REINFORCED
CONCRETE
CODE
CITY OF COLUMBUS
OHIO
DEPARTMENT OF
BUILDINGS
Reinforced
Concrete Code
*
AN ORDINANCE No. 27098
To define 'and describe the term and meaning
of reinforced concrete construction and to
regulate the manner of its use in building
operations.
Be it Ordained by the Council of the City of
Columbus, State of Ohio:
Section 1. Definition. By the term Rein-
forced Concrete in these regulations is meant
an approved structural combination of concrete
and steel, so arranged that the steel resists all
the tensile stresses and may aid the concrete in
resisting shear and compression. No system
of reinforced concrete design shall be used
which is not capable of design and investiga-
tion according to the best engineering practice,
and the principles laid down in this code.
Sec. 2. Requirements for Permit. Before a
permit to erect any reinforced concrete struc-
ture is granted, complete plans and specifica-
tions showing all details of construction, the
size and position of all reinforcing members and
the composition of the concrete shall be sub-
mitted to the Department of Buildings. The
Department of Buildings reserves the right to
demand that the owner, architect or engineer
submit certified copies of all computations or
stress sheets for examination upon application
for a building permit.
Permission to erect any reinforced concrete
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structure does not in any way approve the con-
struction until after tests have been made of
the actual construction to the satisfaction of
the Department of Buildings.
Sec. 3. Unit Stresses. The following unit
stresses shall not be exceeded:
Medium steel, 16,000 lbs. per sq. in.
High carbon steel, 18,000 lbs. per sq. in.
Steel to resist diagnoal tension, 12,000 lbs.
per sq. in.
Concrete, extreme fiber in compression, 700
lbs. per sq. in.
Bond stresses for plain round bars, 70 lbs. per
sq. in.
Bond stresses for twisted bars or deformed
bars, 100 lbs. per sq. in.
Concrete in shear, 50 lbs. per^q. in.
Sec. 4. Assumptions. The following as-
sumptions shall be made as a basis for the cal-
culation of girders, beams and slabs :
(a) The stress strain curve of concrete in
compression is a straight line.
(b) The modulus of elasticity of concrete
remains constant within the limits of unit
working stresses specified in this ordinance.
(c) The adhesion between concrete and steel
is sufficient to make the two materials act
together.
(d) Concrete has no value in tension.
(e) The ratio of the modulus of elasticity of
steel to the modulus of elasticity of concrete
is 15.
Sec. 5. Slabs, Beams and Girders. Slabs,
beams and girders with uniform distribution of
load shall be calculated as follows: When sim-
ply supported the moment equals WL/8; when
continuous over one support the moments shall
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be considered as WL/10 at center and WL/8
over intermediate support; when continuous
over two or more supports with equal or ap-
proximately equal spans, the moments shall be
considered as WL/12 at center and over sup-
ports of intermediate spans, and WL/10 at cen-
ter of end span and over second support; where
“W”=total load and “L”=span in feet.
In continuous slabs, beams and girders, with
uniform distribution of load, continuity rein-
forcing shall extend over and beyond supports
at least one-fourth (J4) of the adjoining span.
Concentrated loads shall be computed accord-
ing to accepted theory, and in the case of con-
tinuous spans proper provisions shall be made
for continuity.
For slabs, beams and girders the span shall
be taken as the distance from center to center
of supports, but need not exceed the clear
span plus the depth of slab, beam or girder.
"Sec. 6. Tee-Beams. Where beams are
made monolithic with the floor slab, with the
slab reinforcing at right angles to the beam,
the slab may be considered as acting in flex-
ture with the beam, provided the width of
slab so considered be governed by the shear-
ing resistance between the slab and beam, but
be limited on either side of the beam to 1/6
of the span of the beam between supports and
also limited on either side of the beam to five
(5) times the thickness of the slab. In case
the reinforcing is not at right angles to the
beam, the portion of the slab so considered
shall be limited on either side of the beam
to three (3) times the thickness of the slab.
In no case shall the total width of flange so
taken exceed the distance center to center , of
beams.
No part of the slab shall be considered as a
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portion of the beam unless the slab and beam
are cast at the same time.
