U.S. patent application number 12/342486 was filed with the patent office on 2010-06-24 for tank shell for an outer lng containment tank and method for making the same.
This patent application is currently assigned to Chevron U.S.A Inc.. Invention is credited to Vincent G. Borov, Lestle R. Shockley.
Application Number | 20100154319 12/342486 |
Document ID | / |
Family ID | 42264066 |
Filed Date | 2010-06-24 |
United States Patent
Application |
20100154319 |
Kind Code |
A1 |
Shockley; Lestle R. ; et
al. |
June 24, 2010 |
TANK SHELL FOR AN OUTER LNG CONTAINMENT TANK AND METHOD FOR MAKING
THE SAME
Abstract
A shell for an outer LNG containment tank and a method of making
the shell from a plurality of precast reinforced concrete shell
elements are described. The shell elements having a precast
concrete body to which are anchored a radially inwardly facing
liner plate and a pair of circumferentially spaced apart side
plates which depend radially outwardly from the liner plate. The
shell elements can be arranged upon a ring beam with side plates
abutting one another. The side plates are welded together to form
radially and vertically extending stiffener ribs which are
circumferentially spaced around the shell. As these stiffener ribs
provide great structural support, the shell can be constructed with
minimal or no cast in place structural joints being needed to
construct the shell. Ideally, the shell elements have bottom base
plates welded to a ring beam or foundation and top end plates that
are welded together to form an annular ring thus enhancing the
structural strength of the shell. A roof can be mounted to the
shell to create an outer LNG containment tank.
Inventors: |
Shockley; Lestle R.; (San
Ramon, CA) ; Borov; Vincent G.; (Martinez,
CA) |
Correspondence
Address: |
CHEVRON CORPORATION
P.O. BOX 6006
SAN RAMON
CA
94583-0806
US
|
Assignee: |
Chevron U.S.A Inc.
|
Family ID: |
42264066 |
Appl. No.: |
12/342486 |
Filed: |
December 23, 2008 |
Current U.S.
Class: |
52/82 ;
52/745.01 |
Current CPC
Class: |
E04H 7/18 20130101 |
Class at
Publication: |
52/82 ;
52/745.01 |
International
Class: |
E04B 7/10 20060101
E04B007/10; E04B 7/00 20060101 E04B007/00 |
Claims
1. A method for constructing a shell for an outer LNG containment
tank, the method comprising: providing a plurality of precast
reinforced concrete shell elements, at least some of the shell
elements having a precast concrete body to which are anchored a
radially inwardly facing liner plate and a pair of radially
extending and circumferentially spaced apart side plates which
depend from the liner plate; juxtaposing the shell elements upon a
ring beam with side plates abutting one another; and welding
abutting side plates together to at least partially form the shell
and to form radially extending stiffening ribs which are
circumferentially spaced around the periphery of the shell.
2. The method of claim 1 wherein: at least some of the shell
elements include a base plate and a top end cap plate; and the base
plates are welded to the ring beam and the top end cap plates are
welded to one another to form an annular ring of top end cap
plates.
3. The method of claim 1 wherein: the liner plates and side plates
cooperate to form a continuous inner radial membrane to the
shell.
4. The method of claim 1 wherein: at least some of the shell
elements have mechanically interlocking surfaces and the at some of
the shell elements interlock with one another before being welded
together.
5. The method of claim 4 wherein: at least some of the interlocking
surfaces include cooperating projections and receptacles.
6. The method of claim 1 wherein: the shell includes at least two
circumferentially extending and vertically arranged courses of
shell elements which are welded together to form at least a portion
of the shell.
7. The method of claim 1 further comprising: constructing the shell
to include a shell access opening therein to allow access within
the shell.
8. The method of claim 7 further comprising: sealing the shell
access opening with at least one temporary liner plate;
pressurizing the inside of the shell to air lift a roof assembly to
the top of the shell; mounting the roof assembly to the shell;
unsealing the shell access opening to access the interior of the
shell to construct an inner tank while roof elements are welded to
the roof assembly to form a roof atop the shell; and permanently
sealing the shell access opening after the inner tank is
constructed.
9. The method of claim 7 further comprising: casting in place a
concrete body which anchors to the at least one temporary liner
plate to effect the permanent sealing of the shell access
opening.
10. The method of claim 7 further comprising: permanently sealing
the access opening utilizing at least one temporary liner plate,
the temporary liner plate being part of a precast reinforced
concrete shell element.
11. A shell for an outer LNG containment tank, the shell
comprising: a plurality of precast reinforced concrete shell
elements, at least some of the shell elements having a precast
concrete body to which are anchored a radially inwardly facing
liner plate and a pair of radially extending and circumferentially
spaced apart side plates which depend from the liner plate; wherein
the at least some of the shell elements are arranged
circumferentially with abutting side plates being welded together
to at least partially form a shell and to form radially extending
stiffening ribs which are circumferentially spaced about the
periphery of the shell.
12. The shell of claim 11 wherein: at least some of the shell
elements further include bottom base plates which are welded to a
ring beam to provide support to the shell.
13. The shell of claim 11 wherein: at least some of the shell
elements further include top end cap plates which are welded to one
another to form an annular ring of end cap plates.
14. The shell of claim 11 wherein: the liner plates and side plates
cooperate to form a continuous inner radial membrane to the
shell.
15. The shell of claim 11 wherein: at least some of the shell
elements have mechanically interlocking surfaces and the at least
some of the shell elements interlock with one another.
16. The shell of claim 15 wherein: at least some of the
interlocking surfaces include cooperating projections and
receptacles.
17. The shell of claim 11 wherein: the shell includes at least two
circumferentially extending and vertically arranged courses of
shell elements which are welded together to form at least a portion
of the shell.
18. The shell of claim 11 wherein: the shell has an shell access
opening formed therein; and the shell access opening is sealed by
at least one cast in place shell element having a liner plate which
cooperates with the liner plates and sides plates of the precast
shell elements to seal the access opening.
19. The shell of claim 11 wherein: the shell has an shell access
opening formed therein; and the shell opening is sealed by at least
one precast shell element having a liner plate, the at least one
precast shell element cooperating with other liner plates and sides
plates of the shell to seal the access opening.
