Note: Descriptions are shown in the official language in which they were submitted.
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GUIDEWAY CONSTRUCTION
Technical Field
~ his invention relates generally to the field of
vehicle supporting guideways and particularly to a guideway
having a generally U shaped upwardly opening cross section
for supporting personal rapid transit vehicles.
Background of the Invention
This invention is related to an earlier filed co-
pending Application Serial No. 444,899, filed January 9, 1984
entitled Switch Mechanism.
With the increase in fuel costs and escalating
construction costs for automobile-type surface roads, the
need for fuel efficient, economical rapid transit has
increased. The state of mass transit at present includes
surface buses and surface railway systems as well as under-
ground subway trains as well as elevated trains and the like.
All of these systems attempt to move large numbers of people
in large vehicles.
Consequently, the vehicle must stop at a plurality
of stations to allow passengérs to embark and disembark as
desired. Therefore, the effective average speed of the
vehicle is reduced by constant stopping and starting, and
most passengers make numerous stops between the point they
get on the vehicle and their intended destination.
A personal rapid transit system would eliminate
several of these problems as each vehicle carries a small
number of passengers desiring to go to the same destination,
and each vehicle bypasses all intermediate stops. Therefore,
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the average speed of the vehicle can be greatly increased
while its maximum speed remains the same, and delays asso-
ciated with stopping at intermediate points are eliminated.
The advantages of ~his design have been known to those
skilled in the art, but ~he construction of a guideway
system which could be constructed economically and which was
durable enough to be practical has eluded those in the art.
General background information on transit systems
can be found in the ~ournal of Advanced Transportation, spe~
cificall~ volume 15, No. 2 dated Summer, 1981; Fundamentals
of Personal_ Rapid Transit by Jack ~. Irving, Ph.D.,
published in 1978 by D. C. Heath and Co~, Lexington,
Massachusetts; and Environment, specifically Volume 22, No.
8, dated October, 1980, which includes an article entitled
"Personal Rapid Transit". Additional information on this
subject can be found in the books Personal Rapid Transit I,
Personal Rapid Transit II and Personal Rapid Transit III~
published at the University of Minnesota, Minneapolis,
Minnesota, in April 1972, February 1974, and June 1976,
respectively.
The elimination of the re~uirement that a vehicle
stop at all intermediate points generally requires that all
stopping points be wayside stations or be located on sidings
or similarly removed from the main track so that stopped
- vehicles do not hinder the passage of through vehicles.
Therefore, th~ construction of a track or guideway for this
type of system is challenging.
The construction of a guideway system supported
above the ground offers several advantages to track systems
located either on the ground or below ground. The below
ground system offers the obvious disadvantage of requiring
tunneling or other expensive right-of-way preparation.~
Surface tracks also require substantial site grading and
right-of-way preparation, and lead to annoying vibration
transmitted to nearby structures and people. Grade level
tracks are also dangerous to cross traffic and require
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crossing gates and safety lights. An elevated guideway
offers obvious advantages, but the construction of an ele~
vated guideway suitable for use with a personal rapid tran-
si-t system is challenging.
The problems associated w:ith an above ground
installation for a guideway system having wayside stations
are numerous, and include the problems associated with har-
monic oscillation of the guideway as vehicles pass along its
length. The construction of a lightweight guideway strong
enough to support a number of individual vehicles passing at
moderate or rapid speeds poses a serious oscillation
problem. Damping of harmonic oscillation frequencies
generally requires an increased guideway mass which further
complicates the oscillation problems and increases the cost
of the guideway.
It is also desirable to construct the guideway in a
prefabricated manne~ to save on construction and erection,
costs. Typically, prefabricated guideways suffer from their
inability to cope with oscillation. This problem is exacer~
bated by the typical const~uction which places guideway sup-
porting posts beneath the ends of each guideway section so
that the point of support of each section is the same as its
point of attachment to adjacent guideway sections. This
construction design causes the center of each guideway sec-
tion to oscillate with the guideway support posts func-
tioning as node points in the oscillation wave along the
length of the guideway.
