U.S. patent number 3,926,134 [Application Number 05/532,016] was granted by the patent office on 1975-12-16 for prestressed concrete tanks for liquid natural gas tankers.
This patent grant is currently assigned to Preload Technology, Inc.. Invention is credited to John J. Closner, Tadeusz Josef Marchaj, Sven Hjalmar Wichman.
United States Patent |
3,926,134 |
Closner , et al. |
December 16, 1975 |
Prestressed concrete tanks for liquid natural gas tankers
Abstract
A tank for cryogenic liquids, specifically liquid natural gas,
adapted for placement within a conventional marine transportation
vessel is shown. The tank is preferably cylindrical and of circular
cross section and is comprised of prestressed concrete with steel
heads. The tank wall is made up of a series of concrete, modular
tank wall sections which are circumferentially prestressed by steel
tendons and which have holes therein for through-passage of axial
prestressing tendons. A steel sheath anchored to the concrete wall
provides a secondary barrier against leakage of the liquid natural
gas cargo within the tank. The modular wall sections are separated
by concrete or steel stiffening disks. The tank is formed by
alternately positioning a number of modular wall sections and
stiffening disks. Flat, concrete, stiffening plates which are
integral with the modular tank wall sections and are
radially-axially positioned within the tank further stiffen the
structure. The walls and the stiffening plates are axially
prestressed and the heads are attached. The tank is supported on
the annular stiffening disks which are joined to the tank wall. The
tank makes efficient use of the vessels cubic and is inexpensive to
construct. By preforming and prestressing the modular units and
thereafter erecting them rapidly at the ship-building site or at a
removed fitting out site, important economies are achieved.
Inventors: |
Closner; John J. (Douglaston,
NY), Marchaj; Tadeusz Josef (New York, NY), Wichman; Sven
Hjalmar (Yaphank, NY) |
Assignee: |
Preload Technology, Inc.
(Garden City, NY)
|
Family
ID: |
26967522 |
Appl.
No.: |
05/532,016 |
Filed: |
December 12, 1974 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
292727 |
Sep 27, 1972 |
3863408 |
|
|
|
Current U.S.
Class: |
114/74R; 220/901;
220/560.12 |
Current CPC
Class: |
F17C
3/025 (20130101); B63B 25/12 (20130101); F17C
2270/0105 (20130101); F17C 2221/033 (20130101); Y10S
220/901 (20130101); F17C 2223/0161 (20130101); F17C
2260/016 (20130101); F17C 2203/0678 (20130101) |
Current International
Class: |
F17C
3/02 (20060101); B63B 25/00 (20060101); F17C
3/00 (20060101); B63B 25/12 (20060101); B63B
025/12 () |
Field of
Search: |
;114/74AV,65A
;52/224,227 ;220/9A,9LG,5A,3 ;248/DIG.1,146 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Blix; Trygve M.
Assistant Examiner: Basinger; Sherman D.
Attorney, Agent or Firm: Curtis, Morris & Safford
Parent Case Text
This is a division, of application Ser. No. 292,727, filed Sept.
27, 1972 and now U.S. Pat. No. 3,863,408.
Claims
What is claimed is:
1. A marine transport system for cryogenic liquids, comprising the
elements of:
a. an outer marine hull;
b. a cradle for a horizontally-oriented, cylindrical tank formed
from prestressed concrete and having a circular cross-section;
and
c. a horizontally-oriented, cylindrical tank of circular
cross-section, adapted for containing cryogenic liquids positioned
in said cradle, comprising the elements of:
1. a concrete, cylindrical tank wall having a plurality of steel
prestressing tendons located therein in axial orientation;
2. a steel sheath anchored to the exterior surface of said
wall;
3. a prestressing tendon wrapped essentially circumferentially
about the exterior of said steel sheath;
4. at least two, annular stiffening disks positioned coaxially
within the said wall said disks having holes therein for
through-passage of axially oriented prestressing tendons;
5. a plurality of stiffening plates positioned radially-axially
with respect to said tank and abutting at both axial extensions
thereof, said stiffening disks and at their radial outermost
extension, the said cylindrical tank wall, said stiffening plates
having essentially axially oriented prestressing tendons
therein;
6. steel heads defining the ends of said cylindrical tank and
attached to said stiffening disks; and
7. inlet and outlet means for said cryogenic liquid.
