Note: Descriptions are shown in the official language in which they were submitted.
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TITLE
FIBER REINFORCED COMPOSITE SHEATHING FOR STORM
PROTECTION
TECHNICAL FIELD
s The invention relates to the use of a high strength laminated
composite sheathing for the reinforcement of walls and doors to resist
penetration by wind-borne debris such as that generated by severe storm
events, particularly tornadoes.
BACKGROUND OF THE INVENTION
io Storm shelters and cellars are necessary to provide a safe haven for
protection against severe storm events in regions prone to tornado or
hurricane activity. These shelters have been typically constructed of poured
concrete, steel reinforced masonry, or heavy weight sheet metal. Details of
adequate designs for storm shelters and cellars are detailed in publications
is from the Federal Emergency Management Agency (FEMA) such as Taking
Shelter from the Storm - Publication 320 and Design and Construction
Guidance for Community Shelters - Publication 361. The current designs
rely on the use of common heavyweight construction materials such as
concrete and steel to provide the resistance to wind-borne debris generated
20 in the storm event.
The current designs are not easily incorporated into current building
practices, and result in significant weight increases in the wall structure.
The
wood framing approaches described in FEMA Publication 320 require the in-
filling of the wall section with solid masonry or continuous sheathing with 14
2s gauge steel plate. Doors for these shelters required the reinforcement with
a
minimum 14 gauge sheet metal to provide the needed penetration
resistance. These approaches are cumbersome, difficult to install and
difficult to field work to size. In regards to doors, the current solutions
result
in heavyweight doors that introduce safety issues and poor aesthetics.
3o A report dated May 31, 2000 by Clemson University submitted to the
Federal Emergency Management Agency entitled "Enhanced Protection for
Severe Wind Storms" describes several additional approaches for the
reinforcement of shelter walls against wind-borne debris. Concepts included
4 walls (numbers 9,10,11 & 17) that made use of Kevlar~ cloth. Figure 12 on
i
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page 36 shows that these flexible cloth concepts provided no more than
44% of the impact resistance required to meet the "National Performance
Criteria for Tornado Shelters". No concept proposed in this study provided
more than 60% of the requirements.
A substantial need exists for a method to reinforce walls and doors
with a lightweight field workable sheathing to provide the penetrative
resistance needed for protection from wind-borne debris such as that
generated in tornadoes and hurricanes. However wind speeds generated by
tornadoes can exceed 200 miles per hour which is greatly in excess of wind
io speeds generated by hurricanes. Therefore a particular need exists for the
lightweight field workable sheathing to withstand wind-borne debris
generated by the higher tornado wind speeds.
SUMMARY OF THE INVENTION
The present invention is directed to:
is a composite comprising:
(a) a first layer of a fabric containing high strength fibers bonded
with a resin wherein the first layer will deflect in a range from
5.0 to 17.5 centimeters employing a 33 kilogram (15 pound)
projectile at a speed of 161 kilometers (100 miles) per hour in
2o accordance with ASTM test procedure E1886-97 mounted on
one layer of 3/4 inch ply wood with #10d nails on a frame in
accordance with FEMA Publication 320, Revision 1 specific to
Drawings AG-5 and 14, and
(b) a second layer of structural sheathing.
2s The material is particularly adapted for construction of storm shelters
and residences located in areas of the world which are subjected to wind-
blown debris not only by hurricanes but also from the substantially higher
wind speeds of tornadoes.
DETAILED DESCRIPTION OF THE INVENTION
3o In formation of a material of construction for protection against wind-
blown debris such as generated by tornadoes with wind speeds in excess of
200 miles per hour a necessary starting material is a fabric containing high
strength fiber. The fabric may be a woven or non-woven although a woven
fabric is preferred. High strength fibers are well known and as employed
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herein means fibers having a tenacity of at least 10 grams per dtex and a
tensile modulus of at least 150 grams per dtex. Yarns can be made from
fibers such as aramids, polyolefins, polybenzoxazole, polybenzothiazole,
glass and the like, and may be made from mixtures of such yarns.
