of about to 3 km/sec, a frequency of 30 Hz or less, and a wavelength of 100 m or less. Thus, the surface waves are almost neglected at a depth of 150 m or more 1.5 times the wavelength.

All the acoustic waves have a speed determined by a ratio of density and elastic modulus. The elastic modulus is classified into three types according to an applied dimension, i.e. Young's modulus applied to one dimension, shear modulus applied to two dimensions and bulk modulus applied to three dimensions. The shear modulus can be treated as a special case in which one plane is fixed at the bulk modulus. The surface waves are two-dimensional waves from the macroscopic viewpoint, and three-dimensional waves from the microscopic viewpoint.

The speed of all the acoustic waves is determined as density ρ and elastic modulus G of a medium by Equation 1. When the acoustic wave passes through a resonant cylinder, no waves are propagated on a specified frequency region corresponding to the vicinity of a frequency region of the resonant cylinder, and the reason is as follows.

Generally, when a pressure is applied to an object, the object is compressed. The capability of resisting the compression is the elastic modulus. Since a volume is reduced when the pressure is applied, the elastic modulus is typically positive. If the volume is rather expanded against an external pressure, the elastic modulus becomes negative. When the wave applies the pressure to air inside the resonant cylinder, the waves inside the resonant cylinder overlap each other, and constructive interference occurs to produce an effect in which a volume of the air inside the resonant cylinder is rather expanded. A frequency region within which the elastic modulus becomes negative is a region from a resonant frequency as in Equation 4 to a frequency slightly higher than the resonant frequency.

When the elastic modulus becomes negative due to resonance, a speed of the wave becomes an imaginary number according to Equation 1. When the speed of the wave becomes the imaginary number, a refractive index n and a wave vector also become imaginary numbers as in Equations 5 and 6, and thus amplitude of the wave is exponentially reduced. This is equal to the principle in which, when an air pressure is applied to a wind instrument through a mouthpiece, resonance occurs inside the wind instrument, and pressure energy is converted into sound energy. When the amplitude of the wave is exponentially reduced, the wave results in disappearance without propagation.

This will be mathematically described below again. The speed of the seismic waves is determined as a square root ratio of the density ρ and the elastic modulus G of the medium by Equation 1.

*v=√{square root over (G/ρ)}* Equation 1

When the elastic modulus G becomes negative, the speed v becomes the imaginary number. The refractive index n proportional to a reciprocal of the speed becomes the imaginary number according to Equation 2.

In Equation 2, n indicates the refractive index, and c indicates the background speed of the acoustic wave. When the elastic modulus G becomes negative, the refractive index n and the wave vector becomes the imaginary number, and the wave is extinguished. A physical quantity of this imaginary number is a concept of the metamaterial. The metamaterial refers to a material having response of an electromagnetic or acoustic material that is not observed previously or that is difficult to be realized by traditional materials.

The structure of the resonant cylinder **100** having the negative elastic modulus has a body whose planes are sealed, and a through part **10** formed in one plane of the body. If there is a plurality of through parts, the through parts follow a combination of series and parallel connections.

When the pressure of the acoustic wave passing through the through part **10** is accumulated in a cavity **30**, and the resonance occurs, an air pressure caused by the acoustic wave is expanded, and the elastic modulus becomes negative. This is the principle of the acoustic metamaterial.

_{eff }of a material is changed according to a frequency w.

In Equation 3, F is the geometrical factor that is experimentally determined according to how to combine the resonant cylinders, i.e. an interval between the resonant cylinders or arrangement of the resonant cylinders, and F is the loss factor. As the connected resonant cylinders increase, a value of F increases, and a region on which the real number part of the elastic modulus becomes negative increases. When the loss factor Γ is very small, a frequency region on which the real number part of the elastic modulus G_{eff }becomes negative can be given as a range as in Equation 4.

*w*_{0}*<w<*√{square root over (1+*F*)}w_{0 } Equation 4

In Equation 4, W_{0 }is the resonant frequency of the resonant cylinder **100**.

When the resonance occurs, an effect of diminishing the seismic waves is produced at an area from the resonant frequency to a given frequency higher than the resonant frequency. The seismic waves are non-uniform waves whose frequency is mostly between 1 and 30 Hz. Thus, a resonant frequency range of the resonant cylinder according to the present invention is preferably set to a range from 1 to 30 Hz.

Referring to

The absorbed energy is converted into heat and sound energy in the resonant cylinder **100**. Assuming that the absorbed energy is completely converted into the sound energy, intensity of a sound can be found as in Equation 15.

