U.S. patent application number 09/775684 was filed with the patent office on 2002-07-25 for composite reinforced wood structural members.
Invention is credited to Fawley, Norman C..
Application Number | 20020095905 09/775684 |
Document ID | / |
Family ID | 26876025 |
Filed Date | 2002-07-25 |
United States Patent
Application |
20020095905 |
Kind Code |
A1 |
Fawley, Norman C. |
July 25, 2002 |
Composite reinforced wood structural members
Abstract
A wood pole having a wood body defined by a stripped tree trunk
is reinforced by strips of composite reinforcement wrapped
helically around the wood body, wherein the reinforcement comprises
parallel high strength filaments in a resin matrix. The thickness
and/or number of layers of reinforcement can be varied along the
length of the pole to best suit the loading to which the pole is to
be subjected. The reinforcement also performs the functions of the
prevention of rot, insect infestation and water absorption, which
are conventionally performed by harmful materials such as creosote.
An electrical conductor can extend the length of the pole,
protected under the reinforcement, which is transparent to
electromagnetic signals, to act as an antenna or as a ground wire.
No-maintenance color, fire retardant and/or reflective elements can
be mixed in with the resin during the reinforcing of the pole.
Inventors: |
Fawley, Norman C.; (San Luis
Obispo, CA) |
Correspondence
Address: |
VENABLE
Post Office Box 34385
Washington
DC
20043-9998
US
|
Family ID: |
26876025 |
Appl. No.: |
09/775684 |
Filed: |
February 5, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60180129 |
Feb 3, 2000 |
|
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|
Current U.S.
Class: |
52/834 |
Current CPC
Class: |
H01Q 1/1242 20130101;
E04H 12/04 20130101; E04C 3/12 20130101; E04C 3/29 20130101 |
Class at
Publication: |
52/736.3 ;
52/738.1 |
International
Class: |
E04H 012/04; E04C
003/36 |
Claims
What is claimed is:
1. A reinforced wood pole comprising: an elongated wood body
defined solely by a core of a tree trunk; and at least one layer of
a strip of composite reinforcing material extending in a helix
around and in engagement with the wood body, the helix defining
adjacent convolutions in continuous contact the composite material
comprising parallel continuous high tensile strength fibers
extending throughout the strip, and a resin matrix encapsulating
the fibers to define the strip.
2. The reinforced wood pole of claim 1, wherein the fibers are
nonmetallic.
3. The reinforced wood pole of claim 1, wherein the pole has a top
end and a 2 bottom end, and the reinforcing covers the entire pole,
except the bottom end.
4. The reinforced wood pole of claim 1, wherein the material of the
wood body has a strength such that a wood body having a diameter of
4 inches has insufficient strength in itself to withstand a load of
7,000 pounds.
5. The reinforced wood pole of claim 1, wherein the strip contains
a first plurality of the fibers extending longitudinally in the
strip and a second plurality of the fibers extending transversely
in the strip, and said fibers of said first and second pluralities
are glass fibers and comprise approximately 70% by weight of the
strip.
6. The reinforced wood pole of claim 5, wherein the strip extends
helically around the pole at an angle of from about 5.degree. to
about 25.degree..
7. The reinforced wood pole of claim 1, further comprising a
plurality of layers of the strips.
8. The reinforced wood pole of claim 7, wherein at least one of the
number of layers of the strips and the thickness of the strips
decreases in a direction from the bottom of the pole to the top of
the pole.
9. The reinforced wood pole of claim 8, wherein the pole is secured
in the ground, and the largest number of layers of the strips
extends from the bottom of the pole to more than one-third the
height of the pole above ground.
10. The reinforced wood pole of claim 1, wherein all of the fibers
of at least one of said strips extend transversely in the strip and
generally longitudinally with respect to the elongate wood
body.
11. The reinforced wood pole of claim 10, wherein the fibers which
extend transversely are glass fibers, and said glass fibers
comprise approximately 70% by weight of said at least one strip of
composite reinforcement material.
