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BUREAU OF YARDS AND DOCKS,

NAVY DEPARTMENT,
Washington, D. C., September 15, 1917.

STANDARDS OF DESIGN, REINFORCED CON-
CRETE.



Details of construction.

1. Materials, methods of mixing, placing and finishing, character of
forms, inspection, etc., shall be in strict accordance with the require-
ments of Navy Standard Specification, concrete and mortar, 59C2c.

2. Protective covering. The minimum thickness of concrete or
mortar for protection of metal against corrosion shall be 1 inch.

The minimum thickness of concrete or mortar for protection of
metal against fire shall be a? follows:

Inches.

Columns and girders 2

Floor beams 1 1/2

Slabs 1

The above dimensions are from face of rod to face of concrete. To
determine distance from face of concrete to center of steel add half
the diameter of the rods to the above dimensions.

All corners and edges of columns, girders, and beams shall be either
beveled or rounded.

3. Splicing reinforcing material and joints in reinforced concrete con-
struction. Where tension or compression reinforcement is spliced it
shall be lapped on the basis of the bond stress and the stress in the
bar at the point of splice, or a connection shall be made between the
bars of sufficient strength to carry the stress.

In columns, small rods (34 inch, and under) shall be lapped as
ified above, and structural shapes or heavy bars shall be properly
spliced and provided with bearing plates at foundations; rods
above 34 inch shall be squared and butted in sleeves, and in foun-
dations bearing plates shall be provided, or the bars shall be carried
into the footing a sufficient distance to transmit the stress of the
steel to the concrete by means of the bond resistance.

'<7 points. Whenever it is found impossible, owing to
the magnitude of the work, to cast the entire structure in one opera-
tion, the following locations shall govern for stopping points for the
respective parts: Joints in columns shall be flush with bottom
surface of girders, and in flat slab construction at the bottom of the
flare of the column head; joints in girders shall be at center of span,
unless a floor beam intersects the girder at this point, in which case

1616317



3C9526



the joint shall be offset a distance equal to at least twice the width
of the beam; joints in floor beams and slabs shall be at the center of
the span. All joints shall be perpendicular to the axis or surface of
the member jointed. In every case planes of cleavage caused by
stoppage of work shall be provided with offsets and extra reinforce-
ment, if necessary, to develop the full designed strength.

5. General assumptions. 'Slabs and floor beams shall be designed
to support the total dead and live loads; girders shall be designed to
support the total dead load and 80 per cent of the live load and
columns shall be designed for the total dead load and 75 per cent of
the live load, except as noted below. For roof loads the full live
load shall be used. In storehouses 80 per cent of the live load
shall be used on columns only; beams and girders shall carry full
live load. Proper provision shall be made for the dynamic effect
of live load, where same justifies consideration, by the addition of a
percentage. In special cases, where conditions justify, girders and
columns shall be designed for 100 per cent of the live load in addi-
tion to the total dead load.

6. Span lengths of slabs, beams, and girders, and column lengths.
The span length for slabs, beams, and gilders, simply supported,
shall be taken as the distance from center to center of supports with
a maximum span length of the clear distance between supports plus
the depth of girder or slab. For continuous or restrained beams
the span length shall be taken as the clear distance between faces of
supports exclusive of brackets. The length of column shall be taken
as the maximum unsupported length.

7. Spacing of rods. The lateral spacing of parallel bars shall not
be less than 3 diameters from center to center and not less than 2
diameters from side of beam to center of rod. The clear space
between 2 layers of bars shall not be less than 1 inch. The use of
more than 2 layers will not be allowed unless special reasons make
same imperative, in which case special provisions shall be made
for tying together.

8. Columns. For columns reinforced longitudinally and with or
without spiral hooping, the ratio of unsupported length of column
to its least over-all diameter shall not exceed 15. For columns
reinforced with spiral hooping only, this ratio shall not exceed 10.
In no case shall the least over-all diameter be less than 12 inches.
The protective covering over the steel shall be 2 inches. The
effective area of hooped columns shall be taken as the area within
the perimeter inclosing the spiral. Longitudinal reinforcement
shall not exceed 4 per cent nor be less than 1 per cent of the effective
area. The total amount of spiral or hooping reinforcement shall not
be less than 1 per cent of the volume of the column, inclosed. The
clear spacing between hoops shall not exceed 1/6 of the diameter
of the inclosed column, and shall in no case be greater than 2 1/2
inches.