2. A marine transport system as defined in claim 1, wherein said
cradle comprises transverse structural members positioned below the
lower parts of said annular stiffening disks.
3. A marine transport system as recited in claim 2, wherein the
diameter of the said annular stiffening disks is greater then the
diameter of the concrete, cylindrical tank wall, so as to provide a
protruding support post, which is positioned upon the said
transverse structural members of said cradle.
Description
This invention relates broadly to the transport of cryogenic
liquids in marine vessels. More specifically, this invention
relates to use of inexpensive prestressed concrete tanks in steel
or concrete barges and ships for carrying liquefied natural gas.
Even more specifically, this invention relates to a modular tank
configuration for liquid natural gas tanks which provides
exceptional safety features and economies in the design,
construction and operation of marine transport vessels.
The art of transporting cryogenic liquids in ships and barges has
developed rapidly in the past several years. The accelerating
world-wide demand for liquid natural gas has resulted in
development of ever larger barges and tankers and has given rise to
several different types of cargo containment systems. World wide
fuel shortages have now been foreseen and in view of the ecological
acceptability of natural gas as a fuel, the demand for it will
certainly increase. Thus, the art is faced with a need to develop
safe and economical systems for liquid natural gas containment and
transport.
BACKGROUND OF INVENTION AND PRIOR ART
Liquid natural gas is comprised of a mixture of primarily methane,
with lesser amounts of ethane, propane and butane. Although the
actual composition may vary according to source and with the degree
of processing during liquefication, typical liquefied natural gas
products have a boiling point, at atmospheric pressure of
approximately -250.degree.F. The natural gas is transported at
these temperatures and at atmospheric pressures and the cargo
containment systems must be designed for service at these
temperatures as well as for cool-down and warm-up cycles.
It has long been recognized that carbon steels, which are used
commonly in ship building are relatively weak at cryogenic
temperatures. For this reason, the tanks are typically made of
nickel steel or aluminum alloys which have superior strength
characteristics at low temperatures and serve to safely contain the
liquid natural gas cargo, protecting the hull of the vessel from
exposure to extremely low temperatures. Several configurations of
tanks, in ships and barges, have been developed, many of which
provide a double barrier between the cargo and the external steel
hull to protect the hull from exposure to low temperatures in the
event of a rupture of the cargo containment system; and numerous
intricate configurations have been developed for insulating the
outer hull from the cryogenic temperatures. Configurations have
also been developed to protect the cargo containment systems from
rupture in the event of a collision which damages the external hull
of the vessel.
Conventional liquid natural gas containment systems heretofore have
fallen within three general categories: prismatic free-standing
tanks, spherical free-standing tanks and membrane tanks. Although
each of the several types of tanks and the several design variants
thereof have been used with success in the past, and although each
type of tank has certain advantages peculiar to it, each likewise
has certain disadvantages. In evaluating each of the several
alternative designs, many factors must be taken into consideration
including the initial cost of the containment systems, the overall
life of the system, operational safety, ease and time of
construction, unit cost per cargo-mile and many other factors.
The prismatic free-standing tank has been used more than the
others. Generally, they are comprised of 9 percent nickel steel,
stainless steel or aluminum alloy and their configuration roughly
follows the interior configuration of the vessel. They include a
secondary barrier between the tank and the steel hull of the
vessel. Among the advantages of such tanks is that they are
relatively efficient in terms of utilizing the internal volume
(cubic) of the vessel. The center of gravity of such tanks is
generally fairly low so that the amount of ballast required to trim
the vessel is not excessive.
