Note: Descriptions are shown in the official language in which they were submitted.
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5APPARATUS AND METHOD FOR SECURING AN
OBJECT AGAINST GALE-FORCE WINDS
Field of Invention
The present invention relates to an appa,dlus and a method for
securing objects, particularly, mobile trailer and motor homes against gale-force
winds, and more particularly to a cont~inm~nt and protective a~aldl~ls and
method for securing such objects to the ground and protecting and co~ inil-g
them in gale-force winds.
Back~round of the Invention
Objects such as aircraft, small sail and motor boats, vehicles and
particularly, trailer and motor homes, due to their light constNction, large surface
area and relative low mass, are highly susceptible to damage and destruction from
gale-force winds. Notably, gale-force winds have commonly been known to
overturn such objects, or worse yet, lift and/or blow them a distance, resultingin severe damage and sometimes complete destruction of the object.
Aircraft are typically anchored to the ground by lines, straps,
chains and the like to specific parts associated with the wheels or StNtS of theaircraft.
Objects such as small watercraft, power and sail boats, typically,
rest on cradles or blocks formed of wood or steel when stored on land or are
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merely restrained by lines secured to and adjacent dockside or buoy when afloat.No other le~ ing means to prevent the boat from being hurled inland in the
event of gale-force winds are employed.
Ruil~lings, including residential homes and commercial and retail
properties which typically rest on the ground by means of concrete footings and
the like are often damaged by gale-force winds. In particular, roofs of buildings
may be blown away. Further, the above objects are often damaged by flying
debris created by the gale-force winds. Yet further, glasshouses for example,
commercial greenhouses, are very susceptible to damage from windborne debris.
Vehicles are also often flung into the air and damaged by such
winds.
Although netting has been used to embrace objects such as vehicles
and aircraft, particularly as a means of carrying camouflage m~tPri~l, such netting
has not been provided over the object as a secure ret~ining means sufficient to
with~t~n~ gale-force winds.
Numerous prior art appa,dt~ls exist for securing mobile or trailer
homes to the ground in the event of hurricane, flood, or gale-force winds. The
majority of these prior art apparatus use a combination or anchor means, elongate
strap members and tightening turnbuckles, whereby such strap members are
placed over and encircle a mobile home and are affixed to anchor means via
turnbuckles to anchor the mobile home to the ground.
U.S. Patents #4,148,162, #4,070,802, #3,051,151, #3,335,531,
#3,644,192, #3,747,288, #3,848,367 and #3,937,437 are all examples of such
al)pa-~dlus which secure a mobile home to the ground via elongate strap members
placed over and encircling the mobile home.
For e~mple, USP #3,054,151 and #4,070,802 each disclose
"elongate metallic web-like hold-down straps 12 and 14" (U.S. Patent '802) or
hing~ 15H which bridge the roof of the mobile home and are secured at their
ends to anchors.
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Indeed, in some states within the United States of America where
the incidence of hurricanes is high, such as in the State of Florida, State
legicl~tion requires that mobile homes be anchored to the ground in a stipulatedmanner requiring utili7~tion of one of more of the above prior art appaldlus andmethods for securing mobile homes to the ground.
The above prior art a~paldtus, however, are often un~uccessful in
preventing damage to mobile homes and small boats due to gale-force winds,
since they completely fail to protect these objects from another source of damage,
namely, damage due to impact with airborne debris, such as uprooted trees,
bricks, flotsam, and the like which may impact the object at high velocity during
a hurricane. For example, despite the utili_ation of such prior art a~dldlus, such
prior art appald~us ~was unable to prevent the extensive damage and destruction
to mobile homes occurred with the State of FloAda due to HurAcane Andrew in
August of 1992. DuAng this hurri~n~, trailer homes despite being secured to the
ground by pAor art appaldtus suffered mass destruction due to being impacted by
airborne projectiles such as trees, bAcks, debAs, the like, which so damaged
trailer homes that the elongate strap members were completely ineffective in
preventing con~in"~nt of the damaged trailer home. This often and, generally
without exception, resulted in the damaged trailer home and its contenls being
completely blown away.
Accordingly, pAor art appalalus do nothing to shield a mobile
home from bombardment by airborne debAs which frequently impacts a trailer
home with such force so as to cause the break-up and disintegldtion of the mobile
home. This is extremely undesirable, not only because of the destruction of the
subject mobile home, but also because the resl-ltAnt debAs from the destroyed
mobile home, including the mobile home's conlellts such as TV's, appliances, andthe like, further add to the airborne debAs circul~ting in a hl-rri.~ne and in turn
become airborne and impact and bombard other mobile homes, causing further
resultant damage and destruction. Accordingly, the elongate strap members
utilized with the appa dlus of the aforementioned patents not only do nothing to
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shield a trailer home from airborne bol,lbardlllent, but they further do nothing to
contain debris from damaged trailer homes and their conte~ from becoming
airborne in a hun~c~n~ and causing further damage and destruction, both to
human life and other propelly.
