PART II.

EXAMPLES IN CALCULATING THE STRENGTHS OF THE RIVETTED JOINTS OF BOILER SHELLS.

ORDINARY JOINTS WITH EVENLY PITCHED RIVETS.

The following 27 examples of the calculations of rivetted joints are all taken from actual practice, and from marine boilers of recent design:

Example 1. Iron Plates. Iron Rivets.

Double Rivetted Longitudinal Lap Joint, such as shown in Fig. 18.

To find the percentage of plate left between the rivet holes, as compared with the solid plate, we proceed as follows:

Rule. The pitch from centre to centre of the rivets, minus the diameter of the rivet, multiplied by 100 and divided by the pitch, gives the percentage of plate left between the rivet holes.

This example may therefore be placed in formula, thus:

Or to carry out the figures in full, we have;

The pitch

= 3

.8125 Rivet diameter 2.1875

100 Constant

Rivet pitch = 3) 218.7500

72= percentage

The plate percentage is therefore shown to be 72 per cent.

Fig. 18.

For the percentage the rivet section bears to the solid plate, we have as follows:

Rule. Multiply the area of the rivet by the number of rivets in one pitch, and then multiply by 100 and divide by the pitch multiplied by the thickness of the plate.

We may place this rule in formula, thus:

The rivet percentage is therefore shown to be 78 per cent. of the solid

plate.

Example 2. Iron Plates. Iron Rivets.

Longitudinal Double Rivetted Zigzag Lap Joint.

The percentages for this joint therefore are, plate 75%, rivet 67%.

Example 3. Iron Plates. Iron Rivets.

Longitudinal Double Rivetted Lap Joint Rivets arranged Zigzag.

Thickness of shell plate.

Diameter of rivet...

Pitch of rivets...

· 1 inch. 1-3 inches.

16

41 inches.

Constant

At this point it becomes advisable to consider more fully the question of the higher percentage required for the rivet over the plate. The English Board of Trade (the highest authority on the subject), say that in iron boilers the percentage of rivet, as compared with the solid plate, should always be in excess of the percentage of plate left between the rivet holes as compared with the solid plate, when both the plates and the rivets are iron.

But when steel plates with steel rivets are used, they say that the rivet section must be greater than the plate section, or in other words, the rivet section must be divided by .

If iron rivets are used with steel plates, then the rivet section must be times greater than the plate section, which must therefore be divided by 15 or 13 *.

Now if we take the last example as being a steel plate with steel rivets, we should have to take the 91 per cent. of rivet section and divide it by to get the percentage of rivet section to be used in the formula for ascertaining the working pressure to be allowed for the boilers, according to the Board of Trade rules.

This we may do by multiplying the 91 by 23 and dividing it by 28, as below:

It is better, however, to place the in the formula, which may be done as follows:

The conditions upon which this latter percentage of rivet section is used, when calculating the working pressure of a boiler, will require further explanation after a few examples of rivet and plate percentages have been given, the subject being merely introduced here in order to familiarize the reader with the formulas for rivet and plate percentages before giving examples of full calculations of the safe working pressure of various cylindrical boilers, and explaining the principles upon which those calculations are based, and thus establishing their soundness clearly in the mind of the reader.

The next example (4) is of an iron shell with iron rivets and double butt straps, as in Fig. 19, double rivetted with the rivets arranged zigzag. With this construction the rivets are brought into double shear, or in other words, each rivet must shear in two places before the shell plates can separate at the joint, and in consequence of this the area of rivet

*See page 46, Board of Trade instructions of 1886.

section, after being calculated in the ordinary way for single shear, is al

%%%
%%

Fig. 19.

lowed to be increased 75 per cent. or multiplied by 1.75.

Example 4. Iron Plates. Iron Rivets.
Longitudinal Seam Fitted with Double Butt Straps.

The next example (5) is of a steel plate with steel rivets, with a longitudinal joint fitted with a double butt strap, the rivet therefore being in double shear, and its strength increased by 1.75, its actual percentage of sectional area.

Example 5. Steel Plates. Steel Rivets.

Longitudinal Seam Fitted with Double Butt Straps.