The fabric may include up to 100 percent aramid fiber. By "aramid" is
meant a polyamide wherein at least 85% of the amide (-CO-NH-) linkages
are attached directly to two aromatic rings. Examples of aramid fibers are
described in Man-Made Fibers -Science and Technologyl Volume 2, Section
titled Fiber-Forming Aromatic Polyamides, page 297, W. Black et al.,
to Interscience Publishers, 1968. Aramid fibers are, also, disclosed in U.S.
Patents 4,172,938; 3,869,429; 3,819,587; 3,673,143; 3,354,127; and
3,094,511.
Para-aramids are common polymers in aramid yarn and poly(p-
phenylene terephthalamide) (PPD-T) is a common para-aramid. By PPD-T
is is meant the homopolymer resulting from mole-for-mole polymerization of p
phenylene diamine and terephthaloyl chloride and, also, copolymers
resulting from incorporation of small amounts of other diamines with the p-
phenylene diamine and of small amounts of other diacid chlorides with the
terephthaloyl chloride. As a general rule, other diamines and other diacid
2o chlorides can be used in amounts up to as much as about 10 mole percent
of the p-phenylene diamine or the terephthaloyl chloride, or perhaps slightly
higher, provided only that the other diamines and diacid chlorides have no
reactive groups which interfere with the polymerization reaction. PPD-T,
also, means copolymers resulting from incorporation of other aromatic
2s diamines and other aromatic diacid chlorides such as, for example, 2,6-
naphthaloylchloride or chloro- or dichloroterephthaloyl chloride or 3,4 -
diaminodiphenylether.
By "polyolefin" is meant polyethylene or polypropylene. By
polyethylene is meant a predominantly linear polyethylene material of
3o preferably more than one million molecular weight that may contain minor
amounts of chain branching or co-monomers not exceeding 5 modifying
units per 100 main chain carbon atoms, and that may also contain admixed
therewith not more than about 50 weight percent of one or more polymeric
additives such as alkene-1-polymers,in particular low density polyethylene,
3s propylene, and the like, or low molecular weight additives such as anti-
oxidants, lubricants, ultra-violet screening agents, colorants and the like
which are commonly incorporated. Such is commonly known as extended
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chain polyethylene (ECPE). Similarly, polypropylene is a predominantly
linear polypropylene material of preferably more than one million molecular
weight. High molecular weight linear polyolefin fibers are commercially
available.
Polybenzoxazole and polybenzothiazole are preferably made up of
polymers of the following structures:
' ~O
V
/
C1
/
. ~ O-r
'i
While the aromatic group shown joined to the nitrogen atoms may be
heterocyclic, they are preferably carbocyclic; and while they may be fused or
1o unfused polycyclic systems, they are preferably single six-membered rings.
While the group shown in the main chain of the bis-azoles is the preferred
para-phenylene group, that group may be replaced by any divalent organic
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group which does not interfere with preparation of the polymer, or no group
at all. For example, that group may be aliphatic up to twelve carbon atoms,
tolylene, biphenylen, bis-phenylene either, and the like.
A further requirement in the present invention is the use of a resin to
bind individual fibers of the high strength fibers in the employed fabric. The
resin may be selected from a wide variety of components such as
polyethylene, ionomers, polypropylene, nylon, polyester, vinyl ester, epoxy
and phenolics and thermoplastic elastomers.
The resin may be applied to the fabric containing high strength fibers
io by coating or impregnation, such as under pressure.
However criticality exists in the present invention in the combination of
fabric with high strength fibers / resin combination. It has been discovered
that this combination must have the ability to deflect within certain
parameters when securely fastened to a support material.
is Accordingly the high strength fabric / resin combination must have an
ability for deflection when tested in accordance with National Performance
Criteria for Tornado Shelters, First Addition, FEMA, May 28, 1999 using
ASTM Test Method E1886-97, entitled "Standard Test Method for .
Performance of Exterior Window, Certain Walls, Doors and Storm Shutters
2o Impacted by Missiles) and Exposed to Cyclic Pressure Differentials."