~ Oscillation of the guideway creates numerous
problems including the requirement for reinforcement struc-
tures along the guideway, thereby increasing the guideway's
weight and cost. When the weight of the guideway is
increased, the oscillation mass is also increased thereby~
aggrevating the problem. Additionaily, oscillation of the
guideway greatly detracts from ride comfort within the
vehicle, and accelerates wear of the guideway itself caused
by flexing. For example, United States Patent No. 3,225,703
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issued December 28, 1965 illustrates a dPvice having beams
affixed at their ends to support columns. This type of
device i.ncludes dash pot like devices to manage force
transmission between adjacent beams.
As the success of the rapid transit system depends
directly on the confidence its ridership has in the
functioning and structure of the system, the elimination of
oscillation and its associated problems is critical to the
construction o~ an economically feasible and viable guideway
and transportation system.
Summary of the Invention
Various aspects of the invention are as follows:
A transportation system for use with a wheeled
vehicle and a vehicle supporting guideway, said guideway
comprising:
a plurality of guideway sections, each section
being of substantially uniform length and affixed in end-to~
end relation ~orming a continuous guideway, each of said
sections including:
a pair of upper horizontal stringers located
parallel to each other and generally defining the width of
said guideway and a pair of lower horizontal stringers
located parallel to each other and placed parallel to and
below said upper horizontal stringers;
a plurality of vertically oriented elongated
dia~onal members having midpoints and affixed to said upper
and lower hori~ontal stringers and lying in vertical planes,
a plurality of horizontally oriented diagonal
members af~ixed to and joining each of said lower horiæontal
stringers;
said stringers and said diagonal members defining a
guideway having an upwardly extending generally U-shaped
construction:
means for elevating said guideway sections a
desired distance above the ground, said elevation means
located beneath said guideway sections and including a
plurality cf support posts, one o~ said posts being affixed
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beneath each of said guideway sections approximately 21~ of
the length of said guideway section from one end of said
sect.ion,
a plurality of upwardly opening U-shaped
reinforcing ribs spaced from each other, said ribs affixed to
and substantially enclosing said stringers, said ri~s in
spaced relation to each.other substantially along the entire
length of said guideway sections said ribs having spaced
inner and outer members with bar means extending
therebetween, said members having joined free ends; and,
means for joining a plurality of said sections in
end-to-end relation forming a continuous vehicle support
channel, said means including expansion joints located
approximately 21% of the distance between adjacent support
posts.
A method of installing a prefabricated vehicle
supporting guideway, said guideway including a number of
sections each having a pair of vehicle supporting lower
support channels running substantially the length of said
section, a pair of upper horizontal stringer~ running
substantially the length of said section, a pair of lower
horizontal stringers running substantially the length of said
section and positioned below said upper horizontal stringers,
a plurality of horizontally oriented diagonal members affixed
to and joining said lower horizontal stringers and forming a
diamond pattern including generally open areas, a plurality
of upwardly opening U-shaped reinforcing ribs, said ribs
affixed to and substantially enclosing said stringers, said
ribs in spaced relation to each other substantially along the
entire length of said section~ said ribs having spaced inner
and outer members with bar means extending therebetween, said
members having joined free ends, and including means for
joining a plurality of said sections in end-to-end relation;
the method comprising the steps of:
(1) installing a plurality of support post means
of uniform length at generally uniform distances along the
desired path of said guideway;
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(2) positioning one of said guideway sections over
one of said post means so that said section end is positioned
approximately 21% of the length of said guideway section from
said post means and one of said generally open areas within
said diamond pattern is positioned vertically above said
post;
(3) lowering said previously polsitioned guideway
section onto said support post means;
(4) clamping said guideway section to said support
post means at four points, each of said clamping points
spaced from each adjacent clamping point at least a distance
equal to a distance between said lower support channels, at
the desired level above the ground and cutting said post
means to the desired length after affixing said section
thereto;
(5) repeating steps 2-4 Eor the adjacent post
means along said desired path with a subsequent section; and
(6) affixing said sections to each other in end-
to-end relation forming a continuou~, smooth vehicle
supporting elevated guideway.
According to another aspact of the invention, a
transportation system for use with a wheeled vehicle ~or
carrying passengers along a vehicle supporting elevated
guideway is provided. The guideway includes a plurality of
guideway sections linked in end-to-end relationship. Each
section has a pair of upper horizontal stringers located
parallel to each other. These upper horizontal stringers
generally define the width of the guideway and are placed
parallel to and above a pair o~ lower horizontal stringers.