A very substantial disadvantage of prismatic, free-standing tanks
stems from their configuration. To follow the shape of the hull
structure, three corner systems are used, and although such
structures are analyzable, design problems are more difficult than
in tanks of more simple configuration. The many structural details
and welded connections involved and the unknown stresses which
develop due to thermal contraction of the steel, torsion of the
hull, impact on the hull, motion of the vessel in a seaway and
movement of the liquid within the tank, lead to a variety of
structural problems. If simpler configurations, such as vertical
cylinders are used, there is an attendant sacrifice in the
efficiency of space usage within the vessel. Due to these problems,
prismatic free-standing tanks tend to have a relatively higher
weight and cost than do other types of tanks now in use.
Spherical, free-standing tanks have a salient advantage in that
they are most easily analyzed for stresses, and accordingly
spherical tank systems can be constructed having no secondary
barrier or only a partial secondary barrier. A related advantage is
that the spherical tanks can be relatively easily fabricated; there
is no necessity for internal structural members to ensure the
integrity of the tank; and there are no unforeseen problems of
metal fatigue due to unforeseen stresses.
On the other hand, spherical tanks have certain disadvantages
primary among which is their inefficiency in regard to use of the
internal cubic of the marine vesel. There is a greater amount of
waste space within the hull although this is partially offset by a
greater availability of hull volume for carriage of ballast. They
are also relatively difficult to support, have a relatively high
vertical center of gravity and extend above the deck level causing
operational problems.
Membrane tanks, which generally include two thin, flexible
membranes comprised of, for example, stainless steel, and at least
two layers of insulation separating the barriers from one another
and the outer barrier from the steel hull of the vessel, have
certain very significant advantages. Their primary advantage is
that their configuration most closely follows that of the outer
steel hull of the vessel and they therefore are most efficient with
respect to use of the internal cubic of the vessel. The
construction cost of membrane tanks is relatively less than that of
free-standing systems because the thickness of the membranes is
considerably less than that of the steel plate used in prismatic
tanks. Thus, the total material cost is drastically lower than for
prismatic tanks although the unit cost for the membrane material
may be slightly higher. The smaller mass of the membranes also
results in a substantially shorter cool-down time as compared with
prismatic tanks. Installation costs for membrane tanks tend to be
somewhat less than for prismatic tanks largely because the weight
of the materials used is less.
The primary disadvantage of membrane tanks, is that they are
virtually impossible to analyze structurally. Unknown problems of
fatigue and stress concentration lead to increased risks, including
the risk of damage to the primary barrier in the event of a ship
collision. The free-standing tanks, particularly the spherical
tanks are less subject to damage in the event of collision because
they have greater structural integrity and are separated from the
hull by additional space. The relatively weak membrane is also
subject to damage during construction and during maintenance
operations. Membranes can be damaged by overpressurization of the
vapor space behind the primary barrier, by movement of liquid
within the tank and by development of fatigue cracks or stresses
within the hull of the vessel. For these reasons, construction of
membrane tanks is more closely supervised by the authorities and
must be attended with more care than with free-standing tanks.
In view of the many, and often conflicting, design, construction
and operational factors which must be considered in the development
of tanks for cryogenic liquids in marine vessels, there is
considerable room for improvement over conventional containment
systems. Several, but by no means all of the objectives facing the
art are hereinafter set forth.
OBJECTIVES
It is the primary object of this invention to provide a tank
construction for marine transport vessels having a configuration
which makes maximum use of the internal volume of the marine
vessel.
It is another primary object of this invention to provide a
construction for such tanks which requires relatively inexpensive
materials and is relatively easy to fabricate and erect within a
conventional concrete or steel ship or barge.
It is still a further primary object of this invention to provide a
tank having a substantial structural integrity to protect the outer
vessel from the cryogenic cargo and to protect the cargo from
damage in the event the outer vessel is ruptured due to
collision.
