U.S. patent application number 11/955637 was filed with the patent office on 2008-06-19 for flexible fiber reinforced composite rebar.
Invention is credited to Alan Fatz, William P. Junk, Brian J. Knouff, A. Dean Thompson.
Application Number | 20080141614 11/955637 |
Document ID | / |
Family ID | 39525468 |
Filed Date | 2008-06-19 |
United States Patent
Application |
20080141614 |
Kind Code |
A1 |
Knouff; Brian J. ; et
al. |
June 19, 2008 |
FLEXIBLE FIBER REINFORCED COMPOSITE REBAR
Abstract
A flexible fiber reinforced composite rebar structure includes a
plurality of continuous fibers embedded within a thermoplastic
resin. The rebar structure has an elliptical cross sectional shape
with an aspect ratio of about two to one and a twist with a twist
pitch of about 30 cm. The thermoplastic resin matrix enables the
rebar structure to be bent in the field by the application of heat
to soften the structure and thereafter cooled to return to a rigid
state.
Inventors: |
Knouff; Brian J.;
(Massillon, OH) ; Fatz; Alan; (Centerville,
OH) ; Thompson; A. Dean; (St. Joseph, MO) ;
Junk; William P.; (St. Joseph, MO) |
Correspondence
Address: |
SHUGHART THOMSON & KILROY, PC
120 WEST 12TH STREET
KANSAS CITY
MO
64105
US
|
Family ID: |
39525468 |
Appl. No.: |
11/955637 |
Filed: |
December 13, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60874828 |
Dec 14, 2006 |
|
|
|
Current U.S.
Class: |
52/857 ;
52/309.1; 52/745.19 |
Current CPC
Class: |
E04C 5/07 20130101; B29C
53/14 20130101 |
Class at
Publication: |
52/740.9 ;
52/309.1; 52/745.19 |
International
Class: |
E04C 5/07 20060101
E04C005/07 |
Claims
1. A composite reinforcement bar structure comprising: (a) a
thermoplastic resin matrix; (b) a plurality of elongated fibers
embedded in said matrix to form a reinforcement bar; and (c) said
bar having a flattened cross sectional shape.
2. A structure as set forth in claim 1 wherein: (a) said bar has a
helical twist.
3. A structure as set forth in claim 1 wherein: (a) said bar has a
helical twist with a twist pitch ranging from about 6 to 24 inches
(15.24 to 60.96 cm).
4. A structure as set forth in claim 1 wherein: (a) said bar has a
helical twist with a twist pitch of about 30 cm.
5. A structure as set forth in claim 1 wherein: (a) said bar has a
cross sectional aspect ratio of about two to one.
6. A structure as set forth in claim 1 wherein: (a) said bar has a
substantially elliptical cross sectional shape.
7. A structure as set forth in claim 1 wherein: (a) said bar has a
substantially elliptical cross sectional shape with a cross
sectional aspect ratio of about two to one. A structure as set
forth in claim 1 wherein: (a) said thermoplastic resin matrix is
formed of a polypropylene resin.
8. A structure as set forth in claim 1 wherein: (a) said fibers are
formed from one of a group of materials consisting of glass,
carbon, aramid, and metal.
9. A structure as set forth in claim 1 wherein: (a) said fibers are
formed of glass.
10. A structure as set forth in claim 1 wherein: (a) said fibers
form approximately 45 percent of a volume of said bar.
11. A composite reinforcement bar structure comprising: (a) a
thermoplastic resin matrix; (b) a plurality of continuous fibers
embedded in said matrix to form a reinforcement bar; (c) said bar
having a substantially elliptical cross sectional shape; and (d)
said bar having a helical twist.
12. A structure as set forth in claim 12 wherein: (a) said bar has
a helical twist with a twist pitch ranging from about 6 to 24
inches (15.24 to 60.96 cm).
13. A structure as set forth in claim 12 wherein: (a) said bar has
a helical twist with a twist pitch of about 30 cm.
14. A structure as set forth in claim 12 wherein: (a) said bar has
a cross sectional aspect ratio of about two to one.
15. A structure as set forth in claim 12 wherein: (a) said
thermoplastic resin matrix is formed of a polypropylene resin.
16. A structure as set forth in claim 12 wherein: (a) said fibers
are formed from one of a group of materials consisting of glass,
carbon, aramid, and metal.