Highlights of the test include mounting the test specimen, i.e., in present
case the combination of fabric with high strength fibers / resin, impacting
the
specimen with a 33 kilogram (15 pound) 2 x 4 missile propelled at a speed of
161 kilometers (100 miles) per hour and observing and measuring the test
2s results. The ASTM test procedure E1886-97 is specific to the various
requirements such as the use of 2 x 4 lumber missile, missile propulsion
device, speed measuring system and use of a high speed video or
photographic camera. It is understood, herein, that the test procedure for
purposes of the present disclosure involves attaching any test specimen,
3o i.e., the high strength fabric / resin combination, with one layer of 3/4-
inch
plywood using #10d common nails spaced per the nailing schedule
described in FEMA Publication 320, Revision 1, specific to Drawings AG-5
and 14, to a wall frame built in accordance with same publication, with
plywood as outermost layer from said frame. Such wall system is then
3s impacted on the plywood face at the center of one of the two middle bays.
The 2 x 4 lumber missile should be marked with suitable indexing marks to
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allow the tracking of the depth of penetration of the projectile. The
photographic or video camera should be positioned to monitor the depth of
penetration of the projectile and such camera should have a minimum frame
rate of 1000 frames per second.
In accordance with the described test procedure" the combination of
the fabric containing high strength fibers bonded with a resin will deflect
within a range from 5.0 to 17.5 cm. More preferably the deflection will be in
a range from 8.0 to 16.0 cm and most preferably 10.0 to 15.0 cm. The
degree of deflection may be determined by its final use in a building
to structure. Illustratively a maximum stated deflection of the fabric / resin
combination may be undesirable in a residence due to the proximity of an
occupant adjacent a wall containing the cloth / resin combination. However,
a minimum deflection within the above range can require an added thickness
of the fabric resulting in a high cost of construction. As employed herein,
is fabric is inclusive of more than one layer of a cloth. As employed herein
deflection means the maximum measured distance of separation of the high
strength fabric / resin combination from the structural sheathing. It is
understood that the measurement must be undertaken in conjunction with
high speed photography. For purposes of illustration for deflection
2o measurement, if during the test procedure with the projectile, there may be
some bowing of the structural sheathing. The measurement for deflection is
the distance, i.e., the separation, of the high strength fabric / resin
combination from the bowed portion of the sheathing. It can be determined
from review of the photographic or video record collected during previously
2s described testing, determining the maximum depth of penetration during the
event, and subtracting the thickness of the structural sheathing.
The use of a fabric containing high strength fibers, i.e, Kevlar~ aramid
in combination with plywood has been previously tested in the Clemson
3o University report referenced in the Background of the Invention. However in
accordance with the test procedure of this report, complete penetration of
the Kevlar~ aramid / plywood took place with a nine pound projectile at a
speed of 73 miles per hour.
In the present invention the combination of the fabric containing the
3s high strength fibers / resin is for employment with a wood based or other
structural sheathing material, since an additional purpose of the combination
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is the structural reinforcement of a wall or door. The term "structural
sheathing" is inclusive of any material which provides structural building
support. The preferred material is wood, particularly plywood, due to
extensive use in the building industry. However other materials are known
for structural sheathing serving as building support: a typical example is
fiberboard reinforced with cement. The fabric / resin combination is
generally flexible and will be employed with the sheathing which for
purposes of illustration may be at least 0.65 cm (one quarter inch) and
preferably for purposes of support, at least 1.27 cm (one half inch). The type
io of structural sheathing is not critical to the success of the present
invention.
The sheathing may be solid such as from hard or soft woods or may be in
the form of a composite such as plywood or a non-wood sheathing such as
cementous fiberboard. As a practical matter, solely from a question of cost,
it is believed that most uses of the present invention will be with plywood
~s since it is a common material used in wall structures. There is no maximum
thickness to the structural sheathing which in a building structure will be or
face an outer wall with the combination of fabric / resin facing the inner
portion of the building, i.e., for example a room where inhabitants are to be
protected.
2o Therefore in construction of a protective shelter or one or more rooms
in a residence it is intended that the structural sheathing face the direction
of
any wind-borne debris such that the debris strikes the wood with penetration
before contact and containment with deflection of the combination of cloth /
resin. It is understood that the invention is particularly advantageous since
2s conventional building construction and techniques with structural sheathing
may be employed.