The four stringers run the length of the guideway. A
plurality of vertically oriented diagonal members are affixed
to the upper and lower horizontal stringers, the diagonal
members lying in vertical planes between respective pairs of
horizontal stringers. A plurality of horizontally oriented
diagonal members are affixed to and join the lower horizontal
stringers so that the sides and the bottom are joined by
diagonal members forming a generally upwardly extending
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U-shaped configuration for the guideway.
The guideway thus described further includes a
plurality of guideway supporting posts, one placed below each
guideway section. The guideway further includes U-shaped
reinforcement ribs, and an all-weather cover which
aesthetically covers the guideway. Th~ guideway sections
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; are joined in end-to-end relation with expansion joints atthe connection points, and the connection points are located
. substantially at one o~ the points of ~ro bending moment
t within the ~uideway between adjacent posts.
.
Brief Descri~tlon of the Drawin~s
Figure l is a partial side elevational view of the
present guideway inventioni
Figure 2 is an end elevational view of the
! guideway shown in Figure l;
Figure 3 is a slightly enlarged parti~l eleva-
tional ~iew of the guideway structure having the covexs
removed;
Figure 4 is a partial diagramatic bottom view of
the guideway shown in Figure 3;
Figure 5 is a partial diagramatic side elevational
view of an expansion joint within the guideway shown on an
enlarged scale;
F.igure 6 is a bottom diagramatic view of the
: expansion joint shown in Figure 5;
Figure 7 is a cross sectional view taken along
~. line 7-7 in Figure 3 shown on an enlarged scale; and
; Figure 8 is a plan view of a portion of the expan-
sion joint shown in Figure 6 with the covers partially s~own
I and t.he support channels installedi
Figure 9 is a partial elevational view on an
enlarged scale showing a support post, a support post
bracket and the guideway;
Figure lO is a partial sectional view on an
; enlarged scale taken along line lO-lO in Figure 9; and
Figure ll is a partial sectional view on an
enlarged scale taken along line ll-ll in Figure 9.
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Detailed Description of the
Preferred Embodiment
In reference now to the drawings wherein like
reference numerals correspond to similar components
throughout the several views, the guideway 10 is shown in
Figure 1 supporting a vehicle 12, and having a track portion
14 held above the ground by posts 16 with support brackets
18 therebetween.
The vehicle 12 includes a body portion and a bogie
portion. The bogie travels substantially within the
guideway on wheels, and the vehicle is powered by linear
induction motors which are affixed to the vehicle. Details
of the vehicle are not shown.
The structure shown in Figure 1 represents a
transportation system for use with a wheeled vehicle 12 sup-
ported on the guideway 10. The guideway 10 forms a
generally open truss having an upwardly opening U-shaped
cross section. (See for example Figure 7.) The guideway is
composed of a number of guideway sections 40 affixed in end
to end relation forming a continuous guideway. Each
guideway section is supported by a guideway support post 16.
Expansion joints 42 are located substantially at the points
of zero bending moment within the guideway. The science of
statics defines the points of zero bending moment of a uni-
formly loaded beam with clamped ends as points lying
approximately twenty one percent of the beams total length
inwardly from each end of the beam. In other words, the
points of 2ero bending moment lie at points approximately
21% and 79% along the length of a uniformly loaded beam.
As shown in Figure 7, the guideway consists of a
pair of upper horizontal stringers 20 and 22 located
parallel to each other and generally de~ining the width of
the guideway 10. A pair of lower horizontal stringers 24
and 26 are located parallel to each other and are placed
parallel to and below the upper horizontal stringers 20 and
22 respectively.
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A plurality of vertically oriented diagonal mem-
bers 30 and 32 are affixed to the upper and lower horizon-tal
stringers 20 and 24, or 22 and 26 as shown in Figure 5 and
form a triangular pattern. A plurality of horizontally
oriented diagonal members 34 are affixed to join each of the,
lower horizontal stringers 24 and 26 and form a diamond pat-
tern. In this way, the guideway 10 is defined as a
generally upwardly extending, U-shaped structure having
upper horizontal stringer 22 and lower horizontal stringer
26 with vertical diagonal members 30 and 32 there~etw~en
defining one vertical leg of the U. ~orizontal stringers 26
and 24 with horizontal diagonal members 34 therebetween
define the base of the U, with stringers 24 and 20 with ver-
tical diagonal members 30 and 32 ~herebetween defining the
second upright leg of the U.