Where reinforced concrete girders support
reinforced concrete beams, the portion of the
floor slab acting as flange to the girder must
be reinforced with rods near the top, at right
angles to the girder, to enable it to transmit
local loads directly to the girder and not
through the beams.
In tee-beams construction the bottom of the
web over continuous supports shall be pro-
vided with haunches, or be reinforced with
sufficient steel in compression, to reduce the
stress on the concrete to within ten per cent
of that allowed at the center of the span. This
steel shall project at least twenty-four inches
on each side of supports and the unit com-
pressive stress in the steel shall not exceed
fifteen (15) times the unit compressive stress
in the concrete at the same distance from the
neutral axis.
Sec. 7. Square and Rectangular Slabs. For
square slabs reinforced in both directions the
moments for each set of reinforcing in the
center half of the slab shall be taken not less
than WL 2 /16 where the slab under considera-
tion is not continuous; WL 2 /20 where the
slab under consideration is continuous over
one support, and WL 2 /24 at center and over
supports where the slab is continuous over
both supports; where “W”=the load per
square foot and “L”=side of square in feet.
The steel in the remaining quarters may be
proportioned by using one-half of the amount
used in the middle half.
For rectangular slabs, with equal spacing of
reinforcing in each direction, the transverse
reinforcing shall be proportioned to carry the
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amount of load given by the following
formula :
Wa 4
w=
a 4 +b 4
Where “w”==load per square foot carried by
the transverse reinforcing.
“W”=total load per square foot of slab.
“a”=length of slab and
“b”=breadth of slab.
The moments in the central half of the slab
for the transverse reinforcement shall be not
less than wa 2 /8 where the slab is not contin-
uous, wa 2 /10 where the slab is continuous
over one support, and wa 2 /12 at center and
over supports where the slab is continuous
over both supports. The steel in the remain-
ing quarters may be proportioned by using
one-half (J4) the amount used in the middle
half. Where the length of a rectangular slab
exceeds one and one-half (1J4) times the
breadth, the load shall be assumed to all be
carried by the transverse reinforcement.
The amount of load carried to the side beams
for square and rectangular slabs shall be taken
according to the above assumptions and mo-
ments, as derived by the assumption of uniform
distribution of load, shall be increased twenty-
five (25) per cent.
Sec. 8. Minimum Thickness of Slabs. Re-
inforced concrete slabs shall not be less than
four (4) inches thick for floors, and three and
one-half (3/4) inches for roofs in beams and
girder construction, except in spans of six feet
or under, in which case the above thicknesses
may be decreased one-half (J4) inch, provided
the unit stresses as herein given are not efcc-
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ceeded. Slabs shall not be less than two (2)
inches thick, with reinforcing at right angles
to the beam, for floors using beams spaced
close together and separated by hollow tile or
other centering or fillers satisfactory to the
Inspector of Buildings.
Sec. 9. Reinforced Terra Cotta Hollow Tile.
(a) By reinforced terra cotta tile is meant a
system of hollow burned clay tile in combina-
tion with reinforced concrete, in which combi-
nation the hollow tile may be used to resist
compressive and shearing stresses, subject to
the following provisions :
The provisions relating to reinforced con-
crete construction shall hold as far as appli-
cable to this system.
All tile to be hard burned terra cotta tile of
uniform quality, deeply scored, free from
shrinkage cracks, with true beds, and having
an ultimate compressive strength of 4000 lbs.
per square inch of the net area of surface
tested.
The following unit stresses and values shall
not be exceeded. Compression, extreme fiber
stress on tile 500 pounds per square inch.
Shearing stress on tile 200 pounds per square
inch. Adhesion between tile and 1:2; 4 con-
crete to 1 :3 mortar, 40- pounds per square inch.
Ratio of modulus of elasticity of steel to that
of tile with cement mortar joints, 10.
(b) Workmanship. The hollow tile shall
be thoroughly drenched with water at the time
the concrete is poured. The lines of tile shall
be true and the joints between tiles shall be
staggered.