S Use of canvas or nylon tarps or tarpaulins to protect prol~elly from
wind and rain is also generally known. However, use of canvas tarps or
tarpaulins, for purpose of pr~tecling mobile homes from damage from airborne
debris in a hurricane, even if employed in the novel and inventive manner
disclosed herein, would highly be un~l-it~hle and indeed unworkable. In
particular, to resist large volumes of wind, any canvas or nylon tarpaulins needto be of such thickness that their weight makes them extremely difficult to workwith in placing over a trailer home, not to mention the increased expense in thenumber and size of ground anchor means ne~es~ry to retain the tarpaulin in high
winds. In addition, once becoming rain-soaked, tarpaulins tend to sag, thereby
trapping water and placing additional weight on the trailer, which if such waterwere allowed to accumulate, may result in structural damage to the trailer home.Accordingly, there exists a real need for a novel a~al~lus and
method to shield and anchor plo~lly such as aircraft, boats, buildings and
particularly, mobile homes from destruction in gale-force winds. In addition,
there exists a further real need to contain res--lt~nt debris from any of such
plopelly which may be destroyed due to impact from airborne debris to prevent
such debris from itself becoming airborne and causing further destruction.
Summary of the Invention
In order to overcome the disadvantages with the prior art, the
present invention discloses a means/apparalus for simultaneously shiel~lin~
anchoring, and containing objects such as aircraft, boats, b~ 1ing~, vehicles and
trailer homes in the event of gale-force winds.
Advantageously, the appal~lus of the present invention uses wind-
permeable pelrol~le sheets means, which in the plerelled embodiment consists of
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flexible webbed netting, which may be placed in a prescribed manner over or
around an object which is sought to be protected against impending gale-force
winds or a h~irri~ne. The flexible netting extends outwardly and downwardly at
an acute angle from an upper part, preferably the top of the object and is affixed
S to ground anchors inte~ ed around the periphery of the object, to thereby
anchor the net in place.
In such manner, the object is contained within an enclosure, and
each of the sides of the object are surrounded by an inclined sloped surface of the
net.
Advantageously, by providing an inclined, subst~nti~lly planar,
sloped surface around the sides of the object? the object may thereby be pr~ ;led
from impact and bombardment by airborne debris during a hurricane, thereby
preventing structural damage to the object. The inclined sloped surfaces of the
net means allow passage of wind therethrough, but prohibit passage of windborne
lS debris such as bricks, stones, such as B3 gravel, trees, flotsam, wood spars and
the like, which would otherwise impact and destroy or at least seriously damage,by penetration thereof or otherwise, the object. The ~lrola~e sheet means or netis of s-lfflci~nt strength to resist impact with such projectiles, but further assists
in preventing airborne debris from impacting the sides of the object by its sloped
configuration, which assists in deflecting such airborne matter over the top of the
object and away from the sides.
Accordingly, in its broadest aspect, the a~a.~lus of the present
invention comprises the combination of:
(i) an oversize wind-permeable perforate sheet means of a surface area
substantially greater than the combined surface area of the top and
sides of an object over which it is adapted to be placed, wherein
such sheet means is extendable downwardly and oulwa~dly from
the top at an acute angle to the sides of the object;
(ii) a plurality of ground anchor means adapted for pl~.e.m~.nt in the
ground surrounding said object; and
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(iii) ~tt~ hm~nt means, ~tt~rh~hle to the periphery of the pelrol~le sheet
means, to allow the pelrol~te sheet means to be secured to the
ground anchor means.
In a further aspect of the present invention, there is ~ie~losed a
method of simultaneously shiel~ling, anchoring, and co~ ining an object in the
event of gale-force winds. Such method comprises the steps of:
(i) casting an oversize, substantially wind-permeable flexible net
means over said object so as to substantially cover the top of the
object; and
(ii) attaching the wind-permeable net means proximate an outer
peripheral edge thereof to ground anchor means, so that the net
extends downwardly and outwardly from the top at an acute angle
to each of the sides of the object, so as to surround at least a
substantial portion of each of the sides with an inclined, wind-
permeable surface.
In a p~efelled embodiment, the ap~al~tus of the present invention
further comprises the combination of:
(i) an oversize wind-permeable perforate sheet means of a surface area
subst~nti~lly greater than the combined surface area of a roof and
outer side walls of a trailer home over which it is adapted to be
placed, wherein such sheet means is extendable downwardly and
oulwal~ly from the roof at an acute angle a to the outer side of the
walls of the mobile home;
(ii) a plurality of ground anchor means adapted for placement in the
ground surrounding said home; and
(iii) att~hmPnt means, ~tt~-h~hle to the periphery of the pelrol~te sheet
means, to allow the pelro~dte sheet means to be secured to the ground
anchor means.