A pair of main wheel support channels 38 (made of
right angle "L" shaped members) are affixed to the guideway
above the horizontal diagonal members 34. The support chan-
~nels 38 lie generally between the vertical diagonal members
and 32 and are adjustable both horizontally and ver
tically ~ithin the U-shaped ~uideway.
The support channels 38 are adjustable with
adjusting bolts or shims 39 which lie betwe~n the support
channels 38 and the guideway 10. These adjusting bolts or
shims 39 are placed along the horizontal diagonal members 34
; below support channel 38 and on the inside surface of the
vertical diagonal membcrs 30 and 32 so as to contact the
main support channels 38. These bolts or shims provide a
means for adjusting the relative position of the main wheel
support channel above and between the horizontal and ~-~r-
tical diagonal members respectively. In this way, a per-
fectly aligned vehicle carrying support track formed by the
support channels 38 can be maintained. Fine adjustments of~
the support channels 38 within the guideway 10 are possible
without the need for expensive, time consuming and difficult
alignment of repairs to the guideway itself. The guideway
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is also provided with upper support channels 35 which stabi-
lize the vehicle as it passes through the guideway.
In reference now to Figures 1 and 2, the guideway
structure is composed of a plurality of guideway sections
40, each of substantially uniform leng~h. ~he guideway sec-
tions 40 are affixed in end-to-end relation at junction
points 42 forming a continuous guideway. The guideway sec-
tions 40 are themselves ~levated above the ground a desired
distance. This elevation is accomplished by a plurality of
support posts 16. Each one of the support posts 16 is
affixed beneath each guideway section 40. Expansion joints
42 are near the point of zero bending moment of the
guideway.
The guideway structure cornposed of the upper
strinyers 20 and 22, and the lower stringers 24 and 26,
respectively, are additionally stiffened by the application
of reinforcing ribs 60 spaced along the length of each
guideway section 40. The reinforcing ribs 60 are con~ected
to each of the stringers running the length of the guideway
sections and are also attached to the vertical diagonal mem-
bers 32. The reinforc1ng ribs 60 provide torsional stiff-
ness to the guideway and thereby increase the natural
frequency of oscillation of the guideway to torsional
twisting. Therefore the resistance of the guideway to side
wind loads and unevenly loaded vehicles is increased.
The reinforcing ribs 60 contact and stiffen the
vertical diagonal members 32 which are held in ccmpression
within each guideway section 40. The remaining vertical
diagonal members 30 are held in tension within the guideway.
The weight of the guideway sections themselves, of course,
exert forces along the truss structure of the guideway sec-
tions 40. These forces hold the vertical diagonal members
30 in tension in that a pulling force is exerted along their
length, and the vertical diagonal members 32 are held in
¦ compression with a pushing force exerted upon their length
By placing the reinforcing ribs 60 to cross approximately in
the middle of the vertical diagonal members 32, the
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resistance of members 32 to buckling is increased four-fold.
The resistance of a member under compression to buckling
increases by a factor of four as the length of the member is
reduced by a factor of two. Therefore, significant strength
is added to the guideway sections 40 without increasing the~
beam's weight by placing the reinforcing rib 60 to intersect
and stiffen the vertical diagonal me~ers under compression.
In re~erence now to Figure 7, the reinforcing ribs
60 themselves are composed of an i~ner channel 62 having a
generally U-shape and conforming closely to the dimensions
and configuration of the guideway as defined by the upper
and lower stringers 20-26, respectively. The reinforcing
rib 60 also includes an outer channel 64 having a generally
U shaped configuration. The outer channel is joined at its
free ends to the free ends of the inner channel 62. The
outer channel 64 is of somewhat longer length than the inner
channel and is spaced there~rom along its length except near
the free ends of the inner and outer channels 62 and 64!
respectively. The inner and outer channels 62 and 64 are
located with respect to each other by a stiffening bar or
channel 66 which is affixed to the inner and outer channels
62 and 64 in alternating fashicn forming a plurality of
triangular shaped openings between the channels. This
design provides a reinforcing rib 60 which provides signifi-
cant torsional stiffness to the guideway.