20. A shell element for constructing the shell of an outer LNG
containment tank, the shell element comprising: a precast
reinforced concrete body to which are anchored a radially inwardly
facing liner plate and a periphery formed by a pair of vertically
extending circumferentially spaced apart side plates, a bottom base
plate and a top end cap plate; wherein a plurality of the shell
elements may be arranged in circumferential abutment and the side
plates welded together to form radially extending stiffener ribs
and the liner plates form part of radial inwardly facing shell
membrane.
Description
TECHNICAL FIELD
[0001] The present invention relates generally to the construction
of LNG (liquefied natural gas) storage tanks, and more
particularly, to methods for constructing shells or tank walls for
very large structures.
BACKGROUND
[0002] Large storage tanks are typically designed with a so-called
"shell"--a reinforced concrete circular wall centered continuously
on top of and integrally connected to the tank foundation. Shell
walls may be large structures and are often cast in place on top of
a ring beam foundation. With very large tanks, this casting in
place construction is a time-consuming process and may be
problematic at remote site locations. Building with precast
concrete elements is a known approach in the construction of
various structures when construction time at the site needs to be
minimized, and when site conditions and location are problematic
for casting in place. However, shells are very specific structural
elements due to their function and configuration in large storage
tanks and are not easily constructed. Effective connections between
the separate precast segments are difficult and time consuming to
construct. Cast in place connections between shell elements have
been one conventional manner for joining such shell elements.
[0003] The walls of large storage tanks need to be reinforced to
handle construction, operating and earthquake loads. Conventional
construction of the shell is to erect the inner metal liner first
then erect rebar and forms followed by slip forming the concrete.
To use precast concrete shell elements, the elements are spaced a
short distance apart to allow rebar connections (either mechanical
or welded) followed by slip form casting of the gaps between the
elements. Then the gap is covered with steel and the concrete is
cured for a short time, i.e., about 3-5 days. The total shell
erection time is dependent on these connection curing times to
complete the shell circumference so that additional construction
load may be safely applied to erect the roof.
[0004] An example of a full containment LNG tank design is defined
in European codes such as British Standard 7777. An outer secondary
container or tank acts as a catch basin in case of a leak or tank
rupture of an inner container, which is often a steel tank. Also,
the outer tank is made of concrete which reduces the fire risk over
that of steel. However, the outer tank shell is either slip formed
in place and post tensioned or a steel liner is used as a form and
rebar added after the steel liner is erected, then slip or jump
formed. Either method can be quite time consuming.
SUMMARY
[0005] A shell for an outer LNG containment tank and a method of
making the shell from a plurality of precast reinforced concrete
shell elements are described. The method comprises providing a
plurality of precast reinforced concrete shell elements. At least
some of the shell elements having a precast concrete body to which
are anchored a radially inwardly facing liner plate and a pair of
radially extending and circumferentially spaced apart side plates
which depend from the liner plate. The shell elements are
juxtaposed upon a ring beam with side plates abutting one another.
The abutting side plates are welded together to at least partially
form the shell. The cooperating welded together side plates form
radially extending stiffening ribs which are circumferentially
spaced around the periphery of the shell.
[0006] Ideally at least some of the shell elements include a base
plate and a top end cap plate. The base plates are welded to the
ring beam and the top end cap plates are welded to one another to
form an annular ring of top end cap plates. Preferably, the liner
plates and side plates cooperate to form a continuous inner radial
membrane to the shell. In one embodiment, at least some of the
shell elements have mechanically interlocking surfaces and at least
some of the shell elements interlock with one another before being
welded together. The shell may be made from a single course of
shell elements or from a number of circumferentially extending and
vertically arranged courses of shell elements.
[0007] A shell for an outer LNG containment tank is also described.
The shell comprises a plurality of precast reinforced concrete
shell elements, at least some of the shell elements having a
precast concrete body to which are anchored a radially inwardly
facing liner plate and a pair of radially extending and
circumferentially spaced apart side plates which depend from the
liner plate. At least some of the shell elements are arranged
circumferentially with abutting side plates being welded together
to at least partially form a shell and to form radially extending
stiffening ribs which are circumferentially spaced about the
periphery of the shell. Preferably, at least some of the shell
elements further include bottom base plates which are welded to a
ring beam to provide additional support to the shell. Further, at
least some of the shell elements can have top end cap plates which
are welded to one another to form a circumferential extending
annular ring of end cap plates. Ideally, the liner plates and side
plates cooperate to form a continuous inner radial membrane to the
shell. Also, in one embodiment, at least some of the shell elements
have mechanically interlocking surfaces and the at least some of
the shell elements interlock with one another. The interlocking
surfaces can include cooperating projections and receptacles. The
shell can include one or multiple courses of circumferentially
extending and vertically arranged courses of shell elements which
are welded together to form at least a portion of the shell.
[0008] The shell can have a shell access opening formed therein.
The shell access opening can be sealed by at least one cast in
place shell element having a liner plate which cooperates with the
liner plates and sides plates of the precast shell elements to seal
the access opening. Another alternative is to seal the shell access
opening with at least one precast shell element having a liner
plate, the at least one precast shell element cooperating with
other liner plates and sides plates of the shell to seal the access
opening.
[0009] A shell element for constructing the shell of an outer LNG
containment tank is also disclosed. The element comprises a precast
reinforced concrete body to which are anchored a radially inwardly
facing liner plate and a periphery formed by a pair of vertically
extending circumferentially spaced apart side plates, a bottom base
plate and a top end cap plate. A plurality of the shell elements
may be arranged in circumferential abutment and the side plates
welded together to form radially extending stiffener ribs and the
liner plates form part of radial inwardly facing shell
membrane.
