Civil Engineering Reference
In-Depth Information
basin outer wall. Where total coverage is required, the modules are supported by radial
members that extend from an inner cone or ring to the outer wall of the basin. Where
partial coverage is used and where the module ring width does not exceed 10 to 12 ft
(3.1 to 3.7 m), the support members may be cantilevered from the exterior walls. In
any application where less than the entire area is covered, a baffle wall must be in-
stalled at the inner perimeter of the modules to ensure that all flow passes through the
modules. The maximum width of a pie-shaped segment at the basin perimeter is limited
by the maximum module length, which varies from manufacturer to manufacturer but
is usually on the order of 10 to 12 ft (3 to 4 m).
In basins that have radial effluent launders, it is often possible to suspend the
modules from the launders, as illustrated in Figure 11-17. In rectangular basins, tubes
are simply oriented with the long axis parallel to the sidewalls of the basin, with the
support beams spanning the width of the basin, as shown in Figure 11-18.
Tube Support Requirements.
The tube support system must be able to support the
weight of the tube modules when the basin is drained, as well as to make some
allowance for the possibility of a worker standing on the modules and solids adhering
to the modules. Most manufacturers recommend a surface loading of 10 lb / ft
2
(48.8
kg/m
2
) above the weight of the tube modules. However, experience with the use of
alum and activated carbon in treating surface waters indicates that a higher loading
should be used for designing the settling tube media support. The bearing surface
width of a support member should be more than 1 in. (25 mm) to prevent possible
shear failure of the module at the points of contact under extreme loading conditions.
Existing Radial Launders
Launder
Support Beam
Baffle
Tube
Module
A
Bottom Support
Section A-A
A
Plan
Fig. 11-17.
Circular clarifier with tube modules suspended from radial effluent launders (From
Culp, Gordon, and Williams, Robert,
Handbook of Public Water Systems.
Copyright
1986 by
John Wiley & Sons, Inc. Reprinted by permission of John Wiley & Sons, Inc.)