It is expected that a guideway constructed with thedesign described above will provide a gui~eway having the
lightest overall weight for its low bearing capacity. Light
guideway weight with a large load bearing capacity has thP
advantange of providing a guideway which ha~ a sufficiently
high natural frequency of oscillation to allow suita~le
vehicle speeds. For example, a guideway constructed of a
heavy material may prove to have a natural frequency of~
oscillation of one cycle per second. Assuming a guideway
section length of sixty feet or twenty meters, a vehicle
speed of only twenty meters per second could be sufficient
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to cause serious oscillation probleins. These problems are
caused by the natural oscillation o the guideway being
amplified by the passage of the vehicle over the guideway at
a speed corresponding to the natura:L oscillation freguency,
i.e. one guideway section per second. This problem is
further increased by a ~uideway design which places support
posts only beneath the joints of adjacent guideway sections.
A guideway having a significantly higher natural
oscillation fregue~cy, (for example an open truss design
j10 being supported by posts, and having expansion joints bet-
ween guideway sections near the points of zero bending
;moment of ~he guideway) can support a vehicle moving at
greater speeds without oscillation problems. Oscillation
problems cause wear to the guideway due to flexing and
bending, and more importantly decrease ride comfort for the
passengers, as the passengers are exposed to vertical acce-
lerations as the guideway oscillates. ~dditionally, the
guideway constructed along the design above described will~
be economical to produce and maintain.
- The guideway itself is substantially enclosed by a
cover 50 having a first half 52 and a second half 54. ~See
Figures 1 and 7.) The cover halves are hingedly affixed to
the reinforcing ribs 60 al~Jng the length of the guideway 10.
The cover halves 52 and 54 are hinged at the bottom of the
25 outer bar 64 of the reinforcing ribs 60 at hinge points 70.
The hinge points 70 are located slightly offset fro~ the
cent r of the outer bar 64. The cov~r halves 52 and 54 are
pinned or otherwise affixed to the tops of the upper
stringers 20 and ~2, respectively, at pin points 72. The
cooperation of the pin fixture points 72 and the hinges 70
allow the covers to be folded back for easy access to the
guideway sections 40 for maintenance procedures and the
like. The cover halves 52 and 54 are stiffened by stif-
fening ribs 55 (See Figure 8) which provide strength for the
attachment of the hinges and pins 70 and 72. Stiffening
ribs 55 axe of "T" shaped cross-section. The cover 50 is
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se~mented, meaning it is ccmposed of a large number oX
smaller pieces each spanning a distance of ~pproximately the
span between ~hree reinforcing ribs 60. In this way con-
venient access to ~he guideway is provided, with the cover
halves being of managea~le size.
It should be noted, that the cover 50 substantially
encloses ~he guideway but fcr an upper slit 58 and a lower
slit 59. The upper slit provides a continuous opening
running the length of the guideway for passage of the sup-
port vehicle. The lower slit 59 allows rain, snow, debxisand other material which may find its way into the guideway
to pass out of the guideway. The cover S0 greatly reduces
the amount of such material which finds its way into the
guideway. Additionally, the cover improves the aesthetic
appearance of the guideway structure. Additionally, the
cover protects the guideway from lightning which can damage
the electrical wiring within the guideway used to power and
control the vehicles 12. The cover 50 also protects the~
guideway support channels 38 and the power rails from the
night time sky which can produce frost on exposed surfaces
during cool weather. The cover 50 also provides containment
should a fire occur within -the guideway, and shields the
environment from e ectromagnetic noise created by the
system.
In reference now to Figures 5 and 6, the two
guideway ~ections 40 are shown in end to end relationship
with an expansion joint 42 therebetween. The expansion
jo~nt includes four fIuid filled cylinders 82 fixed at their
ends to the stringers 20-26 of the guideway sections 40.
The cylinders 82 serve to dampen the transmission of vibra-
tion from one guideway section to the adjacent guideway sec-
tion. It is expected that the cylinders 82 will be filled
with heavy grease or other high viscosity liquid. The
cylinders 82 ~unction as "shock absorbers" and will absorb
low fre~uency vibration, transmitting high frequency vibra-
tion.
12-
In practice, the expansion joints 42 allow ther~al
expansion within the guideway t:o take place without
effecting the ride comfort or smoothness of the guideway.
