JP4257279B2 - Natural frequency measurement system - Google Patents

Description

  The present invention relates to a natural frequency measurement system for measuring a natural frequency of a building, and in particular, when the natural frequency of a building is desired to be measured, the building can be easily vibrated, and the response vibration of the building can be easily determined. The present invention relates to a natural frequency measurement system capable of identifying a natural frequency.

  A building and its natural frequency have a very close correlation in the earthquake resistance of the building. For example, a wooden house having a low natural frequency is said to have a problem in earthquake resistance. Conventionally, in order to measure the natural frequency of a building, a relatively expensive and large shaker and vibration detection sensor are installed in the building, and a specialist engineer measures the natural frequency of the building. It was.

  Patent Document 1 discloses an invention that attempts to measure the natural frequency of the conventional building described above by a simple method. In the invention, on the installation table, a plurality of needles that swing with the vibration of the measurement object on which the installation table is installed are erected, and these needles extend from the tip of the needle to the needle installation surface of the installation table. The present invention relates to a vibration frequency measuring instrument having different lengths from each other. The lengths between the needles can be made different by making the tip level of each needle constant with the upper surface of the installation table as an inclined surface. In addition, vibration frequencies are displayed around the needle erection surface along the vertical and horizontal directions of the needle erection surface.

  This vibration frequency measuring device is installed in a stable place of the building to be measured, and by reading the natural frequency of the needle that vibrates best when the building vibrates, The natural frequency is identified and the natural frequency of the building is measured. Further, since the vibration frequency measuring device is set to a weight that can be easily carried by one person, it can be easily installed on the object to be measured.

JP 2002-107221 A

  According to the vibration frequency measuring device disclosed in Patent Document 1, one person can easily install the measuring device in the building, and it is only necessary to wait for the building to vibrate due to traffic vibration or the like. When a building vibrates, the natural frequency of the building is determined by reading the frequency corresponding to the ripples of the needle that vibrates best among a plurality of needles or the needle group consisting of the most vibrated needles. Can be identified.

  However, in the vibration frequency measuring device described above, it is necessary to wait for the building to vibrate. Buildings vibrate due to traffic vibrations, wind loads, earthquake motions, etc., but wind loads, earthquake motions, etc. depend on natural phenomena, and traffic vibrations are caused by the building being measured from the main line such as roads and railways. In the case of being away, the vibration caused by the vehicle traffic is attenuated before being transmitted to the building. In any case, there is a problem that it cannot be measured when it is desired to measure the natural frequency of the building as the object to be measured.

  In addition, in the case of the needle or group of needles being measured, it is difficult to capture the most vibrated needle (or group of needles) when their vibration is very small, and therefore it is difficult to identify the natural frequency of the building. is there.

The natural frequency measurement system of the present invention has been made in view of the above problems, and is a simple device that can be easily carried and can be measured when it is desired to measure the natural frequency of a building. An object is to provide a frequency measurement system. It is another object of the present invention to provide a natural frequency measurement system that can clearly visually recognize the vibration even when the vibration of the measurement sensor (vibration detecting means in the present invention) is minute.

  In order to achieve the above object, a natural frequency measurement system according to the first aspect of the present invention applies vibration to a building by an excitation means, and calculates the natural frequency of the building from the response vibration of the building measured by the vibration detection means. The natural frequency measurement system to be obtained, wherein the excitation means includes a reciprocally slidable plate and a stopper provided at an end of the reciprocally slidable region, and the plate installed in the building reciprocally slides. However, the building is vibrated by repeatedly colliding with the stopper. Here, the building is a broad concept that means a unit type building for a detached house, a wooden structure, a reinforced concrete structure, and the like.

  By providing the vibration means, the building can be vibrated when it is desired to measure the natural frequency of the building. This vibration means includes a plate capable of reciprocating and sliding within a fixed slide area, and a stopper at the end of the slide area. The reciprocating slide movement of the plate means that, for example, a person rests on the plate and the plate reciprocates within a slide area having a certain width by alternately applying force to the left and right feet. By applying force to the left foot, the plate slides to the left with a person on it, and hits the stopper at the left end to stop. Next, by applying force to the right foot, the plate now slides to the right and stops against the stopper at the right end. When the person on the plate alternately applies force to the left and right feet, the plate can repeat the reciprocating slide motion while repeating the collision with the stoppers at the left and right ends.