In a further plefelled embodiment of the present invention, there
is disclosed a method of simultaneously shielding, anchoring, and conlahlillg a
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trailer home or motor home in the event of gale-force winds. Such method
comprises the steps of:
(i) casting an oversiæ, subst~nti~lly wind-permeable flexible net
means over a mobile home so as to subst~nti~lly cover the roof of
the home; and
(ii) ~t~ching the wind-permeable net means proximate an outer
peripheral edge thereof to ground anchor means, so that the net
means extends dowllwa~dly and oulwar~dly from the roof at an
acute angle ~ to each of outer side walls of the trailer home, so as
to surround at least a substantial portion of each of the outer side
walls with an inclined, wind-permeable surface.
Surprisingly, I have found that by providing a net formed of a
resili~ntly flexible m~t~ri~l, such as a flexible thermoplastics m~teri~l, sufficiently
taut around the object as to give the net one or more flat stationary planes, acutely
angled to the object, that windborne debris can be ~ ined and deflected from
the object to prevent damage thereto. I have found that when such debris hits the
net with app~cciable force, the net is te,l.pol~ily deformed at an area of at least
one of these flat, stationary planes under the impact of the flying debris. The
resilient net m~teri~l absorbs the energy of impact and surprisingly, this energy
is distributed throughout the net ~ nt the impact site and transferred to the
restraining anchor means. The extent of this impact energy distribution throughout
the net to the anchors allows of the unexpectedly high degree of efficacy of thenet in lc~ ining and deflecting the debris.
Thus, the invention provides a combination and method as
hereinabove defined wherein a side or face of the net is so formed as to be
deformable from its stationary plane and so biased as to deflect or restrain
windborne flying debris by absorbing impact energy by distribution thereof
through said m~teri~l.
The net is, thus, so formed and taut as to constitute re~ ontly
flexible deflection means to deflect and restrain flying debris.
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While it is desirable to have the net fully covering the object to be
protected, for example, in the case of a building, trailer or mobile home, the roof
and sides, the invention is applicable to those situations where only one or more
sides need to be protected. One edge of the sheet may be attached to only one
side of a structure to protect a window or the like, with the opposite edge being
secured to the adjacent ground or surface at a ~ t~nce from the base of the
structure. Also within the scope of the present invention are those embc~iment~
wherein the net is spaced away from, but a(ljac~nt an upper part of the object,
structure and the like, to be protecled. The net may be directly or indirectly
~upl)o~led on or by a frame so spaced away from the object but to be effective in
providing the desired proleclion from windborne debris. Such arrangements in
this specification and claims are embraced by the terms "adapted for pl~cem~nt
around said object" and "adapted for placement over the roof" and the like.
Thus, the system of the invention in one aspect has the net fully
covering the top of the object, for example the roof of a trailer home. This
provides a means of ~ inillg and conlaining the home and any contents
contained therein should the sides of the home be penetrated to allow air ples~.lr~
build up within the home. In an alternative embo~im~-nt, the home may be
contained and restrained by the system notwithstanding the net does not fully
cover the top or roof of the home.
The subst~nti~lly wind-permeable, flexible netting extends
outwardly and downwardly at an acute angle from an upper part to provide a
stationary substantially planar inclined sloped surface around the sides of the
object and is of sufficient strength and resilience so as to effect distribution of the
energy of impact between windborne debris and the netting throughout the nettingand, optimally, as far as the anchor means. Such efficacious distribution of theimpact energy reduces the likelihood of a breakthrough of the net to allow
airborne debris to pass therethrough.
P,cfe"ed flexible m~teri~l~ are resiliently flexible thermoplastics
such as the polyolefines, polyesters and polyamides. Preferred polyolefines are
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polymers and copolymers of ethylene and propylene with for example other
olefines and vinyl acetate. Most prert,led polyethylenes have oriented molecularstructures. A p,efe.led polyamide m~teri~l is Nylon 6,6 copolymer of 1,6-
diaminohexene and adipic acid.
I have found that one of the benefits of the pro~;li-~e net system
of the invention is a reduction in wind p,~s~.l,e on the windward surface of theobject protected by the net, due to reduced passage of wind through the net.
I have found that when prefe,~d nets of use in the invention were
tested to failure by the impact on the net of either a heavy test weight in a drop
test or by a projectile fired from an air cannon to effect breakthrough, that the
res.llting hole caused by the impact was so localized that the efficacy of the net
in continuing to provide a plo~li~e membrane around an object was subst~nti~lly
not affected. A protective system capable of such continued efficacy is most
valuable. This should be contrasted with systems formed of non-resili-ontly
flexible m~teri~ls such as lel-lpel~d and heat strengthened glass, wood, such asplywood, chipboard and the like, aluminum sheeting and steel wire, which are
most likely to break, shatter or collapse under co,npandble impact energies.
The mech~nic~l char~cteri~tics of the net of use in the practice of
the invention, such as mesh size, fabric denier and fabric and net construction
may be readily and suitably determined from the physical characteristics of the
flexible material in view of the desired efficacy.
