Note: Descriptions are shown in the official language in which they were submitted.
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Noboru Hiraoka
BINDER FOR FIXING AN ANCHOR ROD
BACKGROUND OF THE INVENTION
The present invention relates to a binder for fixing an
anchor rod such as an anchor bolt, reinforcing bar, pile and the
like to a concrete body, concrete foundation, rock foundation
and the like.
Anchor bolts, piles and the like (hereinafter referred to
as "anchor rod") which are bonded to concrete bodies, concrete
foundations, rock foundations and the like (hereinafter referred
to as "foundation bed") are used to fix structures, structural
members, machines, equipment, temporary supporting frame-works
and the like. The following is known as a method for fixing an ;
anchor rod to foundation bed; the anchor rod is inserted into a
lS mounting hole bored in the foundation bed and a binder ;
comprising reactive resin material as its chief component is
inserted into an opening formed between the mounting hole and
the anchor rod to bond the anchor rod to the foundation bed. ;
Hitherto, binders which have been widely used have included
reactive thermosetting resin as its chief component, a curing
agent contained in a small inner capsule to isolate the binder
from the chief component and aggregates. In such conventional
binders, the aggregates are ordinarily made of inorganic
material, for example, sand and powders of natural stone or
artificial stone, fiber glass, glass beads and the like.
As described above, such prior art binders for securing an
anchor rod to a foundation bed comprising a chief agent, a
curing agent and aggregates have been contained and sealed in an
outer capsule. Within the outer capsule, the curing agent is
further sealed in a small inner capsule to isolate it from the
~ chief component. In use, the outer capsule in which the binder
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is contained is inserted into a mounting hole bored in the
foundation bed, and an anchor rod is driven into the mounting
hole so as to both break the outer capsule and the small inner
capsule which contains the curing agent, so that the chief
component and the curing agent are brought into contact with
each other to start reacting and curing, whereby the anchor rod
i5 fixed to the foundation bed by the cured resin.
The above method for fixing anchor rods to foundation beds
makes it possible to embed an anchor rod in a foundation bed
with a high degree of accuracy, to expect an improved higher
bond strength and to realize a considerable time saving.
Consequently, the above method is widely employed in the fields ;
of civil engineering and building engineering. In the field of
civil engineering, such an anchor system is widely employed for
fixing supporting and anchoring components and/or elements of ;
bridges, bridge piers, mold frames for fresh concrete and the
like. In the field of building engineering, it is also widely
employed for fixing flanges for piping, exterior structures such
as vehicle bridges connecting warehouses, reinforcing building
floors and fixing advertising displays on buildings and for like
works .
It has been believed that the pull-out load bearing force
of an anchor fixed in a mounting hole with a ~onventional binder
as shown in Fig. 1, unless the load bearing capacity of anchor
rod 4 is not too weak, increases as the diameter D or the depth
L of the mounting hole is increased. More specifically, it has
been believed that the pull-out load bearing force increases in
proportion to the entire side wall area ~DL or the projected
area ~D(L + 2D), in other words, approximately in proportion to
the diameter D or the depth L of the mounting hole 2. ;
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However, in actuality, the pull-out bearing force of such
an anchor system does not increase in proportion to the diameter
D of mounting hole 2. Consequently, the conventional anchor
system has occasionally had a problem of insufficient strength
in spite of its assumed sufficient strength. It is found that
such trouble is attributable to a negative size effect of the
diameter of anchor D.
The negative size effect inherent in the conventional
technique will be discussed. In Fig. 1, when a tensile load is
applied to the anchor and the load is increased to a certain
level, the material of the foundation bed is sheared off in the ;
uneven portion of the surface area of the mounting hole adjacent
to the layer of the eured binder 3 loeated around the anchor
rod. The shearing-off of the foundation bed material 1 produces
a slip plane 5 having two uneven surfaces of whieh eoncave and
eonvex portions are still engaged together. When the load is
further inereased, these two uneven surfaees start to sl$de in
opposite directions, and the eoneave portions interfere with
eaeh other to produce a high compressive stress which, in turn,
produees a frietional foree between those two surfaces. This
frictional force constitutes the major portion of the pull-out
load bearing foree of the anehor system. The magnitudes of such
compressive stress and frictional force can be estimated as
follows. The height u of the convex portion of the uneven
surfaces divided by half of the hole diameter D gives an
approximate estimate of the strain ~ produced, that is, 2u/D
whieh in turn, being multiplied by Young's modulus E of the bed
material, gives the compressive stress ad. That is:
ad = ~ x E
i = u/(D/2) x E ;~
= 2uE/D (1)
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where: d = compressive stress
u = height of convex portion of slip plane
~ = compressive strain
E = Young's modulus
The frictional force per unit area r to be produced is
given by multiplying the compressive stress d and the
frictional coefficient of the material ~ of bed as follows: ;
r = d x ~
5 2uE~/D (2)
The value of "u" in Equation 2 above depends upon the
properties of the bed material but very little on the diameter
D, unless D is very small. Therefore, the frictional force r
per unit area is known to be approximately inversely
proportional to the hole diameter D. This is demonstrated
graphically by a curve A in Fig. 2 in terms of an average
frictlonal force per unit area. The frictional force per unit
area represented by the ordinate is shown as a normalized
relative term, the actual values being divided by an arbitrary
reference value.