Where structural steel shapes are used for reinforcing columns,
they shall be provided with lattice bars or plates to tie them together,
no dependence being placed on the concrete for this purpose. All
splices, connections, etc., shall be designed in strict accordance
with structural steel practice.



9. Reinforcement for shrinkage and temperature stresses. Reinforce-
ment should be equal to about 1/3 of 1 per cent and should be of a
form to develop high bond resistance. It shall be placed near ex-
posed surface and shall be well distributed.

10. T-beams. Where a floor slab and beam are built as a mono-
lithic structure, the width of that portion of the slab, which is used
as the flange of the T beam, shall not exceed the width of the stem
plus eight times the thickness of the slab; also it shall not exceed
three times the width of the stem. For isolated beams the width of
the flange shall not exceed three times the width of the stem. In
all cases the total width of flange shall not exceed one-fourth of the
length of the span.

11. Maximum allowable unit stresses and ratio of moduli of elas-
ticity. The allowable unit stresses shall be the percentages given
herein of the ultimate strength of the particular concrete which is
to be used, as shown in the following:

Table of ultimate compressive strengths of different mixtures of concrete.
[In pounds per square inch.]



Aggregate.


1:1:2


1:1 J a


1:2:4


1:2J:5


15:6


Granite, trap rock gravel, hard limestone, and
hard sandstone


3 000


2 500


2 000


1 600


1 300


Soft limestone and sandstone


2,200


1,800


1,500


1,200


1,000


Cinders .


800


700


600


500


400















ALLOWABLE UNIT STRESSES FOR PIERS AND FOUNDATION'S.

(a) Plain bearing on a concrete surface of at least twice the loaded
area, 35 per cent of compressive strength.

(6) Plain bearing on other surfaces, 25 per cent of compressive
strength.

(c) Axial compression in a plain concrete pier, the length of which
does not exceed four diameters, 22.5 per cent of compressive
strength.

ALLOWABLE UNIT STRESSES FOR SLABS, BEAMS, AND GIRDERS.

(d) Compression in extreme fibers of concrete, 32.5 per cent of
compressive strength.

^ (e) Compression in extreme fibers of concrete at supports of con-
tinuous beams, 37.5 per cent of compressive strength.

(/) Vertical shearing stress, horizontal bars only and without web
reinforcement, 2 per cent of compressive strength.

(<7) Vertical shearing stress, bent-up bars only and without
vertical stirrups, 3 per cent of compressive strength.

(h) Vertical shearing stress, combination of bent-up bars and
vertical stirrups fastened securely to the bars and spaced horizon-
tally not more than one-half of the depth of the beam, 5 per cent of
compressive strength.



(i) Punching shear with diagonal tension provided for, 6 per cent
of compressive strength.

The unit shearing stress shall be computed by formula 22, given
in the appendix.

In providing for diagonal tension the web reinforcement shall be
designed to take two- thirds of the total vertical shear.

ALLOWABLE UNIT BOND STRESS.

(j) Bond between concrete and plain bars, 4 per cent of compres-
sive strength.

(&) Bond between concrete and deformed bars, 5 per cent oi
compressive strength.

(I) Bond between concrete and drawn wire, 2 per cent of com-
pressive strength.

ALLOWABLE UNIT STRESSES IN COLUMNS.

(m) Columns with longitudinal bars held by bands, the bars
being not less than 1 per cent nor more than 4 per cent of the area
of the column core, the bands being not less than 1/4 inch in diameter
and approximately 12 inches on centers, shall have a unit stress on
the concrete core not to exceed 25 per cent of the compressive
strength.

(ri) Columns with close hoops or spirals only, of not less than
1 per cent of the column core and spaced not more than one-sixth
of the diameter of the column core nor more than 2 1/2 inches on
centers, shall have a unit stress on the concrete core not to exceed
27 per cent of the compressive strength.

(o) Columns with close hoops or spirals and with longitudinal
bars all within the limits specified above, shall have a unit stress
on the concrete core not to exceed 33 1/3 per cent of the compres-
sive strength, and in no case to exceed 800 pounds per square inch.

