Note: Descriptions are shown in the official language in which they were submitted.
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Muff joint for concrete reinforcing rods
Specification:
The present invention relates to a muff joint for concrete
reinforcing rods comprised of materials having different moduli of
elasticity, particularly for a steel concrete reinforcing rod and a
rod comprised of fiberglass reinforced plastic, wherewith one
connecting end of each such concrete reinforcing rod is connected to
a muff part which has at least one first recess for accommodating a
first concrete reinforcing rod having a relative low modulus of
elasticity, and said muff part has another connecting configuration,
e.g. in particular a second recess, for a second concrete
reinforcing rod having a relatively high modulus of elasticity.
Such muff joints and muff parts for providing such connections
are known. The muff part may be a two-part structure having a male
section and a female section, as disclosed in, e.g., EP 1277892 Al
or DE 201 10 720.
As a rule, the concrete reinforcing rods which are to be
joined, and the muff part(s), are all comprised of steel material,
and have generally the same parameters, particularly the same
modulus of elasticity, so that when under load there is no tendency
to suffer slippage between the connected components, which slippage
is a hazard when a difference in moduli of elasticity is presented.
The Applicant has had occasion to use rods of other materials
than steel (particularly stainless steel) as concrete reinforcing
rods, in particular rods comprised of fiberglass reinforced plastic
(FRP);
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FRP rods have lower thermalconductivity than steel rods, and are
less expensive. Also, they are easy to drill through and are more
easily machinable -- both of which characteristics are advantageous
in, e.g., tunnel construction.
When one seeks to join FRP rods and steel reinforcing rods, a
problem arises in that the modulus of elasticity of the FRP rods is
much lower than that of the steel rods, by a factor which in
practice may be, e.g., 3.5. As mentioned, such a difference in
moduli of elasticity can result in slipping at the joint locations,
with the consequence that the joints do not have optimal resistance
to loads. To determine the slipping, the quotient of the stress
divided by the modulus of elasticity is integrated over the path;
accordingly, lengthening the overlap length in the region of joining
of the FRP and steel components, by means of a correspondingly
constructed muff joint, does not solve the problem, but is in fact
counterproductive.
In light of the preceding, the underlying problem of the
present invention was to devise an improved muff joint of the
general type described supra, such that the muff joint can provide a
reliable and firm joint between concrete reinforcing rods which are
comprised of materials having appreciably different moduli of
elasticity.
This problem is solved according to the invention by a muff
joint having the features set forth in Patent Claim 1.
Advantageous refinements of the invention are set forth in the
dependent claims, the wording of which is expressly incorporated in
this Specification by reference (for the sake of avoiding
redundancy).
According to the invention, a muff joint is provided which is
usable for concrete reinforcing rods comprised of materials having
different moduli of elasticity, particularly
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for a steel concrete reinforcing rod and a rod comprised of
fiberglass reinforced plastic, wherewith one connecting end of each
such concrete reinforcing rod is connected to a muff part which has
at least one first recess for accommodating a first concrete
reinforcing rod having a relative low modulus of elasticity, and
said muff part has another connecting configuration, e.g. in
particular a second recess, for a second concrete reinforcing rod
having a relatively high modulus of elasticity; characterized in
that at least one additional interior structure is provided in the
first recess, which interior structure engages or otherwise
cooperates in a mutual interaction of surfaces with complementary
structures on the connecting end of the first concrete reinforcing
rod which connecting end comes to be inserted in the muff part.
According to a basic concept of the invention, the
configuration of the interior structure of the muff part and the
complementary structures on the connecting end of the first concrete
reinforcing rod provide an increased surface for contacting and
activation [sic], between the given concrete reinforcing rod and the
muff part, resulting in improved behavior under loads, which may
enable a substantial reduction of the overlap length between the
muff part and the inserted concrete reinforcing rod (compared to
customary structures). The abovementioned additional activation
[sic], combined with the reduced overlap length, contributes to
reduced slipping, resulting in a more reliable and firm (robust)
joint between the muff part and the said concrete reinforcing rod;
the muff joint is completed by connecting a second concrete
reinforcing rod to the other end of the muff part.