The total frictional force, which is obtained by
multiplying the frictional force per unit area r and the
effective area of side-wall of mounting hole 2, determines the
.
pull-out bearing force Pm. That is:
Pm = r x ~DL'
z (2uE~/D) x ~DL'
= 2~uE~LI (3)
.
where L' = effective embedment depth which is normally slightly
: .:,
shorter than the hole depth L.
In Equation 2 above, the term D is eliminated out of the
equation so that the total pull-out bearing force Pm is now ~ -
. . .
affected almost solely by the depth L' but little by the ~
. ..
diameter. The above description clearly reveals a negative size
effect of the hole diameter inherent in the conventional method. ~
SUMMARY OF THE INVENTION .
It is known from the above investigation that, in order
prevent the frictional force constituting the anchor strength
from decreasing due to the size effect, it is necessary to
compensate for the decrease by introducing a new mechanism to ;
produce some additional compressive stress. In the present
invention to provide a compensation mechanism, the aggregates to
be mixed into the chief component are made of cured
thermosetting resin so that the binder, when cured, can deform
considerably more under loading, and the deformation or flow
thus produced is diverted in the direction perpendicular to the
anchor axis. The flow is thus blocked by the bulges on the
anchor rod, such as the ribs on a deformed bar, the thread
ridges of a bolt and the like, whereby an additional compressive
stress is produced around the anchor to compensate for the
decrease and solve the problem encountered with the conventional
method.
In the binder of the present invention, the aggregates are
made of cured thermosetting resin. Thus, the rigidity of the
cured binder of the present invention is lowered considerably in
comparison with that of the conventional binder containing
inorganic aggregates, so that a deformation or flow of a
considerable magnitude under loading can occur in the binder of
the present invention. The deformation is blocked locally :
around the bulges on the anchor rod so as to be diverted in the
direction perpendicular to the anchor axis, whereby an ;
additional compressive stress is produced to compensate for the
negative size effect.
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BRIEF DESCRIPTION OF THE DRAWINGS
The above mentioned and other features and objects of this
invention and the manner of attaining them, will become more
apparent and the invention itself will be better understood by
reference to the following description of an embodiment of the
invention taken in conjunction with the accompanying drawings,
wherein:
Fig. 1 is a longitudinal sectional view of the conventional
anchor to illustrate its construction;
Fig. 2 is a diagrammatic illustration of the relationship
between the frictional force and the mounting hole diameter;
Fig. 3 is a longitudinal sectional view of an embodiment of
the present invention;
Fig. 4 is a longitudinal sectional view of another
embodiment of the present invention showing a double walled
cap~ule construction; and
Fig. 5 is a partially enlarged diagrammatic view showing
ths action of the binder of the present invention.
Corresponding reference characters indicate corresponding
parts throughout the several views of the drawings.
The exemplifications set out herein illustrate a preferred
embodiment of the invention, in one form thereof, and such
exemplifications are not to be construed as limiting the scope ~ ;~
of the disclosure or the scope of the invention in any manner.
pESCRIPTION OF THE PREFERRED EMBODIMENT
As shown in Fig. 3, chief component 6, which is made of
thermosetting resin such as unsaturated polyester resin, is
sealed in outer capsule 7. Curing agent 8 is inserted into an
inner capsule 9 which is encapsulated in the outer capsule 7
together with the chief component 6. Aggregates 10 are also
inserted into the outer capsule 7 and are mixed with chief
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component 6. Aggregates 10 are made of a cured thermosetting
resin which is nearly equivalent in its rigidity to the cured
chief component 6, for example, such as unsaturated polyester
resin, epoxy resin, epoxy-acrylate resin and like thermosetting
resins.