It is a further and important object of this invention to provide a
fully determinate tank system wherein the stresses can be readily
analyzed without excessive design or testing work and wherein
excessive safety factors and redundant structural systems need not
be employed.
It is a further related object of this invention to provide a tank
configuration which does not require the structural and operational
complexities of a double barrier system.
It is still a further object to provide a tank which because of its
structural simplicity and reliability will enjoy the benefit of
relaxed design requirements of the authorities having jurisdiction
over the design and erection of these tanks.
It is still a further object of this invention to provide economies
in construction and specifically to reduce or eliminate the use of
expensive alloy steels in the construction of cryogenic tanks in
marine vessels.
It is a further object of this invention to provide a tank which is
simple to erect in a ship yard and whose construction does not
grossly disturb other operations within that yard.
It is a further object of this invention to provide a modular
construction for such tanks which simplifies the tank construction
and reduces the time required to complete such construction.
It is still a further object of this invention to provide a simple
method for constructing the modular components of the tank.
It is another object of this invention to provide compartments
within the tank to reduce movement of the cryogenic liquid
contained therein during ship movement.
It is another object of this invention to provide a tank in which
the weight of both the tank and its contents are distributed along
the tank so as to reduce the concentrated loads normally
encountered at the ends of horizontal cylindrical tanks;
It is another and related object of this invention to provide a
tank structure which cooperates with the ship structure to reduce
the requirements of the ship structure.
It is yet another object of this invention to provide a tank which
has a low vertical center of gravity.
SUMMARY OF THE INVENTION
These and many other objectives of the invention are achieved in a
tank for containment of cryogenic liquid, for placement within a
marine transportation vessel which comprises a cylindrical tank
wall, of any suitable curved cross-section for tank service but
preferably of circular or elliptical cross-section comprised of
prestressed concrete, and end closure means such as heads attached
thereto. In order to withstand, the very considerable hydrostatic
and vapor pressures which are developed within the tank, the
cylindrical tank wall is prestressed by steel tendons positioned
essentially circumferentially about its exterior surface and by
other steel tendons, positioned within the tank wall itself, and
oriented essentially parallel to the axis of the tank. To provide
stiffness, one or more annular stiffening disks are positioned
coaxially within the wall of the tank and are attached thereto. The
stiffening disks are formed from steel or concrete and a portion
thereof may extend past the exterior surface of the tank wall to
provide support or retainer posts for the tank. Desirably a
plurality of these stiffening disks are attached at intermediate
locations between the heads of the tank. A series of planar
stiffening plates (or ribs) are positioned in a radial-axial
orientation with respect to the tank wall and are connected to the
stiffening disks and to the interior of the tank wall. Desirably,
the stiffening plates are flat, prestressed concrete plates and
they, as well as the cylindrical tank wall have essentially axially
positioned prestressing tendons therein. To provide a "secondary"
barrier, a steel sheath may be anchored to the outer surface of the
cylindrical wall. This sheath may be of carbon steel since it acts
compositely with the prestressed concrete, and thus is not subject
to tensile stresses when subjected to the low temperatures of the
cryogenic liquid within the concrete container.
In the preferred tank configuration, the tank wall is concrete and
of circular cross-section. A series of axial holes are located
within the tank wall through which steel prestressing tendons are
passed. A carbon steel sheath is anchored to the exterior of the
tank wall by studs and external to the sheath are prestressing
tendons wrapped essentially circumferentially. Either one
continuous tendon in a helical wind or a series of individual
tendons can be used. Annular concrete stiffening disks are
positioned coaxially within the tank wall and are attached to the
steel sheath. The disks have holes along an outer circle and along
certain radii, for through-passage of axially oriented prestressing
tendons. Between the several stiffening disks and abutting their
surfaces are a plurality of flat, concrete, stiffening plates which
are positioned radially-axially with respect to the tank. These
stiffening plates abut the interior of the tank wall at their
radial outermost extension. Located within these stiffening plates
are axially oriented holes for prestressing tendons. Defining the
remainder of the tank structure are steel heads which are attached
to the end-most stiffening disks. Inlet and outlet means are
provided for the cryogenic liquid.