The second recess provided for accommodating the second
concrete reinforcing rod is not absolutely mandatory according to
the invention. E.g. the connecting end of the second concrete
reinforcing rod may be merely adhesively bonded in the aforesaid
first recess.
In a refinement of the invention, the interior structure may be
in the form of a geometrical body (such as a frustum of a cone, a
hollow cylinder, or a group of lamellae or pins or the like) which
project(s) into the first recess. The complementary structures on
the
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connecting end of the first concrete reinforcing rod are preferably
formed in said rod when it is in its curing state of its FRP
material.
According to a preferred refinement of the invention, the muff
part has a reduced material thickness in its region of the first
recess, compared to the rest of the muff part, in particular a
reduced outer diameter. This feature contributes to avoidance of
slipping [sic].
According to another refinement of the invention, the muff part
has a generally frustoconical taper with progression toward its end,
in the region of the first recess, the purpose of this taper being
to reduce the material thickness of the muff part. The taper need
not be a uniform straight-line taper; the outer periphery of the
muff part in the tapering region may be curved, in particular
concavely curved.
Preferably, the interior structure is symmetric with respect to
(and/or is disposed symmetrically with respect to) the longitudinal
axis of the muff part (or of the overall muff joint). In
particular, this symmetry may be rotational symmetry.
According to yet another refinement of the invention, the inner
wall of the first recess has a configuration which is complementary
[sic] to the configuration of a corresponding wall of the interior
structure. The configurations which are candidates for this may in
particular be configurations in which the inner wall of the first
recess and the corresponding wall of the interior structure are both
parallel to the longitudinal axis of the muff part (or of the
overall muff joint). It is also possible for the said two walls to
be inclined with respect to the longitudinal axis of the device.
In order to increase the reliability and robustness of the
joint, according to a highly preferred refinement of the invention
at least one thread means is provided on the connecting end of the
first concrete reinforcing rod; and
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at least one corresponding thread means is provided in the first
recess of the muff part and/or in/on the interior structure.
Advantageously, the recess has a first interior thread and the
interior structure has a first exterior thread. Complementarily to
this, the connecting end of the concrete reinforcing rod has a first
exterior thread which cooperates with the first interior thread of
the muff part, and has a second interior thread which cooperates
with the exterior thread of the interior structure of the muff part.
In particular in a situation where an adhesive material, such
as a plastic resin or the like, is employed in the formation of the
muff joint connection, it is advantageous if the aforesaid thread
means and corresponding cooperating thread means respectively have
different pitches and/or are shifted (e.g. offset) to some extent
with respect to each other (so as to form a gap), with the aim of
better distributing the adhesive material.
According to still another preferred refinement of the
invention, in order to avoid slipping problems on the opposite end
of the muff part, the muff part is comprised of a material which
essentially corresponds to that of the second concrete reinforcing
rod.
Additional features and advantages of the invention will be
apparent from the following description of exemplary embodiments
with reference to the accompanying drawings.
Fig. 1 is a specific embodiment of the inventive muff joint in
a separated state;
Fig. 2 is a cross section along line B-B in Fig. 1;
Fig. 3 is a cross section along line C-C in Fig. 1;
Fig. 4 is a representation of the inventive muff joint
according to Fig. 1 in the assembled state;
Fig. 5 is a cross section along line A-A in Fig. 4;
Fig. 6 is an alternative embodiment of the inventive muff joint
in a separated state;
Fig. 7 is a cross section along line B-B in Fig. 6;
Fig. 8 is a cross section along line C-C in Fig. 6;
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Fig. 9 illustrates the muff joint according to Fig. 6 in the
assembled state;
Fig. 10 is a cross section along line A-A in Fig. 9;
Fig. 11 is yet a third embodiment of the inventive muff joint
in a separated state;
Fig. 12 is a cross section along line B-B in Fig. 11;
Fig. 13 is a cross section along line C-C in Fig. 11;
Fig. 14 illustrates the muff joint according to Fig. 11 in the
assembled state; and
Fig. 15 is a cross section through line A-A in Fig. 14.