[0010] It is an object to provide precast concrete shell elements
that have steel liner plates that can be quickly fit together and
the shell elements welded to form a shell circumference.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] These and other objects, features and advantages of the
present invention will become better understood with regard to the
following description, appended claims and accompanying drawings
where:
[0012] FIG. 1A is a perspective view of an inner tank being
constructed within an outer containment tank as the roof of the
outer tank is being constructed;
[0013] FIG. 1B is a perspective view of a completed outer tank, in
partial cutaway, showing a base mat assembly, a ring beam, a shell
or tank wall and a roof mounted atop the shell as well as the inner
tank;
[0014] FIG. 2 is a plan view of the base mat assembly or foundation
and a ring beam or ring beam foundation which are to be joined by a
cast in place concrete connection (not shown);
[0015] FIG. 3A is a plan view of a pair of base mat elements
juxtaposed and interconnecting with one another;
[0016] FIG. 3B is a perspective view of a liner plate and attached
J-hooks which are to be cast within a concrete body when making a
reinforced concrete base mat element;
[0017] FIG. 3C is a perspective view of a base mat element,
including concrete body, showing a pair of tensile members passing
through tensile conduits disposed within the concrete body;
[0018] FIG. 3D shows a plurality of base mat elements juxtaposed in
lateral and longitudinal directions with tensile members and
cooperating anchors clamping the base mat elements together in the
lateral and longitudinal directions;
[0019] FIG. 4 shows an exemplary pile with L-shaped brackets
mounted thereon which can be used to support base mat elements or
ring beam elements at predetermined heights so that the base mat
elements or the ring beam elements can be readily welded
together;
[0020] FIG. 5 shows a matrix of piles which can be used to support
base mat elements which can then be welded together to form the
base mat assembly;
[0021] FIG. 6A is a plan view of a pair of cooperating juxtaposed
ring beam elements;
[0022] FIG. 6B is a perspective view of a liner plate welded to a
thicker base plate and attached J-hooks welded beneath the plates
which are used in casting a reinforced concrete ring beam
element;
[0023] FIG. 6C is a perspective view of a reinforced concrete ring
beam element including the liner plate and base plate anchored to a
concrete body with tensile members extending through tensile
conduits embedded in the concrete body;
[0024] FIG. 7 is a fragmentary sectional view of a cast concrete
joint joining the base mat assembly and the ring beam with a shell
element being welded to the ring beam;
[0025] FIG. 8A is a perspective view of a shell element;
[0026] FIG. 8B is a perspective view of a pair of shell elements
which are welded together to form part of the outer shell with the
shell elements also being welded to base plates of ring beam
elements;
[0027] FIG. 8C shows a sectional view of a second embodiment of a
shell made with two courses of lower and upper shell elements
rather than using a single course as seen in the shell of FIG.
8B;
[0028] FIG. 8D shows a bottom view of the upper shell element which
includes a base plate supporting two downwardly depending alignment
pipes;
[0029] FIG. 8E shows a plan view of a top end cap plate of a lower
shell element having two downwardly depending alignment sockets
designed to receive the alignment pipes of the upper shell
element;
[0030] FIG. 9A is a roof frame formed by radial and
circumferentially extending wide flange beams;
[0031] FIG. 9B illustrates a typical welded connection between a
tubular mounting beam of a roof assembly and a pair of roof
elements;
[0032] FIG. 9C shows the roof assembly and attached seal being
raised by air pressure within the outer shell so that the roof
assembly can be welded to temporary gusset plates mounted to the
top of the shell;
[0033] FIG. 9D is a fragmentary perspective view of the roof
assembly and peripheral seal being raised to be temporarily welded
to a gusset plate;
[0034] FIG. 9E is a fragmentary perspective view of a roof membrane
of the roof assembly being temporarily welded to a gusset
plate;
[0035] FIG. 9F is a fragmentary perspective view of the roof
assembly permanently welded to the shell with the temporary gusset
plates and seal having been removed and with a roof element
attached to the roof assembly and shell;
[0036] FIG. 10A is a perspective view of a roof element frame used
in casting a typical roof element; and
[0037] FIG. 10B is a perspective view of an exemplary roof element
which is to be mounted to the roof assembly during construction of
the roof.
DETAILED DESCRIPTION
I. Overview
[0038] In a first embodiment, a full containment LNG tank 18 is
shown in FIGS. 1 and 2. The LNG tank 18 comprises an outer
secondary container, hereinafter "outer tank 20" surrounding an
inner primary container, hereinafter "inner tank 22". Inner tank 22
is intended to store LNG. Outer tank 20 is preferably a full
containment tank in which both LNG and gas vapor are fully
contained in the event of a leak from the inner tank 22.
[0039] In this particular embodiment, outer tank 20 is primarily
made of precast reinforced concrete elements which reduce fire risk
relative to using a primarily steel outer container or tank. The
construction of outer tank 20 involves assembling precast
reinforced concrete elements for a foundation 24, including a base
mat assembly 100 and an outer ring beam 200, an outer wall or shell
300 and a roof 400. As an example of order of magnitude, outer tank
20 in this embodiment has a diameter of approximately 80 meters, an
overall height (to the top of the dome of roof 400) of about 50
meters, and a height to the top of shell 300 of about 40 meters.
Those skilled in the art of LNG facilities construction will
appreciate that much larger or smaller tanks can be built and still
use the design considerations described herein. However, tanks
having diameters of at least 25 meters are particularly well suited
to the construction methods described herein which utilize precast
reinforced concrete elements. These elements ideally can be welded
together to form structural welds thereby minimizing the number of
cast in place concrete structural joints which have to be made to
form an outer containment tank.
[0040] Ideally, inner tank 22 can be assembled at the same time as
roof 400 is being built to save time and money in the overall
construction of inner tank 22 and outer tank 20. Note in FIG. 1
roof elements 402 are being added ring by ring to a roof assembly
404 while inner tank 22 is being constructed. A construction access
or shell opening 350 in shell 300 allows for materials to be
carried into outer tank 20 so that inner tank 22 can be built as
roof 400 is being constructed. After inner tank 22 is completed,
special half height shell elements 302' can be installed to close
opening 350. An annular gap of approximately 1.5 meters exists
between inner tank 20 and shell 300 to permit circumferential
access to build inner tank 22 and to accommodate insulating
materials (not shown) which are to be installed between outer and
inner tanks 20 and 22.
[0041] Inner tank 22 can be built in any of a number of ways which
may require welding processes to connect individual plates. For
example, the plates can be joined using shielded metal arc welding
(SMAW) and submerged arc welding (SAW) for 9% nickel tanks of the
size described above, i.e. having a diameter greater than 25
meters. In this particular example, inner tank 22 can be friction
stir welded (FSW) by plate at a time erection method. A course of
plates at a time can be welded with the bottom (thickest) first and
then subsequent (thinner) courses welded there above. Scaffolding
(not shown) can be used as each course is added. Alternatively,
inner tank 22 can be constructed course down either by supporting
the tank from the roof to allow insertion of the next course or by
supporting on jack stands to allow insertion of the next course.
For the last two methods, the scaffolding need be erected only one
time. By way of example and not limitation, another alternative
method is to use coil material shaped to the curvature required for
the tank. Coil tank building occurs from the top course down either
using jacking or by roof supported. Expanded pearlite insulation is
typically used in the annulus formed between inner tank 22 and
outer tank 22. Although not shown, an under bottom insulating
layer, which can be made of foam glass, is applied on the top of
base mat assembly 100 with inner tank 22 prior to inner tank 22
being placed there on.
