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On the Natural Frequency of the Same Type

House Evaluated by Mass-Observation

journal or

publication title

福井大学工学部研究報告

volume

13

number

2

page range

391-396

year

1965-09

URL

http://hdl.handle.net/10098/5029

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391

On the Natural Frequency

of the Same Type House Evaluated by Mass-Observation

*

Isao TORIUMI

(Faculty of Engineering, Fukui University)

(Received 31 March 1965)

abstract

Auto-correlation of natural noise in vibration at the top of the house gives correctly its natural frequency. As a sample, we selected 235 houses of 5 storied standard type in 27

J.

H. C. housing estats. The results are as follows,

1. Even in one estat, there are pretty deviations in natural frequency of house. 2. The difference among the estats appears clearly.

3. As these houses vibrate themselves in rocking mode according to the deformation of the ground around the foundation, the distribution of natural frequency relates closely to the geological conditions.

1. To evaluate the effect of the ground to the natural frequency of house, it is suita-ble to compare the natural frequencies of the same type houses which are founded on different grounds, as the various conditions in house itself are almost eliminated. So far, several authors have discussed the above problem. In their observations,

how-ever number of sample house is rather small (less than 10 houses) as the observation by shaker etc. is laborious.

Auto-correlation of natural noise in vibration at the top of a house offers correectly its natural frequency. We used a motor car for observation which carried a magnetic data recorder, moving coil type pick-up and amplifier to record a natural noise in vibra-tion. This system reduces the laborious work at the actual place, shortens remarkably the observation time and makes it possible to realize mass-observation.

As a sample, we selected 5 storied standard type house in J. H. C. (Japan House Corporation) housing estats. In all, there are 235 houses in 27 estats in Kinki zone (including Aichi district).

Though there are some minor changes in type, the factors affecting mainly the natural, frequency (size, mass and rigidity) are nearly the same except the condition of the ground, so we can pick up the effect of the ground pretty well. The outline of the standard type house is shown in Fig. 1. Photo. 1 shows another type with minor change. The measuring point is set at the center of top floor, as these houses vibrate themselves in rocking mode. Horizontal vibration of displacement in thin direction in plan (shown in Fig. 1 by arrow) is recorded for 2 minutes. As the nature of the

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392

system with small damping, the records (Fig. 2) contains a large quantity of the natu-ral frequency of its house though the amplitude fluctuates.

Photo. 1. Observaion.

13.4 m

f - - -- ---I

6.4 m

Fig. 1 Standard type house observed.

1

-Fig. 2 Record of horizontal vibration (displacement) at the top floor.

-

-

I

Reproduced records are analyzed by a magnetic correlator. An example of auto-correlogram is shown in Fig. 3.

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On the Natural Frequency of the Same Type House Evaluated by Mass-Observation 393

Fig. 3 Auto-correlogram

2. 22 estats (except Aichi district and Kobe city) around Osaka Bay are plotted in the geological map (Fig. 4). In Fig. 4, North and East parts are covered with rocky mountain chains Rokko and Ikoma respectively, South area is composed of pretty hard soils and the center area (Yodo River and Osaka City) is delta zone of alluvium.

N

t

lB

RocK

["lTI

Dill4vil.lm

D

All\(v!Lll!\

9S

ql). , §,K)l

Fig. 4 Geological map aroumd Osaka Bay.

(5)

394 2.5 3.0 I t

ilL

'2 s 3 1 0 :m**~I~rm7jjf~¥li11r ~13~~ 2 i5-Natural Frequency 3.5 4.0 ~ .---~---(c / s) 4.5 5.0 5.5 I I i i I I I i I I

Satsukigaoka _ _ _ _ ~ _ _ ~~I~I_~ _ _ _ _ _ _ _ _ _ _ _ _ _ _ ~~i~l_ Akashi

" I

Mikage

Number of House Higashi -maiko~

tI, ,

I

~"

I I ( 2.5 Kori Tsurumai

r

t ami __ ....I...-_ _ _ . l . . . . - _ - - L - _ Kangetsuky_o_-L _____ ~I~I_L_ Shirasagi Nakamozu Nijigaoka (Aichi Di strict) Nikawa Ikeda I " , II Rokko 11 II

III

I /I I I I I I I I Higashi ,- toyonaka

"I,

m'

,

I I Kasugaoka I I Harinakano I III A sah i gaoka ___ -'---LJIIL--.l---L--.l--_

I II Ii I I I I

,

I 3.0 I I t , I ,I! I I I I ., 'I Sojiji Sukematsu Hato - oka (Aichi District) Mukogaoka iMiyakojima Hamakoshien Higashi - yodogawa Dekijima I I I I I I I , , I I I I I I I 3.5 4.0 4.5 5.0 Fig. 5 Distribution of natural frequency

t I

(6)

On the Natural Frequency of the Same Type House Evaluated by Mass-Observation 395

N

+

,

r::.-:

:]

Fig. 6 Micro map (Higashi-yodogawa)

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\

(7)

396 m**~I~~Wf1E*'\5" $13~re 2 %

--.----~.---3. Fig. 5 shows that

1) Even in one estat. there is pretty deviation in natural frequency of the same type house.

2) The range of deviation in the estats which are newly opened on the hill (Kori, Satsukigaoka etc.) is more wide than the one in the estats which are situated on the field (Dekijima, Harinakano etc.).

3) In spite of the width of range in natural frequency, the difference among the estats appears clearly.

4) The rank of estats in Fig. 5 is proportional to the popular estimation about the stiffness of the ground.

5) In Fig. 4. the contour of natural frequency of everyestat represented by the mean value is shown in fulllines. These contours closely correlate to the geological phase of the ground.

6) Fig. 6 and 7 are micro contour maps of natural frequency in a estat itself (Higa-shi-yodogawa and Dekijima). In Fig. 6, the contour suggests the existence of an old pond previously filled up with earth. The micro map should also talk to us something much more. According to these micro map. the available range of the ground to the natural frequency of the house is pretty short.

Fig.  1  Standard  type  house  observed.
Fig.  4  Geological  map  aroumd  Osaka  Bay.
Fig.  5  Distribution  of  natural  frequency
Fig.  6  Micro  map  (Higashi-yodogawa)

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