It is noted that use of an aramid fiber / wood combination has been
disclosed in German DE 195 12582 as claddings of walls, ceilings and floors
in indoor firing ranges. However, the requirements of a firing range with a
3o high speed / low weight projectile are entirely different than the
requirements
of the present invention with wall deflection and with an ability to stop
penetration of wind-borne debris due to wind speed of over 200 miles per
hour.
To further illustrate the present invention, the following examples are
3s provided.
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EXAMPLES
Example 1
A 3-foot wide by 4-foot long fiber reinforced composite sheathing
panel was prepared by stacking 3 layers of a 13.5 oz. / square yard, plain
s weave fabric made from aramid fiber, between 2 layers of 0.0045 thick film
made from an ionomeric polyethylene resin. The stack of fabric and resin
was placed in a heated hydraulic press that had been pre-heated to
300°F.
A pressure of 160 psi was applied to the stack of material for 1 hour to melt
the outer layers of polymer and infuse it into the layers of fabric that were
in
io between. The press was then cooled below 150°F and the pressure
released.
The resulting sheathing was nailed to a wooden frame made from 2x4
framing timber as prescribed in FEMA Publication 320. #10 power driven
nails were used to fasten the composite sheathing to the wooden frame, with
is a single layer of 3/4" plywood covering the sheathing on the face to be
impacted.
The wall panel was mounted on a rigid test frame with the 3-foot
dimension on each side of the wall panel fully supported. The sample was
impacted with a 15-Ib 2x4 timber projectile traveling at 100 mph, to access
2o ability to meet the "Windborne Missile Impact Resistance on Shelter Wall
and Ceiling" provisions of the National Performance Criteria for Tornado
Shelters, First Addition, FEMA, May 28, 1999. Cannon set-up and firing was
done in accordance with ASTM E 1886 -97.
The wall segment stopped the projectile from passing through it as
2s required by the FEMA provisions, and the projectile was rebounded back.
High speed photography taken during the event showed the projectile to
penetrate approximately 15.2 cm into the wall cavity before being
rebounded back. Deflection of the composite sheathing was calculated to
be 13.4 cm. The plywood layer on the outside of the wall showed damage
30 only locally around the point of projectile entry.
Example 2
A 3-foot wide by 4-foot long fiber reinforced composite sheathing
panel was prepared by stacking 7 layers of a 10 oz. / square yard, plain
weave fabric made from S-2 glass fiber, with 4 layers of 0.0045 thick film
3s made from an ionomeric polyethylene resin. The stack of fabric and resin
s
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was placed in a heated hydraulic press that had been pre-heated to
300°F.
A pressure of 160 psi was applied to the stack of material for 1 hour to melt
the layers of polymer and infuse it into the layers of fabric that were in
between. The press was then cooled below 150°F and the pressure
s released.
The resulting sheathing was nailed to a wooden frame made from 2x4
framing timber as prescribed in FEMA Publication 320. #10 power driven
nails were used to fasten the composite sheathing to the wooden frame, with
a single layer of 3/4" plywood covering the sheathing on the face to be
io impacted.
The wall panel was mounted on a rigid test frame with the 3-foot
dimension on each side of the wall panel fully supported. The sample was
impacted with a 15-Ib 2x4 timber projectile traveling at 100 mph, to access
ability to meet the "Windborne Missile Impact Resistance on Shelter Wall
is and Ceiling" provisions of the National Performance Criteria for Tornado
Shelters, First Addition, FEMA, May 28, 1999. Cannon set-up and firing was
done in accordance with ASTM E 1886 -97.
The wall segment stopped the projectile from passing through it as
required by the FEMA provisions, and the projectile was rebounded back.
2o High speed photography taken during the event showed the projectile to
penetrate approximately 11.4 cm into the wall cavity before being rebounded
back. Deflection of the composite sheathing was calculated to be 9.6 cm.
The plywood layer on the outside of the wall showed damage only locally
around the point of projectile entry.
2s Example 3 - Dry Fabric Control
A 3-foot wide by 4-foot long dry fabric sheathing material was
prepared by sewing 3 layers of a 13.5 oz. / square yard, plain weave fabric
made from aramid fiber around the edges.
The resulting fabric pack was nailed to a wooden frame made from
30 2x4 framing timber as prescribed in FEMA Publication 320. #10 power
driven nails were used to fasten the fabric sheathing to the wooden frame,
with a single layer of 3/4" plywood covering the sheathing on the face to be
impacted.