17. A structure as set forth in claim 12 wherein: (a) said fibers
are formed of glass.
18. A structure as set forth in claim 12 wherein: (a) said fibers
form approximately 45 percent of a volume of said bar.
19. A composite reinforcement bar structure comprising: (a) a
thermoplastic resin matrix; (b) a plurality of continuous fibers
embedded in said matrix to form a reinforcement bar, said fibers
being formed from one of a group of materials consisting of glass,
carbon, aramid, and metal; (c) said bar having a substantially
elliptical cross sectional shape with a cross sectional aspect
ratio of about two to one; (d) said bar having a helical twist with
a twist pitch ranging from about 6 to 24 inches (15.24 to 60.96
cm).
20. A structure as set forth in claim 20 wherein: (a) said bar has
a twist pitch of about 30 cm.
21. A structure as set forth in claim 20 wherein: (a) said
thermoplastic resin matrix is formed of a polypropylene resin.
22. A structure as set forth in claim 20 wherein: (a) said fibers
are formed of glass.
23. A structure as set forth in claim 20 wherein: (a) said fibers
form approximately 45 percent of a volume of said bar.
24. In a process for forming a composite reinforcement bar
structure including a plurality of elongated fibers embedded in a
polymeric matrix, the improvement comprising the steps of: (a)
providing a thermoplastic resin to form said polymeric matrix; (b)
embedding said elongated fibers within said matrix to form a
reinforcement bar; (c) flattening said reinforcement bar to result
in a cross sectional aspect ratio greater than one to one; and (d)
twisting the flattened bar to achieve a twist pitch ranging from
about 6 to 24 inches (15.24 to 60.96 cm).
25. A process as set forth in claim 25 wherein said flattening step
includes the step of: (a) flattening said bar to result in a
substantially elliptical cross sectional shape having an aspect
ratio of about two to one.
26. A process as set forth in claim 25 wherein said twisting step
includes the step of: (a) twisting the flattened bar to achieve a
twist pitch of about 30 cm.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority under 35 U.S.C. 119(e) and
37 C.F.R. 1.78(a)(4) based upon copending U.S. Provisional
Application, Ser. No. 60/874,828 for FLEXIBLE REBAR, filed Dec. 14,
2006, which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] Concrete and other masonry or cementitious materials have
high compressive strength but relatively low tensile strength.
Thus, when concrete is employed as a structural material, it is
conventional to incorporate reinforcing members to enhance the
tensile strength of the structure. The reinforcing members are
usually comprised of a rigid rod or bar, such as a steel rod or
bar. Such reinforcing members are typically referred to as "rebar".
Unfortunately, steel and other metals are susceptible to oxidation.
In addition, such materials are quite rigid prior to use so that
the placement of such reinforcing members can be difficult and
time-intensive. As a result, conventional metal rebar must be cut
into pieces and joined in order to form a "criss-cross" or other
desired pattern.
[0003] One possible solution is to use glass fiber formulations as
structural rebar in conjunction with a thermoplastic resin. For
example, U.S. Pat. No. 6,048,598 to Bryan, III et al. discloses a
twisted rope rebar having individual fibers bound to each other by
a thermosetting resin. U.S. Pat. No. 5,580,642 to Okamoto et al.
discloses a reinforcing member comprised of reinforcing fibers and
thermoplastic fibers. U.S. Pat. Nos. 5,593,536 and 5,626,700 to
Kaiser disclose an apparatus for forming reinforcing structural
rebar including a combination of pultrusion and SMC (sheet molding
compound). The modified pultrusion produces a rebar having a core
of thermoset resin reinforcing material and an outer sheet molding
compound. U.S. Pat. No. 5,077,113 to Kakihara et al. proposes an
inner filament bundle layer spirally wound around a
fiber-reinforced core, a plurality of intermediate filament bundles
oriented axially along the core, and an outer filament bundle
spirally wound around the core and the other bundles. U.S. Pat. No.
4,620,401 to L'Esperance et al. proposes a fiber reinforced
thermosetting resin core and a plurality of continuous fibers
helically wound around the core and impregnated with the
thermosetting resin. The Jackson U.S. Pat. No. 2,425,883 discloses
a rod or bar formed of fine glass fibers with a phenolic resin
cured under heat.