Fig. 1 shows an embodiment of the inventive muff joint for
concrete reinforcing rods of materials having mutually different
moduli of elasticity; the joint as a whole is designated with
reference numeral 1. The joint 1 is shown in Fig. 1 in a separated
state, with the concrete reinforcing rods (of which only one, the
rod 2, is shown in Fig. 1) not having been inserted in the muff part
3. The muff joint 1 is particularly suited for joining a steel
concrete reinforcing rod with a rod 2 comprised of a fiberglass
reinforced plastic (FRP), where the materials have sharply differing
moduli of elasticity.
For the stated purpose, the muff part 3 has a first recess 4
and a second (optional) recess 5, the two recesses being formed in
opposite ends of the muff part 3. The first recess 4 serves to
accommodate the illustrated concrete reinforcing rod 2 which has a
relatively low modulus of elasticity. The second recess 5 serves to
accommodate a second concrete reinforcing rod (not shown) which has
an appreciably higher modulus of elasticity than rod 2.
The muff part 3 is preferably comprised of a material which has
properties relating to its modulus of elasticity which properties
are comparable to those of the material of the (not shown) second
concrete reinforcing rod, wherewith preferably the material of the
muff part 3 is a suitable steel. In particular in this connection
it may be provided that the muff part 3 and
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the second concrete reinforcing rod may be joined (as an
alternative) by simple adhesive bonding means, obviating the need
for the second recess.
In order to avoid slippage [sic] in the region of connection of
the first concrete reinforcing rod 2 and the muff part 3 as a result
of the described difference in moduli of elasticity, the muff part 3
has a reduced material thickness (compared to the rest of muff part
3) in the region of the first recess 4. For this purpose, the outer
diameter of the muff part in the said region is progressively
reduced, e.g. in a tapering, with progression toward the
corresponding end of the muff part 3.
Further means of avoiding slippage are provided in that the
overlapping length UL of the first concrete reinforcing rod 2 and
the muff part 3 can be reduced, in that means are provided whereby,
in the illustrated embodiment of the muff joint 1, an additional
interior structure 6 is provided in the first recess 4 which
interior structure primarily comprises a frustoconical member (as
seen particularly clearly in the cross sectional view in Fig. 3)
which projects into the first recess 4. On the end of the first
concrete reinforcing rod 2 which end is destined to be inserted into
the recess 4, a complementary structure 7 corresponding to the
interior structure 6 is provided, which structure 7 comprises a
frustoconical recess, wherewith the structures 6 and 7 closely
interengage when the concrete reinforcing rod is inserted in the
muff part 3. The "close interengagement" is such that an enlarged
abutting surface (contact surface) is provided via the interior
structure 6 and complementary structure 7, between the concrete
reinforcing rod 2 and the muff part 3, whereby despite the
relatively short overlapping length UL an improved material
activation [sic] for stress transmission is provided, which
contributes to reduction of slippage.
Additional engineering design features of the embodiment
according to Fig. 1 will now be discussed, with reference to Figs. 2
and 3.
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The interior strucuure 6 of the muff part 3 and the
complementary structure 7 of the concrete reinforcing rod 2 are of
configurations which are symmetric with respect to (and/or are
disposed symmetrically with respect to) the longitudinal axis L of
the muff joint 1, as shown.
The concrete reinforcing rod 2, which preferably is comprised
of FRP, has a conically tapering connecting end, and the first
recess 4 of the muff part 3 has a complementary shape. In the ideal
case, this special configuration will result in linear loading
behavior in the contact and connection region.
The concrete reinforcing rod 2 also has on its connecting end
an outer thread 8, and the muff part 3 has a corresponding inner
thread 9 in the region of its first recess 4. Also in the region of
the complementary structure 7 the concrete reinforcing rod 2 has a
second inner thread 10 (see Fig. 2), and the interior structure 6 of
the muff part 3 has a complementary outer thread 11 (see Fig. 3).
The threading of the concrete reinforcing rod 2 on the one hand and
of the muff part 3 on the other hand can be mutually shifted and/or
can have different pitches, with the aim of ensuring a firm
interconnection of the two components, particularly when an adhesive
agent is applied (e.g. a plastic resin) in the region of the first
recess in order to contribute to a secure connection.
