h.

144
342

 

HTHS

AN EXPERIMENTAL STUDY OF
HOOK ANCHORAGE
FOR RRMORCINO BARS

Thesis {cr the Degree of B. S.

MKCHEGAE‘X STATE COLLEGE
Chariés W. Aiwater

I939

 

Yperimcntal Study Of Hook Anchorage

>
:3
{I}

for Reinforcing Bcrs

A Thesis Submitted to

The Faculty of
MICHIGAN STATE COLLEGE
of

AGRICULNURE ACD APPLIED SCIENCE

by

Charles W. Atwater

Candidate for the Degree of

Bachelor of Science

July 1959

THESIS

o "'7 *1" ‘ 'r~n**'**7ar‘1c'
[K 1:1 -( v.IJ-4;J~J - $1.4.LNJ

 

The author wishes to acknowledge “is
incentedness to Prefessor C. L. Allen whose help in
criticizing the manuscript has aided materially in
the preparation Of this thesis.

He also wishes to express his gratitude to
the Concrete Steel Fireproofing Company of Detroit
for their cocperation in furn shing the reinforcinfi
bars used in obtaining the data used in this survey.

Likewise the author desires to acknowledge
,.

or the hel given n n by Professor

'6

a.

3. A. Killer in selecting tne subject, and planning
the surve;r .

Finally, he wishes to express his firetitude
to his fellow student, G. Gebbcn whose nelp in tsst-
ins the soecimens was great?r appreciated.

A
J t.—

JUly, 1939 Co A.

(“I .TTY“I:“?F".C‘
\J ’llJ. '..al-‘ LN)

Pa
Introflueticn ---------------- - ----- - ------------
Chapter I, General Theory of Anchorage ---------
Chapter II, Description of Apparatus ---------- -
Chapter III, Investigation -------------------
Conclusion ------------------------------------ - 1

8

9

7'1

The Designiig engineer, figuring the
reinforcing bars to be placed in a concrete structure,
must, during the course of his investigations, do two
things:

(1) Determ

u).

.ne the size and number
of bars needed to supply suffic-
ient bond between the steel and
concrete.

(2) Determine the length of bar
necessary to furnish sufficient

anchorage so that the bar will

Ho

not be pulled from its or ginal
position.

After finding the final length of the
straight Ear, a hook is put in the end as an added
measure of safety. In general practice this hook is of
standard size determined by the size of the bar. The
dimensions of the hook will be discussed in detail
later.

When studying Reinforced Concrete, nothing
was ever said as to how much of the total strain was

taken by the hook, or its actual strength. The

necessity of writing a thesis gave an excellent

H
H

(‘1'
O

Opportunity for investiga n, and upon inquiring,

nothing was found to signify that work had been done

to any extent along tiese lines.

It was therefore deternined that the object

of this paper would he to test the standard sizes of
hooks by embedding them in concrete, curing the spec-

imens, and exerting a tensile force on the bar until
there occured one of the four following failures:
(1) Straightening of the hook.
(2) Crusning the concrete.
(3) Breaking of the bar, leaving
the hook intact.

W

(4) A combination of the above three.

Due to a limit on time and materials, it was

possible to use only one mix of concrete therefore, a

3

complete set cf data could not be obtained. If time
hal been allowed, different lengths of bars, and
7

perhaps a different dimension of hook could nave been

used in these tests.

H

r . P ~
gene: 91 flea-317 of Anchorage

e, for tension steel, begins only

3 have cassed out of the tension regions.l

L

4

anchorage is lolt to the

oiscretion of the designing engineer.

 

 

 

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h—h- ‘—

 

 

 

hj
Ho

(7’9
0
H

Round Bar:

when f8 0 uals the fiber stress of the steel

.A

H H

and a the diameter of the round bar or the sides of
the seuare bar,
{'1 c- D I. 2
i - .LO A8 -' ES TT a .
L) 4

To prevent force T from causing the bar to

l

P-

Q
.;U

p, T n“ t h halanced by a bond force between the

U)

a \l

4.
L

.eel and concrete.

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Let u equal the bond stress,

9,. h ‘ 5‘ - [3 . -3 a ,

t en: pone f ree — u A suriace area oi bar
= u x N a L
- I

and: T - Bond force

(C)

u fl'a L

d2
0
*3
rt)
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0
0.
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9.) m

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the same for

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This equation for finding L

both square and round bars.

. l‘. ‘ n v- ‘ x '* ‘ ‘
PlQlU irame, snall have a lenbtn of anc era

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‘, - 1 ‘A Q run V" . ‘ . ~
,ne face 0: the SlfiDOPtinp menb r sufficient to

1 ‘ . y 1 3 .- - 3 L— - b. '-
oevelop tne fill naximum tension at an arerabe ban}

1. J‘ ,4 I ‘ - P i .
stress oi not Creator than .04 fé ior plain bars, and

not more than .05 f' for deformed bars.