12. The reinforced wood pole of claim 10, comprising a plurality of
said layers, wherein all of the fibers of at least one of said
strips extend longitudinally in the strip and generally
circumferentially with respect to the elongate wood body.
13. The reinforced wood pole of claim 1, further comprising an
electrically conductive wire extending longitudinally under the
composite reinforcing material, from the top of the pole to the
bottom of the pole.
14. The reinforced wood pole of claim 1, further comprising a
barrier layer of a material defining a barrier against ultraviolet
light, said barrier layer substantially covering the composite
reinforcing material.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims the priority of U.S. Provisional
Patent Application No. 60/176,056, filed Feb. 3, 2000, which is
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to wood structural members
and, more particularly, to elongate, composite reinforced wood
structural members for uses such as utility poles, piles and
beams.
[0003] In the United States alone, there are more than 100 million
electric distribution poles and about 8 million to 10 million
electric transmission poles. The distribution poles are typically
45 feet to 50 feet in length, whereas new transmission poles are
usually from 85 feet to 100 feet in length and carry high voltage
lines. Wood is, by far, the material of which most of these utility
poles are made, although some are made of steel, concrete and
composites. In order to make wood utility poles, trees are cut,
delimbed and then peeled to the proper taper.
[0004] It is estimated that more than 250,000 transmission poles
and 3 million to 4 million distribution poles need to be replaced
every year. Rot that occurs at the ground line and woodpeckers
destroy many wood poles or make them too weak for further service,
and wind and ice storms can destroy all types of utility poles. In
some places, the life of a wood utility pole can be as low as 10 to
15 years. The severe ice storms in the northeastern United States
and in the Canadian provinces of Ontario and Quebec in January,
1998, destroyed or damaged many thousands of utility poles,
including about 50,000 utility poles in Ontario and Quebec. In
conditions like those of an ice storm, the weight of ice on lines
and poles puts at least close to a maximum load on the poles. If
one pole fails under such conditions, it very likely pulls down
neighboring poles in a domino effect, thereby resulting in
extensive damage.
[0005] Wood utility poles are less expensive than utility poles
made of other materials. Composites are 5 to 10 times the cost of
wood in distribution pole length sizes. As a result, many prime
trees are cut down to satisfy the need for utility poles. Over the
years, most wood utility poles have been made from trees of the
following types: western red cedar, lodgepole pine, red pine, jack
pine, Scots pine, southern yellow pine, Douglas fir and radiata
pine. Softwood trees, such as southern yellow pine, have a quick
growth rate but lack durability. Scrub trees and other trees are
unsuitable because they are too weak. Species such as hemlock and
spruce do not absorb the materials normally used to prevent
infestation and rot. Therefore, they are not used as utility poles.
The materials normally used to prevent infestation and rot include
such hazardous materials as pentachlorophenol, chromate copper
arsenate, ammoniacal copper arsenate, copper naphthenate and
creosote wood preservatives. The carcinogenic aspect of creosoted
utility poles has been widely discussed, and in many cases
creosoted poles must be disposed of in separate land fills due to
potential contamination from the creosote. Furthermore, because
wood utility poles are made from trees, and trees have limbs, the
bases of the limbs (commonly referred to as "knots") become stress
raisers in the poles. In the examination of many utility pole
failures, it has been found that the failure originated at a knot
area, usually about one third of the way up the pole. Wood utility
poles are relatively inflexible and usually fail along a plane
extending down at an angle from one side of the pole to the center,
with the wood on one side of the plane pivoting away from the wood
on the opposite side of the plane. In addition, in some conditions,
wood utility poles become saturated with moisture and cause ground
shorting, in which current flows from lines carried by the pole
through the pole to the ground. Saturation also leads to rotting
and failure.