Because of the alternating inner and outer surfaces with
progression in the transverse direction (surfaces of the interior
structure 6 and exterior structure 7), a mutual "resistance" to
transverse contraction is provided by the concrete reinforcing rod 2
and muff part 3 in the face of the tensile and compressive stresses
which will occur. Particular effective resistance to transverse
contraction is provided by straight surfaces presented in the
outward direction by the first concrete reinforcing rod 2 and in the
inward direction by the muff part 3 (for a good example of which see
the particular embodiment illustrated in Fig. 5).
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In the region of the second recess 5, which serves to
accommodate the (not shown) second concrete reinforcing rod, a
thread 12 is provided which may be configured to connected to the
said second rod in a manner which is per se known.
Figs. 4 and 5 show the embodiment of the inventive muff joint
according to Figs. 1-3 in an assembled state, wherewith the
reference numeral 2' designates the second concrete reinforcing rod;
no further description of Figs. 4 and 5 is needed beyond that
provided above.
Figs. 6-10 illustrate a second embodiment of the inventive muff
joint 1. For reasons of brevity, only the important differences
between that embodiment and the embodiment according to Figs. 1-5
will now be described.
The muff part 3 and concrete reinforcing rod 2 illustrated in
Figs. 6-10 [lit., "4-6"] have yet a shorter overlap region UL. Also
the reduction in radius a and in cross section, of the muff part,
according to Fig. 6, is more pronounced than in Figs. 1-5.
To accommodate these features, the interior structure 6 in the
region of the first recess 4 of the muff part 3 also has a
frustoconical cross section (see Fig. 8), but it further has a
central frustoconical recess 13, which is oriented oppositely to the
frustoconical shape of the remainder of the interior structure 6.
The structure 7 on the connecting end of the concrete
reinforcing rod 2 is once again complementary to the interior
structure 6 (as described), being comprised of a conical recess
(similar to that of Figs. 1-5) but which has invading its center
region an oppositely oriented frustoconical projection 14 which is
configured so as to suitably engage the added recess 13 in the muff
part 3.
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Unlike the concrete reinforcing rod 2 of Figs. 1-5, the rod 2
of this embodiment does not narrow on its connecting end; and
correspondingly the outer wall 15 of the recess 4 of the muff part 3
is parallel to the longitudinal axis L of the muff joint 1.
This configuration also provides a large surface of engagement
between the concrete reinforcing rod 2 and the muff part 3 in the
region of the joint, contributing to improved material activation
[sic], thereby allowing a smaller overlap region UL while reducing
slipping.
In Figs. 9 and 10 the described second exemplary embodiment of
the muff joint 1 is illustrated in the assembled state.
As with the embodiment according to Figs. 1-5, suitable thread
means may be provided at the connecting end of the concrete
reinforcing rod 2 and complementary thread means may be provided in
the region of the first recess 4 of the muff part 3; for the sake
of simplicity in the drawings, these threads are not shown in
detail.
Figs. 11-15 illustrate a third exemplary embodiment of the
inventive muff joint 1; once again, in the description that
follows, only appreciable differences between this third embodiment
and the embodiments already described will be discussed.
The embodiment illustrated in Figs. 11-15 resembles that of
Figs. 6-10, with the principal difference being that in this third
embodiment the projecting structures in the region of the first
recess 4 of the muff part 3, which structures form the so-called
"interior structure" 6, have walls (16, 17) which are parallel to
the longitudinal axis L of the muff joint 1. The overall general
configuration of the interior structure 6 is that of a hollow
cylinder; and the structure on the connecting end of the concrete
reinforcing rod 2 has a complementary shape, as seen in the Figures.
In the region of the recess 4 and the connecting end of the
concrete reinforcing rod 2, thread means may be provided
(analogously to the examples described above); these are not shown
explicitly in Figs. 11-15.
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It should be noted that the present invention is not limited to
the above-described exemplary embodiments, all of which, e.g., are
rotationally symmetric. For example, the interior structure 6 may
be in the form of a (preferably uniform) parallel array of lamellae
(1-dimensional array) or pins (2-dimensional array) or the like,
which engages complementary structures (recesses) at the connecting
end of the concrete reinforcing rod 2, in order to provide the
maximum possible contact surface.
