Storage tank construction

This invention relates to an elevated liquid storage tank and a method of constructing same. An upright, hollow, cylindrical concrete shaft is constructed having a closed upper end portion forming a tank support floor. An upper, outer ledge is formed around the periphery of the shaft adjacent to the tank support floor; and a central, upright access tube is mounted in the tank support floor. An annular, steel tank wall is fabricated around the base of the shaft and hoisted to the top of the shaft using a plurality of jacks. The tank wall includes a lower annular ring beam and the space between the ring beam and the shaft upper end portion is filled with reinforced concrete to connect and retain the tank in position. Roof plates extend between the access tube and the tank wall to close the storage tank roof.

BACKGROUND OF THE INVENTION 
This invention relates to elevated liquid storage tanks and methods of 
constructing same. 
In the past, it has been common practice to construct elevated liquid 
storage tanks, which are sometimes referred to as water towers, either out 
of concrete or structural steel. An economical form of concrete storage 
tank is a simple concrete cylinder which may be completely hollow, or it 
may be formed with an elevated concrete floor, the tank of course being 
that part of the cylinder above the floor. A difficulty with this type of 
storage tank is that it lacks aesthetic appeal. Also, in cold climates it 
is usually not desirable to have the concrete in contact with the liquid 
being stored, because freezing and thawing can have a deleterious effect 
on the concrete. Of course, a liner or some form of coating could be used 
to protect the concrete, but this increases the cost of the storage tank 
considerably and can cause maintenance problems, especially if leaks 
appear in the liner or coating. 
An all steel elevated storage tank is sometimes better than a concrete 
storage tank from the point of view of water tightness and associated 
maintenance problems. Most elevated steel storage tanks, however, are 
supported on structural steel tower structures which are themselves 
aesthetically unappealing, not to mention the maintenance problem of 
having to periodically paint the structural steel tower. 
As an improvement over the all steel or all concrete constructions elevated 
storage tanks have been made where the tower or column part is formed of 
concrete and the tank itself is formed of steel. Ordinarly, it would be 
very costly to fabricate a steel tank on the top of a concrete tower, but 
a method has been used in the past to construct a major portion of the 
steel tank at ground level and hoist same into position at the top of the 
concrete tower where a concrete tank floor is poured to interlock the 
steel tank and the concrete tower. This prior art method of construction 
is described in the applicants' previous Canadian Pat. No. 1,091,883 and 
U.S. Pat. No. 4,312,167. The construction of the storage tank itself is 
described in applicants' previous Canadian Pat. No. 1,091,884 and U.S. 
Pat. No. 4,327,531. While the liquid storage tanks described in these 
patents are aesthetically appealing, economical to produce and relatively 
maintenance free, the elevated storage tank and method of construction of 
the present invention is an improvement thereover, in that the storage 
tanks of the present invention are even more economical to produce, and if 
desired, the tank portion can be made into a continous steel water 
containment chamber, so that none of the structural concrete comes into 
contact with the liquid in the tank. 
SUMMARY OF THE INVENTION 
According to one aspect of the invention, there is provided an elevated 
liquid storage tank comprising an upright, hollow, cylindrical shaft 
adapted to be anchored to a supporting base foundation. The shaft has an 
upright wall and a closed upper end portion with a top surface forming a 
partial tank support floor. The upper end portion has an upper, outer 
ledge formed around the periphery of the shaft spaced below the top 
surface. A tank is mounted at the top of the shaft, the tank including a 
wall having a lower annular ring beam attached thereto and forming a lower 
tank opening. The ring beam has radially, inwardly projecting support 
means, the ring beam and tower upper end portion forming an annular 
recess. Also, means are provided for filling the recess to connect the 
tank to the shaft and complete the tank support floor. 
According to another aspect of the invention, there is provided an elevated 
storage tank comprising an upright, hollow cylindrical shaft adapted to be 
anchored to a supporting base foundation. The shaft has an upright wall 
and a closed upper end portion with a top surface forming a tank support 
floor. A tank is mounted at the top of the shaft, the tank having a 
peripheral wall connected to the shaft around the top peripheral edge of 
the shaft adjacent to the tank support floor. A central, upright access 
tube assembly is mounted in the tank support floor, and a plurality of 
radial roof closing members are supported by and extend radially, 
outwardly from the top of the access tube assembly to the tank wall to 
form the tank roof. 
