OFFICIAL GAZETTE

uildings of height less than 4 meters and with
total floor area less than 30 sq.m., or to fence
with height not over 3 meters.
(Materials for Concrete)
Article 72. Materials to be used for concrete in
reinforced concrete buildings shall satisfy the
requirements in the following items :
(1) Sand, gravel, crushed stones and water shall
be free from acids, salts, organic matters or
particles of mud liable to cause rusting of steel
or injurious to obstruct normal process of setting
of concrete;
(2) Gravel or crushed stones shall be hard and
of size to go through easily between spaces in
reinforcing bars and space between reinforcing
bar and form.
(Joints and Fixing of Reinforcing Bars)
Article 73. Ends of reinforcing bars shall be hooked
to prevent from slipping.
2 Joint of main bar shall be at a partwhere
tension stress acts least excepting the case of
welding, the length of lap shall be more than 25
times its diameter (in the case of making joints
of main bars of different diameters, the smaller
diameter; hereinafter the same in this Article).
However, in case the joint may not be made at
a point where tension is not working at full
stress, then, the lap shall be more than 40 times
the diameter or bars.
3 Of the tension steel bars in beam framed with
column, excepting the case of welding with main
bars in column, the length of anchor shall benot
less than 40 times its diameter.
(Proportion of Concrete Mix)
Article 74. Concrete to be used in reinforced concrete
construction shall show compressive•E
strength of more than 90 kg/cm2 at age of 28
days.
2 Water-Cement ratio of concrete shall be kept
down from the value obtained by the following
formula according to the required strength for
structural purpose, except in cases where it is
determined by the testing of strength by Japanese
Industrial Standard A 1108 (Method of testing
compression stress) :
In case of
Cement
commonPortland
In case of high early strength
Portland Cement
In case of slag cement or
silica Cement
0.85 K
"F+0.64 IT
0.47 K
"F+0.05K
1.4K
"F+1.48K
In above formula, F, K and x shall showthe
following values respectively :
F=Compressive strength of concrete at age
of28 days given in table in Article 91.
K=Compressive strength of mortar at age of
28 days according to Japanese.
Industrial Standard R 5210 for Portland
Cement. However, in case the period of
2 weeks after concrete is poured happens
to fall on a month having average temperature
for that month less than 10°C, the
value of the stress to be decreased by 50
kg/cm2.
x-Water-Cement ratio
3 Mixture of Concrete shall be determined so that
the product shall be uniform, and compact.
(Curing of Concrete)
Article 75. Curing of concrete shall be done so as
to keep the temperature of concrete above 2°C,
while pouring and during the period of 5 days
after concrete is poured and care shall be taken
to prevent it from setting and hardening by dryout
or vibration.
(Removing of Supports of Forms)
Article 76. Supports for forms for beams and slabs
as principal structural part shall not be removed
before 6 weeks (4 weeks in case of roof floor or
in case of no floor bsing directly above).
2 The provisions of the preceding paragraph shall
not apply in case high early-strength Portland
cement is used or other cement is used and in
case } of the period of time or more mentioned
in said paragraph has elapsed and only in case
building official approves that he has no objection
thereto from standpoint of structural strength
due to favorable condition in respect to temperature,
humidity and others.
(Construction of Columns)
Article 77. Construction of columns as principal
structural part shall satisfy the structural requirements
as provided for in the following items :
(1) Main bars shall consist of more than 4 reinforcing
bars with properly spaced ties ;
(2) Spacing of ties shall be less than 30 cm.,
and at the same time not over 15 times the
diameter of smallest bars used ;
(3) Least diameter of column shall be more
than 1/15 of the distance between the main
supports unless it is checked as safe in consideration
of its slenderness ratio in structural
calculation.
(4) Sum of area of main bars shall be not less
than 0.8% of the area of cross-section of concrete
(if area of bar exceeds the area under
the provision of the preceding paragraph or
under the result of structural calculation, that
required area,,
(Construction of Beams)
Article 78. Beam as principal part for structural
strength shall be reinforced double, and shall
have stirrups at space not exceeding 3/4 of the
depth of a beam.
(Thickness of Protection for Embedded Bars)
Article 79. Thickness of concrete covering of the
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