[0006] SUMMARY OF THE INVENTION
[0007] By the present invention, elongate structural members made
of wood, such as wood utility poles; can be reinforced with a
composite material and thereby made stronger by a factor of from
about 2 to about 4, depending on the specific arrangement of the
composite material. Reinforced wood utility poles and other
reinforced elongate wood structural members according to the
present invention can comprise an elongate wood body defined solely
by a core of a tree trunk. The composite reinforcement increases
the flexural strength of wood structural members and gives them
greater ductility. As a result, wood structural members reinforced
according to the present invention bend farther without failing
than bare wood structural members do. Furthermore, elongate wood
structural members reinforced according to the present invention
have sufficient strength to perform their intended functions, even
though the wood bodies have insufficient strength in themselves to
perform the functions. Wood utility poles or other wood members of
a given cross sectional area can be made much stronger, or wood
poles or other wood members of a smaller cross sectional area can
be made strong enough to function as utility poles. Poles of lesser
strength classes can be strengthened to the strengths of higher
strength classes. The utility industry defines various classes of
utility poles, with varying amounts of strength required for each
class in accordance with the job that a pole must perform.
Furthermore, poles from trees of inferior species, that is, species
of soft woods and species otherwise too weak to be used as utility
poles previously, can be reinforced to be suitable for utility
poles, thereby saving the trees of more valuable species. It is
even contemplated that palm trees reinforced according to the
present invention can be used as utility poles, especially where
other types of trees are not available.
[0008] The composite reinforcement according to the present
invention performs the functions of the creosote and other
treatment materials. As a result, the present invention makes
possible the use of the non-absorbing woods as utility poles. By
performing the functions, such as the prevention of rot and insect
infestation and water absorption, previously provided by harmful
materials such as pentachlorophenol and creosote, the composite
reinforcement eliminates the use of the harmful materials and the
associated contamination and disposal problems. Wood members
reinforced according to the present invention can be totally
wrapped by the reinforcement, including, in the case of utility
poles, the areas where cross-arms are to be attached. In addition,
a cap of composite material can be placed on the top of the wood
member. As a result, moisture cannot get into the wood and cause
the associated problems, such as rotting and ground shorting in the
case of utility poles. Materials to discourage woodpeckers, such as
cayenne pepper, can be added to the resin during or prior to making
of the reinforced pole. Known fire retardant materials, such as
cayenne pepper, can be added to the resin during the reinforcing of
the poles so that the poles will be protected against fire from
brush fires and the like. Moreover, the reinforced structural
members can be made in any color by adding color to the resin
component of the composite reinforcement as the structural members
are being wrapped. As a result, there is no need for painting or
maintenance. An outer winding of nylon, Reemay polyester or other
polyester, or glass malts or veils, can be used to provide a
significant long-term barrier to degradation of the underlying
composite reinforcement from ultraviolet light and other
weather-related elements. Especially where the poles are to be
installed close to vehicular traffic, glass beads or other
reflective elements can be mixed in with the resin to be used in
all or a portion of the outer layer of reinforcement in order to
provide greater visibility at night. As an alternative, reflective
tape can be placed around the pole under an outer covering of
resin. The resin can be transparent, so that the reflective tape
shines through the resin, while the resin protects the reflective
tape from degradation. Furthermore, the high strength filaments of
the reinforcement, such as glass fibers, and the resin can be
chosen to have the same index of refraction. As a result, the
composite reinforcement is transparent, and the reflective tape can
shine through one or more layers of the composite reinforcement.
The composite material also prevents ground shorting by acting as a
dielectric shell for wood utility poles. In this regard, E-type
glass fibers, which are electrically non-conductive and transparent
to radio and other electromagnetic signals, can be used as high
tensile strength filaments in the composite reinforcement.
Arrangements conventionally used for attaching steps and cross-arms
to wood utility poles can be used with reinforced utility poles
according to present invention due to the thinness of the composite
reinforcement and the presence of the solid wood core. Such
arrangements cannot be used with totally composite utility poles,
which are typically hollow. Because the composite reinforcement
provides so much strength, the present invention prevents, or at
least greatly reduces, the failures of wood structural members due
to stress concentrations at knots. Composite reinforced wood
utility poles according to the present invention can be smaller in
diameter and greater in height than unreinforced wood utility
poles. Wood structural members reinforced according to the present
invention have higher flexural strength and greater ductility and
can carry greater loads than unreinforced wood structure members.