According to yet another aspect of the invention, there is provided a 
method of constructing an elevated liquid storage tank comprising the 
steps of erecting an upright, hollow, cylindrical shaft including a closed 
upper end portion forming a partial tank support floor having a top 
surface. The shaft also includes an upright wall having an upper, outer 
ledge formed around the periphery of the shaft and spaced below the top 
surface. A partial annular steel tank is fabricated concentrically about 
the base of the shaft. The partial tank includes a wall having a lower 
annular ring beam with inwardly projecting support members. The partial 
tank is hoisted to the top of the shaft so that the ring beam is opposite 
to the ledge forming a continuous annular recess around the periphery of 
the shaft, and the annular recess is filled with reinforced concrete to 
connect the partial tank to the shaft.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
Referring to the drawings, a preferred embodiment of an elevated liquid 
storage tank or tower according to the present invention is generally 
indicated by reference numeral 10. Storage tank 10 includes an upright, 
hollow, cylindrical shaft 12 formed of reinforced concrete and a steel 
tank 14 mounted on top of the shaft. Shaft 12 is supported on a foundation 
16 indicated by dotted lines in FIG. 1. Foundation 16 is not considered to 
be part of the present invention, so it will not be described in detail. 
However, it will be appreciated by those skilled in the art that 
foundation 16 must be suited to the soil conditions and capable of 
supporting the weight of the storage tank 10 and the liquid contained 
therein. 
Shaft 12 is shown to be circular in cross-section in the drawings, but it 
could be octagonal or hexagonal or have any other cross-sectional 
configuration as desired. The term "cylindrical" as used in this 
specification is intended to include any desired cross-sectional 
configuration. For the purposes of clarity, the reinforcing steel used in 
concrete shaft 12 and perhaps foundation 16 has been omitted. The exact 
pattern and type of reinforcement used in shaft 12 is conventional and 
typically would include steel reinforcing bar and welded wire mesh as 
required. 
The dimensions of storage tank 10 are such that tank 14 would typically 
hold between 100,000 and 3,000,000 gallons (450,000 to 13,000,000 liters) 
of liquid, such as water, at a height of about 100 to 150 feet (30 to 45 
meters) above the ground. Shaft 12 is typically 10 to 50 feet (3 to 15 
meters) in diameter, with a wall thickness of between 6 and 20 inches (15 
to 50 centimeters). 
As seen best in FIGS. 1, 2, 5 and 8, shaft 12 includes an upright wall 18 
and an upper end portion 20 including a partial tank support floor 22 
having a top surface 24. Partial tank support floor 22 and upright wall 18 
are joined together by an integral, enlarged peripheral thrust ring 26. 
The mass of thrust ring 26 is balanced about the centre line of the 
partial tank support floor 22 to minimize bending stresses in the support 
floor 22 and the shaft wall 18. Partial tank support floor 22 supports 
only an interior part of the complete tank, as will be described further 
below. In the preferred embodiment, a corbel 28 is formed adjacent to the 
shaft upper end portion 20 and the upper surface of corbel 28 forms an 
upper, outwardly disposed outer ledge 30 (see FIG. 13) on which steel tank 
14 is mounted. Outer ledge 30 is spaced below top surface 24 and extends 
around the periphery of shaft 12. Outer ledge 30 and corbel 28 are formed 
with a plurality of radially disposed outwardly opening recesses 32, the 
purpose of which will be described further below. The top edges of 
recesses 30 are reinforced by steel angles 34 which are cast into the 
concrete when it is poured. As seen best in FIG. 6, steel angles 34 have 
forward anchors 36 and a rear bridge member 38 to increase the reinforcing 
capability of the angles. Concrete gussets 40 are formed between outer 
ledge 30 and thrust ring 26, so that the resulting construction joint at 
the surface of gussets 40 is perpendicular and symmetrically placed about 
the line of thrust indicated by chain dotted line 41 (see FIG. 5). Thrust 
line 41 is the line of thrust of the floor of steel tank 14 when it is 
filled with liquid. Concrete gussets 40 extend circumferentially around 
the upper end portion 20 with interruptions at each recess 32 as seen best 
in FIG. 13. 
Shaft 12 is also formed with the usual access door 42 and a machine room 44 
for housing the usual pumps, valves and controls, etc. A ladder 46 is 
mounted on the inside of shaft wall 18 for gaining access to tank 14 and 
the usual fill and drain pipes 48, 50 are also mounted on the inside of 
wall 18 leading up to tank 14. 
The wall of steel tank 14 has several parts or portions starting at the 
bottom with an upwardly and outwardly disposed conical floor portion 52, a 
vertical side wall portion 54 attached to floor portion 52, and an 
upwardly and inwardly disposed conical top wall portion 56 attached to 
side wall portion 54. For the purposes of this specification, floor 
portion 52, side wall portion 54 and top wall portion 56 are all 
considered to be part of the wall of steel tank 14, although floor portion 
52 could be considered to form part of the floor of the completed tank. 
