RIVETING. 151 



the excess of strength of rivets in double-shear over those in 

 single-shear. We have already assumed that the resistance of 

 rivets per square inch to single-shear is 38,000 Ibs. If we 

 add to this 85 per cent., we shall have 70,300 Ibs. as the safe 

 estimate of the resistance of iron rivets per square inch to 

 double-shear. Further experiments may change these fig- 

 ures slightly, but I regard them as safe for use in all places 

 where joints riveted with iron rivets are used. The use of the 

 double-welt butt-joint in the construction of boilers is becom- 

 ing quite common. This arises from the use of boilers of 

 much larger diameter than those formerly used, and also the 

 necessity for higher pressures on account of the introduction 

 of compound engines. 



With larger diameter and higher pressures, we find our- 

 selves confronted with a very important problem. We must 

 keep within .the bounds of safety, for these large vessels are 

 very destructive to life and property if we disregard the im- 

 portance of good material, good workmanship, and the well- 

 established factors of safety. It is not always safe to assume 

 the highest results obtained by experimental tests. There 

 will always be those who will insist upon higher pressures than 

 safe rules will allow. Hence it becomes important that the 

 consulting engineer shall thoroughly understand the principles 

 of safe construction, and not allow himself to be moved in his 

 judgment where the question of safety is involved. We will 

 now apply the above data to the following problem : 



Steel plate, tensile strength per sq. in. of section, 5 5,000 Ibs. 



Thickness of plate f in. decimal 0.375. 



Diameter of rivet-holes || in. = decimal 0.8125. 



Area of rivet-hole = decimal 0.5185. 



Pitch of rivets in inner rows 3^ ins. = decimal 3.25. 



Pitch of rivets in outer rows 6 ins. = decimal 6.50. 



Resistance of rivets in single-shear = 38,000 Ibs. 



Resistance of rivets in double-shear = 70,300 Ibs. 



