684
MODERN GASWORKS PRACTICE
condition applies, of course, to those cases where the rivet exactly fits the hole, and the work and design is of a first-class character. An example of a typical vertical seam butt-joint is shown in Fig. 424.
Tanks'with Bulging Sides
One of the chief objections to the steel tank, when its depth becomes appreciable, is the necessity for providing plates of abnormal thickness, which are often difficult to obtain and
cumb e r s o m e to handle. For this reason it has been suggested that the tank should be designed in such a männer as to per-mit of the side plates being of uniform thickness throughout, whilst the v e r y thick plates common to the cylindrical tank could be dispensed with. The prin-ciple involved is that of curving or bulging the sides of the tank in. such a männer that the horizontal stresses due to the head of water are trans-rnitted to the top curb (which must, accordingly, be of
SECTION
ELEVATION
Fig. 424.—Vertical Seam Butt-joint for Steel Tank.
stout construction) and to the tank floor. A tank of this description, designed on Bonnet’s system, is seen in Fig. 425. It will be noticed that vertical posts are placed at intervals romid the tank ring. The static pressure of the water is then transformed into—
(a) A horizontal pull at the base, this being balanced by the tension in the floor plates (see Fig. 426).
(b) A pull at the upper surface of the tank acting at a tangent to the curve at that point. This tangential pull will be distributed as a vertical downward thrust in