Positive Steel:

The anchorage for positive steel

extended at least 1L h

s car ClRKEtClS past the
sunnorts.l

1' :- _. 0 A _ w, ‘0. - i. -w 4“
hose: lé - ultizate con,ressive strenb n 0;

1'10

1.03.61. ’ Pp. I. ()

.1 £4

must be

face of

U)

cription of Apparatus

Fieure two Wives the dimensions of the

U

standard hooks used in this eXperinent.

30

The diameter of the bar itself determines the radius
of the hook, as well as the tangent length- on the end
of the hook.

D : Bill” D

In).

.anoter.
A test bar three feet long was chosen as a convenient
length, and the hook placed in the end.
In order to give all bars of the same size

,i~ 3:1 , and in order to test only the
strength of the hook tself, the bond between the
steel and concrete was destroyed along the shaft
borinninf at point 1, the point of tangency to the

c. This we accomplished in two different

1. Plain bars—-oilinj the shaft

Q'V . 1“ w I >a G
hit“ a medium weirht of grease.

to
so

. Deformed bark—~0il alone on

deforned as s would not allow

"3

the slafts to be free, so they

were wrapped with heavy paper

as well.
Both of these methodé effectively destroyed all of the
bond as was in evidence when the snecinens were

broken.

 

 

 

 

 

 

Figure 3 gives a cross-sectional View ficow-

q

in” how the her was placed in the concrete. At

I-J
CD
C3
(0
C1,.

three inches allowance was left between the her and
the edge of the specimen to give a good bond as well
as good strength.
In bars up to 5/3 " inclusive, the specimen
was made in the regdlar 6" cylinders used for conn-

ressive strength tests. With bars of larger sizes it

,1

was necessary to buill forms so that the three inch
clearance could be maintained.

Choosing a proper mix of concrete to give
the best average strength tended to present another
major problem. It was finally decided that a concrete
mix of between 2500 and 3000 ha. per square inch
compressive strength would swit the problem, so
towards that end the following mix was desig
Later Cement Ratio: 6 to l

Kix by Vol.: Cement Sand Gravel
l 2 3
The sand weighed 112 lbs. per Cu. ft., and

the gravel 114 lbs. per cu. ft.. A slump of between

1 a 0 fl 0 -
12 and 5 inches gave the desired stren“th at 28 days.

“a,

CD

After the specimens had couired their

ILJO

nitial set, they were removed from he ferns and
placed in a water-vapor room and allowed to remain
there for the full 28 days. The shafts of the bars
which stood out from the concrete were rubbed with an

oiled cloth at frequent intervals to prevent corrosion.

\

The nachine used to break the specimens was

a Riehle materials tester made in hiladelpha. It

was composed of a stationarv apner

U

jaw, and a noveable
lower jaw. The upper jaw was removed, the Specimen t

be tested inverted, and the bar placed through the

Openin” left by the removal of the upper jaw. The

i;

moveable low r jaw was then clamped to the bar, rrid
pressure applied until failure took place. The
breaking force came from a hydro pressure pump, and the

force recorded on a beam scale

.f‘ylrpv.).l'T-I
J; -L $4.11.

III

Upon completion of th- 0? day period of curing,
each specimen was removed from the water-vapor room and
prepared for breaking by drying the rods and removing
the grease.

The specimens were then fractured and the data
on the following pages was recorded. An inspection will
show that in all but one case the fracture which took
place was due to failure of the bar itself in tension,
outsife the regions of the hook, and not a crushing of

the concrete or straightening out of the hook.

-9-

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lump.

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8

no

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J—a

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12”“

1;.

5/4-

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to

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8,410
8,275

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s-s
3-11

30. Date Slunp load leadin“ Fracture
——.—-— *— ————-—-—-‘- ——~———.—c —.————¢—. .54 m--.~ho
2 inch round deformed
é-i 5/15 lg” 3,700 Tension s eel
! H '7 ": ' H H
C -2 ' 11, ’ ’_ r/ 5
=1-L, 4.1.,xJ—J
H H '- Y! H
C -4 1.!" , k -'2\
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n-3 H I! 1:7 ’ 610 f? H
3.; " " 13 , 9:0 " "
“-1 h" 2" 1/ ,mr/ H H
1,‘_2 H H 3 ,830 H H

0 " 5 -
2 inch squaee deiormed

3‘3 5/15 2" 19,100 " "
v_4 u n 19,230 n H
3-5 5/16 3" 19,310 " "
f-Q " " 19,190 H n
:_4 I! vr 19,33: n n
3-1 5/19 5" 13,460 " N
G-s " " 1e,avo " "
G-4 " " 19,540 " n

7' I C '
{-1 " is" 18,760 ' '

I7_4: H N 19,120 ” "

1 inch

 

 

233. lDate Slfirnw
nch round deformed
‘-1 5/10 3"
1—5 5/18 5"
E-B " 1;"
if”: n I!
I-1 n 2!!
:_2 n n
1‘?) I! I!
1-4 H 3!
square deformed
Tone 5/11 3"

T 7
.gJOCn. Cl.