ALLOWABLE UNIT STRESS IN STEEL REINFORCEMENT.

(p) The tensile or compressive stress in steel shall not exceed
16,000 pounds per square inch. Steel in compression shall be
considered to be stressed "n" times the stress 'in the adjacent con-
crete, where "n" represents the ratio of the modulus of elasticity
of steel to that of concrete, as given below.

MODULI OF ELASTICITY.

In designing reinforced concrete, the ratio of the modulus of
elasticity of steel to the modulus of elasticity of concrete shall be
taken as

(q) Forty, when the compressive strength of the concrete does
not exceed 800 pounds per square inch.

(r) Fifteen, when the compressive strength of the concrete is
greater than 800 pounds per square inch and less than 2,200 pounds
per square inch.



(s) Twelve, when the compressive strength of the concrete is
greater than 2,200 pounds per square inch and less than 2,900
pounds per square inch.

(t) Ten, when the compressive strength of the concrete is greater
than 2.900 pounds per square inch.

12. STANDARD NOTATION.

RECTANGULAR BEAMS.

The following notation shall be used:
/= tensile unit stress in steel.
/ = compressive unit stress in concrete.
E s = modulus of elasticity of steel.
I e =modulus of elasticity of concrete.



3f=moment of resistance, or bending moment in general, in

inch-pounds.
A= steel area in square inches.

6= breadth of beam in inches.

d= depth of beam, to center of steel, in inches.

k= ratio of depth of neutral axis to effective depth d.

2= depth of resultant compression below top.

.?=ratio of lever arm of resisting couple to depth d.
jd=dz=a,rm of resisting couple.

p= steel ratio (not percentage).
w/'=load per lineal foot of slab or beam.

?=length of span in feet.

T-BEAMS.
6=width of flange.
b'= width of stem.
=thickness of flange.

BEAMS REINFORCED FOR COMPRESSION.

-A=area of compressive steel.
;/= steel ratio for compressive steel.
/ / s = compressive unit stress in steel.

C= total compressive stress in concrete.
(7=total compressive stress in steel.
c?'=depth to center of compressive steel.

2=depth of resultant of C and C".

SHEAR AND BOND.

V= total shear.
v= shearing unit stress.

u=bond stress per unit superficial area of bar.
o= circumference or perimeter of bar.
2 =sum of the perimeters of all bars.



COLUMNS.

A= total net area.
J. g =area of longitudinal steel.
-4c=area of concrete.

P= total safe load.

DESIGN.

13. Beams and slabs.
(a) Continuous spans:

Slabs ^ wl 2 at center and over supports.
Beams ^ wl 2 at center and over supports for interior spans.
fa wl 2 at center and over support for end span of a series.
Beams and slabs % wl 2 over center support for 2 spans only.

fa wl 2 at center of spans for 2 spans only.

At ends of continuous beams the amount of negative moment
depends on the form of construction.

No smaller moments than the above shall be allowed over supports
even if more reinforcement is put in at the center of the span.
Steel on compression side may be considered as acting.
(6) Ends free and simply supported:
Beams and slabs % wl 2 at center.

14. Slabs supported along four sides and reinforced in two
directions.

(a) Square slabs. One-half the load shall be considered as carried
by each system of reinforcement.



(6) Rectangular slabs. If w is the total load per square foot,
I and Z t are the length and breadth of panel respectively in feet and

r= ,-, then the load per square

*i
of reinforcement shall be taken



r= ,-, then the load per square foot carried by the transverse system



wr 4
or



and the load per square foot carried by the longitudinal system shall
be taken



w



Assuming these unit loads as determined above for (a) and (6),
two-thirds of the calculated moments shall be assumed as carried by
the center half and one-third by the outside quarters of each system
of reinforcement.

15. Stirrups should be spaced by the formula:

16000



(u-40)6
for 1:2:4 concrete where

v=unit shearing stress, see formula (22) of the Appendix.
6=breadth of beam in inches.
s=distance between stirrups in inches.
a cross-sectional area of 1 stirrup in square inches.
Note. The unit shear on cross section should never exceed 120
pounds per square inch.



If main reinforcing rods are bent up for web reinforcement, the
points of bending shall be calculated. For this purpose the method
used for designing cover plates of built-up steel girders is applicable,
the formula for uniform load on a simply supported beam being:

L' /a'

L = -\A

where L 7 =length of horizontal part of bent rods.