In case the binder of the present invention must be
preserved for a long period of time until use, aggregates 10,
composed of cured thermosetting resin, are required to have a
good degree of corrosion resistance against the organic solvent
contained in the chief component, or as shown in Fig. 4, outer
capsule 7 must be provided with a double-walled construction
including an inner capsule 11 in which aggregates 10 are
inserted so as to be isolated from the chief component 6. In
this case, aggregates 10 may be filled and sealed in an inner
cap~ule 11 together with curing agent 8 which normally assumes a
powder-like form.
In use of the binder of the present invention, binder
capsule 7 prepared as above is first inserted into a mounting
hole 2 bored in foundation bed 1 as shown in Fig. 1, and then,
an anchor rod 4 is rotated and driven into mounting hole 2 to
impact on outer capsule 7, thereby causing the binder capsule 7
of the present invention to break. In an embodiment as shown in
Fig. 3, inner capsule 9 containing curing agent 8 and in an
embodiment as shown in Fig. 4, the inner capsule 11 is also
broken together with outer capsule 7 so that the curing agent is
agitated and mixed with chief component 6 to initiate its curing
and form the cured binder 3 with which anchor rod 4 is fixed to ;
the foundation bed.
As shown in Fig. 5, when a tensile load P is applied to
anchor rod 4 which is fixed to foundation bed 1, a deformation
of a considerable magnitude is produced in the cured resin
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binder 3 whose rigidity is lower than that of the conventional
binder containing aggregates made of natural or artificial
ston~. Such deformat~on or flow of the binder 3 is locally
blocked by the bulges on the surface of anchor rod 4 and the
flow of binder 3 is diverted in the direction perpendicular to
the anchor axis. A vector component perpendicular to the anchor
axis of such deformation or flow produces a compressive stress
around the anchor in the direction indicated by arrows "b",
which serves as an additional compressive stress to compensate
~or the decrease due to the negative size effect in the
compressive stress to be produced in slip plane 5 as discussed
in connection with Fig. 1.
~ he areas denoted by the letter "X" in fig. 5 are called an
effective frictional areas since large concentrated compressive
stresses occur at those locations on the slip plane and thus a
large concentrated frictional force also occurs there. As shown
by the principal stress lines "b", the distribution of
compressive stresses becomes nearly homogeneous having little
stress concentration in the portion of the foundation bed which
is far from the slip plane.
.
In the present invention, as described above, an additional ; ~
.
compensatory radial compressive stress is produced by
deformation of the less rigid resin binder 3 which is made
nearly wholly of cured resin and a small amount of fractured ~;~
capsule glass from the fractured capsules 7 and 9. Here, it -
shall be noted that the additional compressive stress can not
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increase without limit since the material of the foundation bed
1 has a limit of compression, and the compressive stress can not
increase beyond this limit. The concentrated compressive stress
around the bulges is very high and is close to or reaches this
upper limit. The curve denoted by "B" in Fig. 2 shows the
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relationship of the frictional force and the diameter of
mounting hole 2 corresponding to this limit state. The curve is
nearly flat and virtually independent of variation in the hole
diameter. The height of this flat line is determined by the
above-mentioned "effective frictional area", and the larger the
effective frictional area, the higher the position of the limit
line. Therefore now:
d = constant, therefore
~ = ad x ~ = constant,
where ad depends on the effective frictional area.
The resin binder by the present invention, comprising a
reactive thermosetting resin as its main component, a curing
agent and aggregates made of cured thermosetting resin, has a
much lower rigidity, when cured, than that of the conventional
binder in which aggregates are made of hard inorganic material.
Thus, the former can exhibit more deformation or flow under
loading than the latter thereby creating the areas of
compressive stress as shown in Fig. 5.
The deformation or flow in the binder of the present ;~
invention under tensile loading is diverted by the bulges on an
anchor rod in the direction perpendicular to the anchor axis, ~;
produces additional large compressive stresses around the slip
plane to compensate for the negative scale effect due to the ;
anchor diameter inherent in conventional binders, and makes it ;~
possible to produce an anchor embodying the so far assumed but
actually not attainable property that the pull-out load bearing
force of an anchor fixed with a binder containing aggregates
increases when its mounting hole diameter is increased.
While this invention has been described as having a
preferred design, it will be understood that it is capable of
further modification~ This application is therefore intended to
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cover any variations, uses, or adaptations of the invention
following the general principles thereof and including such
departures of the present disclosure as come within known or
customary practice in the art to which this invention pertains
and fall within the limits of the appended claims.
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