[0004] Despite these advances, there remains a need to provide an
improved structural rebar that overcomes the disadvantages and
complexities of the prior art.
SUMMARY OF THE INVENTION
[0005] The present invention provides an improved composite
reinforcement bar or rebar structure. The rebar structure is
generally formed by continuous fibers embedded in a thermoplastic
resin matrix to form a reinforcement bar. The bar is flattened to
achieve a cross sectional aspect ratio greater than one to one. The
bar is then twisted in a substantially helical manner. In one
embodiment of the rebar structure, the bar has a substantially
elliptical cross sectional shape with a cross sectional aspect
ratio of about two to one and a twist pitch of about 30
centimeters. The matrix may be a thermoplastic resin such as
polypropylene, and the fibers may be formed of glass. The
thermoplastic resin matrix allows the matrix to be softened by the
application of heat to thereby bend or flex the bar to desired
shapes. The capability of being conveniently bent is also aided by
the cross sectional shape and aspect ratio and by the twist applied
to the bar. Once bent to a desired shape, the bar is allowed to
cool and re-harden to a substantially rigid state.
[0006] Objects and advantages of this invention will become
apparent from the following description taken in conjunction with
the accompanying drawings wherein are set forth, by way of
illustration and example, certain embodiments of this
invention.
[0007] The drawings constitute a part of this specification and
include exemplary embodiments of the present invention and
illustrate various objects and features thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a diagrammatic view of a pultrusion process for
forming the flexible fiber reinforced composite rebar of the
present invention.
[0009] FIG. 2 is a fragmentary perspective view of a length of the
flexible fiber reinforced composite rebar of the present
invention.
[0010] FIG. 3 is a greatly enlarged cross sectional view of the
rebar taken on line 3-3 of FIG. 2.
DETAILED DESCRIPTION OF THE INVENTION
[0011] As required, detailed embodiments of the present invention
are disclosed herein; however, it is to be understood that the
disclosed embodiments are merely exemplary of the invention, which
may be embodied in various forms. Therefore, specific structural
and functional details disclosed herein are not to be interpreted
as limiting, but merely as a basis for the claims and as a
representative basis for teaching one skilled in the art to
variously employ the present invention in virtually any
appropriately detailed structure.
[0012] Referring now to the drawings in more detail, the reference
numeral 1 generally designates a flexible fiber reinforced
composite reinforcement bar or rebar structure embodying the
present invention. The rebar structure 1 generally includes a
plurality of reinforcement fibers 2 (FIGS. 2 and 3) embedded within
a thermoplastic resin matrix 3. The rebar structure 1 is twisted in
a generally helical manner.
[0013] FIG. 1 diagrammatically illustrates system and process 10
for manufacturing the rebar structure 1. A creel arrangement 12,
including a plurality of spools or bobbins 14 of pays out a
plurality of continuous reinforcement fibers 2 into a set of fiber
guides 16. The fibers 2 are provided in the form of "rovings" or
twisted strands on the spools 14. The fibers 2 may be man made or
artificial continuous filaments, such as carbon, glass, aramid,
organic and/or metallic fiber. The creel arrangement 12 provides
the fibers with optimum pre-tension in order to maximize the
impregnation of the polymer 3 into the fibers 2. The particular
arrangement of the creel system 12 may vary depending upon the form
of the reinforcement/roving 2 provided by the suppliers.
[0014] The fibers move through a guides 16 which might consist of
guide pins and tensioners, depending upon the final size of the end
product. The guides 16, apart from guiding the path of the fibers
2, helps increase the surface area of the within a matrix
impregnation chamber 18. The illustrated process 10 includes a
dryer 20 into which thermoplastic resin 3 is fed. A heater
component 22 heats the thermoplastic resin to a plastic state. A
screw "pump" 24 forces the heated resin into the impregnation
chamber 18.
[0015] The impregnation chamber 18, an important component of the
process 10, includes two parts. In a first part 26, the fibers 2
come into contact with the thermoplastic polymer 3 pumped into the
impregnation chamber 18. The design of the chamber 18 enables
creation of high shear zones for the thermoplastic polymer 3 that
results in significant reduction of the viscosity thereof. This
reduction of the viscosity tremendously improves the impregnation
of the high viscous polymeric material 3 into the fibers 2. In a
second part 28 of the impregnation chamber 18, the impregnated
fibers 2 are converged into a consolidated impregnated rebar 30.