Sec. 10. Girderless Floor. By girderless
floors is meant a type of reinforced concrete
construction in which the columns are pro-
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vided with flaring heads and the loads are
carried directly to the columns by the slab and
not through beams and girders. •
The bending moment at the center of the
slab shall not be less than WL/30 where
“W”=total load on panel and “L”=length in
feet of the side of a square panel and of the
side of an equivalent square in rectangular
panels. This length shall be taken center to
center of columns. The steel to resist this
moment shall be divided into four bands, two
in cross and two in diagonal direction over the
column head.
Each band of steel shall be approximately
7/16 L in width and the total amount of steel
in any one band shall not exceed .30 of 1 per
cent for high carbon and .36 of 1 per cent for
medium steel. In determining the percentage
of steel, the width of concrete band so consid-
ered shall not exceed the width of band of
steel plus twice the thickness of the slab.
All splices shall be made at the column
heads and the amount of lap of each bar shall
be approximately one-fourth L (J^L). At
least 50 per cent of all the bars shall be spliced
over each column. In this construction provi-
sion shall be made to take care of the circum-
ferential stresses. Proper provisions shall be
made for resisting the* shear at the capital and
for holding the steel in the proper position over
the column head.
The diameter of the column head shall never
be less than .25L and its profile shall not fall
inside of a line drawn from its periphery to the
edge of the column and making an angle of
45 degrees with the vertical. The spiral rein-
forcing of the column shall extend into the
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capital approximately to the under side of the
slab.
The minimum thickness of the slab shall be
seven (7) inches for floors and six and one-
half (6 J4) inches for roofs.
In end panels or wall panels, in which wall
columns of reinforced concrete “with flaring
heads are omitted an allowance of ten (10)
per cent shall be made for increased moments.
Wall columns shall be designed to carry one-
half the panel load and such other loads as
may come upon it, and if necessary the col-
umns shall be designed for eccentric stresses.
The wall beams shall be designed for one-third
the panel load plus any other loads which may
come upon them.
Sec. 11. Web Stresses. Shear on concrete
shall not exceed one hundred and twenty (120)
pounds per square inch, but where said shear
exceeds fifty (50) pounds per square inch, web
reinforcement of approved design shall be used.
The reinforcement shall be designed to take all
web stresses in excess of fifty (50) pounds per
square inch, without exceeding the unit stresses
hereinbefore given, and must be so spaced as
to intersect any 45 degree line of rupture from
the neutral axis to the center of the steel.
Where unattached stirrups are used, they shall
pass under the main reinforcing bars. At-
tached stirrups shall have connections of suf-
ficient strength to develop the elastic limit of
the steel without slipping along or shearing
from the main bars. All web reinforceing
shall be provided with sufficient anchorage
above the neutral axis to develop the safe
strength of the member without exceeding the
bond stresses hereinbefore given. In comput-
ing the intensity of the vertical shear only the
area of the web between the center of grav-
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ity of the steel and the center of compression
of the concrete shall be considered as effective.
Sec. 12. Protection Against Fire and Cor-
rosion. All reinforcing steel shall be protected
by concrete of the following minimum thick-
ness : Two (2) inches in columns, one and one-
half (1J4) inches for beams and girders, and
three-fourths ($4) inches in slabs.
Sec. 13. Reinforced Concrete Columns.
Reinforced concrete columns shall not exceed
in length fifteen (15) times the least diameter
of the column, including the reinforcement, and
where such ratio is more than twelve (12)
times, the stresses shall be reduced in accord-
ance with the best engineering practice. In
computing the strength of columns only the
area within the limits of the ties, bands, hoop-
ing or spirals shall be considered as effective
area. The concrete which must in all cases
be provided outside of the ties, bands, hooping
or spirals as provided in Section 12, shall be
considered only as protection against fire and
corrosion. No reinforced concrete column
shall be used whose least side or diameter,
including the protection against fire and corro-
sion, is less than twelve (12) inches.
Wall columns and other columns subject to
eccentric loads of and indeterminate amount
shall have the stresses, as hereinbefore given,
reduced by twenty (20) per cent. Eccentric
loads of determinate amount shall be computed
according to accepted theory, but in no case
shall the sum of the stresses due to direct and
eccentric loads exceed the maximum stresses
hereinafter given for each type of column.