In its erected configuration, the tank is prestressed both
circumferentially and axially. The circumferential prestressing is
by means of the tendons positioned around the circumference of the
tank and the axial prestressing is by means of the tendons passing
through the holes in the tank wall. The stiffening plates are also
prestressed by tendons which pass through an axial series of plates
located between adjacent stiffening disks, the tendons passing
through the radially located holes in those disks. Where the tank
is of large diameter, it may be desirable to form the steel head
from a central dome and a surrounding torus, in order to limit the
amount of steel which is required. The head is attached to the end
stiffening disks and the toroidal section of the head is further
anchored to the cylindrical wall by the axial prestressing tendons
and by tendons external to the tank which are oriented diagonally
of the tank axis.
The advantages of the tank configuration of this invention are
many. The circular or elliptical cross-section, particularly in a
horizontal orientation, makes very efficient use of the internal
cubic of conventional ships or barges. Prestressed concrete is
markedly more economical than the expensive alloy plates of
free-standing, prismatic tanks or the even more expensive materials
and complicated construction techniques associated with membrane
tanks. Since the configuration of the tank is relatively simple,
the structure is a fully determinant one, and does not require a
secondary barrier to protect the ship hull and the cargo from one
another. With the steel sheath a measure of secondary barrier is
provided, nonetheless. Thus, the tank configuration of the
invention provides all of the advantages of a two barrier system
while being fully determinant and thus subject to the less rigid
design controls promulgated for determinant systems. The structural
integrity of the system, by virtue of its circumferential and axial
prestressing, provides a very substantial measure of safety for
tank and cargo, should the vessel be involved in a collision and
lends a stiffness to the ship structure. The compartments which are
formed within the tank, due to the presence of stiffening disks and
stiffening plates, reduce sloshing of the cargo within the tank and
make the overall operation more safe. The relatively high weight of
the concrete, is an advantage insofar as it substantially reduces
the ballast requirements of the vessel and lowers the center of
gravity. Still a further advantage of the tank configuration, is
that it is relatively easily positioned within a supporting cradle
in the ship structure and can be firmly positioned therein without
requiring elaborate support systems.
To facilitate construction of the tank, a modular wall component is
fabricated. The component is comprised of a length of concrete,
cylindrical tank wall of suitable curved cross-section having
axially oriented holes passing through its length, a steel sheath
anchored to its exterior surface and prestressing tendons wrapped
essentially circumferentially about the exterior of the steel
sheath. The concrete stiffening plates are integrally cast with the
modular tank wall, and axial holes are provided therein. To erect
the tank, from the modular components, it is necessary only to
combine several of the wall modules, end to end and position,
between them, annular, steel or concrete stiffening disks. The
assembled tank is then prestressed axially as described above and
the steel heads are attached to the end disks.
By providing a number of the modular components, together with the
annular disks, a tank having the configuration described above can
be relatively easily constructed within a conventional steel or
concrete vessel. Desirably, the vessel will include a grid-like
cradle which comprises transverse and axial structural members
positioned in registration with the lower stiffening disks and the
lower stiffening plates respectively. The transverse members are
provided with a balsa wood support upon which the exterior portion
of a stiffening disk is mounted. The axial structural members are
positioned beneath the lower stiffening plates within the tank.
Desirably, the tank is fixed to its cradle at only one position
along the axis of the tank, i.e., at one transverse structural
member and is slidably supported on several other structural
members. The purpose of the fixed support is to preclude axial
movement of the tank within the vessel and the purpose of the
sliding supports is to permit axial contraction and expansion of
the tank during cool-down and warm-up. Chocks may be provided at
the sides and top of the tank to prevent it from rotating. However,
the chocks should permit axial expansion and contraction of the
tank.