  On the other hand, the vibration means described above is installed relatively firmly on the floor of the building so that the vibration means does not move on the floor when the plate reciprocates as described above. By fixing the vibration means on the floor of the building in this way, the impact force (horizontal force) generated by the collision between the plate and the stopper is transmitted to the floor of the building (that is, the building). When the collision between the plate and the stopper is repeatedly performed, horizontal force is repeatedly transmitted to the building in the left-right direction (reverse direction), and vibration is excited in the building by the horizontal force.

  The vibrating means is manufactured as a compact device that can be easily carried by one person, but the scale can be appropriately adjusted according to the building scale to be excited. It is also possible to install a plurality of vibration means in the building at the time of vibration so that a plurality of people can be placed on the respective vibration means and simultaneously generate a horizontal force to excite vibrations in the building.

  A building that vibrates generally vibrates at a natural frequency unique to the building. Strictly speaking, the building has not only the above-described natural frequency (frequency of the first-order mode) but also higher-order mode frequencies such as second-order, third-order,. Among them, the natural frequency, which is the frequency of the primary mode, is the most prominent, and therefore the natural frequency is the frequency when the building vibrates significantly during an earthquake. The number measurement is extremely important.

  Building vibration detection means will be installed on the floor of the building. For example, it is good to install on the same floor as the above-mentioned vibration means.

By measuring the response vibration of the building that vibrates with the vibration detecting means, the natural frequency of the building can be obtained. A preferred embodiment of the vibration detection means will be described later.

Further, in the natural frequency measurement system according to claim 2 , the vibration detection means includes a plurality of strings tensioned between two fulcrums, and each of the strings has a different natural frequency. It is characterized by that.

  The natural frequency of a string that is tensioned between two fulcrums is determined by the distance between the fulcrums, the linear density of the strings, and the tension that tensions the strings. Therefore, by providing a plurality of strings whose settings are changed using these as parameters, it is possible to prepare vibration detecting means composed of a plurality of strings having different natural frequencies. For example, vibration detection is performed by placing on a plate member about 5 to 10 strings with natural frequencies set in advance, such as 0.2 Hz, 0.3 Hz, 0.4 Hz,... By preparing the means, it is possible to easily identify the natural frequency of the building by selecting the most vibrated string during the vibration of the building. Here, as a string, a piano wire etc. can be used, for example. Further, a light bead or the like may be attached to the center of the string so that the vibration mode of the string can be visually recognized more clearly.

Further, in the natural frequency measurement system according to the invention of claim 3 , the vibration detection means includes a plurality of vibration bodies composed of a vibration mass and elastic bodies attached to both sides of the vibration mass, Each of the vibrators has a different natural frequency.

  When elastic bodies are attached to both sides of the vibration mass and the vibration mass is pressed to one elastic body side and then released, the vibration mass is biased by the elastic bodies on both sides and moves to the other elastic body side, this time in the opposite direction Moves when energized. The repetition of such movement, that is, the reciprocating motion of the vibration mass is determined by the mass of the vibration mass, the elastic coefficient of the elastic body, and the like. Therefore, as in the case of the vibration detection means including the strings described above, the vibration detection means including a plurality of vibration bodies whose settings are changed using the mass of the vibration mass, the elastic coefficient of the elastic body, and the like as parameters are facilitated. The natural frequency of the building can be identified by selecting the vibration body whose vibration mass has vibrated most vigorously from the vibration bodies whose natural frequency is set in advance. In addition, a coil spring etc. can be used as an elastic body.

Further, in the natural frequency measurement system according to claim 4 , the vibration detecting means comprises a plurality of pendulums having different lengths, and each of the pendulums has a different natural frequency. To do.

The pendulum is, for example, a weight suspended from a string, and facilitates a plurality of pendulums having different string lengths. Since the natural frequency of the pendulum is determined by the length of the string, vibration detection means including a plurality of pendulums made of strings having different lengths is used, for example, a plurality of pendulums are suspended and installed on the ceiling of a building. By selecting the pendulum with the most vibration when the building vibrates, the natural frequency of the building can be identified.

Furthermore, in the natural frequency measurement system according to the invention described in claim 5 , the vibration detection means is composed of a plurality of vibration bars having different natural frequencies.

  For example, the plurality of vibrating bars have a constant cross-sectional shape and a cross-sectional area, and a plurality of vibrating bars having different lengths project from the plate member to serve as vibration detection means. The vibrating rod is preferably manufactured from an elastic body. The vibration characteristics of a rod made of an elastic body can be replaced with a skewer dumpling model in which a virtual dumpling having the mass of the rod is pierced at the tip of a skewer having the elastic coefficient of the rod. Therefore, the natural frequency of such a vibrating rod can be determined by its elastic coefficient and mass. Among the plurality of vibration bars, the vibration bar that vibrates most greatly at the time of vibration of the building can be selected, and the natural frequency of the building can be identified.