The wall panel was mounted on a rigid test frame with the 3-foot
3s dimension on each side of the wall panel fully supported. The sample was
9
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impacted with a 15-Ib 2x4 timber projectile traveling at 100 mph, to access
ability to meet the "Windborne Missile Impact Resistance on Shelter Wall
and Ceiling" provisions of the National Performance Criteria for Tornado
Shelters, First Addition, FEMA, May 28, 1999. Cannon set-up and firing was
s done in accordance with ASTM E 1886 -97.
The wall segment stopped the projectile from passing through it as
required by the FEMA provisions, and the projectile was rebounded back.
High speed photography taken during the event showed the projectile to
penetrate approximately 17.8 cm into the wall cavity before being rebounded
io back. Deflection of the fabric sheathing was calculated to be 16 cm, which
was 2.6 cm more than that noted in example 1 with the resin present. The
plywood layer on the outside of the wall also showed significant cracking
beyond the point of impact. There was as well, significant pull-out of the
fabric around the fasteners.
~s Example 4 - Control
A 4-foot wide by 8-foot long fiber reinforced composite sheathing
panel was purchased from the Sioux Manufacturing Company that had been
produced from 3 layers of 13.5 oz / square yard plain weave aramid fabric
coated with phenolic resin and molded as described in the MIL-L-6247A
2o specification for ballistic armor.
The resulting sheathing was nailed to a wooden frame made from 2 x
4 framing timber as prescribed in FEMA Publication 320. #10 power driven
nails were used to fasten the composite sheathing to the wooden frame, with
2 layers of 3/4" plywood covering the sheathing on the face to be impacted.
2s The wall panel was mounted on a rigid test frame with the 4-foot
dimension the wall panel supported. The sample was impacted with a 15 Ib.
2 x 4 timber projectile traveling at 100 mph, to assess ability to meet the
"Wind-borne Missile Impact Resistance on Shelter Wall and Ceiling"
provisions of the National Performance Criteria for Tornado Shelters, First
3o Addition, FEMA, May 28, 1999. Cannon set-up and firing was done in
accordance with ASTM E1886-97.
The Wall did not stop projectile from passing through it as required by
the FEMA provisions and the 2 x 4 imbedded itself into the wall.
io
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Example 5
A 3-foot wide by 4-foot long fiber reinforced composite sheathing
panel was prepared by stacking 3 layers of a phenolic prepreg produced
from 13.5 oz. / square yard, plain weave fabric made from aramid fiber in
s accordance with Mil Spec MIL-L-62474. The stack of prepreg was placed in
a heated hydraulic press that had been pre-heated to 330°F. A pressure
of
160 psi was applied (versus 200 psi as required by MIL-L-62474) to the
stack of material for 30 minutes to cure the resin. The press was then
cooled below 150°F and the pressure released. The resulting material
was
io more flexible than the commercially acquired laminate pressed in
accordance with the Military Specification.
The resulting sheathing was nailed to a wooden frame made from 2x4
framing timber as prescribed in FEMA Publication 320. #10 power driven
nails were used to fasten the composite sheathing to the wooden frame, with
is a single layer of 3/4" plywood covering the sheathing on the face to be
impacted.
The wall panel was mounted on a rigid test frame with the 3-foot
dimension on each side of the wall panel fully supported. The sample was
impacted with a 15-Ib 2x4 timber projectile traveling at 100 mph, to access
2o ability to meet the "Windborne Missile Impact Resistance on Shelter Wall
and Ceiling" provisions of the National Performance Criteria for Tornado
Shelters, First Addition, FEMA, May 28, 1999. Cannon set-up and firing was
done in accordance with ASTM E 1886 -97.
The wall segment stopped the projectile from passing through it as
2s required by the FEMA provisions, and the projectile was rebounded back.
High speed photography taken during the event showed the projectile to
penetrate approximately 10.2 cm into the wall cavity before being rebounded
back. Deflection of the composite sheathing was calculated to be 8.4 cm.
The plywood layer on the outside of the wall showed damage only locally
3o around the point of projectile entry.
m