Sec. 14. Square Core Columns. In the
square core type of columns, where four rods
are used, and the minimum area of each rod
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is not less than .4418 of a square inch, and the
total area of the rods is not less than one-half
(y 2 ) and not more than four (4) per cent of
the required area of the column, and the max-
imum tie spacing does not exceed twelve (12)
inches, and in no case more than one-half the
distance between two of the vertical rods, and
the minimum area of the ties is at least .0625
of a square inch, the following values shall not
be exceeded:
7000 pounds per square inch on the vertical
steel.
500 pounds per square inch on the concrete.
In the square core type of column, where
eight rods are used and the minimum area of
each rod is not less than .4418 of a square inch,
and the total area of the vertical rods is not
less than one-half (^) of one per cent and not
more than fiv'e (5) per ‘cent of the required
area of the column, and the maximum tie spac-
ing does not exceed twelve (12) inches and in
no case more than seven (7) times the diam-
eter of the vertical rods, and the minimum
area of the ties is at least .0625 of a square inch,
and two sets of ties are used, one in the form
of a square inscribed within the outer tie; and
the ends of the ties secured in such a manner
as will fully develop the elastic limit of the
ties; the following values shall not be ex-
ceeded :
9000 pounds per square inch on the vertical
steel.
600 pounds per square inch on the concrete.
Sec. 15. Round Core Columns. For round
core columns vertically reinforced and hooped
with circular bands or spirals, the vertical rods
shall not be less than four (4) in number, nor
the area of the cross section of each rod less
12
than .4418 of a square inch, nor the maximum
spacing of the verticals more than twelve and
one-half (12 1 / 2 ) inches measured on the cir-
cumference of the spiral, the percentage of
spiral hooping shall not be less than one-half
of one per cent and not more than one and one-
half (1 1 / 2 ) per cent of the area within the
hooping, the spacing of the spirals, if such are
used, shall not exceed one-seventh (1/7) of the
diameter of the core and in no case more than
three (3) inches. Provided, however, that in
cases where properly welded bars are used and
there are enough vertical rods of the proper
area to give the same restraint as a grill, the
spacing of the bands shall not exceed, for the
values hereinafter given, seven (7) times the
diameter of one such vertical rods.
The following values shall not be exceeded
for either of the foregoing conditions :
10,000 pounds per square inch on the vertical
steel.
700 ponds per square inch on the concrete.
10,000 pounds per square inch on 2.4 times
the volume of the spirals considered as imag-
inary verticals, provided that the spirals are
continuous, machine made, provided with ac-
curate spacers and secured at every intersec-
tion.
Provided, however, that if wire hooping is
used not less than five-sixteenth (5/16) of an
inch in diameter (of 80,000 pounds ultimate
strength and 50,000 pounds elastic limit) an
allowance of twelve thousand pounds per
square inch may be used for hooping, provided
that whenever such value is allowed, said
spirals shall be continuous, machine made, and
provided with accurate spacers and secured at
every intersection.
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Sec. 16. Column Splices. All vertical re-
inforcing in columns shall be spliced in such
manner as will transmit the stresses for which
it is designed. Sharp bends in the steel shall
be avoided. The splicing of verticals having
an area of less than one and one-fourth (1*4)
square inches may be done by -lapping, the
lapped bars to be wired securely to each other.
Verticals having an area in excess of one and
one-fourth square inches shall be spliced by
putting the bars squarely one over the other,
and tying the same together by some mechan-
ical means that will not utilize the adhesive
strength oT the concrete. All splices shall
occur only at floors or some other means of
lateral support.
Sec. 17. Tension in Columns. In tall nar-
row buildings special provisions shall be made
for tension in columns.
Sec. 18. Additional Stories. Where addi-
tional stories are to be added to work over
two years old, the strength of the concrete in
the existing columns may be taken fifteen (15)
per cent higher, than the values herein
specified.