  As can be understood from the above description, according to the natural frequency measuring system of the present invention, measurement can be easily performed when it is desired to measure the natural frequency of a building. In addition, since the excitation means and vibration detection means can be manufactured to be relatively light and compact, it can be easily carried by one person and installed in a building. Also, excitation to the building and measurement of the natural frequency of the building All of this can be done by one person. Furthermore, the vibrating body constituting the vibration detecting means is easy to visually recognize its vibration mode, and therefore, measurement is extremely easy.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an explanatory diagram showing an outline of a natural frequency measurement system of the present invention in which vibration is applied to a building by a vibration means and a natural frequency of the building is measured by a vibration detection means. FIG. 2 is a perspective view showing an embodiment of the vibration means together with a situation where a person is vibrating on a plate, and FIG. 3 is a perspective view showing another embodiment of the vibration means. is there. FIG. 4 is a perspective view showing an embodiment of the vibration detection means, and FIG. 5 is an explanatory view showing a situation where the strings constituting the vibration detection means of FIG. 4 are vibrating. 6 and 8 are perspective views showing other embodiments of the vibration detecting means, and FIG. 7 is a front view showing another embodiment of the vibration detecting means. In the following description, a two-story unit type building will be described, but it goes without saying that the application of the natural frequency measurement system of the present invention is not restricted to such a building.

  FIG. 1 shows that a natural frequency measurement system 1 is configured by installing a vibration means 2 and a vibration detection means 4 on the second floor of a building 8, and a person N is placed on the vibration means 2 in the X1 direction and the Y1 direction. Fig. 2 shows the situation of reciprocating sliding.

As a specific example of the vibrating means, FIG. 2 shows an embodiment thereof. The vibration means 2A shown in FIG. 2 includes guide rods 24, 24 in holes of two fixing members 23, 23 placed at a predetermined interval and attachments 25, 25 extended on the upper surfaces thereof. Installed and integrated. Further, guide rods 24 and 24 are fitted on fitting members 27 and 27 extended from the lower surface of the plate 21. The fitting members 27, 27 have rollers 28, 28 attached to the lower ends thereof, and the plate 21 can reciprocate between the reciprocally slidable regions L. Further, a coil spring 26 is attached around the guide rod 24 to the guide rod 24 between the plate 21 and the fixture 25. Due to the coil springs 26 and 26 attached to both sides, the plate 21 can be urged by the coil springs 26 and 26 during a reciprocating sliding motion to perform a smooth sliding motion. For example, rod-shaped stoppers 22 and 22 are attached to the fixing members 23 and 23 so that the surfaces of the end portions face the plate 21. In addition, embodiment which does not attach this coil spring 26 may be sufficient.

  The vibration means 2A having the above-described configuration is placed on the floor 81, and a person N is placed on the plate 21 and the plate 21 is placed in the X1, Y1, and X1 directions while alternately applying force to the left and right feet. , ... and so on. When the plate 21 comes to one end of the reciprocating slidable region L, the plate 21 stops by colliding with the stoppers 22 and 22 and is urged by the coil springs 26 and 26 to start sliding toward the other end.

  Returning to FIG. 1, for example, when the plate 21 slides in the X1 direction and collides with the stopper 22, the horizontal force F1 in the X1 direction is transmitted to the floor 81 via the fixing member 23 at the time of the collision. Next, when the plate 21 slides in the Y1 direction and collides with the stopper 22, the horizontal force F2 in the Y1 direction is transmitted to the floor 81 via the fixing member 23 at the time of the collision. The horizontal forces F1 and F2 are alternately transmitted to the floor 81 by the reciprocating motion of the plate 21, and the horizontal forces F1 and F2 excite vibrations (repetition of shaking in the X2 direction and the Y2 direction) in the building 8.

  Another embodiment of the vibration means is shown in FIG. This vibration means 2B is provided with a disk 32 that can rotate around a support shaft 33 on a support shaft 33 extending from one side surface of the plate member 31. A pin 34 extends from the upper surface of the disk 32, the pin 34 is inserted into a pin hole provided on one end side of the bar member 35, and a weight 36 is attached to the other end side of the bar member 35. . For example, when the disk 32 is manually rotated in the X direction, the weight 36 moves while drawing an elliptical locus in the Y direction as the disk 32 rotates. That is, the rotation of the disc 32 causes the weight 36 to perform a certain reciprocating sliding motion, and even if the vibration means 2B is used as the vibration means 2 shown in FIG. it can.

