The spacing of the rivets is also important. Lloyd’s Register of Shipping published the following minimum requirements for shell riveting:


• The distance from the edge of the plate to the centreline of the first row of rivets is to be one and a half times the diameter of the rivet shank regardless of the type of joint.


• In the case of butt laps the distance between the rows of rivets is to be three and a half diameters measured from centre to centre of the shanks.


• For a plate landing or seam the distance between the rows of rivets is to be three diameters centre to centre.


• For a butt strap the distance between the rows of rivets is to be two and a half diameters centre to centre.


or


By equating Formulae (6) and (7) above and substituting as before the pitch of the rivets should be: p p


= =


)σt


= =


8.64tp 3.40d π/4 x d2 .τs τs


mm mm


Further, equating right hand sides of Formula (5) and (8), we obtain (p – tp p


- πd2 4tp.σt and substituting for τs


and (8b) we obtain: p p


= 60 MPa and for σt


= =


= 75 MPa and using the values in Formulae (9a)


2.73 d (in single shear) mm 1.86 d (in double shear) mm


(16a) (16b)


The pitch of rivets in the row nearest to the edge must be as small as possible to avoid leakage. That pitch is called caulking pitch and helps the edges to be caulked effectively. The pitch is usually calculated from following empirical relationship:


pc = The Edge Set in Riveted Joints


Equating the area of plate in the wake of the rivet hole times the allowable shear stress and Formula 14 we obtain:


2etp and substituting τs


e e


τs = dtp


- 60 MPa and σc = =


.σt a = 130 MPa d.σc/2.σt 1.08d


mm mm


(19) (20)


There are a number of practical considerations due to which the theoretical design dimensions are modified. The most important of those is the watertightness of the joint which is achieved by the caulking of the plate butt and seam edges.


The caulking becomes easier with shorter pitches and smaller rivets which also makes it desirable that the edge set should be 1.5 d but not greater. The results in this section are indicative of calculation procedure and by no means be treated as standard formulae. Those results are valid only for a particular case and the allowable stresses adopted.


The marine surveyor will find that the Formula (16a) for diameter will give reasonable results for shell and bulkhead plating and framing but the pitch suggested by Formulae (12) and (13) will prove to be too large and it is better to use the Lloyd’s Register rules given above. Similar Formulae can be developed for single riveted and double or triple chain riveted seams.


The Report • June 2021 • Issue 96 | 49 - (18) d + 13.80tp¾ /σt¼ mm (17) + d mm


(12) (13)


(14) (15)


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