[0042] Foundation 24, i.e., base mat assembly 100 and ring beam
200, is designed to support inner tank 22 and outer shell 300.
Outer shell 300 rests upon and transfers loads directly to outer
ring beam 200 preferably through welded connections. A particularly
significant load is the torsional load applied to ring beam 200
from outer shell 300. Base mat assembly 100 is secured to and
transfers loads to outer ring beam 200 as well through a cast in
place joint 270, which is best seen in FIG. 7. Depending on soil
conditions, base mat assembly 100 and/or outer ring beam 200 can be
supported upon compacted soil or else on piles, as will be
described below. Roof 400 of tank 20 includes a roof assembly 404
comprising a skeletal steel frame 406 (FIG. 9A), a membrane 412
(FIG. 9B) of liner plates 410 and radially and circumferentially
extending tubular mounting beams 414. Roof 400 is supported atop
outer shell 300. Roof assembly 404 supports and is strengthened by
a number of concentric rings or courses of precast reinforced
concrete roof elements 402 and 402'. FIG. 2 shows a completed outer
tank 22 with shell opening 350 being sealed and closed by special
half shell elements 302' which are permanently welded to the
remainder of shell 300.
II. Base Mat Assembly 100
[0043] FIG. 2 shows base mat assembly 100 disposed within outer
ring beam 200. A cast in place concrete connection 270 (not shown)
is to be formed there between, as best illustrated in FIG. 7. In
this particular exemplary embodiment, a large number of generally
rectangular base mat elements 102 are connected together to form
base mat assembly 100 having a contiguous top membrane 140 made
from welded together steel liner plates 104. Membrane 140 ideally
cooperates with similar membranes formed from liner plates on
connection 270, outer ring beam 200, shell 300 and roof 400 to form
an overall air tight vapor barrier within outer tank 20. As will be
described later in greater detail, base mat assembly 100 and outer
ring beam 200 preferably have discrete reinforced concrete elements
that are clamped together by post-tensioned tensile members 150,
250, i.e., steel cables, and anchors 152, 252. Precast elements
102, 202 are then welded to together to form, respectively, base
mat assembly 100 and outer ring beam 200.
A. Base Mat Elements 102
[0044] FIG. 3A shows a pair of juxtaposed base mat elements 102.
FIG. 3B shows a generally rectangular liner plate 104 having a
series of projections 106 and recesses 110. Liner plate 104 is
preferably made of carbon steel although it can instead be made of
other appropriate metals. The thickness is of liner plate 104 in
this exemplary embodiment is about 10 mm. As an example, in this
embodiment the size of liner plate 104 and base mat elements 102
are approximately 2 meters by 3 meters. A plurality of J-hooks 112
is welded to the lower surface of liner plate 104.
[0045] FIG. 3C depicts a base mat element 102 having a concrete
body 114 cast about J-hooks 112 to anchor liner plate 104 to
concrete body 144. Although not shown to simplify the drawing,
formed in the concrete body 114 are two or more layers of
reinforcing bars or welded wire fabric running in two generally
perpendicular directions. For example, the reinforcing bars can be
ASTM A 615 deformed carbon-steel bars for concrete reinforcement.
Also formed within concrete body 114 is a plurality of laterally
extending lower and upper tensile conduits 120, 122 and
longitudinally extending lower and upper tensile conduits 124, 126
which extend in generally perpendicular directions to one another.
These tensile conduits 120, 122, 124 and 126 can be HDPE (high
density polyethylene) tubing or steel piping or other appropriate
structural conduits.
[0046] Concrete ribs 130 and grooves 132 are also formed on the
longitudinally and laterally extending edge surfaces of concrete
body 114. Locating projections 106 and ribs 130 and receiving
recesses 110 and grooves 132 allow a plurality of base mat elements
102 to be placed in interlocking juxtaposition as suggested in FIG.
2, FIG. 3A and FIG. 3D when base mat assembly 100 is being
constructed. Note that concrete body 114 has downwardly and
upwardly opening steps 134 and 136 so mating base mat elements 102
can interlock in the vertical direction as well as in the lateral
and longitudinal directions.
[0047] The rows of tensile conduits are disposed below and above
the central horizontal plane 144 of concrete body 114. These
laterally and longitudinally extending tensile conduits are
designed to receive tensile members 150 there through which allow
multiple base mat elements 102 to be clamped together utilizing
anchors 152 (FIG. 3D) upon the post-tensioning of the tensile
members 150. Only some of the tensile members 150 are shown in FIG.
3D.
B. Construction of Base Mat Assembly 100
[0048] Base mat assembly 100 is constructed by juxtaposing base mat
elements 102 in both first and second generally perpendicular
directions as seen in FIG. 2. Locating projections 106 and concrete
ribs 130 cooperate with receiving recesses 110 and grooves 132 on
adjacent elements 102 to align base mat elements 102 in first and
second generally perpendicular directions. Steps 134, 136 allow
base mat elements 102 to interlock in the vertical direction as
well.
[0049] Tensile members 150 are fed through tensile conduits 120,
122, 124 and 126 as base mat elements 102 are being juxtaposed to
one another. After the mating surfaces on the base mat elements 102
are properly located relatively to one another, tensile members
150, i.e. cables, are post-tensioned and anchored by anchors 152 to
clamp base mat elements 102 together. In this particular example,
tensioning can be accomplished such as by using a Williams Strand
Anchor System available from Williams Form Engineering of Belmont,
Mich., USA. Those skilled in the art will appreciate that other
tensioning systems can also be used to post-tension and anchor
tensile members 150. After the tensioning is complete, anchors 152
are locked in place on tensile members 150 to maintain the tension
in tensile members 150 with anchors 152 bearing upon base mat
elements 102.
[0050] Liner plates 104 of each of base mat elements 102 are then
welded together to form a part of a generally contiguous membrane
140 on the top of base mat assembly 100. As tensile conduits 120,
122, 124 and 126 are located above and below the central horizontal
plane 144 of concrete body 114, the top and bottom surfaces of base
mat elements 102 are held together and do not separate due to the
post tensioning of tensile members 150 with anchors 152 clamping
about base mat elements 102, preferably even under construction and
operating loads applied to base mat assembly 100.
