Tablas Pca Rectangular Concrete Tanks

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1

INFORMATION

Rectangular Concrete Tanks
While cylindrical shapes may be structurally best for
tank construction, rectangular tanks frequently are preferred for specific purposes. Special processes or operations may make circular tanks inconvenient to use.
When several separate cells are required, rectangular
tanks can be arranged in less space than circular tanks
of the samecapacity. Tanks or vats needed inside a
building are therefore often made in rectangular or
square shapes. For these and other reasons, breweries,
tanneries, and paper mills generally use rectangular
tanks.
Data presented here are for design of rectangular
tanks where the walls are subject to hydrostatic pressure of zero at the top and maximum at the bottom.
Some of the data can be used fordesign of counterforted retaining walls subject to earth pressure for which
a hydrostatic type of loading may be substituted in the
design calculations. Data also can be applied to design
of circular reservoirs of large diameter where lateral
stability depends on the action of counterforts built integrally with the wall.
Another article on tank construction, Circular Concrete Tanks WithoufPrestressing, has been published
by the Portland Cement Association.

Moment

Coefficients

Moment coefficients were calculated for individual
panels considered fixed along vertical edges, and coefficients were subsequently adjusted to allow for a certain rotation about the vertical edges. First, three sets of
edge conditions were investigated, in all of which vertical edges were assumedfixed while the other edges
were as follows:
1. Top hinged-bottom hinged
2. Top free-bottom hinged
3. Top free-bottom fixed*
Moment coefficients for these edge conditions are
given in Tables 1, 2, and 3, respectively. In all tables, a
denotes height and b width of the wall. In Tables 1, 2,
and 3, coefficients are given for nine ratios of b/a, the
limits being b/a = 3.0 and 0.5. The originof the coordinate system is at midpoint of the top edge; the Y axis is
horizontal; the X axis is vertical and its positive direction
downward. The sign convention for bending moments is
based on the coordinate fiber that is being stressed. For
example, A$ stresses fibers parallel to the X axis, The
sign convention used here is not compatible with two
other conventions-namely, that (1) thesubscript is the
axis of the moment, and (2) that the moment is in a par-

Q Portland Cement Association 1969

Revised

1961

titular principal plane. Coefficients are given-except
where they are known to be zero-at edges, quarter
points, and midpoints both in X and Y directions.
The slab was assumed to act as a thin plate, for which
equations are available in textbooks such as Theoryot
Plates and Shells by S. Timoshenko,” but since only a
small portion of the necessary calculations for moment
coefficients for specific cases is available in the engineering literature, they have been made especially for
this text.
Table 4 contains moment coefficients for uniform
load on a rectangular plate considered hinged on all
four sides. The table is for designing cover slabs andbottom slabs for rectangular tanks with one cell. If the
cover slab is made continuous over intermediate supports, the design can follow procedures for the design of
slabs supported on four sides.
Coefficients for individual panels with fixed side
edges apply without modification to continuous walls
provided there is no rotation about vertical edges. In a
square tank, therefore, momentcoefficients can be
taken directly from Tables 1, 2, or 3. In a rectangular
tank, however, an adjustment must be made, as was
done in Tables 5 and 6, similar to the modification of
fixed-end moments in a frame analyzed by moment
distribution.
In this procedure the common-side edge of two adjacent panels is first considered artificially restrained so
that no rotation can take place about the...