Furthermore, by increasing or decreasing the amount of the high
tensile strength filaments in the composite which are oriented
generally in the longitudinal direction of the wood structural
members, the members can be made with greater or lesser stiffness,
whatever is desired for a particular application.
[0009] The reinforced utility poles according to the present
invention are also well-suited to define the uprights and the
horizontal member or members of towers for long distance energy
transmission. H-towers constructed with composite reinforced wood
horizontal members, or cross-arms, and with the reinforced utility
poles as uprights are less costly than conventional wood H-towers
and yet have greater wind resistance and ice load bearing
ability.
[0010] The present invention can also be used for reinforced wood
piles for piers and other marine applications. Unlike utility
poles, the piles typically are not tapered. However, some marine
piles are tapered from the top to the bottom, the smaller end being
pounded into the earth.
[0011] In addition to providing the advantages described above in
connection with composite reinforced utility poles, the composite
reinforcement prevents the ends of the piles from splitting due to
pounding. In addition to poles having circular transverse
cross-sections, the present invention can be used with poles and
uprights having non-circular transverse cross-sections, and with
beams having non-circular or circular cross-sections. The wood
structural elements to be reinforced, whether uprights or beams,
experience an increase in shear modulus with the reinforcement
according to the present invention.
[0012] In order to provide the above advantages, a wooden pole is
covered with one or more layers of a composite reinforcing material
comprising a large plurality of parallel, continuous, lightweight,
high strength, electrically non-conductive nonmetallic fibers and a
resinous material encapsulating the fibers. The pole can be tapered
from bottom to top, like a conventional utility pole. The pole can
be the same diameter as a conventional utility pole, or can be
smaller in diameter than a conventional utility pole, since the
composite reinforcing material will provide the necessary strength.
Because loads on a pole are significantly less at the top than at
the bottom, the number of layers of reinforcement can be decreased
from the bottom to the top and/or the reinforcement can be
otherwise arranged to provide the greatest reinforcement for the
areas of the pole that will be subjected to the greatest stress.
Because the utility poles are subject to side-to-side loads, as
well as vertical compression, a large plurality of parallel
longitudinal fibers, as well as a large plurality of parallel
circumferential fibers, are in the composite reinforcement to
provide an adequate side-to-side load reinforcement. The composite
reinforcement applied in accordance with the present invention
prevents the typical failure of the wood utility pole by hinged
separation along a plane extending down at an angle from one side
of the pole to the center. It also changes the mode of failure to
end-to-end tension shear, the overall result of which is a
horizontal break. This change in the mode of failure gives the
reinforced wood utility poles greater flexibility and greater
toughness, increases the loads the poles can bear, and eliminates
from pole failures the domino effect by which neighboring utility
poles fail as a result of the failure of a first utility pole.