C. Mounting of Base Mat Elements on Piles
[0051] Base mat elements 102 can be assembled on a graded, level
surface if the underlying surface or soil is sufficiently stiff.
However, if the soil does not provide adequate support, base mat
elements 102 can be mounted on piles 160. The upper portion of a
typical pile 160 is seen in FIG. 4. Pile 160 includes a post 162
which is driven into the ground such as in soft soil 163. Four
L-shaped brackets 164 can be bolted or welded to post 162 at an
appropriate location with horizontally extending flanges 166 being
at a predetermined height. Ideally, a laser positioning system is
used to maintain all of the flanges 166 within a predetermined
tolerance of height. Mounting base mat elements 102 on flanges 166
will then provide for easy welding of liner plates 104 together as
the liner plates 104 should all be at about the same height.
Reinforcing bars 170 extend upwardly from post 162 to facilitate
later cast in place connections between piles 160 and base mat
elements 102.
[0052] FIG. 5 depicts a couple of base mat elements 102 being
mounted upon flanges 166 of a matrix of piles 160. Note in this
case of utilizing piles 160 for support, base mat elements 102 are
notched in their corners and along their long sides to mate with
posts 162, as seen in FIG. 5.
[0053] The corners and long sides of base mat elements 102 will be
supported by six cooperating supporting flanges 166. Voids 174 are
created by the intersection of the corners and along the sides of
cooperating base mat elements 102. In the case where piles are
used, base mat elements 102 can include reinforcing bar loops (not
shown) which are embedded in concrete body 114 and extend laterally
and longitudinally from concrete body 114. The loops will loop over
vertically extending reinforcing bars 170. Concrete is cast in
these voids 174 about the loops and reinforcing bars 170. Fitted
liner plate 176 is anchored by J-hooks in the cast concrete so that
liner plates 104 and 176 can be welded together to form generally
continuous top membrane 140 on base mat assembly 100.
III. Outer Ring Beam 200
[0054] FIG. 2 shows a plan view of the foundation 24 including base
mat assembly 100 and outer ring beam 200. The numbers of base mat
and ring beam elements 102, 202 needed to construct these
components will vary depending on the size of the desired outer
tank 20 and the selected size of the various ring beam elements 202
and base mat elements 102. Various methods can be used to join base
mat assembly 100 to outer ring beam 200. Preferably, ring beam
elements 202 are clampingly held in a circumferential abutment by
post-tensioning tensile members 250 and clamping anchors 252 about
the ring beam elements 202. Then base plates 206 anchored within
each of ring beam elements 202 are welded together to form an
annular ring of such base plates 206. Similarly, inner liner plates
204 are also welded to one another to increase strength and
stiffness and to form a membrane 244 of liner plates 204.
Post-tensioned tensile members 250 and anchors 252 assist outer
ring beam 200 in resisting bending, shear and torsional forces
applied to ring beam 200 by outer shell 300 and by base mat
assembly 100 to maintain ring beam elements 202 in the proper
abutting relationship with respect to one another.
A. Ring Beam Element 202
[0055] FIGS. 6A-C illustrate an exemplary embodiment of a ring beam
element 202. In plan view, FIG. 6A shows a pair of ring beam
elements 202 interlocking with one another when placed in side by
side position. FIG. 6B shows an inner liner plate 204 secured to a
thick base plate 206. Liner plate 204 and base plate 206 are
preferably made from carbon steel. Liner plate 204 is approximately
10 mm thick and base plate 206 is about 50 mm thick in this
example. J-hooks 212 are welded to the bottom sides of liner plate
204 and base plate 206. Projection 214 and recess 216 are formed on
the edges of liner plate 204. FIG. 6C illustrates that ring beam
element 202 includes a concrete body 220 in which liner plate 204,
base plate 206 and J-hooks 212 are embedded. An outer radial
surface 222 and an inner radial surface 224 define what will be
part of the radially outer and inner surfaces of ring beam 200. A
plurality of locating concrete ribs 226 and receiving recesses 230
allow juxtaposed ring beam elements 202 to be cooperatively
interlocked with one another, as seen in FIG. 2 and FIG. 6A, to
form outer ring beam 200.
[0056] Also formed within concrete body 220 are circumferentially
extending lower and upper tensile conduits 232, 234. In this
particular embodiment, there are four such tensile conduits 232,
234. Two of these tensile conduits 232 are generally arranged below
and two conduits 234 are arranged above the horizontal center plane
236 of ring beam element 202. Also, two of the tension conduits
232, 234 are arranged beneath base plate 206 and two are located
radially inwardly beneath liner plate 204 closer to the inner
radial surface 224. These cooperating locations of tensile conduits
232, 234 allow tensioning members 250, i.e., cables, to pass
through each of ring beam elements 202 and assist in counter
balancing the bending, shearing and torsional loads applied to base
plate 206 by outer shell 300. Also, tensile members 250 and anchors
252 cooperate to clamp about ring beam elements 202 to prevent the
abutting ring beam elements 202 from displacing with respect to one
another. In this particular example, high density polyethylene
(HDPE) tubing is used to form the tensile conduits 232, 234 in
concrete body 220. Of course, the tensile conduits could be made of
other suitable materials such as steel or other structurally strong
materials. Downwardly and upwardly opening steps 238 and 240 allow
elements 202 to be vertically interlocking as well. Also, located
within concrete body 220 is a plurality of reinforcing bars (not
shown) which are conventional for adding tensile strength to cast
concrete bodies. Extending radially inwardly are reinforcing bars
or J-hooks 242 which are later to be included in cast concrete
connection 270 which connects base mat assembly 100 with ring beam
200.
[0057] FIG. 6C illustrates a ring beam element 202 having four
circumferentially extending tensile conduits 232 and 234 extending
there through. This embodiment may be appropriate for cases where
outer ring beam 200 is supported by stiff underlying soil or
surface. In the event that a softer underlying soil is available at
a site, it may be preferably to include an additional pair of
tensile conduits located radially outboard of the locations where
the tensile conduits 232, 234 are positioned in FIG. 6C. This
allows additional clamping force to be applied across the ring beam
elements 202. FIG. 7 shows a ring beam element 202 with three pairs
of vertical spaced apart tensile conduits 232 and 234. Also, as
discussed above with respect to base mat elements 102, ring beam
elements 202 can also be mounted on leveled flanges of piles to
insure proper support and vertical alignment between ring beam
elements 202 which are to have liner plates 204 and base plates 206
welded together.
