Abstract of Special Research Report (SRR-81-1)

National Institute of Occupational Safety and Health, Japan

Special Research on Countermeasures for Safety of Scaffold etc. against Strong Wind


Yoshitada MORI and Yoshimasa KAWAJIRI

: Failure accidents of scaffold have generally been decreasing but those caused by wind still occur.
    Table 1-1 shows principal failure accidents of scaffold caused by wind in the last several years. Thus this type of accident does not occur frequently, but when once it occurs, many workers may be injured and furthermore public passers-by may suffer. The typical example is the accident of scaffold occurred at the mending construction site in Otemachi, Tokyo, on October, 1978. In this accident one was killed, one was severely wounded, two were slightly wounded and they were all public passers-by.
    Now, provisions for safety countermeasures of scaffold against wind are not contained in Japanese laws and regulations for occupational safety. Therefore safety of scaffold against wind depends on judgement of contractor.
    Taking into account above-mentioned situation and compiling with the request from occupational safety administration, our group carried out special research on countermeasures for safety of scaffold against strong wind.
    In this paper, the summary of research is described so that; determination of the basic wind velocity all over Japan in next chapter, actual size experimental examination of wind force acting on scaffold in third chapter, reactive force of ties-to-wall with horizontal load in forth chapter, pulling-out strength of the anchors for tie-to-wall in fifth chapter.
    In this chapter, we also describes the outline of investigation on answer of questionnare, earring out previous to our study in order to grasp the actual structures of scaffold and actual countermeasures for strong wind.

Determination of the Basic Wind Velocity All Over Japan

Yoshitada MORI, Kinichi KINOSHITA and Yoshimasa KAWAJIRI

: For the purpose of computation of wind load for scaffold and other temporary equipments, the basic wind velocity in each place of Japan has been studied in consideration of followings ;
  1) We selected principal meteorological stations of 149 in Japan, and picked up the maximum values in every month of wind velocities that were measured at these stations from 1964 to 1977.
  2) According to the power low of 1/7, we arranged all above data for the wind velocities at a height of 10m from ground surface.
  3) In the computation of expected wind velocity, we assumed that 12 months is proper for the return period to scaffold and others, and we excluded the data that were measured at the stations where were within a radius of 150 km of typhoon because of that it is usually taken care of the stability of scaffold and others by the information of it.
    As the results of expected wind velocities and its contour line-map, we propose that basic wind velocity of 14m/sec. is appropriate for scaffold and temporary equipments expect special strong wind districts, and these districts are shown in Table 2.4.

Actual Size Experimental Examonation of Wind Force Acting on Scaffold

Kinichi KINOSHITA and Yoshimasa KAWAJIRI

: Wind force acting on scaffold depends on not only the aspect of scaffold but also states of back building, and nowadays they were little made clear. Wind tunnel tests are usually carried out in order to make clear them. In this study we also intended to have wind tunnel tests in cooperation with any university and any construction company, but for certain reasons we left the execution of tests to their hands, and we took part in the planning of tests and completion results. On the wind tunnel tests, wind force coefficients were decided tentatively.
    The purpose of this study is to make sure the propriety of wind force coefficients above-mentioned by actual size experiments. Scaffold used in experiments was a frame type scaffold, which was erected along the model building in Kiyose field station, which was about 26 m (15 stories) high and 9 m (5 spans) wide, and which had two kinds of protector, one being sheet and the other being expanded-metal net.
    In experiment wind velocity, wind direction, wind pressure on the surface of scaffold and force acting on tie-to-wall measured on seasonal windy days. From the analysis of experimental data, it was confirmed that the experimental values of force on tie-to-wall almost considered with the theoretical values and then wind force coefficients decided on wind tunnel tests were almost appropriate.

Reactive Force of Ties-to-Sall with Horizontal Load

Kiyoshi FUKAYA and Noboru SUGIMOTO

: It is difficult to calculate theoretically the reactive force of ties-to-wall with horizontal load because scaffold is the structure which has some "play" in coupling point and is not statically determinate.
    Thus, experiments using commercial scaffolds were carried out to measure the reactive force of ties-to-wall when it is applied with horizontal load under following conditions :
  1) The widths of scaffolds tested were 600, 900 and 1200 mm.
  2) In same experiments horizontal load is applied to the point of scaffold upper than the top tie-to-wall and in others to the point between the top tie-to-wall and the next to the top one. Furthermore installing the ties-to-wall are carried out at five kinds of vertical distance.
    The results may be summarized as follows.
    When horizontal load is applied to the point of scaffold upper than the top tie-to-wall,
  1) the longer the vertical distance between the neighbouring ties-to-wall, the smaller reactive force both of the top tie-to-wall and the next to the top one is measured smaller.
  2) as the horizontal load is applied to higher position of scaffold, reactive force of each tie-to-wall is measured bigger.
  3) reactive force is bigger in the top tie-to-wall than the next to the top one.
  4) reactive force of the ties-to-wall which are other than the top and the next is small.
    Empirical formulae for the reactive force of the top tie-to-wall and the next one are shown by equations (4.3) (4.7) and (4.14) - (4.17).

Pulling-out Strength of the Anchors for Tie-to-wall

Katsunori OGAWA

: Ties-to-wall for scaffolds are usually used when their tensile and compressive strength is higher than 1,000 kg.
    However if strength of the anchor for setting the tie-to-wall of building is not sufficient, the use of such strong ties-to-wall is not effective.
    Thus experiments were carried out to examine the followings' pulling-out strength,
  1) "Insert" in concrete of young age
  2) "Hole-in-Anchor" and "Chemical Anchor" in various degree of execution.
    In results, pulling-but strength of "Insert" buried in young age concrete whose compressive strength is 50 kg/cm2 , is higher than 1,800 kg. Therefore "Insert" buried in wall of buildings may be connected with the tie-to-wall.
    Pulling-out strength of "Hole-in-Anchor" and "Chemical Anchor" is much affected with the degree of execution.
    According to the method to bury the anchors they have sufficient strength as the anchor for the tie-to-wall.

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