Floor portion 52 is attached to an annular ring beam 58 which is itself 
formed of several components. Ring beam 58 serves two main functions. 
During the lifting of the tank into position at the top of shaft 12, ring 
beam 58 provides a stiff member to distribute the local point reactions 
applied by the attachment of lifting cables 60 (see FIGS. 12 and 13). When 
tank 14 is in its final position, ring beam 58 serves as a means for 
transferring the structural forces from the tank floor portion 52 into the 
concrete of the upper end portion 20 of shaft 12. 
As seen best in FIG. 5, ring beam 58 includes an annular vertical skirt 62 
and a top angle 64 to which floor portion 52 is attached. Ring beam 58 
also includes an annular bottom plate 66 and vertical knife plates 68. 
Knife plates 68 have lifting holes 70 for attachment of lifting cables 60. 
Knife plates 68 are typically circumferentially spaced apart at about 5 
foot (1.5 meter) intervals. Ring beam 58 also includes a lower painter's 
rail 72 and an upper forming angle 74. Top angle 64 also has 
circumferentially spaced apart strengthening gussets 76. Top angle 64 and 
knife plates 68 are radially inwardly projecting support means for tank 
14. The various components of ring beam 58 are dimensioned so that the 
ring beam provides the necessary bending and torsional support for lifting 
and retaining tank 14 in position as mentioned above. 
As seen best in FIG. 4, the tank floor portion 52 is formed of a plurality 
of steel plates in the form of conical segments 78. If desired, conical 
segments 78 can be formed with inner and outer portions, the inner 
portions being thicker for higher strength. Radial strengthening plates 80 
are provided at the junctions of the segments 78 with the ring beam top 
angle 64. It will be appreciated that ring beam 58 forms a lower tank 
opening before the tank is hoisted and secured in position. The knife 
plates 68 project radially, inwardly to rest on outer ledge 30 to support 
the tank while it is being secured in position, as will be discussed 
further below. 
The chain dotted lines in FIG. 5 indicate the direction of the thrust from 
the tank wall and the tank support floor. The angle of inclination of the 
floor portion 52 and the convexity of the partial tank support floor 22 
are such that the thrust from the floor portion and the thrust from the 
tank support floor meet approximately at the centre line of shaft wall 18 
when tank 14 is filled with liquid. 
Referring next to FIGS. 1, 7 and 8, a central vertical access tube assembly 
82 is mounted in partial tank support floor 22 for access from the inside 
of shaft 12 to the roof of the structure. Access tube assembly 82 includes 
a central tube 84 having a lower portion 86 cast into the concrete of 
partial tank support floor 22, and an upper portion 88 joined to lower 
portion 86. Annular flanges 90 are attached to lower portion 86, and 
partial tank support floor 22 is thickened to form a haunch about lower 
portion 86 which locks to flanges 90 to fully support the access tube 
assembly. By forming central tube 84 in two parts, the lower portion 86 
can be easily cast into the partial tank support floor, and thereafter, 
the upper portion 88 is just attached thereto. For this purpose, temporary 
angle brackets 92 and leveling bolts 94 can be provided at the connection 
of the two portions 86, 88. After plumbing and aligning the upper portion 
86, the two tube portions are welded together and temporary angle brackets 
92 and leveling bolts 94 are removed. 
A roof landing 96 is mounted at the top of central tube 84. Roof landing 96 
includes a top plate 98 and a plurality of radial support members 100. The 
periphery of roof landing 96 has an annular stiffening member 102 and a 
painter's rail 104 is attached thereto. A vent opening 106 and an access 
opening 108 are provided in top plate 98 and suitable covers are provided 
for vent opening 106, access opening 108, and the top of central tube 84. 
Ladders 110, 112 are attached to central tube 84, so that a person can 
climb upwardly inside tube 84 out on to roof landing 96 and down through 
access opening 108 into the interior of tank 14. Grip rails 114 are 
provided as well as an upper railing 116 (see FIG. 1) for safety purposes. 
An overflow weir 118 is mounted near the top of tube 84 and a drain pipe 
120 passes downwardly from weir 118 through partial tank support floor 22 
to be connected to the drain pipe 50 mounted on the inside of concrete 
shaft 12. A flange 122 is attached to drain pipe 120 where it passes 
through partial tank support floor 22 and performs a function similar to 
flanges 90. 