Depending upon the final shape required, the consolidated rebar 30
is given its final shape while it is still hot.
[0016] Once the rebar 30 with its final shape leaves the
impregnation chamber 18, it goes through a cooler system 32. The
design of the cooler system depends upon the final form of the
product. For thermoplastic rebar 30, the cooler system 32 might be
in the form of a long tube with water sprinklers (not shown)
attached along its length. The sprinklers would be used to spray
water on the thermoplastic rebar 30 to cool its surface.
[0017] The impregnated rebar 30 next moves through the puller 36.
The puller 36 pulls the impregnated rebar 30 though the entire
device throughout the manufacturing process 10. Finally, the
impregnated rebar enters a cutter station 38, which cuts the final
product to its required length.
[0018] One embodiment thermoplastic rebar 30 consists of E-glass,
or electrical grade glass, as the fiber reinforcement 2 and
polypropylene as the thermoplastic matrix 3. The fiber volume ratio
is approximately 45% of the total volume of the rebar 30, a
representative value for typical long fiber thermoplastic
processes. A thermoplastic rebar design optimization was performed
using ABAQUS.TM. finite element analysis software (Dassault
Systemes Societe Anonyme France, www.simulia.com). An optimal
profile for the rebar 30 was found to be an elliptical cross
sectional shape having an aspect ratio of about 2:1, with specific
dimensions varying for different rebar sizes. In one embodiment,
the rebar 30 has a major axis of about 0.75 inch (19.05 mm) and a
minor axis of about 0.375 inch (9.53 mm). It is foreseen that the
rebar 30 could alternatively have other flattened shapes which are
not specifically elliptical. Further, the optimal profile also
includes a twist pitch of 30 centimeters (cm) or about one twist
per 12 inches of rebar 30. Alternatively, the twist pitch may fall
within a range of about 6 to 24 inches (15.24 to 60.96 cm). An
example profile is illustrated below in FIG. 2, and additional
highlights of the design optimization are described below.
[0019] A thermoplastic matrix 3 was chosen over thermoset because a
thermoplastic material has the potential for being bendable in the
field. One embodiment of the rebar structure incorporates a
polypropylene resin as the thermoplastic matrix 3. However, it is
foreseen that other thermoplastic resins could be advantageously
employed for use in some applications and environments. Bending the
rebar 30 may require onsite heating, which will reduce the stresses
resulting from the applied bending force. The heating is preferably
not of a temperature which would actually melt the thermoplastic
material 3, but only to temporarily soften the rebar 30 for
bending. The heating temperature may range from about 150 to 200F
(65.6 to 93.3.degree. C.).
[0020] A rebar structure 1 having an elliptical cross-section with
bends along the major axis appears to meet the demands of being
bendable in the field. The elliptical shape minimizes transverse
stress, while twists allow ease of bending without having to align
the rebar. The twist pitch represents the resolution of bend
length; that is, if the pitch is 30 cm, the rebar can only be bent
every 30 cm. It was determined that increasing the twists in the
rebar 30 (that is, decreasing the twist pitch) increases stress and
strain values. Of the many twist pitches considered during
analysis, the profile which showed the least longitudinal stress
was the pitch 30 cm. Further, rebar was found to be optimally
bendable in the horizontal to normal plane of the cross section,
that is, about the major axis.
[0021] Various aspect ratios were also considered during analysis.
It was found that increasing the aspect ratio reduced the
longitudinal stress, but increased the transverse stress.
Increasing the aspect ratio also increased the likelihood for
buckling. An aspect ratio of 2:1 was identified as the optimal
design parameter, and is illustrated in FIG. 3 below.
[0022] In summary, an optimized embodiment of the thermoplastic
rebar structure 1 meeting the criteria of bendability in the field
yet not requiring alignment included a polypropylene matrix 3 with
E-glass fibers 2 at a 45% fiber volume ratio, a substantially
elliptical profile with an aspect ratio of about 2:1, and a twist
pitch of about 30 centimeters.
[0023] It is to be understood that while certain forms of the
present invention have been illustrated and described herein, it is
not to be limited to the specific forms or arrangement of parts
described and shown.
* * * * *
References