[0013] The present invention is well adapted to the use of utility
transmission poles as antennas for cellular phones and for other
non-wired communications. By placing a conductor against a wood
pole, running from the top to the bottom of the pole, a protected
conductor can be provided. Such a conductor can also be used as a
grounding device to prevent stray current from short arcing across
the insulators and to take any stray currents at the ground. The
conductor can be placed either in a groove cut longitudinally down
the pole or simply on the surface of the pole, in either case,
prior to applying the composite reinforcement. The conductor can be
in a straight vertical line, in a spiral around the pole, or in
other configurations.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The foregoing and other objects, aspects and advantages will
be better understood from the following detailed description of a
preferred embodiment of the invention with reference to the
drawings, wherein:
[0015] FIG. 1 is a perspective view of an installed reinforced wood
utility pole according to the present invention;
[0016] FIG. 2 is a front elevation of a reinforced wood utility
pole according to the present invention before installation;
[0017] FIG. 3 shows a portion of a wooden core receiving first and
second layers of composite reinforcing material and a conducting
wire in the manufacture of a reinforced wood utility pole according
to the present invention;
[0018] FIG. 4 is a transverse cross-section along the line 4-4 in
FIG. 2;
[0019] FIG. 5 is a transverse cross-section of a reinforced utility
pole according to the present invention having five layers of
reinforcing material;
[0020] FIG. 6 is a schematic showing of a portion of a strip of
composite material having randomly oriented filaments for use in a
reinforced wood utility pole according to the present
invention;
[0021] FIG. 7 is an enlarged portion of a strip of composite
reinforcement for use in a reinforced wood utility pole according
to the present invention, wherein all filaments are parallel to the
length of the strip;
[0022] FIG. 8 is an enlarged portion of a strip of composite
reinforcement having an arrangement of filaments in the
longitudinal direction woven with filaments in the transverse
direction;
[0023] FIG. 9 is an enlarged portion of a strip of composite
reinforcement for use in a reinforced wood utility pole according
to the present invention, wherein all of the filaments are
transverse to the length of the strip;
[0024] FIG. 10 is a load versus position curve for a bare wood test
sample;
[0025] FIG. 11 is a load versus position curve for a wood test
sample reinforced according to the present invention with three
specific layers of composite reinforcing material;
[0026] FIG. 12 is a load versus position curve for a wood test
sample reinforced according to the present invention with three
specific layers of composite reinforcing material;
[0027] FIG. 13 is a load versus position curve for a wood test
sample reinforced according to the present invention with five
other specific layers of composite reinforcing material; and
[0028] FIG. 14 is an H-tower in accordance with the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0029] As can be seen from FIG. 1, a utility pole reinforced
according to the present invention which is designated generally by
the reference numeral 10, comprises a wood core 11 wrapped with one
or more layers of a composite reinforcement material 12. Cross-arms
14 are mounted on the pole 10, and insulators 16 are mounted on the
cross-arms to support one or more lines 18 for the transmission or
distribution of electrical power.
[0030] As can best be seen from FIG. 2, the pole 10 has different
thicknesses of reinforcement at different sections along the length
of the pole 10. The different thicknesses are due to differing
numbers of layers of reinforcement. The pole 10 includes an
elongate wood body 20 (FIGS. 3-5), which can be defined by a
conventional, tapered wood utility pole. The thickest reinforcement
on the pole, reinforcement 12a, extends from the bottom of the pole
to a point which is at least one-third of the height of the pole
above the ground, when the pole is installed. The reason for this
is that many utility pole failures occur at about one-third of
their height above the ground. A middle section of the pole 10 is
wrapped with composite reinforcement material 12b having a total
thickness less than the thickness of the material 12a on the bottom
section of the pole. The top section of the pole is wrapped with
composite reinforcement material 12c having a total thickness less
than the thickness of the material 12b of the middle section. In
FIG. 2, the difference in the thickness of the reinforcement on the
various sections of the pole is exaggerated for clarity of
illustration. As an alternative to the thicknesses just described,
the middle section can have a greater thickness of reinforcement
than the other sections of the pole 10, if such an arrangement is
called for by the loading on the pole. In addition, or as an
alternative to the thickness arrangements described above, the
individual layers can have different thicknesses from one another,
and/or the directions in which the high tensile strength filaments
extend in the reinforcement can vary from one layer to another.
Still other configurations of reinforcement can be used to suit the
loading to be imposed on the utility pole.
[0031] An end cap 22 made of composite material comprising
high-strength filaments in a resin matrix is positioned at the top
and bottom of the pole 10 to cover the top of the wood body 20. The
cap 22 has a skirt extending for a short distance along the length
of the pole 10, and the skirt is covered by the composite
reinforcement material 12 covering the pole to help hold the cap on
the pole.