  Next, as a specific example of the vibration detecting means 4 shown in FIG. 1, FIG. 4 shows an embodiment thereof. The vibration detecting means 4A shown in FIG. 4 has two plate members 42, 42 provided with legs 43, 43 placed at a predetermined interval, and a pulley 44 is attached on one plate member 42. A plurality of strings 41, 41... Are tensioned between the plate members 42, 42 at predetermined intervals in the extending direction of the plate members 42, 42, respectively. That is, one end side of the string 41 is bonded to one plate member 42, the other end side of the string 41 is suspended from a pulley 44 on the other plate member 42, and a weight 45 is attached to the end portion thereof. The string 41 is tensioned by the weight of the weight 45.

  For example, a piano wire can be used as the string 41. Although the vibration mode can be clearly visually recognized only by such a piano wire, a lightweight bead 47 colored on the piano wire can be attached in order to further clarify the vibration mode.

  Further, as shown in FIG. 4, each of the strings 41, 41... Is supported by a support leg 46 provided in the middle of the plate members 42, 42. By adjusting the installation position of the support leg 46, the distance between the fulcrums that determines the vibration region of the string 41 can be changed. FIG. 4 shows an embodiment in which the distances between the fulcrums of the five strings 41, 41.

The fundamental frequency (primary frequency) of a string is generally calculated by the following equation.
[Formula 1]
f = 1 / 2L × (T / σ) ^1/2
Here, f is the frequency, L is the distance between the fulcrums, T is the tension, and σ is the linear density of the string.

From the above equation, the natural frequency of the string 41 tensioned between the two fulcrums is determined by the distance between the fulcrums, the linear density of the string 41, and the tension that tensions the string. Can be adjusted. In this embodiment, the weights 45, 45... Are constant, the strings 41, 41... Having the same linear density are used, only the distance between the fulcrums is changed, and the strings 41, 41 having five patterns of natural frequencies are used. The vibration detecting means 4A is constituted by.

  An example of the result of vibration detection using the vibration detection means 4A is shown in FIG. In FIG. 5, each of the strings 41, 41... Vibrates with the amplitudes a1 to a5. Among them, the natural vibration of the building 8 as the object to be measured has the natural frequency of the string 41 showing the maximum amplitude a2. Numbers can be identified.

  In order to measure the natural frequency of the building 8 in more detail, the chord 41 that swings with the amplitude a2 as described above, and the chord 41 with the inter-fulcrum distance that is slightly longer or shorter than the distance between the fulcrums. .., 41..., 41..., 41..., 41. By repeating this operation, the natural frequency of the building 8 can be measured with higher accuracy.

  In addition to the fact that the vibration mode of the string 41 is very easy to visually recognize, it becomes easier to visually recognize if the colored light-weight beads 47 are attached as in this embodiment. In particular, when the vibration mode of the string 41 is the same in all the strings 41, 41..., The string 41 that vibrates best compared to the vibration of a standing needle or the like can be clearer.

  Returning to FIG. 1, the person N who is placed on the vibration means 2 and has excited the vibration in the building 8 can then go down from the vibration means 2 and measure the vibration detection means 4. From the excitation of 8 to the measurement of the natural frequency of the building 8 can be easily performed.

  Another embodiment of the vibration detection means is shown in FIG. The vibration detection means 4B shown in FIG. 6 has a vibration mass 51 and a vibration body 50 in which one end of elastic bodies 52, 52 is attached on both sides on a pedestal 53. For example, the other ends of the elastic bodies 52, 52 made of coil springs are respectively attached to locking members 54, 54 extending upward at the end of the base 53. The vibration mass 51 includes a plate member 511 having rollers 512 and 512 on the lower surface, a support shaft 513 extending upward on one side surface, a weight 514 attached to the support shaft 513, and the like. Two locking tools 515 and 515 extending upward are provided on one side surface of the plate member 511, and one ends of the elastic bodies 52 and 52 are respectively locked. When a bolt having a thread groove is used as the support shaft 513, the nut can be screwed onto the support shaft 513 by using a nut as the weight 514. By attaching the weight 514 to the support shaft 513 as necessary, the weight of the vibration mass 51 can be adjusted. In addition, it can also be set as the structure provided with several vibrating body 50,50 ... on the one base 53. FIG.

In general, the natural frequency of the mass in the mass-spring system vibration model is calculated by the following equation.
[Formula 2]
f = 1 / 2π × (k / M) ^1/2
Here, f represents the frequency, k represents the spring constant, and M represents the mass of the mass.