—-

 

no
5.1/1 ’

20

(:rv

290

11“,

Cylinders for compressive strength

0;
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q-0

d ‘J

5/4
5/9

A-ll

r7 0 N
LJ-LJ
B-v "

5/18

M
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cylinder,

5"

100,000

<1
0

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CO

(D
C)
Q
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(.1

57 050
56,000

—J

Loafiggg Enactiég
Tension Steel

H H

H I!

Y? if

It I!

H H

Y! H

H H
Concrete failed “ere

Comp. Concrete

H H

H H

N H

H H

H H

H H

H H

H H

H H

0

strength equals

“.9

860 lbs/sq.

in.

H

H

 

S 11 ran
‘—
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0 H
L;
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(g

 

lgadin;
Comp.
H
H
H

:1: M A 1- . 4... c : ° w .1 °
:1 ure a s'evs we chlcal speeinens used in
o o 4.: -
t'is anCSbioutlono

Specimen LO. F—l in part A had already been
broken, but the point of fracture was not show: in the
pic ure. The rod stretched until the yield point was
reached, and then parted. The cross-sectional area of
the bar at the point of fracture was much smaller than
the cross-sectional area of the rest of the bar.

Specimen Io. 0-1 in part B illustrates a typical
test bar before fracture. An inspection of all the

broken specimens revealed no cracks or failures of any

kind in the concrete.

-15-

5D'\\u\_.l \il‘K‘\v\/h\\l \Ik.\

 

k»? \Ss‘§\\ n

-15-

E‘it‘ure 5 s‘r-ows one of the tested Specimens which
Had been broken open to show the bond on the hook, and to
see how effectively the bond on the shank had ceen
destroyed. At point A is shown where the paper wrapping
begins so as to protect the shank. how well it did its
work was shown as the entire piece of concrete, labeled
as "B", could be moved to any position on the bar.

The hook to the right of point "A" was still

well bonded to the concrete.

In only one case did the concrete fail before the

bar, and that was with a one inc? scuare deformed bar.

5 shown in E

LJ.

A View of this

 

‘. ._ z-))\.\\\.\\

If)

Above point "A" in figure 6, can be seen the
protective paper covering around the shank of the bar.
here again is another proof of the effectiveness of this

n5 the bond. In this test the concrete

Ho

method of destroy

fail

0

d before the bar broke because of unequal pressure

his caused the bar to sprinr outward in

Q

on the concrete. T
the direction of the piece which broke off, putting the
concrete under tension. The bond between the hook and the

concrete had not been destroyed and gave no evidence of

J

onclusion

The purpose of this tbesis was not to revise
the anchorage design for reinforcing bars, or to deter-

mine a new method of anchorage, but to see how effectiv-

o
"I
_I

$.10

ely the present resign accenpl shed ts purpose, and

in some cases make possible a saving of reinforCing

steel. Hot sav n3, however, that this could be acconn-

?"

shed with the relativelv small amJunt of research done

:r H

ere, but further investigation might make it possible
to economize on large construction jobs. It has been

shown in this tiesis, as far as was accomplished, that

tself.

1L

the anchorage hook was stronger than the bar

The followinfi are examples seowinq now much

\
1

could be saved on reinforcing steel by using 'he results

shown in this r,aoer:

.05 x 2,000

L = f a 3 20,000 x l
4 u 4X100

 

= 50" past face of support

Iew length

L = 2 x 5 D + 2 fl’r
2
2 6 x l + 4 fl‘l
= 6 + 12.56
= 18.56"

Saving 31.44" reinforcing bar.

 

 

u = .0r fé = .05 x 5000
= 150
L = f6 a l 20,500 x 3
4 u 4 x 150

l I
H
(D
O
C‘:
\7
h
t)
ct-
F b
"D
0

..e of support
Kev: length:

L - 2 X

£4
E)
+
N)
(‘3 q
*‘3

’ .1
I

6.28

ll
Ca
+

B 9.28"

Saving 7.30" reinforcing bar.

finch more work must be done, however, before

resent

a definite rule could be stated to decrease the

‘d

anchorare dCSign. All designs of concrete must be
tested as well as all sizes of bars before we can be

certain that a new design would work as efiectivelv as

the nresent set un.

TAT

M'cillifilmflllfll
311

93

ll

1
0

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