B. Construction of Outer Ring Beam 200
[0058] Ring beam elements 202 are juxtaposed with respect to one
another with locating concrete ribs 226 of one ring beam element
being held within locating recess 230 of the adjacent ring beam
element. Similarly, cooperating steps 238 and 240 assist in
vertical alignment between ring beam elements 202. Tensile members
250 are placed through tensile conduits 232 and 234 as the ring
beam elements are being positioned adjacent one another. As seen in
FIGS. 1A and 1B, at four locations along the circumference of outer
ring beam 200, there are pairs of special abutting ring beam
elements 202' through which the ends of tensile members 250 extend.
Tensile members 250 are tensioned utilizing tensioning devices 260
and anchors 252 are anchored about ring beam elements 202. In this
particular example, tensioning can be accomplished such as by using
the aforementioned Williams Strand Anchor System. Those skilled in
the art will appreciate that other tensioning systems can also be
used to post-tension and anchor tensile members 250.
[0059] After the individual ring beam elements 202 are aligned and
clamped together using tensile members 250 and anchors 252, base
plates 206 are welded together along their radially extending
abutting edges to form an annular ring which strengthens outer ring
beam 200. Finally, liner plates 204 on ring beam elements 202 are
also welded together along their radially extending edges to form a
continuous membrane 244 on the radial inner side of outer ring beam
200, as best seen in FIG. 8B.
C. Connection Between Base Mat Assembly 100 and Ring Beam 200
[0060] FIG. 7 illustrates an example of how a base mat assembly 100
can be connected to the outer ring beam 200. Concrete is cast in
place about reinforcing bars 142, 242 extending outwardly from
adjacent base mat elements 102 and radially inwardly from ring beam
elements 202 to form a cast in place joint 270 between the base mat
assembly 100 and outer ring beam 200. Liner plates 272 are cut to
the necessary size and shape to mate between liner plates 104 of
base mat assembly 100 and inner liner plates 204 of outer ring beam
100. J-hooks 274 are welded to the bottom side of liner plates 272.
Concrete is cast in place between base mat assembly 100 and base
ring 200 to create a concrete body 276 anchoring liner plates 272
and J-hooks 274, 142 and 242 in the cast concrete to form joint
270. Although not shown, appropriate reinforcing bars will also be
positioned in the space to be occupied by joint 270 prior to the
concrete being cast to enhance tensile strength of joint 270.
IV. Outer Shell 300
[0061] FIG. 8A shows a perspective view of a typical shell element
302. FIG. 8B depicts a pair of shell elements 302 which are welded
together and form a part of outer tank wall or shell 300. To reduce
construction time for outer tank 20, shell 300 is built using
precast reinforced concrete shell elements 302 that are joined by
welding shell elements 302 together to form a generally annular,
tapered thickness annular shell 300. Shell elements 302 are thicker
at their bottoms to handle greater loads applied there to near ring
beam 100 as compared to the loads imposed by roof 400. Preferably,
there is minimal or no need to cast in place any significant
structural connections to join shell elements 302 together or to
ring beam 200 or to roof 400. Shell elements 302 will be precast to
the number, widths and heights required for the size of outer tank
22. Typically, the inner diameter of outer tank 20 will be about 3
meters larger in diameter than inner tank 22 to allow for
construction of inner tank 22 and to provide for insulation in the
annulus between the tank shells. Precasting of shell elements 302
can be started as soon as the tank diameter and height are
known.
A. Shell Element 302
[0062] Each of shell elements 302 includes a pair of tapered carbon
steel side plates 304 and a carbon steel liner plate 306 forming a
generally U-shaped steel cross-section. In this example, the liner
plate 306 is about 10 mm thick and side plates 304 are about 25 mm
thick. The width of side plates 304 is about 800 mm at their bottom
and 400 mm at the top providing the tapered shape to shell element
302. A base plate 312 connects side plates 304 and liner plate 306
at the bottom of shell element 302. Numerous reinforcing bars 310
are welded to and extend from side plate 304 to the opposing side
plate 304 and from base plate 312 to top end cap 314. Base plate
312 is about 50 mm in thickness in this example. A steel end cap
plate 314, also about 50 mm thick, is welded to side plates 304 and
steel liner plate 306 at the top of shell element 302. Concrete is
cast in place in the U-shaped volume defined by side plates 304 and
steel liner plate 306 and about reinforcing bars 310 and J-hooks
316 to form reinforced concrete body 318. Liner plate 306 acts as a
vapor/gas barrier
B. Constructing Shell 300
[0063] Shell 300 is constructed by arranging shell elements 302
vertically upon outer ring beam 200. Initially, base plates 312 are
arranged radially slightly outside of their final position for
welding with shell elements 312 being slightly radially spaced
apart. Shell elements 302 are then moved radially inwardly until
all base plates 312 and side plates 304 are brought into abutment
at the proper radial position atop of base plates 206 of ring beam
202. Erection gear will be used to finally align and pull the side
plates 304 closely together to begin welding.
[0064] As seen in FIG. 8B and FIG. 1A, vertically extending weld
joints 320 are made on the inside and outside of abutting side
plates 304. Weld joints 320 ideally are designed to be strong
enough to carry the loads on shell 300 without any or little other
significant reinforcement, in particular, the need for post
tensioning or utilizing any type of significant cast in place
joints. End cap plates 314 are welded to one another forming weld
joints 322 and creating a continuous upper ring on shell 300. As
best seen in FIG. 7, base plates 312 of shell 300 and base plates
206 of ring beam 200 are welded together along the inner and outer
radial surfaces on base plate 312 to form base plate welds 324.
Shell elements 302 are splice welded to accommodate load transfer
even under earthquake or missile impact. If additional strength is
needed, shell elements 302 may be designed to be mechanically
interlocking with one another as well as being joined by welds such
as weld 320. Ideally, the welded connections between shell elements
302 will be comparable in strength to conventional cast in place
connections formed between shells.
[0065] All of shell elements 302 are permanently welded together to
form shell 300, with the exception of 2-4 special half shell
elements 302'. Half shell elements 302' are similar to shell
elements 302 except they are only about half the height of regular
shell elements 302. These special shell elements 302' will be
temporarily sealed with shell opening 350 to accommodate air
raising of roof assembly 404, as suggested in FIG. 9C. These
special half shell elements 302' are removed after roof assembly
404 is attached to shell 300 to provide access so that inner tank
22 can be concurrently erected as reinforcing roof elements 402 and
402' are welded to roof assembly 404. When inner tank 22 is
completed, along with insulation added in the annulus formed
between inner tank 22 and outer tank 20, the special half shell
elements 302' are permanently welded to the remainder of shell 300
to seal shell opening 350, as shown in FIG. 1B. Although not shown
in FIGS. 1A and 1B, manhole access openings will be provided in
roof 400 to provide access to perform welds on the interior of
outer tank 20. Also, the manhole access openings allow future
maintenance to be performed within outer tank 20.