[0032] As can be seen from FIGS. 2-4, the composite reinforcement
material 12 on the pole 10 comprises one or more layers of strips
26 and 27 of the composite reinforcement material 12 wrapped
helically around the wood body 20. Typically, the strips are
wrapped at a small helical angle `a` (FIG. 2) in the range of about
5.degree. to about 30.degree., for which approximately 14.5.degree.
is typical. A first strip defining a first layer, such as strip 26,
can be wrapped with the helical angle extending in one direction
relative to the horizontal and a next strip defining a second
layer, such as the strip 28, can be wrapped with the helical angle
extending in the opposite direction with respect to the horizontal.
A third strip 29 defining a third layer can be wrapped with a
helical angle in the same direction as the first layer, and so on.
The strip can comprise a large plurality of unidirectional parallel
high tensile strength filaments brought together in a resin matrix
prior to curing of the resin but otherwise unattached. As an
alternative, the filaments can be stitched together. As another
alternative, the strip can comprise two groups of parallel
filaments, the filaments of one group lying at an angle with
respect to the filaments of the other group. Additional groups of
filaments lying at still other angles can be included. The groups
of filaments can be unattached, or can be stitched together or
woven together.
[0033] As can be appreciated from FIGS. 3 and 4, a wire 30 can be
installed running the length of the pole 10, either in a notch 31
in the wood body 20, or simply on the outer surface of the wood
body. In either case, the composite material 12 is wrapped over the
wire 30 to protect it and secure it in place. The wire 30 can
extend in a straight line, spiral around the pole, or have another
configuration to function as an antenna. As an alternative, the
wire 30 can also act as a grounding device to prevent stray
currents from short arcing across the insulators mounted on the
pole and to take any stray currents at the ground. A plurality of
wires 30 to serve a plurality of functions can be applied to the
pole.
[0034] As can be appreciated from FIGS. 5 and 7-9, the strips 26-28
of composite reinforcement material 12 wrapped around the wood
bodies 20, and additional strips, if used, such as strips S4 and S5
of the pole 10' of FIG. 5, are made from strips of parallel high
tensile strength non-metallic filaments, such as glass fibers,
having various orientations. In each case, the fibers are arranged
in parallel groups and embedded in a matrix of a curable resin,
such as an isophthalic polyester resin, to form a composite
reinforcement material having high strength. Such resins are wet
and viscous before curing and, preferably, the strips of high
tensile strength filaments are saturated with the resin before the
strips are wrapped helically around the wood body 20. When this is
done, the resin causes the strips to adhere to the wood body or to
underlying strips. After the wood body 20 is wrapped, the resin is
cured by conventional means. The cured resin makes the composite
reinforcement material 12 impervious to the ingress of
moisture.
[0035] FIG. 6 schematically shows a portion a type of strip 32,
called a "matt", which contains thousands of randomly oriented
fibers or filaments 34, such as glass fibers, either chopped or
continuous strands, adhered to one another. Such a strip is not
nearly as strong as strips having parallel filaments but is very
conducive to absorbing resin, and the resin acts as a barrier to
ultraviolet rays, moisture and other elements. Each line in FIG. 6
represents dozens of filaments. Actually, there are many more
dozens of fibers 34 adhered together per square inch than is
indicated by FIG. 6, and the open spaces are much smaller than
indicated. Such a strip 32 can be placed around the strips 26-28
designed for high strength, as is shown in FIG. 4.
[0036] FIG. 7 shows a strip 36 made of bundles 38 of high tensile
strength filaments all oriented parallel to the length of the
strip. A few strands 40 of transverse thread are used to hold the
longitudinal filaments 38 together. Each bundle 38 of filaments
indicated in FIG. 7 contains hundreds or thousands of high-strength
filaments of glass or other material.