L =span length.

of =area of bent rods.

A total area of reinforcement.

For continuous beams, bending up at the 1/4 points will be satis-
factory, but sufficient steel must be placed top and bottom, on each
side of the quarter points, to take care of the stresses resulting from
irregular loads.

16. In girders and beams use 1:2:4 concrete and the following
maximum unit stresses:

Tension in steel pounds. . 16,000

Compression in concrete do 650

This gives

M= 0.3786d

jd= 0.8738d

A= 0*.0077 bd

17. Outside work, such as piers, wharves, sea walls, etc., shall not
exceed the following unit stresses used in their design:

Tension in steel pounds . . 12, 500

Compression in concrete do 600

This gives

A= o!oi bd
jd= o!861d



APPENDIX.

The formulae given in the above standards are based on the fol-
lowing general formulae, which were compiled by the committee on
concrete and reinforced concrete, appointed by the American
Society of Civil Engineers:

1. RECTANGULAR BEAMS.




ir



Position of neutral axis,

k
Arm of resisting couple,



y-i-i*



(i)



(2)



(For/ 8 =15,000 to 16,000, and/ c =600 to 650, k may be taken at *)
Fiber stresses,

M



, __
J * Ajd pjbd*

2_^_2p/ 8
Jo ~jkbd*~ k

Steel ratio, for balanced reinforcement,



(3)
(4)



P=2-



/cWc

(8)



9

2. T-BEAMS.



A








i


jf




'/*








d


X






/


x






u




Cose /. When the neutral axis lies in the flange, use the formulas for
rectangular beams.

Case II. When the neutral axis lies in the stem, the following formulas
neglect the compression in the stem:

Position of neutral axis,



kd -



2ndA+ bt*



~2nA +2bt
Position of resultant compression,



_Skd-2t t_
z ~2kd-t* 3



Arm of resisting couple,
Fiber stresses,



jd=d-z

f M

J *~Ajd



Mkd _/, k
Jo ~bt(kd-$t)jd~ n 1-fc



(6)

(7)

(8)

(9)

(10)



(For approximate results the formulas for rectangular beams may
be used.)

The following formulas take into account the compression in the
stem; they are recommended where the flange is small compared
with the stem:

Position of neutral axis,



kd -



= 2ndA+(b-b')t 3



nA+(b-b')t



(11)



10



Position of resultant compression,



jd=dz



t(2M-t)b+(kd-t)*b'

Arm of resisting couple,
Fiber stresses,

J^Ajd
2 MM



(12)

(13)
(14)

(15)



3. BEAMS REINFORCED FOR COMPRESSION.
fc




Position of neutral axis,



Position of resultant compression,



Arm of resisting couple,



jd=d z



(16)



(17)



(18)



11

Fiber stresses,






nr (20)



4. SHEAR, BOKL, AND WEB REINFORCEMENT.

In the following formulas 2_ refers only to the bars constituting
the tension reinforcement at the section in question, and jd is the
lever arm of the resisting couple at the section.

For rectangular beams,

-133 (22)

- (23)

(For approximate results j may be taken as |.)
The stresses in web reinforcement may be estimated by the fol-
lowing formulas:
Vertical web reinforcement.

P-g (24)



Web reinforcement inclined at 45 (not bent-up bars),



(25)



in which P=stress in single reinforcing member, T 7 ==amount of total
shear assumed as carried by the reinforcement, and s=horizontal
spacing of the reinforcing members.

The same formulas apply to beams reinforced for compression as
regards shear and bond stress for tensile steel.

For T beams,

-5?3 (26)

< 27)



12

(For approximate results j may be taken at f.)

5. COLUMNS.
Total safe load,

Unit stresses,

S = A[l+(n-l)p\

/.='/ (30)



THE FLAT SLAB FLOOR WITHOUT BEAMS.

1. SYMBOLS FOR SQUARE PANELS.

I =distance center to center of columns in feet measured

along the side of a square panel.
C= diameter of column capital in feet measured on the

bottom surface of the slab or dropped panel.
5= side of square dropped panel in feet.
B= width of any band of rods in feet.
u'=sum of live and dead loads in pounds per square foot.
M= bending moment in foot-pounds.
d= effective depth of slab in inches.
D effective depth of dropped panel in inches.
t= total thickness of slab in inches.
T= total thickness of dropped panel in inches. Other sym-

bols are those used in the Standard Notation.