The net of a typical 4m x 4m ~imen~ion, preferably, should be able
to withstand an impact energy of at least 400 Joules, more preferably more than
500 Joules and most preferably at least 800 Joules.
The net may optionally be formed, for example, of an extruded,
woven or non-woven, knotted, knotless, knitted, crocheted or braided web.
Preferred configurations are those known as a raschel crocheted knit or as a
loc1~titch configuration.
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A woven i.e. interlocked perpendicular threads configuration is less
prer~lled in the practice of the invention. Intersections can easily slip to allow
relatively large holes to be formed without actual breakage of any fibres.
In extruded netting, net e4m~nt~ are solid strands of m~t~.ri~l,
instead of assemblages of fibres having solid inler~;lions. Extruded netting canbe very cheap, but strength is low due to the lack of the ~lignment of moleculesand stiffnt.ss may be quite high.
Knotted netting is generally formed with pre-assembled cord.
However, small mesh sizes are generally impractical to manufacture, and strengthis lost in the knots. Thus, use of such a configuration requires a heavier net with
reduced ability to stop small debris.
Braided netting, where yarns cross each other in a regular pattern,
allows for high strength and a high degree of stretch. Intersections can be
knotless (e.g. Ultra Cross 0 configuration), giving no reduction in strength.
Intersections allow some limited slip, which may allow failure to a limited degree
to propagate from one ~1.omPnt to another.
One edge of net arrangement of use in the invention consists of
reinforcement with either 5 cm wide nylon, polyester or polypropylene webbing
folded over the edge of the net and stitch~ on, typically with two rows of
stitc,hes, to leave a 2.54 cm strip of webbing along the edge. The net may itself
be reinforced at the edge by increasing the amount of m~t~.ri~l used in the raschel
knit. This is a straightforward procedure with raschel m~.hin~.s, Rings are
attached to the edging using 2.54 cm webbing, and straps are used to attach these
rings to a peripheral cable, which is in turn ?~tt~h~cl to ground anchors.
The size of the mesh of the net not only influences the range of
projectile sizes which the net will stop, but also is a factor in the capability to
absorb the energy of an impact. Smaller mesh sizes allow objects to strike more
net elements, which better dissipates the impact energy. In order to withstand agiven impact, a net with larger mesh size has to weigh more than a net with
smaller mesh size.
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Further objects and advantages of this invention will appear from
the following detailed description of the invention.
Brief Descliption of the DrawinPs
5In order that the invention may be better understood, plef~lled
emb~liments will now be described by way of example only with reference to the
acco.npanying drawings, wherein:
Fig. 1 is a perspective view of the a~)paratus of the present
invention, in its intended-use position to shield, anchor, and contain a trailer home
10in gale-force winds;
Fig. 2 is a plan view of the appal~lus of the present invention, in
the direction of arrow "A" in Fig. l;
Fig. 3 is a section view of the appa-~tus of the present invention,
taken along plane B-B of Fig. 2;
15Fig. 4 is an enlarged cross-sectional view of the attachment means
and anchor means of the present invention shown in Fig. 3;
Fig. 5 is a view of an arrow 'c' of Fig. 4;
Fig. 6 is a pel~ re view of another embodiment of the
appa,~lus of the present invention, in its intended-use position to shield, anchor,
20and contain a trailer home in gale-force winds; and
Fig. 7 is an enlarged view on the area de~ign~ted as 'F' in Figs.
1 and 6 showing coupling means for joining sections of pelro~te sheet together.
Detailed Descli~ion of the Invention
25Figs. 1 and 6 show a perspective view of two different
embo~im~nt~ of the ap~a~atus 10 and method of the present invention for securin~trailer homes and motor homes 12 (hereinafter mobile homes) against gale-force
winds.
An oversized, substantially wind-permeable pelrolale sheet means
3014, capable of being cast or placed over the roof 16 of a mobile home 12, -is
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conleml)lated as an essen~i~l component of the app~dlus 10 of the present
invention. In the prert;ll~d embodiment, the pelroldle sheet means 14 is a
flexible woven net, preferable formed of a water-resistant braided polyethylene.The surface area of the sheet means or net 14 of the present
invention is greater than the combined surface area of the roof 16 and side walls
18 of the trailer home 12. This excess size is ill~ t, since a n~es~ry
requirement of the invention is that net 14 when placed over the roof 16 of the
mobile home be adapted to extend downw~rdly and also oulw~dly from the roof
16 at an acute angle a to the outer side walls 18 of the mobile home so as to
create a protective inclined sloped surface 25 around each outer wall 18, as shown
in Fig. 1, 2 and particularly Fig. 3.
In a plefe~led emboliment net 14 extends downwardly and
outwardly so that the outer pe~ipht;l~l edge 20 thereof extends to at least the level
of the lowermost portion 22 (floor) of the mobile home 12, so as to provide a
protective inclined surface 25 proximate the entire surface of each outer wall 18
of the mobile home, as shown in Fig. 3.