The invention also embraces the method for forming the modular
component for the cryogenic tank. A length of concrete, cylindrical
tank wall of circular or elliptical cross-section is cast with
axially oriented holes extending through it and radial-axial
stiffening plates extending inwardly from its inner surface at
spaced locations. A steel sheath is anchored to its exterior
surface. The steel sheath may be studded to the concrete, as it is
poured, according to conventional techniques. After the concrete
has set, the tank wall is prestressed by wrapping one or more steel
tendons, in tension, about the outer surface of the steel sheath.
The latter step may be carried out by mounting the cast wall on a
turntable and rotating the turntable while tendons are wrapped
about the tank wall. Alternatively, a carriage may be supported
from the tank wall and moved about the circumference thereof while
wrapping a tendon thereabout, as is conventional procedure in the
construction of stationary tanks. A group of components positioned
one above the other may be prestressed in a single operation.
The advantages in the methods of this invention are numerous.
Modular components may be formed by conventional techniques in the
shipyard, but at a distance from the site of the ship construction,
or at a remote location. The erection of the tank is simplified
because the modular components should be sized so as to be of such
weight as will be within the lifting capacity of available lifting
apparatus at ship building sites. The axial tensioning of the
modules and stiffening plates is performed with suitable jacks.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a simplified, side elevation view of a steel tanker
containing five liquid natural gas tanks according to the present
invention;
FIG. 2 is a side elevation view of one of the tanks shown in FIG.
1;
FIG. 3 is a fore and aft elevation view, in section, of the tank of
FIG. 2 taken along lines 3--3 of FIG. 2;
FIG. 4 is a partial section view of the tank shown in FIG. 2,
showing details of the modular wall construction;
FIG. 5 is a partial fore and aft elevation vview of the portion of
the modular wall construction of FIG. 4 taken along lines 5--5 of
FIG. 4;
FIG. 6 is a simplified, exploded, view of the modular components of
the tank, showing their juxtaposition prior to assembly;
FIG. 7 is a view of the tank in partially assembled state;
FIG. 8 is a detailed view of a fixed support pedestal for the tank
of FIG. 2; and
FIG. 9 is a detailed elevation view of a sliding support pedestal
for the tank of FIG. 2.
With reference to FIG. 1, reference numeral 10 refers generally to
a conventional tanker. Reference numeral 12 refers to a hull and
reference numeral 14 to a tanker super structure. Reference
numerals 16, 18, 20, 22 and 24 refer to five, horizontally oriented
tanks for containment of cryogenic liquid having the configuration
more fully described below.
With reference to FIGS. 2, 3, 4 and 5, it can be seen that tank 16
is comprised of a cylindrical tank wall of circular cross-section
26 and includes heads 28 and 30. Head 28 comprises a central dome
32 and a torus 34. However, this head design is optional and may be
employed in large tanks to reduce the amount of expensive alloy
metal required. In smaller tanks, the heads may be elliptical or
hemispherical. Inlet and outlet means for the cryogenic liquid are
not shown, however, they may be provided at suitable locations in
the top of the tank or through the steel heads.
As shown in FIG. 3, cylindrical tank 16 is supported within hull 12
on a cradle 36 which includes several parallel, transverse,
partially circular support members 38 and three parallel, axial
support members 40, 42 and 44. The entire tank is surrounded by
insulation 46 which may be mineral wood, perlite or other suitable
insulating material. The tank 16 is prevented from rotating within
hull 12 by means of a chock 48 which includes a bracket 50 attached
to the top of the tank having a recess section 52 in which is
placed restraining member 54 attached to the hull or deck
structure. Chocks may also be attached to the sides of the
tank.
Tank 16 is comprised of a plurality of modular, concrete wall
components 60a, 60b, 60c, etc. Each of these modular wall
components is cylindrical and of circular cross-section and has a
plurality of axial holes passing therethrough designated by
reference numeral 62. Located within axial holes 62 are
prestressing tendons 64. Located externally of modular components
60a, 60b, 60c, etc. are steel sheaths 65a, 65b and 65c, etc. which
pass circumferentially around the exterior surface of the concrete.