[0037] FIG. 8 shows a strip 42 in which bundles 44 of longitudinal
filaments are woven with bundles 46 of transverse filaments. Again,
there are at least hundreds of filaments in each bundle. About 80%
of the filaments by weight can be longitudinal and about 20% of the
filaments by weight can be transverse (80/20), or about 50% can be
longitudinal and about 50% transverse (50/50). Any relative amounts
of longitudinal and transverse filaments can be chosen in order to
satisfy the strength requirements for the loads the pole will bear,
[longitudinal for bending; circumferential for ?] Rather than being
woven, the bundles 44 and 46 can be stitched together at right
angles to one another. It can be particularly useful to choose the
angles between the bundles 44 and the length of the strip 42 and
between the bundles 46 and the length of the strip such that, when
the strip 42 is wound around the wood body 20 at a helical angle,
the bundles 44 extend precisely circumferentially around the wood
body and the bundles 46 extend precisely longitudinally, or vice
versa.
[0038] FIG. 9 shows a strip 48 in which all of the high tensile
strength filaments, which are in bundles 50, extend transverse to
the length of the strip. Each bundle 50 contains hundreds of
filaments. A few longitudinal threads 52 are used to hold the
transverse bundles 50 together.
[0039] At least when the strips of composite material defined by
the high tensile strength filaments and the resin are cured, the
strips have tremendous tensile strength in a direction parallel to
the filaments. For each of the strips relied on to provide strength
in one or more specific directions, which, among the illustrated
strips, includes the strips of FIGS. 7-9, the filaments comprise
about 70% by weight of the composite strip of filaments and resin
and about 50% by volume, when the filaments are glass filaments or
fibers.
[0040] The various types of strips of high strength filaments can
be used in various combinations, depending upon the properties
desired. If it is desired to particularly increase the flexural
strength and stiffness of the wood body 20, more layers of
reinforcement formed by strips having transverse filaments, such as
the strip 48 of FIG. 9, are used. It can be appreciated that, when
a strip of the material of FIG. 9 is wrapped around an elongate
wood body 20, the filaments will extend generally longitudinally of
the wood body. The filaments are not precisely longitudinal because
of the angle of the helix along which the strip is laid. However,
since the angle `a` of the helix is small (e.g., 14.5.degree.), the
tensile strength component of the filaments is almost entirely in
the longitudinal direction of the wood body 20. Similarly, for the
strips 36 of FIG. 7, the tensile strength component of the
filaments is almost entirely in the circumferential direction of
the wood body 20, when the strip is wound helically around the wood
body.
[0041] The following table shows the results of flexural bend tests
on 4"-diameter wood test poles (peeler poles, center heart). Each
test pole was 40" long and was place horizontally on supports
spaced 28" apart, with a force imposed by a slow moving machine
element at the center of the 28" span of the test pole between the
supports. Thus, the force was applied transverse to the length of
the pole by the machine element, which started from a position in
engagement with the pole.
1 TABLE 1 Load in Lbs. Test Sample A B Average Bare (Control) 5,094
5,564 Bare (Control) 6,741 4,859 System 1 6,737 6,931 6,834 System
2 12,072 12,878 12,475 System 3 13,613 13,841 13,727 System 4 7,975
8,178 8,076 System 5 17,663 19,150 18,406 System 6 19,342 20,556
19,949
[0042] With respect to the various systems of strips wrapped around
the test poles for which the test results are shown in Table 1,
there are three layers of strips used in Systems 1-3 and five
layers used in Systems 4-6. For System 1, the innermost layer has
randomly oriented filaments, such as the strip 32 of FIG. 6, and
the middle and outer layers are made from strips in which all of
the filaments are longitudinal, such as the strips 36 of FIG. 7. In
System 2, the inner layer is made from strips comprising woven
filaments of which 80% are longitudinal and 20% are transverse,
such as the strips 42 of FIG. 8. The middle and outer layers are
made from strips in which all of the filaments are longitudinal.
For System 3, the innermost layer is made from a strip in which all
of the filaments are transverse, such as the strip 48 of FIG. 9,
and the outer two layers are made from strips in which all of the
filaments are longitudinal.