Attachment means 24 are further provided, as shown in Fig. 1 and
in greater detail in Figs. 4 and 5, ~tt~t~h~hle to the pelroldte sheet means 14
proximate the outer peripheral edge 20 thereof. Such attachment means 24 allow
net 14 to be ~tt~hPd to ground anchor members 30 located in the earth
surrounding the mobile home 12 (see Figs. 4 and 5), to thereby m~int~in net 14
in the angular outwardly extending position as shown in Fig. 3 around all outer
sides 18 of mobile home 12. More particularly, it is desirous that the anchor
means 30 be int~ cd about the periphery of mobile home 12, as shown in
Figs. 1 and 2, and the ~im~nsinns of net 14 be such that net 14 is m~inhined at
an outwardly extending angle c~ from the outer walls 18, as shown in Fig. 3. In
a p~relled embodiment angle a so formed between the net and the outer side
walls is between 15-60 and preferably between 20-35. Angle ~ should be a
coll,promise between as high a value as possible to thereby afford as a "shock-
absorbing" distance between net 14 and outer walls 18 to allow net 14 to protect
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walls 18 from airborne debris, while at the same time being as low a value as
possible to thereby minimi7P. the size of the net means 14 required.
Since mobile homes are generally of sizes ranging from 30 ft. - 45
ft. in length (floor to roof), by 10 ft. in width, net 14 needs to be of a general
rectangular shape of at least 30' x 50' (1,500 sq. ft.) for the .sm~llest trailer home
size of 30' x 8' x 10', in order to have a protective in~`lin~ sloped surface 25extending outwardly and angularly downw~dly to protect subst~nti~lly all of the
outer side walls 18 of mobile home 12 to the level of the floor 22 of the trailer
home. Dimensions of this si7e will permit an angular slope o~ of net 14 of up toapproximately 30. Angle ~Y should be the greate~t value possible at which net
14 will extend with its peripheral edge 20 to a position level with the floor surface
22 of the mobile home, to thereby ensure walls 18 are entirely pro~led from
horizontally-moving airborne debris.
Mobile home sizes greater than 30' x 8' x 10' require nets 14 of
dimPn~ions larger than 1,500 sq.ft. if an angle ~ is to be m~int~ined and if
peripheral edge 20 of net 14 is to extend to a level of floor 22 to thereby protect
- all of the surface area of the outer walls 18 from impact damage due to airborne
debris.
Notable, in order that net 14 when placed over the mobile home be
adapted to extend evenly and uniformly downwardly and outwardly with a
minimum of bunching and folding in a plerelled embodiment the pelroldte sheet
means is comprised of two or more irregular shaped ~lr~ldte sheets or nets 14'
joinable along various seems 40, as shown for example in Figs. 1, 2 and 7.
Accordingly, when a pelrolate sheet means 14 assembled in the prece~lin~ manner
is placed over mobile home 12 and attached to the anchor means 30, a wrinkle
and bunch-free sloped surface 25 is thereby formed proximate each of outer walls18 of mobile home 12, as shown in Figs. 1, 2 and 6.
To accomplish the joining of each of the various perforate sheets
14' which comprise entire net 14 releasable coupling means 42 may be utilized
to join the pe,roldle sheets along a seam 40 thereof, as shown in Fig. 7. These
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coupling means 42 may be of any type commonly known in the art, but in a
pl~relred embodiment are a steel 'D'-shaped snap-ring.
Advantageously, releasable coupling means 42 along one or more
seams 40 allows entry by a person in and out of the mobile home 12 when the
appal~lus 10 of the present invention is assembled about the mobile home.
Notable, the force exerted by gale-force winds of up to 150-160
miles per hour, as was recently experienced in H--rrir~ne Andrew which struck
the eastern seaboard of the State of Florida and some of the other states
surrounding the Gulf of Mexico, including Louici~n~ in August 1992, can be
quite ~ignific~nt.
Utilizing the formulas:
P = C x v2 and
F = PxA
where: P is p~s~ul~ in lbs. force exerted on an area,
C is a constant of 0.0027 x lb hr2
ft2mi2
(~sllming air at a specified density at standard te.l-pel~lure and pressure)
V is velocity in miles per hour, and
A is the surface area,
the maximum force exerted by a wind of a given velocity against a
perpendicularly-disposed outer wall 18 of a trailer home of a given area A can
easily be calculated.
From Table 1, it can be seen that the force exerted by a gale-force
wind of 160 miles per hour on a mobile home size of 45' x 8' (xlO') can exceed
24,000 pounds.