2. FOUR-WAY SYSTEM WITH DROPPED PANEL.

The following formulas shall be used in design:
=0.42Z.
C=0.225Z.



d=, on basis of moment, for w not greater than 440
61

pounds and p=0.77 per cent.

d=^-~= Q , on basis of shear, for w greater than 440 pounds.

L.to

D=1.5rf.
t=d-\- 1.5 inches.
T=Z>+2 inches.

Total negative M at column (in any direction)=0.032w;Z 3 .

Positive 3/at middle of bands=0.012wZ 3 .

Negative M over middle of side bands=0.009wP.

NOTE. The above proportions for S, C, B, and D make it neces-
sary to solve only two of the other formulas. Assume a total thick-
ness, t, to determine a tentative value of w. Solve for d and deter-
mine the correct value of w . D then becomes 1.5rf. Find the posi-
tive moment at the middle of the bands from the formula positive
jtf=0.012w;Z 3 . From the moment thus found find the amount of
positive steel required at .the middle of each band. Carry this same
amount of steel over the column in each band, which will take care
of the total negative moment at the column. Finally, take three-
fourths of this positive steel and distribute it in the top of the slab
over the side bands and over the central half of the panel to take
care of the negative moment at the middle of the side bands.

(13)



14

3. Two-WAr SYSTEM WITH DROPPED PANEL.

The following formulas shall be used in design:
S=OAl
C=0.225Z.
=0.4Z.

^ = -E7p on basis of moment, for w not greater than 576

pounds and p=0.77 per cent.
^ = f2Q0 on basis of shear, for w greater than 576 pounds.

D=1.25c?, for p=1 per cent.
=e/-f-l. 5 inches.

T=D+2 inches.

Negative Mat column for each band=0.034:?/;Z 3 .
Positive M at middle of side band=0.0174:wZ 3 .
Negative M over middle of side band=0.015wZ 3 .
Positive M at middle of center band=0.008wZ 3 .

4. DETAILS OF CONSTRUCTION.

The above formulas apply to square panels and uniformly dis-
tributed live loads. For heavy concentrated loads special provision
will have to be made by the use of beams or girders.

The diameter of the column capital shall be considered to be
measured where its vertical thickness is at least 1 1/2 inches, pro-
vided the slope of the capital below this point nowhere makes an
angle with the vertical of more than 45 degrees.

Points of inflection on any line joining two column centers may
be taken as one-fifth of the clear distance on that line between the
perimeters of the column capitals and measured from the perime-
ters.

If the length of end panels is made equal to 0.9 of the length of
interior panels, it will not be necessary to compute the moments
for end panels, and the same distribution of steel may be used in
both end and interior panels.

Punching shear at the face of the column shall not exceed 120
pounds per square inch.

5. RECTANGULAR PANELS WITH UNEQUAL SIDES.

The following applies to both the four-way and the two-way
systems:

In determining the thickness of slabs and dropped panels the
factor Z, occurring in the formulas for thickness, shall be the longest
side distance center to center of columns.

In determining moments in side bands and center bands the
factor Z, occurring in the formulas for moments, shall be the distance
center to center of columns parallel to the band in question.

In determining moments in diagonal bands the factor I, occurring
in the formulas for moments, shall be the average of the two side
distances center to center of columns.



THIS B*OOK IS DUE ON THE LAST DATE
STAMPED BELOW



AN INITIAL FINE OF 25 CENTS

WILL BE ASSESSED FOR FAILURE TO RETURN
THIS BOOK ON THE DATE DUE. THE PENALTY
WILL INCREASE TO SO CENTS ON THE FOURTH
DAY AND TO $1.OO ON THE SEVENTH DAY
OVERDUE.



NOV 11 1932

JUN 3 20fl1



LD 21-50m-8,'32



36952G



YB 51932



UNIVERSITY OF CALIFORNIA LIBRARY





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Online LibraryUnited States. Bureau of Yards and DocksStandards of design, reinforced concrete → online text (page 1 of 1)