The steel sheaths are anchored to the concrete wall by means of
studs 66. Located on the outer surface of steel sheaths 65 are
prestressing tendons 68 which pass circumferentially about the
sheaths and are in tension causing the concrete and steel sheath to
act compositely. A series of discrete tendons may be used or
helically wound tendons may be employed. A layer of gunnite or
other suitable bitumastic material or plastic coating such as epoxy
serves as protective overcover for the circumferential prestressing
tendons as designated by reference numeral 70. Positioned at the
right end of modular tank component 60a and between each of
components 60a and 60b, 60b and 60c, etc. are annular, concrete
stiffening disks 72a, 72b, 72c, etc. Each of these stiffening disks
are positioned coaxially with respect to the tank. Head 28 is
attached, by suitable connection to endmost stiffening disk
72a.
As seen best in FIGS. 4 and 5, a series of flat, concrete
stiffening plates 74 are provided. Each of these stiffening plates
are positioned both radially and axially with respect to tank 16.
They are integral with the inner surface of the cylindrical tank
wall at their radial outermost extension 76 and abut, at their
axial extensions 78 and 80, the two stiffening disks between which
they are located, i.e., in FIG. 4, disks 72a and 72b. These
stiffening plates have essentially axially oriented holes therein
designated by reference numeral 82 through which prestressing
tendons 84 are passed. Suitable holes are provided in stiffening
disks 72 for through-passage of tendons 64 through the holes 62 in
modular wall components 60, and through an axial series of
stiffening plates 74. Prestressing tendons 84 terminate in suitable
tensioning heads 86 on the end most stiffening disk, 72a.
Desirably, stiffening disks 72 are spaced from one another by
uniform modular wall components 60 and the rows of stiffening
plates 74 are positioned at a uniform angular distance from one
another around the inner circumference of the tank. These outer
extensions of the disks may form support posts or positioning rails
for the tank, and as seen in FIG. 3, these posts are received in
cradle 36 in transverse structural member 38.
As shown in FIGS. 6 and 7, the tank configuration of this invention
is most easily assembled by positioning modular wall components
100, comprised of cast concrete wall sections of circular
cross-section having holes 102 therein and circumferential
prestressing tendons 104, alternately with stiffening disks 106
which have circumferential holes 108 and radial holes 110 for
through-passage of prestressing tendons. The axial prestressing
tendons which pass through the wall of the concrete tank are
designated by reference numerals 120 and the prestressing tendons
which pass through the series of stiffening plates are designated
by reference numerals 122. As seen best in FIG. 7, the interior of
the assembled tank has a partially compartmentalized configuration,
which is of advantage in reducing sloshing when the tank is filled.
To complete the overall tank structure, heads are fixed to either
end of the assembled cylindrical structure as shown in FIG. 2. As
further shown in FIG. 2, where the heads are toroidal, the torus
may be further anchored to the assembled cylindrical wall be
prestressing tendons 125 and 127 which are oriented diagonally of
the tank volume enclosed by the torus.
FIG. 8 shows a fixed support for the tank. Reference numeral 38
represents a transverse support member for the tank. Within support
member 38 is a recess 39 containing balsa wood 41 which provides a
support for the tank. The lower extension of stiffening disk 72 on
one end of the tank is thus fixed with respect to the axis of the
tank and accordingly the tank cannot move when affected by impacts
due to waves or other disturbances encountered by the vessel.
In FIG. 9, reference numeral 138 refers to a transverse, cradle
support member, of partial circular shape, having a recess at 139
filled with balsa 141. As shown, the lower extension of the
stiffening disk 172 sits on the upper surface 143 of balsa 141 and
can slide across that surface under the influence of contraction
and expansion forces encountered in the cool-down and warm-up of
the tank.
* * * * *