[0066] As an alternative to permanently closing construction
opening 350, liner plates can be welded to close shell opening 350.
Then reinforcing bars and steel rib stiffeners can be placed in a
form and concrete can be cast in place to form a cast in place
shell element similar to that used in the design of the precast
shell elements 302. Shell 300 should have great strength when
completed due to the welded connections 320 on the inner and outer
edges of side plates 304 which cooperate to form a large number of
radially extending stiffeners arranged around the circumferential
periphery of outer tank 20.
C. Alternate Shell Design
[0067] FIGS. 8C, 8D and 8E show an alternative shell design. Rather
than using a single course of precast reinforced concrete shell
elements 302 to form shell 300, multiple courses of similar upper
and lower shell elements 302a and 302b are utilized. Those skilled
in the art of LNG tank construction will appreciate that any number
of courses of shell elements could be used to form a shell.
However, shorter shell elements are easier to transport and move
but require additional welds as compared to using a single course
of shells to construct a shell. Lower shell element 302a includes a
concrete body 316a to which a pair of circumferentially spaced
apart side plates 304a, liner plate 320a, upper end cap plate 314a
and lower base plate 312a are anchored or embedded (anchors and
reinforcement bars not shown). Base plate 312a is welded by welds
324a to base plate 206 of ring beam 200. Upper end cap plate 314a
has two downwardly depending sockets 362 formed therein.
[0068] Upper shell element 302b includes a concrete body 316b to
which a pair of circumferentially spaced apart side plates 304b,
liner plate 320b, upper end cap plate 314b and lower base plate
312b are anchored (anchors and reinforcement bars not shown). Two
downwardly depending and circumferentially spaced apart alignment
pipes 360 are welded to lower base plate 312b. As seen in FIG. 8C,
alignment pipes 360 can be used to align and guide an upper shell
element 302b as it is positioned upon lower shell element 302a.
Also, alignment pipes 360 held within alignment sockets 362 provide
mechanical interlocking between shell elements 302a and 302b. Base
plate 312b is welded by horizontal welds 364 to end cap plate 314a
of lower shell element 302a along their inner and outer radial
edges. A horizontal extending cutout 364 on the outer radial edges
of shell elements 302a and 302b permits the outer radial weld 364
to be easily made. After welding, cutout 364 is filled with grout
for fire protection.
V. Roof 400
[0069] Referring in general now to FIGS. 9A-F, roof 400 has a roof
assembly 404 which includes a skeletal roof frame 406 (FIG. 9A),
liner plates 410 covering roof frame 406 (FIG. 9B and 9C) to form a
generally air tight membrane 412 and tubular mounting beams 414
welded atop membrane 412. In this exemplary embodiment, after a
temporary skirt or seal is attached to its circumferential
periphery, roof assembly 404 is air lifted to the top of shell 300
from upon base mat assembly 100 by pressurizing the inside of shell
300, as suggested in FIG. 9C. Roof membrane 412 of roof assembly
404 is welded to circumferentially spaced apart steel gusset plates
450 (FIGS. 9D and 9F) that are temporarily attached atop end cap
plate 314. This prevents the roof seal from blowing out and allows
weld joints to be made between the roof membrane 412 and gusset
plates 450. Air pressure is maintained while welds are made between
end cap plate 314 and roof membrane 412.
[0070] Once enough weld joints have been formed to safely support
roof 400, the pressurization within shell 300 is removed. Personnel
can then access the inside of the outer tank 20 to construct inner
tank 22. Additional welding is done to complete the circumferential
weld joint between the roof membrane 412 and shell membrane 340.
Special extra strength roof elements 402' are attached to shell 300
and roof frame 404 forming the radial outermost course of roof
elements 402. Then typical roof elements 402 are attached to roof
frame 404 with the radial outermost course of roof elements 402
being attached first. Then the successive next radial outermost
course of roof elements is added until all the rings of roof
elements 402 are in place forming roof 400.
A. Roof Assembly 404
[0071] Roof assembly 404 is built on the ground in this particular
preferred exemplary embodiment. Roof frame 406 comprises a
plurality of radially and circumferentially extending wide flange
beams 420, as best seen in FIG. 9A. In this particular exemplary
embodiment, eight concentric rings of openings 422a-h are formed
between the wide flange beams 420. Wide flange beams 420 used in
the radial direction are W18.times.76 in the center and gradually
increase in size to W18.times.143 near the outer radial ends. In
the circumferential direction each row of wide flange beams 412 has
the same section size such as W18.times.40, W18.times.50,
W18.times.76 and W18.times.97 with the larger wide flange beams
being used nearer the outer radial edge. Of course, other sizes of
wide flange beams can be used, particularly if outer tank 20 is to
be of a smaller or larger size than suggested in the present
example.
[0072] FIG. 9B shows a typical joint construction for roof assembly
404. Liner plates 410 are appropriately sized and are welded to the
top flange 424 of wide flange beams 420 to cover openings 422 and
thus provide a generally air tight roof membrane 416. A tubular
mounting beam 414 is shown which is welded atop of adjacent liner
plates 410. Tubular mounting beams 414 generally run in the same
direction as the web of the underlying wide flange beams 420, i.e.,
radially and circumferentially. As can be seen in FIG. 9B, roof
elements 402 are designed to mount and be welded to tubular
mounting beams 414, as will be described in greater detail
below.
B. Raising and Mounting Roof Assembly 404 to Shell 300
[0073] FIG. 9C shows a roof assembly 404 being raised by air
pressure along an outer tank wall or shell element 302. The three
dots shown adjacent shell element 302 indicates that shell 300 is
comprised of a large number of such shell elements 302, which are
not shown. A temporary skirt or seal 424 is attached around the
circumferential periphery of roof assembly 404. FIG. 9D shows a
fragmentary sectional view of roof assembly 404, seal 424, and end
cap plate 314 and liner plate 306. Air pressure is applied to seal
424 from within shell 300. Seal 424 bears against liner plate 306
of shell 300 to minimize the loss of air there between. A temporary
gusset plate 450, one of 240 such gusset plates 450 located around
the periphery of the ring of end cap plates 314 in this example, is
temporarily welded to end cap plate 314 and extends radially
inwardly.