Sec. 19. Footings. Footings for walls and
columns may be constructed of reinforced con-
crete, providing the working stresses, as given
in this code, for concrete and steel are not
exceeded, and the steel is protected by at least
three (3) inches of concrete.
The vertical rods in reinforced concrete col-
umns shall be anchored to the footings by
anchor bars or other means satisfactory to the
Inspector of Buildings.
Sec. 20. Reinforced Concrete Curtain Walls.
Exterior and interior walls of reinforced con-
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crete shall be not less than eight (8) inches
thick and reinforced with not less than three-
tenths (3/10) of one per cent of steel in each
direction, vertically and horizontally. Rods
shall be spaced not more than twelve (12)
inches on centers and shall be wired to each
other at each intersection.
Sec. 21. Cement. Only Portland cement
shall be used which conforms to the standard
specifications of the Society for testing ma-
terials. All cement shall be tested in lots of
not more than one carload, and the Department
of Buildings may at any time demand that cer-
tified copies of all test records be submitted
for examination.
The minimum requirements for tensile
strength for briquette one (1) inch square in
section shall be :
NEAT CEMENT.
24 hours in moist air 175 pounds
7 days (one day in air, six in
water) 500 pounds
28 days (one day in air, twenty-
seven in water) 600 pounds
ONE PART CEMENT, THREE PARTS
SAND.
7 days (one day in air, six in
water) 175 pounds
28 days (one day in air, twenty-
seven in water) 275 pounds
Sec. 22. Sand. Fine aggregate shall con-
sist of a mixture of fine and coarse grains of
clean, natural sand, screened to pass a one-
fourth inch screen, with the coarse grains pre-
dominating. Sand shall be composed of hafrd
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silicious particles, free from all decomposed
materials, loam or other deleterious matter.
Sec. 23. Aggregate. Coarse aggregate
shall consist of crushed stone or washed gravel.
It shall pass through a one (1) inch screen and
be retained on a one-fourth {%.) inch screen,
preferably graded from small to large particles.
Crushed stone shall be reasonably free from
crusher dust. The particles composing the
aggregate shall be clean, hard, durable and free
from all decomposed materials, loam or other
deleterious matter.
Sec. 24. Proportions for Mixing Reinforced
Concrete. Reinforced concrete shall consist of
a mixture of one part Portland cement to not
more than four (4) parts aggregate fine and
coarse either in proportion of one part cement
to two parts sand and four parts aggregate, or
in such proportion that all voids in the aggre-
gate shall be properly filled.
Mixing shall be done by approved batch
mixer, unless the conditions of the work would
make hand mixing preferable ; hand mixing
shall be done only under the approval of the
Department of Buildings. Enough water shall
be added to the mixture to make it a plastic
mass capable of being rammed into all parts
of the mould and around all reinforcing mem-
bers. In all mixing the separate ingredients
shall be measured and thoroughly mixed to a
uniform color, appearance and consistency be-
fore placing. Thirty days after mixing, the
concrete shall develop a compressive strength
of 2000 pounds per square inch by testing a
six-inch cube.
Sec. 25. Bending and Elongation of Steel.
The reinforcing steel used in reinforced con-
crete construction shall conform to the follow-
ing requirements :
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The Inspector of Buildings may require cer-
tified tests of each size of bar used in the con-
struction, said test to be acceptable for not
more than ten tons of material.
The tests for bending may be made on the
ground under the supervision of the Inspector
of Buildings or his authorized assistant.
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Sec. 26. Placing Concrete and Steel. All
reinforcement shall be free from paint, loose
rust, scale or coating of any character that
would tend to destroy the bond. Steel must
be accurately located and secured against dis-
placement before concrete is poured around
it. All concrete shall be tamped in place
within* one-half (J4) hour after mixing, and
shall be conveyed in place in such a manner
that no appreciable separation of the ingredi-
ents occurs. Concrete must be worked con-
tinuously with suitable tools as it is put in
place, and in warm weather must be kept moist
for at least seven (7) consecutive days after
pouring. Work must be laid out so that par-
tially set concrete will not be subjected to
shocks from handling or wheeling materials
over it.