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Table 1
Wind Speed
(mph) Wall Size
S P r e s s u r e of Mobile Force (lbs
(lb/ft2) Home (ft2)
1890
6.75 280 (35' x 8') 2430
6.75 360 (45' x 8')
2722
9.72 280 (35' x 8') 3499
9.72 360(45' x 8')
3704
13.23 280 (35' x 8') 4763
13.23 360 (45' x 8')
4838
17.28 280(35' x 8') 6221
17.28 360 (45' x 8')
6124
21.87 280 (35' x 8') 7873
100 21.87 360 (45' x 8')
7560
27 280 (35' x 8') 9720
110 27 360 (45' x 8')
9148
32.67 280 (35' x 8') 11761
120 32.67 360 (45' x 8')
10886
38.88 280 (35' x 8') 13997
130 38.88 360 (35' x 8')
12776
45.63 280 (35' x 8') 16427
140 45.63 360 (45' x 8')
14818
52.92 280 (35' x 8') 19051
150 52.92 360 (45' x 8')
17010
60.75 280 (35' x 8') 21870
160 60.75 360 (45' x 8')
19354
69.12 280 (35' x 8') 24883
69.12 360 (45' x 8')
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To resist a force of such m~nihlde applied by a 160 mile per hour
wind perpendicularly cont~cting a wall of a mobile home, the net means 14 is
affixed to suitable anchoAng means 30. It is cont~lnplated that anchor means 30
of the present invention be comprised of elong~t~, multi-helix screwable anchors30, which may be m~h~ni-~lly screwed into the ground (see Fig. 3).
A number of such anchor members 30 are commercially available.
One such product is multi=helix anchor manufactured by Dixie Electrical
manuf~t~lring Company of Birmingh~m, ~l~h~m~, under Cat. No. D-284 for a
tandem 8" helix anchor. According to information supplied by said co~llpany,
such anchor ~lepen(ling on soil type and length of anchor, when inserted into the
soil can resist a load of between 10,000 to 30,000 lbs. Using such information,
knowing of the approp,iate soil conditions, the n~s~ry approximate spacing of
such anchor means 30 around the periphery of a mobile home can be delell--ined
to secure net 14 about a mobile home 12.
To avoid anchor means 30 protruding upwardly and creating a
safety hazard, it is conle...plated in a p~re"~ embodiment that anchor means 30
be recessed below the surface of the earth, as shown in Fig. 3, 4 and 5. To
f~r,ilit~t~. this, a r~ss~d well 70 may be further provided to su"ound anchor
means 30, within which a cylindrical hollow canister 50 may be placed level withthe surface of the ground, as shown in Figs 3, 4 and 5. When anchor means 30
and appal~tus 10 of the present invention is not in use, a cylindrical cover plate
(not shown) may be placed over the cylindrical canister 50, to thereby conceal
and hide anchor means 30 from view.
Commercially available cylindrical canister devices 50 and cover
plates suitable for such purposes are presently commercially available. For
example, Brooks Products Inc., Polyplastic Division, of Cucamonga, California
provides a "60 series Valve Box" which is ideally suited to this pu,~ose.
The ~tt~l~hment means 24 of the present invention may simply
comprise a releasable attachment mçch~ni~m, such as a snap-ring, for releasably
~tt~rhing the net 14 at any point proximate the peripheral edge thereof directly to
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anchor means 30, as shown in Fig. 6. In a pferel~d emb~liment, however, it
is conte,l-plated that the ~tt~hm~nt means 24 further comprise means for
tight~n~l~ly securing flexible net 14 to anchor members 30.
Accordingly, it is further contelllplated that ~tt~hm~nt means 24
comprise a pair of releasably securable hooks 60, 62, one of which may be
secured to anchor 30 and the other to net 14 as shown in Figs. 4 and 5. Rollablewebbing connects the two hooks 60, 62, and crankable tip=htenin~ means 70 is
further provided to rollably wind the webbing 72 onto a spool 74, thereby
bringing hooks 60, 62 together to thereby tighten net 14 to anchor 30, as shown
in Figs. 4 and 5. An example of such a commercially available ti~htening means
ideally suited to this purposes is model FE 400 (P/N802) Ratchet Strap, sold by
Kenedyne Corporation of North Branch, New Jersey, having a breaking strength
of 11,000 lbs., with a 2" cranking handle, and hooks 60, 62 interposed at each
end.
An extremely lightweight and water resistant high-strength fibre
particulary suited for net means 14 of the present invention is a braided line
netting comprised of a polyethylene homopolymer having a high modulus of
elasticity and a molecular weight of over 500,000. An example of such a
commercially available fibre is SPECTRA~' manufactured by Allied Fibers, a
division of Allied Signal Inc. of Petersburg, Virginia. In ~4 " single braid format,
such fiber has a break strength of approximately 48,000 lbs., and a weight of
approximately 22 lbs. per 100 ft. of rope.
EXAMPLES
1. Raschel Nylon Tension Tests
In order to accurately model the impact of a projectile on the
netting, data regardillg the stiffness and strength of the netting was obtained.
Trade Mark of Allied Signal Inc. for polyethylene twine and rope.
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Simple static tension tests were pelrolllled, with load and strain data recorded at
several points for each sample.
Sample Pr~)al~lion
Specimens of nylon fibres were cut from a large section of netting.