According to Equation 2, the refractive index of the medium is given as a reciprocal of the speed V of the wave in the medium. In other words, when G_{eff }becomes negative on a specified frequency region, the refractive index becomes the imaginary number, and the refractive index can be expressed as in Equation 5.

*n=i|n|* Equation 5

The surface waves such as an L wave and an R wave take a plane wave form obtained by the product of amplitude and a sine function. When a traveling direction of the surface waves is an x direction, and the refractive index is the imaginary number, the wave equation can be expressed as in Equation 6.

According to Equation 6, as the surface wave travels, i.e. as X increases, the amplitude of the wave is exponentially extinguished.

Here, a magnitude M according to the Richter scale can be expressed as in Equation 7.

In Equation 7, A is the maximum amplitude of the seismic wave measured at a point of 100 km from the epicenter, and A_{0 }is the maximum amplitude of the background wave when no earthquake occurs and is set to 1 μm (10^{−6 }m).

When the seismic wave passes through an earthquake-proof barrier that is a seismic barrier, the amplitude of the acoustic wave is reduced as in Equation 8.

When initial magnitude before the seismic wave passes through the resonant cylinder is defined as M_{i}, and final magnitude after the seismic wave passes through the resonant cylinder is defined as M_{f}, Equation 8 is given as in Equation 9.

When a difference between the initial magnitude and the final magnitude is given as ΔM=M_{f}−M_{i}, an X-axial distance and a width X_{c }of the earthquake-proof barrier are obtained as in Equation 10.

As can be seen from Equation 10 above, the width X_{c }of the earthquake-proof barrier is proportional to the wavelength λ of the seismic wave, and is inversely proportional to the refractive index n of the earthquake-proof barrier. As such, when the resonant cylinder is made of cement concrete having a very high refractive index, the width of the earthquake-proof barrier can be reduced. The refractive index of the earthquake-proof barrier is determined by refractive indexes of the resonant cylinder and its surrounding spatial materials, and is approximately similar to the refractive index of the resonant cylinder. ΔM is the magnitude difference intended to weaken the seismic waves entering into the earthquake-proof barrier.

The wavelength λ of the seismic wave mostly ranges from 50 to 200 m. The refractive index of the cement concrete mostly ranges from 1 to 2. The width X_{c }of the earthquake-proof barrier requires a range from 8 to 67 m to diminish magnitude 1. In consideration of a safety factor, the width of the earthquake-proof barrier is fitted to the long side, and is preferably set to a range from 20 to 100 m in order to reduce magnitude 1.

For example, assuming that the seismic wave is intended to lower magnitude 6 to magnitude 3, ΔM is 3. It is assumed that, when the earthquake-proof barrier for diminishing magnitude 3 is constructed, the wavelength X of the seismic wave is about 100 m. In this case, the width X_{c }of the earthquake-proof barrier is 110 m when the refractive index is about 1, and about 55 m when the refractive index is about 2, as in Equation 11.

Now, the resonant frequency of the resonant cylinder is obtained from the structure of the resonant cylinder as follows. Referring to **30** inside the resonant cylinder **100** corresponds to a capacitor in the LC circuit. To indicate the inductor and the capacitor on the left of

Here, V is the volume of the resonant cylinder **100**, ρ is the density of the medium (air) inside the resonant cylinder, and v is the background speed. L′ is the effective length of the neck **15** of the through part **10**, and S is the cross-sectional area of the inlet of the through part **10**. The effective length is a value that adds a radius of the inlet of the through part to a thickness of the through part. When the inlet of the through part is not circular, its radius is a radius when its area corresponds to a circle.

Here, the resonant frequency ω_{0 }of the resonant cylinder **100** of

The resonant frequency of Equation 14 is a resonant frequency obtained from Equations 1 and 13.

In Equation 14, v is the background speed. According to Equation 14, the resonant frequency of the resonant cylinder **100** depends on the structure of the resonant cylinder **100**. In other words, as the effective length L′ of the through part **10** bored in the resonant cylinder **10** becomes longer, as the cross-sectional area S of the inlet of the through part becomes narrower, and as the volume inside the resonant cylinder becomes larger, the resonant cylinder resonates at a low frequency.

When it is assumed that the seismic wave is converted into sound and heat at the earthquake-proof barrier, and is completely converted only into the sound, the intensity of the sound is expressed by decibel. In Equation 15, M is the magnitude of the seismic wave on the basis the Richter scale, and b is the experimentally obtained constant and is about 1.5. D is to express a distance from the epicenter in units of km (see References 1 and 2 below).