Referring next to FIGS. 9, 10 and 11, the tank roof will now be described 
in detail. It will be noted from FIG. 9 that the upper peripheral edge of 
top wall portion 56 is formed with a stiffening rim element 124 held in 
position by gussets 126. An interior painter's rail 128 is attached to 
gussets 126. Roof plates 130 span the distance between the top wall 
portion 56 and roof landing 96. As seen best in FIG. 11, roof plates 130 
are in the form of conical segments. Radial stiffening ribs 132 are 
provided on the underside of roof plates 130 and knives 134, 136 are 
provided on top of roof plates 130 above stiffening ribs 132 to support 
the roof plates in position. It will be appreciated that knives 134 extend 
beyond roof plates 130 to overlap rim elements 124, so spacer plates 138 
are used to fill the gap therebetween. Spacer plates are not required at 
the inner ends of roof plates 130, because the roof plates themselves 
extend inwardly to overlap the roof landing top plate 98. It will be seen 
from FIG. 11, that the knives 134, 136 and associated stiffening ribs 132 
are located closer to one side edge of roof plate 130 than the other. This 
is to keep one side edge of the roof plate straight. The other side edge, 
therefore, is a little more flexible so that it can conform with the 
adjacent mating side edge of the next plate. However, if desired, 
stiffening ribs 132 can be evenly spaced from each longtitudinal edge of 
roof plate 130 or other combinations of roof elements can be employed. 
The method of constructing storage tank 10 begins with the erection of 
upright, hollow, cylindrical shaft 12 including the closed upper end 
portion 20. Shaft 12 can be constructed using any suitable procedure such 
as a jump forming or slip forming techinque. A particularly convenient 
method and apparatus is described in applicants' previous Canadian Pat. 
No. 1,091,883 and the corresponding U.S. Pat. No. 4,312,167. Of course, 
prior to erecting shaft 12, a suitable foundation 16 would be constructed, 
and while partial tank support floor 22 is being made, central tube lower 
portion 86, drain pipe 122 and a similar fill pipe would also be 
installed. Otherwise, the construction of shaft 12 is done using 
conventional techniques, including the placement of suitable reinforcing 
steel therein as would be apparent to those skilled in the art. 
Once shaft 12 has been substantially completed, the wall portions and lower 
ring beam of tank 14 are fabricated concentrically about the base of shaft 
12 to form a partial tank 139. This may be done using suitable jig 
structures 140 as shown in FIG. 12. Jack stands 142 (see FIG. 13) are then 
temporarily mounted on outer ledge 30 in the spaces between concrete 
gussets 40. Each jack stand 142 is in the nature of an A-frame with upper 
and lower tie back plates 144, 146. Removeable braces (not shown) are 
connected to the back plates 144, 146 to anchor or retain the jack stands 
in position. The legs of the jack stands are located on resilient pads 148 
typically formed of 1 inch thick neoprene rubber. There are typically 12 
to 36 jack stands 142, and the resilient pads 148 balance or equalize the 
load carried by each jack stand as the partial tank 139 is hoisted into 
position. Hydraulic jacks 150 are mounted on top of jack stands 142, and 
these jacks act on lifting cables 60 which are connected to knife plates 
68 as mentioned above. Spring loaded jaw-type anchors 152 are mounted in 
jack stands 142 to grip and retain the lifting cables 60 when jacks 150 
reach the limit of their extension and must be returned for a fresh grip 
on the lifting cable. 
Jacks 150 are hydraulically connected to a common source of hydraulic 
pressure so that they can be operated in unison for lifting the tank. The 
jacks can also be operated separately for lifting and alignment of the 
tank as well. The jacks are operated until the partial tank 139 is lifted 
into the position shown in chain dotted lines in FIG. 12. It will be 
appreciated from FIGS. 5 and 6, that as the partial tank is hoisted to the 
top of shaft 12, lifting cables 60 and knife plates 68 pass upwardly 
through recesses 32. The partial tank is hoisted until knife plates 68 are 
slightly above outer ledge 30. At this point, closure plates 154 are 
inserted to span the gap between ring beam 58 and outer ledge 30. Shims 
156 are then placed under knife plates 68 to bridge recesses 32. The tank 
is then lowered slightly until knife plates 68 rest on and are supported 
by shims 156. Lifting cables 60 are then detached from knife plates 68 and 
jack stands 142 are removed. At this point, it will be appreciated that 
ring beam 58, closure plates 154 and the upper end portion of shaft wall 
18 form an annular recess. Suitable reinforcing steel is then placed in 
this recess and it is filled with concrete 158 to form a complete tank 
support floor, to connect the steel partial tank 139 to the upper end 
portion of the concrete shaft, to form a water-tight tank, and to transmit 
the forces generated in the conical tank floor and ring beam to the 
concrete thrust ring 26 when the tank is filled with liquid. 