Where it is not possible to cast the entire
structure in one operation the work shall be
stopped ; for columns, at the under side of the
girders; for girders, at a point midway be-
tween supports unless a beam should occur
at this point, in which case the joint should
be offset a distance equal to twice the width
of the beam; for slabs and beams, at the cen-
ter of the span. Under no circumstances shall
a joint be made where high present or future
shearing stresses may occur. The plane of all
joints shall be made at right angles to the
direction of the beam, girder, column or slab.
When work is resumed the joints shall be
thoroughly cleaned, drenched and slushed with
neat cement mortar.
Beams and girders shall not be constructed
over freshly placed columns without permit-
ting a period of at least ten (10) hours to
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elapse to provide for the shrinkage in the
columns.
The longitudinal steel in beams and girders
shall be so designed that there is a thickness
of concrete between the separate pieces of steel
of not less than one and one-half (1*4) times
the maximum sectional dimensions of the steel
and in no case less than one (1) inch. Some
means satisfactory to the Inspector of Build-
ings shall be used to hold all reinforcing steel
in its proper position.
Sec. 27. Centering and Forms. All forms
shall be substantially built and secured to pre-
vent movement or deflection during the prog-
ress of the work. They shall be tight to pre-
vent leakage of the concrete. An opening shall
be left at the bottom of all column forms for
removing foreign matter and adjusting the
steel, and said openings shall not be closed
until just before the concrete is poured. Be-
fore placing the concrete, the forms must be
thoroughly cleaned of all chips, .dirt, old con-
crete and other foreign matter. Forms shall
not be removed until the concrete has set suf-
ficiently to safely resist all stresses to which
it may be subjected. Two weeks of good dry-
ing weather with a temperature above 60
degrees Fahrenheit shall be taken as the min-
imum time for the removal of forms where
the concrete will support only its own weight.
The joists and lagging may be removed in
not less than ten days, providing the sheating
under the slabs is properly shored. The time
of removal of forms and^shores under heavy
beams and girders, varies with the design and
weather, but in no case shall they be removed
in less than three (3) weeks after pouring, pro-
viding the beams carry their own weight only.
When beams and girders carry construction
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loads from above, sufficient shores shall be left
in place to carry the loads until the completion
of the work. If sufficient shores are provided
to support the loads on slabs and girders, the
column forms may be removed in not less than
four (4) days. M
Sec. 28. Placing Concrete in Cold Weather.
When concrete is placed in freezing weather,
the material must be heated and such provi-
sions made that the concrete can be put in
place without freezing..
The use of frozen lumpy sand or aggregate
depending on hot wateir used in mixing to thaw
it out, will not be permitted. All reinforced
concrete shall be kept at a temperature above
freezing for at least forty-eight (48) hours
after being put in place. All forms under con-
crete placed in freezing weather shall remain
until all evidences of frost are removed from
the concrete and the natural hardening of the
concrete has proceeded to the point of safety.
Sec. 29. Inspection. When any reinforced
concrete is used in construction, the owner
shall provide for the inspection of cement and
inerts ^ as required by this ordinance. Unless
otherwise authorized in writing by the* In-
spector of Buildings, the owner shall also pro-
vide a special inspector, who shall be on the
work continually during the building and
removing of forms and the placing of concrete
and steel. Said special inspector shall be
acceptable to the Inspector of Buildings, and
may be required to pass an examination given
by said Inspector. He shall make daily reports
to the Inspector of Buildings of the progress
of the work, on blanks furnished by the
department.
Sec. 30. Test for Safety. Within a reason-
20
able time after erection, and before the build-
ing is occupied, a -test shall be made of the
work as directed by the Inspector of Buildings.
For such test the floor panels selected by said
Inspector must be loaded to twice the com-
puted live load and must sustain this load for
twenty-four (24) hours without undue deflec-
tion or other evident signs of failure.
Sec. 31. When to Take Effect. This ordi-
nance shall take effect and be in force from
and after the earliest period allowed by law.
DAVID T. LOGAN,
President of Council.
Passed April 7, 1913.
Approved April 7, 1913.
GEORGE J. KARB, Mayor.
Attest :
JOHN T. BARR, Clerk.
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