A single strand (o.25 cm) of the netting was followed through a series of
intersections. To avoid adverse effects on the test strand, intersection strandswere cut roughly five diameters away from the intersection. All cuts were made
with a soldering iron to elimin~te unravelling. Typical sample lengths were
1.2 m.
To f~ilit~te gripping of the spe~im~n, and to ensure that failure
occurred in the test section of the sample, the ends of each sample were threaded
through the hollow core of a short length of 0.5 cm braided nylon rope. A clamp
on the end of the rope nearest the test section, along with a knot a short distance
away, elimin~ted the possibility of slippage of the specimen through the rope.
Experimental Procedure
The test apparatus used was a Tinius-Olsen tension/colllpression test
rig. Samples (inside the rope) were wound around a 4 cm dia. steel pipe) to
avoid stress concentrations and tied off to a post. Elastic strands were ~tt~rlled
to each sample at the end of the test section as references for strain
measurements.
Typical crosshead separation rate was 20 mm/min. Deflections
were manually measured at specific loads (e.g. every 4 Kg).
Maximum load ~uppolled by each sample was also recorded.
Results
A typical plot of load vs. deflection is shown in Table 2.
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Table 2
Load (N) Strain (no. units)
O O
49 0.09
0.15
140 0.20
175 0.24
225 0.27
260 0.28
310 0.30
355 0.32
400 0.33
2. Dropped Projectile Impact Tests
Large samples of netting were tested for impact absorption
capability through drop tests. The sample to be tested was securely fastened to
a rigid frame, and a projective of measured weight and dim~nsions was dropped
onto the specimPn from a range of measured heights.
Apparatus
The netting used was 210/20 twine, (Hafner Fabrics, Toronto,
Ontario Canada), 1.27 cm of stretched mesh 100% Nylon 6,6 (Du Pont) raschel
- knit configuration. The raschel knit is a knotless configuration, with strands and
intersections 'crocheted' together. The design~tion 210/20 indicates that 20 ends
of 210 denier fibre form the yarn. The res--lting twine was roughly 1 mm in
~ m~ter. The mesh had a breaking strength of 25 kgs. and the mesh squares
were roughly 6 mm wide.
Breaking strength is an indication of the net's capabilities.
Breaking strength is measured by pulling apart one square of the fini~hed product,
so the element strength is half the breaking strength. Denier is a measure of a
fibre's weight. One denier is equivalent to the weight in grams of a 9000 m
length of the fibre. Thus, a 9000 m length of 210 denier fibre would weigh 210
grams. Stretched mesh size indicates the ~ t~nce between inte~ ions, along
two sides of a square. Thus 1.27 cm stretched mesh colr~sponds to roughly
0.635 cm squares.
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The raschel knit construction technique consists of es~P-nti~lly
crocheting the yarns (three yarns together at a time) and forming loops in the net
elPmPnt~. Intel~clions between elemPnt~ of the net are accomplished without
knots; the crochet process continues through the int~,r~;lion, with one yarn being
exchanged between the int~,~cling ele~ment.~. A main advantage of the raschel
knit is its ability to stretch to a large degree: as much as 50% strain-to-failure for
an element.
Another advantage of raschel is that, if one elPment of the net is
damaged, there is no ten-lPncy for adjacent inlersections, or adj~cent el~Pm~-nts~ to
unravel. This avoids single-point failures.
A third advantage is that intersections cannot slip signific~ntly, due
to the exchange of yarns. Thus an opening can not be stretched wider by wind
or impacts.
One more advantage is that no ~ignifit~nt strength is lost in
inte~s~;~ions. Knotted netting configurations lose ~ignific~nt p~lroll-lance due to
the stress concentrations of the knots.
A system for edge ~ttaçhmPnt was installed on each sample of
netting to be tested. Earlier versions of this consisted of a rope or cable strung
through the outside squares of the netting, the latter version consisted of a length
of 5 cm webbing sewn onto the edge of the netting, with D-rings ~tt~t~he~ to this
webbing using small 2.54 cm pieces of webbing
A rigid frame, roughly 4 m square, was constructed from 10 cm
angle iron to support the test samples. 2.5 cm eye bolts were attached to the
inside corners and at the centres of each side of the frame. A 0.6 cm cable was
strung through the eye bolts and tight~PnP-d with a turnbuckle. The netting was
attached to this cable by stringing a rope between the edge attachment system and
the cable every foot or so along the perimeter of the sample.
The degree to which the test specimen was stretched into place
depended on the type of edge ~tt~chmPnt - the webbing allowed for very little
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stretch, whereas the rope strung through the edge allowed for ample pre-stressing
(approximately 13.7%).
The projectile used was a still cylinder roughly 9 cm di~mPt~r,
roughly 20 cm long, and 11.7 Kgs weight. As the projectile had fairly sharp
S edges, tape was placed around the bottom edge to avoid cuffing the test specimen.
A ring was ~tt~ ed to the tope of the weight to support it from the crane.