Although tank 14 is watertight at this point, it is desirable to instal a 
steel floor liner 160 to cover the tank support floor. The peripheral edge 
of floor liner 160 is welded to angle 74 and also to the central access 
tube 84 and the drain and fill pipes, so that tank 14 has a continuous 
steel floor to make it absolutely watertight. In order to ensure that 
floor liner 160 does not itself support any structural loads, holes are 
drilled in the floor liner and grout 162 is forced beneath floor liner 160 
to fill any voids located beneath the liner. The holes are then capped or 
plugged in a suitable manner. 
Access tube assembly 82 is then installed as mentioned above and roof 
plates 130 are installed to complete the tank roof. Finally, the remaining 
elements such as the covers for access and vent openings 106, 108, the 
remainder of the piping, additional ladders, cat walks, etc., and the 
pumps and valves are installed to complete the construction. 
Referring next to FIGS. 14 and 15, another embodiment of an elevated liquid 
storage tank and method of constructing same according to the present 
invention will now be described. In FIGS. 14 and 15, primed reference 
numerals are used to illustrate components which are similar to the 
embodiments shown in FIGS. 1 to 13. The main difference between storage 
tank 10' and the previously described storage tank lies in the manner in 
which the steel tank 14' is connected to the concrete shaft 12'. 
Rather than providing a corbel adjacent to the shaft upper end portion, 
shaft 12' has an upper, peripheral, annular recess 164 forming the upper, 
outwardly disposed outer ledge 30'. Ring beam 58' is formed without knife 
plates and partial steel tank 139' is lifted into position by attaching 
lifting cables 60 to circumferentially spaced apart gusset plates 166 
connected between floor portion 52' and top angle 64'. Annular recess 164, 
ring beam 58' and closure plates 154' then form a U-shaped annular recess 
which is filled with reinforced concrete (not shown) in a manner similar 
to the previous embodiments to connect the partial tank to the upper end 
portion of the concrete shaft. In this embodiment, top angles 64' form 
radially inwardly projecting support means for tank 14'. As in the case of 
the previous embodiments, the annular connection or seal between tank 14' 
and shaft 12' makes the tank water-tight and transmits the forces 
generated in the conical tank floor and ring beam to the concrete trust 
ring 26' when the tank is filled with liquid. A steel floor liner (not 
shown) can also be installed as in the previous embodiments. 
In order to ensure that lifting cables 60 remain generally vertical while 
partial tank 139' is being lifted, it is necessary to provide a cantilever 
structure 168 to hold each of the jacks 150' out over the point of 
attachment of the lifting cables. Cantilever structures 168 are anchored 
to the tank partial support floor 22' by suitable temporary anchors 170 
and resilient pads 148' are provided under the outer ends of cantilever 
structures 168 to balance or equalize the load carried by each jack as in 
the previous embodiments. Jacks 150' must remain in place until the 
concrete joint or seal is made between partial tank 139' and shaft 12', 
and thereafter the jacks and cantilever structures are removed and the 
remainder of the tank is completed in a manner similar to that for the 
previously described embodiments. 
Having described preferred embodiments of this invention, it will be 
appreciated that various modifications may be made to the structures and 
methods described. For example, where knife plates 68 are used, they do 
not have to pass through recesses 32 in corbel 28. The knife plates, or or 
supporting members, could be made so that they do not project inwardly as 
far as the outer ledge 30, and some other type of shim member could be 
used for supporting the knife plates on the outer ledge. After the 
reinforced concrete 58 has been poured to connect the ring beam to the 
upper end portion of the shaft, it is this reinforced concrete filler that 
transmits the load of the tank wall to the shaft. Knife plates 68 could be 
installed after the tank has been hoisted into position at the top of the 
shaft, and in this case, the recesses in the corbel could be also be 
eliminated. In fact, the corbel itself could be eliminated by forming 
outer ledge 30 in the top of wall 18 as in the embodiment shown in FIGS. 
14 and 15. It may be necessary to attach the lifting cables at a different 
location on the ring beam or move the jacks further outwardly to keep the 
lifting cables generally vertical. It will also be apparent to those 
skilled in the art that the tank support floor 22 could be other 
configurations than convex, such as flat or conical. In fact, tank support 
floor 22 could be formed of steel rather than reinforced concrete. Also, 
the access tube assembly could be mounted in the tank support floor in 
another manner, with or without an access opening through the floor. The 
access opening could be provided in another location in the floor, or 
access to the interior of the tank could be through the roof only. Various 
other modifications or alternatives will be apparent to persons skilled in 
the art, and all of these variations or modifications are considered to be 
within the scope of the present invention.