The expansio~ joints 42 fuxther include end plates
84 which run between the upper and lower stringers 20 -26
and stabilize the ends thereof. A further aspect of the
expansion joints 80 is shown in E~igure 8. To provide a
smooth vehicle path over the expansion joint 42, the support
channels 38 are provided with support channel fingers 37
attached to the ends of the support channels 38. The sup-
port channel fingers 37 are arranged to interlock so that as
the support channel sections 40 expand or contract, a
smooth, continuous surface is provided for the vehicle tra-
veling on the suideway. Similar fingers (not shown) are
placed on the upper support channels 35. The smooth joint
is produced by placing the expansion joint substantially at
the point of zero curvature, or zero bending moment within
the guideway.
In reference now to Figures 9, 10 and 11, the
design of the support bracket 18 and its installation on the
support posts 16 and the guideway 10 is shown. The support
bracket 18 includes a generally X-shaped member 90 placed in
a plane paral~el to the guideway. A sleeve 92 is provided
;~ for fitting over the posts I6. A number of stiffening fins
94 are placed between the X-shaped member 90 and the sleeve
92 to stiffen the support bracket 18. The bracket itself is
attached to the lower stringers ~4 and 26 by bolts 96 or the
like.
It should be noted that the support bracket 18 and
the support posts 16 are ~ositioned along the length of the
guideway section so that the support post is centered
beneath a diamond shaped opening formed by the horizontal
diagonal members 34. ~See Figure 10.) This positioning~
becomes important to an understanding of how the guideway is
installed as will be described below.
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It is anticipated that the preferred method for
installing the guideway will include prefabricating the
major components including the support posts 16, the support
brackets 18, and the guideway sections 40. These components
will then be shipped to the installation site wh-ch has been~
prepared. The support posts 16, being of uniform length,
are installed at generally unifonn distances along the
desired path of the guideway. At this point, the support
bracket 18 is installed over the top of the su~port posts,
~0 or the bracket can be installed prior to erecting the posts.
Next, one prefabricated guideway sectio~ 40 is installed on
the support post 16 and support bracket 18. The exact
height of the guideway section above the ground is variable
by adjusting the support bracket vertically on the post,
and/or by placing shims or other spacing members between the
support bracket and the guideway itself. The guideway sec-
tion 40 is installed so that the support post 16 is
generally centered throu~h the diamond shaped opening formed~
by the horizontal diagonal members 34 approximately 21% of
the distance from the end of each guideway section 40.
The guideway section 40 can then be affixed to the
support bracket 18 which is slid vertically up and do~m on
the sup}ort post 16 until the guideway 40 is at the desired
heigh~ above the ground. The support bracket 18 can then be
welded or otherwise affixed to the~ support post 16 and any
excess length of the support posts 16 can be removed with a
cutting torch or the like. The guideway sections can then
be connected to each other with expansion joints 42 as
described above. The guideway sections 40 are linked in
end-to-end relationship by the expansion cylinders 82 which
stabilize the ends of the guideway sections and permit the
guideway to be fully supported along its length. In this
way a continuous, smooth, vehicle supporting guideway is-
provided.
Certain materials are expected to produce satisfac-
tory results when e~ployed in the manufacture of the above-
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described g~ideway. For example, octagonally tapered steel
posts are expected to prove satisfactory for the support
post 16 and common rolled steel stock is expected to perform
satisfactorily for the stringPrs 20-26. These should, as
shown, be of channel construction and sho~1ld be positioned
within the guideway so as not to accumulate moisture or
~ snow. The outer reinforcing rib~ 60 can be composed
- entirely of thin stock steel or either conventional or exo-
tic alloys having a channel-shaped cross-section. The sup-
port channels 38 should be made of a steel right angle stock
or other magnetically permeable rigid material, and it is
e~pected that they should have an aluminum clad layer along
~heir surface for improved interaction with the linear
induction motors which propel the vehicle. (Linear induc-
tion motors are not shown in the drawings.) The sovers 50may be of aluminum or may be made of thin silicon steel
alloy or reinforced fiberglass. The cover panels 52 and 54
can have a reinforcing member of steel or other material,
increasing their rigidity and providing convenient anchoring
points for the hinges and pin points 70 and 72, respec-
tively.
A number of characteristics and advantages of the
invention have been set forth together with the structure
and oper~tion of the perferred embodiment of the guideway
construction. Novel features thereof are poin-ted out in the
following claims. The above disclosure is merely illustra-
tive, and changes may be made in detail with respect to
size, shape, choice of materials and structural arrangement
within the principles of the invention to the full extent
intended by t~e broad general meaning of the terms expressed
in the claims.