[0043] In System 4, the two innermost layers are made from strips
in which the filaments are randomly oriented, and the other three
layers are made from strips in which all of the filaments are
longitudinal. In System 5, the two innermost layers are made from
strips of woven filaments, of which 80% by weight are longitudinal
and 20% by weight are transverse. The other three layers are made
from strips in which all of the filaments are longitudinal. In
System 6, the two innermost layers are made from strips in which
all of the filaments are transverse, and the other three layers are
made from strips in which all of the filaments are
longitudinal.
[0044] FIG. 10 is a graph of the vertical load in pounds on the
bare test pole of Column A of Table 1 versus the position of the
movable test machine element in inches from the starting position.
The force on the pole increased with the movement of the test
machine element until 6,741 lbs. was reached. After that point, the
bare test pole broke and the load supporting ability of the pole
dropped precipitously.
[0045] FIG. 11 is a load versus position graph for the test pole in
Column A of Table 1 with the System 3 reinforcement according to
the present invention. It can be appreciated from FIG. 4 that the
System 3 reinforcement comprises an inner layer or wrapping of
composite material made from a strip in which all of the filaments
are transverse, as shown in FIG. 9. The middle and outer layers are
made from strips in which all of the filaments are longitudinal, as
shown in FIG. 7. As can be seen from FIG. 11, the load increased
with increasing movement of the test machine element to 13,613 lbs.
At that point, there was a slight decrease in the load, indicating
a failure of the test pole, but the pole continued to bear a
substantial load for about 1/3 of an inch additional travel of the
machine test element. Thus, there was some warning before a
complete failure of the test pole.
[0046] In the 5-layer reinforcement of the present invention
according to System 6, FIG. 12 shows that the test pole in Column A
of Table 1 withstood 19,342 lbs., and there was considerable
additional travel by the machine test element before there was a
sudden large drop in load supporting ability from about 17,500 lbs.
to about 8,750 lbs. FIG. 13 shows that, with the System 6 test pole
of Column B, the ultimate load before failure was 20,556 lbs.,
after which there was a substantial decrease in load bearing
ability to a lower plateau at about 12,400 lbs., before a further
drop in a load bearing ability with a substantial additional
movement of the machine test element.
[0047] As can be seen from FIG. 4, the outermost layer of composite
reinforcement can be covered by a layer to protect the composite
reinforcement layers from degradation by ultraviolet light and
weathering. The barrier layer can comprise nylon, Reemay polyester
or other polyester fibers in a strip which is would helically
around and covering the underlying composite reinforcement
layers.
[0048] Although the present invention has been described herein in
connection with new utility poles, it is understood that the
present invention can be used in connection with utility poles
already in service, whether or not they are damaged or
weakened.
[0049] As can be seen from FIG. 14, an H-tower 58 can be
constructed in accordance with the present invention. The H-tower
58 includes two uprights 60, each having the same construction of
the utility pole 10 of FIGS. 1 and 2, including the composite
reinforcement material 12. The uprights 60 are connected by a
crossbeam 62 that is also reinforced with the composite
reinforcement material 12. For the cross beam 62, the composite
reinforcement material 12 typically has a uniform thickness across
the entire crossbeam, and the crossbeam typically is not tapered.
Of course, the thickness of composite reinforcement material 12 and
the cross section of the crossbeam 62 can vary where conditions
warrant. Both the uprights 60 and the crossbeam 62 are covered with
the composite reinforcement 12 where they are joined to one
another. Holes can be drilled through the uprights 60 and the
crossbeam 62, including the composite reinforcement material 12, to
receive bolts for securing the crossbeam to the uprights.
[0050] The present invention can also be used to reinforce wood
cores for use as marine pilings. Such marine pilings have many of
the same advantages as reinforced utility poles according to the
present invention. In addition, the wrapping of the wood cores with
the strips of composite reinforcement material helps prevent the
resultant reinforced marine pilings from splitting when they are
driven into the earth. The reinforcement protects the pilings from
elements which tend to cause the pilings to deteriorate.
[0051] Having thus described the present invention and its
preferred embodiments in detail, it will be readily apparent to
those skilled in the art that further modifications to the
invention may be made without departing from the spirit and scope
of the invention as presently claimed.
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