  From the above equation, the natural frequency of the mass in the mass-spring system model can be determined by the spring constant and the mass of the mass. Therefore, while adjusting these parameters, a plurality of vibration detection means 4B, 4B,... Are installed on the floor, and the natural frequency of the building 8 can be identified from the vibration mass 51 that vibrates most intensely. .

FIG. 7 shows another embodiment of the vibration detection means. The vibration detecting means 4C shown in FIG. 7 is configured such that a plurality of pendulums 60 each including a string 61 and a mass 62 are prepared and the pendulums have different lengths. In the illustrated embodiment, each pendulum 60 has a different length. , 60... Are vibration detection means suspended from the ceiling of the building 8. In FIG. 7, the length of each of the four pendulums 60, 60... Is set to L1 to L4.

In general, the natural frequency of the pendulum is calculated by the following equation.
[Formula 3]
f = 1 / 2π × (g / L) ^1/2
Here, f represents the frequency, g represents the gravitational acceleration, and L represents the pendulum length.

  From the above equation, the natural frequency of the pendulum is determined by the length of the pendulum. Therefore, as shown in the drawing, a plurality of pendulums having different lengths can be facilitated, and the natural frequency of the building 8 can be identified from the pendulum that vibrates most intensely. In addition, it can also be set as the embodiment which suspended several pendulum on the horizontal member which comprises a frame frame instead of the structure which suspended the pendulum from the ceiling.

  Furthermore, another embodiment of the vibration detection means is shown in FIG. The vibration detecting means 4D shown in FIG. 8 is obtained by extending a plurality of vibrating bars 72, 72. The vibrating rod 72 can be a plate spring or a rod-shaped spring, and has a configuration in which, for example, a bead 73 that is light enough to ignore the weight is provided at the upper end of the vibrating rod 72 so that the vibration mode can be clearly recognized. You can also The natural frequency of the vibrating bar 72 is generally calculated by inserting a virtual dumpling having the mass of the vibrating bar 72 into the tip of the skewer having the elastic coefficient (spring constant) of the vibrating bar 72. It can be replaced with a dumpling model and can be calculated from Equation 2 above. Therefore, the natural frequency of the building 8 can be identified from the natural frequency of the vibration rod 72 that vibrates most intensely among the vibration rods 72, 72.

  The natural frequency measurement system of the present invention can be a combination using the vibration means 2A or 2B as the vibration means and using a known vibration sensor as the vibration detection means. A known motor shaker or the like may be used as the means, and the vibration detection means 2A to 2D may be used as the vibration detection means.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and there are design changes and the like without departing from the gist of the present invention. They are also included in the present invention.

Explanatory drawing which showed the outline | summary of the natural frequency measurement system of this invention. The perspective view which showed one Embodiment of the vibration means. The perspective view which showed other embodiment of the vibration means. The perspective view which showed one Embodiment of the vibration detection means. Explanatory drawing which showed the condition where the string which comprises the vibration detection means of FIG. 4 is vibrating. The perspective view which showed other embodiment of the vibration detection means. The front view which showed other embodiment of the vibration detection means. The perspective view which showed other embodiment of the vibration detection means.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Natural frequency measurement system, 2, 2A, 2B ... Excitation means, 4, 4A, 4B, 4C, 4D ... Vibration detection means, 8 ... Building, 21 ... Plate, 22 ... Stopper, 36 ... Weight, 41 ... String, 50 ... vibrating body, 51 ... vibrating mass, 52 ... elastic body, 60 ... pendulum, 72 ... vibrating rod

Claims (5)

A natural frequency measurement system for obtaining a natural frequency of a building from a response vibration of the building measured by a vibration detecting means by applying vibration to the building by an excitation means,
The vibration means comprises a reciprocally slidable plate and a stopper provided at the end of the reciprocally slidable region,
The plate is formed in a size that can be placed by a person, and a roller is attached to the lower end of the fitting member extending from the lower surface of the plate,
A natural frequency measurement system that vibrates the building by repeatedly striking the stopper while the plate installed in the building reciprocally slides. The natural frequency measurement system according to claim 1, wherein the vibration detection means includes a plurality of strings tensioned between two fulcrums, and each of the strings has a different natural frequency. . The vibration detection means includes a plurality of vibration bodies each including a vibration mass and elastic bodies attached to both sides of the vibration mass, and each of the vibration bodies has a different natural frequency. The natural frequency measurement system according to claim 1 . 2. The natural frequency measurement system according to claim 1, wherein the vibration detection unit includes a plurality of pendulums having different lengths, and each of the pendulums has a different natural frequency. 2. The natural frequency measuring system according to claim 1, wherein the vibration detecting means is composed of a plurality of vibrating bars having different natural frequencies.

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