Experimental Procedure
The hook of a crane was placed above the centre of the net. A
rope was strung through the hook and ~tt~hed to the projectile. A tape measure
attached to the hook was used to measure the height of the projective above the
net. The projectile was dlopped from increasing heights until the net failed. A
video camera recorded all tests, and was used to measure displ~Rm~nt of the net,as indicated by a scale on the far side of the frame.
Results
lS The maximum height from which a projectile could be dropped
without d~m~ging the net ranged from 9.3 m (for the pre-stretched sample) to
I0.21 m (for the unstretched sample), which col~s~nds to an impact energy of
1100 to 1200 Joules. The maximum displ~rem~-nt of the pre-stretched sample was
approximately 1.0 m whereas the maximum displacement of the unstretched
sample was approximately 1.3 m. The holes left by imp~t~ from a greater height
were typically 20 cm in ~i~me~er. The force of impact was s~-fficient to do
.~ignifi(~nt damage to the corner eyebolts. After the series of roughly lS tests,
the eyes had been forced open, leaving gaps as large as 2 cm.
The nets were tested to failure. After the first intentional failure
of the netting, several subsequent drop tests were pelroll"ed on the netting.
Results from these tests and direct observations in~ t~ that damage to the net
was limited to the imm~i~te vicinity of the actual hole; outside a small lS cm
distance away from the hole, the net ~l~o~l"ed as well as it had before being
damaged.
3. Air Cannon Tests
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Impact tests were pe,rol-l-ed using a standardised air-propelled
wood projectile at American Test Laboratory in Pompano Beach, Florida,
U.S.A., to simulate hurri~ne force winds-windborne debris.
Apparatus
Similar netting - Nylon 6,6 raschel knit, was used for this test as
in the previous drop-tests. The edge attachment system used was a 5 cm webbing
sewn around the edge of the samples, with D-rings att~hed with 2.54 cm
webbing, spaced roughly 30 cm apart.
A bolted wooden frame of approximately 4 m square was used as
part of the le~ ing means. 1.3 cm eye bolts were mounted through the wood
at each corner of the frame and in the centres of the sides. 0.6 cm cable was
strung through the eye bolts and tightened with a turnbuckle. Rope was used to
attach the D-rings to the cable. Tension in the netting was low.
The cannon used to propel the projectile consisted of an air
col--pressor, an air reservoir with a pressure gauge, a 10 cm air line, a manually
activated bulle~lly valve, and a 10 cm PVC tube as a barrel of the cannon.
The end of the cannon was approximately 7.5 m from the flat, vertical stationaryplane of net.
The projectile was a 4 Kg, 5 cm x 10 cm x 2.4 m Southern Pine
member having its front end slightly rounded. A 10 cm ~ m~ter disc was
attached to the back end to provide a p~ess..le seal for the barrel of the air
cannon.
Procedure
Four tests were pe,rol-lled at increasing speeds: 65, 80, 90, and
100 feet per second (fps). Speed had been previously calibrated to reservoir
pres~.lre at ples~u~s up to 80 fps, and an extrapolation was made from this datato calculate the pres~u~ required to provide the higher speeds. The tests were
recorded on videotape and also provided the displacement of the netting during
impact.
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Results
The net withstood the impact of the 5cm x 10 cm x 2.4 m
rectangular wood projective at the aforesaid ~4cted three speeds of up to 90 fps,
with net defo~ a~ion from its flat stationary plane of up to 1.1 m. At 100 fps,
the net failed, leaving a 33 cm x 30 cm rectangular hole. Surprisingly, the
eyebolts in each of the corners of the frame showed $ignifi~nt alteration in that
their eyes had been prised opened and the bolt shanks bent by as much as 15
degrees. This in~ ~ted that the cumulative force of impacts of the four speeds
had been si~nific~ntly large and had been transferred through the net material to
each of the bolts. It should also be noted that the 90 fps test success indicates
that the net is capable of with~t~n~ling more than three times the energy of thestandard impact test of 50 fps.
Similar air cannon impact tests with the 5 cm x 10 cm x 2.4m
wood member conducted on 1.5 cm thick plywood and on 6 mm thick l~l-lpe ed
and heat strengthened glass produced penetration of the plywood and breakage of
the glass at 50 fps.
The degree of resiliency of the material e1enl~nt of the net was
measured for two netting configurations: 210/20 nylon, and 18/80 polypropylene
raschel. Maximum elongation for the nylon was roughly 34%, whereas the
poly~r~ylene stretched as much as 50%. Tests showed that in one test an impact
energy of approximately 800 joules on the above nylon 210/20 netting was readilyabsorbed by the net system while providing a displacement of approximately
0.7m. A 18/18 polypropylene net of 65% of the areal weight of nylon 210/20
also withstood the same impact of the wooden member at 20 m/s and provided
a deformation of approximately 1 m.
Although the disclosure describes and illustrates plere.led
embo limPnts of the invention, it is to be understood that the invention is not
limited to these particular embo~im~nt~. Many variations and modifications will
now occur to those skilled in the art.