[0074] Referring now to FIG. 9E, when roof assembly 404 is raised
to the appropriate height, welds 452 are made between liner plates
410 and gusset plates 450. An outer portion of a circumferential
weld 454 is then made between end cap plate 314 and roof liner
plates 410 to form an air tight seal there between joining shell
membrane 340 and roof membrane 412 of roof assembly 404. Ideally,
weld 454 is a full fusion, full penetration weld requiring welding
from both outside and inside outer tank 22. When sufficient welds
have been made to safely secure roof assembly 404 to shell 300, air
pressure can be removed from shell 300. Then, seal 424 and gusset
plate 450 are removed.
[0075] Half shell elements 302' are removed to provide access from
within shell 300. Referring now to FIG. 9F, the inner portion of
circumferential weld 454 is then completed between end cap plate
314 and liner plates 410 to form an air tight seal there between
joining shell membrane 340 and roof membrane 412. A series of
circumferentially spaced apart permanent flange extension plates
462 are welded between liner plate 306 and beneath the lower
flanges of wide flange beams 420. Also, web extension plates 464
are welded on to the web of wide flange beam 420 and to liner plate
306. On the outside of roof assembly 404, extension tubular
mounting beams 414a and 414b are, respectively, welded atop liner
plates 410 and end cap plate 314 extending radially from mounting
beam 414. With tubular extensions 414a and 414b in place, the
outermost row of roof elements 402' can then be welded to shell 300
and to roof assembly 404, as will be described in greater detail
below.
C. Roof Elements 402 and 402'
[0076] Roof elements 402 and 402' are mounted to roof assembly 404
after roof assembly 404 has been affixed by weldments to shell 300.
FIG. 10A shows a typical roof element frame 428 which includes four
L-shaped brackets 432 welded together to form a generally open
rectangular frame. Depending inwardly from brackets 432 are a
plurality of J-hooks 434.
[0077] Reinforcing bars 436 extend laterally and longitudinally
between opposing brackets 432. Roof element frame 428 is used to
construct precast reinforced concrete roof elements 402, as seen in
FIG. 10B. Roof element 402 includes a cast concrete body 440 which
surrounds J-hooks 434 and reinforcing bars 436 and supports roof
element frame 428. The L-shaped brackets 432 are located on all
four sides of roof element 402 to provide attachment to tubular
mounting beams 414 of roof assembly 404 in the case of typical roof
elements 402. The size of each roof element 402 is generally
between about 2 meters to about 3 meters in width and between about
5 meters to about 6 meters in length in this exemplary embodiment.
Of course, other size roof elements could be selected and will
depend on the size of outer tank 22.
[0078] For the outermost concentric course of roof elements 402'
which secure to both roof assembly 404 and to shell 300, the design
is slightly different from that of roof elements 402 disposed on
the inner radial concentric courses. As shown in FIG. 9F, concrete
body 440' in this example tapers from a thinner 150 mm on its inner
radial end to a maximum thickness of 300 mm adjacent its radial
outmost end. The typical concrete body 440 of a typical roof
element 402 has a constant thickness of about 150 mm. Second, roof
element 402' includes L-shaped bracket 432 on only three edges with
the radially outermost fourth side instead having an overhang 470
sized and shaped to fit over end cap plate 314. Provided in
concrete body 440' are four access openings 472 (two seen in FIG.
9F) which provide access to four studs 474 which are to be stud
welded to end cap plate 314.
D. Mounting of Roof Elements 402 to Roof Assembly 404
[0079] The outer concentric ring or course of roof elements 402'
are located adjacent shell 300 and this outer ring of roof elements
402' is first welded to roof assembly 404 and to shell 300. This
outer ring of roof elements 402' adds significant strength to roof
400. Subsequently, second through eighth courses of roof elements
402 are sequentially welded to roof assembly 404 starting from the
radially outermost course and then each concentric course of roof
elements is added until all rows of roof elements 402 are in place
to form a complete roof 400 such as seen in FIG. 1B. FIG. 1A shows
two courses of roof elements 402', 402 mounted to roof assembly
404.
[0080] L-shaped brackets 432 of roof elements 402 are mounted atop
and are welded to tubular mounting beams 414 creating welds such as
the weld joint 436 seen in FIG. 9B. In the case of special roof
elements 402', roof elements 402' are welded to tubular mounting
beams 414, 414a and 414b. Studs 474 are placed in access openings
472 and are stud welded to end cap plate 314. The thickness of
tubular mounting beams 414 is less than the thickness of concrete
bodies 430, as seen in FIG. 9B. Any voids formed between any of
concrete bodies 440, 440' of the roof elements 402, 402' are
grouted in place to form concrete joint 442 to provide fire
protection to roof 442. An example of a concrete joint 442 is shown
in FIG. 9B.
[0081] While in the foregoing specification this invention has been
described in relation to certain preferred embodiments thereof, and
many details have been set forth for purpose of illustration, it
will be apparent to those skilled in the art that the invention is
susceptible to alteration and that certain other details described
herein can vary considerably without departing from the basic
principles of the invention. For example, any one or more of base
mat assembly 100, ring beam 200, outer shell 300 or roof 400 could
be constructed using conventional cast in place construction
techniques while the other components are constructed using the
precast elements as described herein. As another example of an
alternative embodiment, the roof assembly could be directly built
atop shell 300 such as by using a crane. In this instance, roof
assembly 404 would not have to be airlifted and attached atop shell
300. However, ideally even in this embodiment, the shell elements
402 could be welded to the roof assembly concurrently with the
construction of the inner tank 22 to save construction time on
building outer tank 20 and inner tank 22.
[0082] While beam ring 200 described in the above particular
exemplary embodiment was used in conjunction with a full
containment LNG tank, a beam ring could certainly be used in other
applications. For example, the ring beam could be used in cases
where neither a liner plate or thick structural base plate is
necessary. In this case, the ring beam need only comprise ring beam
elements having precast reinforced concrete bodies with embedded
tensile conduits which receive tensile members there through so
that the tensile members may be tensioned and anchored by anchors
to form the beam ring. Although not required, preferably the ring
beam elements would be interlocking with one another.
* * * * *