1) Sang-Hoon Kim and Mukunda P. Das, “Artificial Seismic Shadow Zone Made of Acoustic Metamaterials,” Modern Physics Letters B, Vol. 27, No. 20, pp. 1350140 (July 2013).

2) A. Udias, Principles of Seismology (Cambridge, N.Y., 2010) Ch. 15.

Hereinafter, embodiments of the earthquake-proof barrier using buried resonant cylinder according to the present invention are presented in greater detail, and it should be understood that the present invention is not limited to the embodiments presented below.

**Embodiments**

First, the resonant cylinder **100** serving as a basic unit of the earthquake-proof barrier is manufactured. As in Equation 10, the width of the earthquake-proof barrier is inversely proportional to the refractive index of the earthquake-proof barrier. As such, when the resonant cylinder is made of a material having a higher refractive index, the width of the earthquake-proof barrier may be further reduced.

Referring to **10** having the same function as the upper and lower through parts **10** are formed in both radial sides of the cylindrical resonant cylinder **100**. Each through part of the resonant cylinder serves as an inductor, and an interior of the resonant cylinder serves as a capacitor.

Referring to

When the resonant cylinders **100** having different resonant frequencies are mixed and connected, the seismic wave regions having various frequencies can be absorbed.

Referring to

The upper and lower through parts of the resonant cylinders are also fitted and connected to each other in a vertical direction.

In _{c }indicates an underground depth at a place at which the resonant cylinders **100** are buried.

Further, the depth at which the resonant cylinders **100** are buried is preferably equal to or deeper than a depth of foundation work of a building. However, it is not necessary to be deeper than a wavelength length of 100 m.

A volume V of one resonant cylinder buried for an earthquake-proof barrier is dependent on the frequency of the seismic wave, and is set to a range from 1 to 100 m^{3}. The width X_{c }of the earthquake-proof barrier can be fitted and adjusted to a desired earthquake-proof level.

The earthquake-proof barrier formed by the resonant cylinders **100** is buried underground, and is not shown outside.

An earthquake-proof barrier installed in such a manner that a ditch is dug and filled with water has little effect when considering that a seabed earthquake reaches land without obstruction.

Although the embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

**DESCRIPTION OF REFERENCE NUMBER**

**10**: through part

**20**: inlet

**30**: cavity

**100**: resonant cylinder

**110**: empty space

**150**: earthquake-proof barrier

## Claims

1. An earthquake-proof barrier formed by burying a plurality of resonant cylinders underground, in which: each resonant cylinder is enclosed to form an internal cavity by planar barrier parts or a curved barrier part; at least one of the planar barrier part or the curved barrier part has at least one through part communicating with the cavity from an outside thereof; and the resonant cylinders are buried between 1 and 100 in below a ground.

2. The earthquake-proof barrier according to claim 1, wherein the resonant cylinders have a resonant frequency of 1 to 30 Hz.

3. The earthquake-proof barrier according to claim 1, wherein the resonant cylinders have a cylindrical shape, a hexahedral shape, an octahedral shape, or a spherical shape, and are interconnected by the through parts thereof,

4. The earthquake-proof barrier according to claim 1, wherein the earthquake--proof barrier has a refractive index (n) and a width (Xc), both of which are adjusted to obtain target magnitude (DM) intended to be lowered, and the width ranges from 20 to 100 in to diminish magnitude 1.

5. The earthquake-proof barrier according to claim 1, wherein the cavity of each resonant cylinder has a volume of 1 to 100 m3.

6. The earthquake-proof harrier according to claim 2, wherein the resonant cylinders have a cylindrical shape, a hexahedral shape, an octahedral shape, or a spherical shape, and are interconnected by the through parts thereof.

7. The earthquake-proof barrier according to claim 2, wherein the earthquake-proof harrier has a refractive index (n) and a width (Xc), both of which are adjusted to obtain target magnitude (DM) intended to he lowered, and the width ranges from 20 to 100 m to diminish magnitude 1.

8. The earthquake-proof harrier according to claim 2, wherein the cavity of each resonant cylinder has a volume of 1 to 100 m3.

**Patent History**

**Publication number**: 20140305049

**Type:**Application

**Filed**: Nov 29, 2012

**Publication Date**: Oct 16, 2014

**Inventor**: Sanghoon Kim (Gwangju-si)

**Application Number**: 14/359,338

**Classifications**

**Current U.S. Class**:

**Dynamic Force Generator (52/167.2)**

**International Classification**: E04B 1/98 (20060101); E04H 9/02 (20060101);