JOINTS AND CONNECTIONS 193 



two holes will be deducted. Similarly three holes will be deducted 

 for three lines, etc. It means that a strip of metal equal to the 

 width of the rivet hole is ignored provided all the rivets are 

 driven within the strip, or if the rivets are driven in two or more 

 strips then these strips are ignored in making computation for 

 strength in tension. 



A structural designer will determine the number of rivets in 

 the manner described. He may then arrange them in a group 



O O j O O 

 O O ! O O 



o o i o o 



Fig. 113. Fig. 114. 



similar to that shown in Fig. 113, for structural designers do not 

 always study joint efficiency. A boiler maker, on the contrary, 

 would study the joint in order to obtain the maximum efficiency 

 and his detail would resemble Fig. 114. There is no reason why 

 a structural designer should not obtain the highest possible 

 efficiency in designing rivet ted joints. 



Assume that the tension in the joint is 30,000 Ibs. and each 

 rivet carries 5000 Ibs. In Fig. 113 three rivet holes must be de- 

 ducted, which means additional material added to the member, 

 for only the material left after the holes are made can carry ten- 

 sion. The rivets carry shear at an assumed unit shearing stress. 

 The holes, however, cut out an area which carries tension at an 

 assumed unit tensile stress. 



In Fig. 114 the end rivet carries one-sixth of the stress as 

 shear. The plate on a section through the hole carries the total 

 stress. The diameter, therefore, of the rivet hole is one-seventh 

 of the total width of the plate. On a section through the two 

 rivets the plate loses in each hole one-seventh of the total width, 

 but as it had enough area to carry seven-sixths of the load the 

 cutting of two holes leaves enough area to carry five-sevenths- of 

 the load. 



The plate with an area sufficient to carry five-sevenths of the 

 load then reaches the section near the end where there are three 

 rivet holes. Each hole has a diameter of one-seventh the width 

 of the plate and the three holes leave four-sevenths of the area 

 intact. 



At the single rivet one-sixth of the stress is carried in shear, 



