598 



THE DESIGN OF STEEL DETAILS. 



CHAP. XVII. 



Other considerations such as water-tightness enter into the design of joints; see Table 113. 

 Table I la, page 370 gives the properties of water tight joints. By efficiency is meant the ratio 

 of the strength of the joint to the strength of a plate of equal thickness. Under effective section 

 of plates in Table I la, page 370, is given the thickness of an unriveted plate which would have 

 the same strength as the joint. 



The most efficient joint for a given thickness of plate is found as follows: For single riveted 

 lap joint in a ^ in. plate, 



k .j = 4 X 24,000 

 fa 3.14 X 12,000 



: I-9U in- (IS/) 



d = 



X 0.25 = 0.637 i 



p-d 

 r * *_ - 0.67. 



Use % in. rivets with 2 in. pitch. 



Formulas for Riveted Joints. The general formulas for the investigation of lap joints with 

 any number of rows of rivets are (For Nomenclature, see Chapter XVI.), 



P P P 



For design of a joint of maximum efficiency, 



*'/ -^i. d 



~ 2f t -e' 



= _i/L.,. fi = [ 



~ Vfa *' P 



(29) 



ft + k-fc' 



where k = number of rows of rivets. 



For a butt joint with a single strap plate and a single row of riyets the joint becomes two 

 single riveted lap joints and the formulas for riveted lap joints may be used (Structural Mechanics 

 13 and 15). For a butt joint with double strap plates and a single row of rivets on each side, 



p _ p _ p 



*\ = (P-d)t ' fe=z Td ] fv = j^n ' 



For a butt joint with double strap plates and double riveting on each side, 



P P P 



When a single strap plate is used it should never be thinner than the main plate, and when double 

 strap plates are used they should never be thinner than J^ the thickness of the main plate. 



For data on riveted joints for tanks and stand-pipes, see Table Ila, page 370. 



DESIGN OF LACING BARS FOR COLUMNS. It is difficult to calculate the bending 

 stresses in a built-up column, and since the shearing stresses depend on the bending stresses the 

 design of lacing bars must be largely a matter of judgment until sufficient tests are made to 

 establish empirical formulas. The following method gives results that agree with tests and with 

 good practice. 



For a column with a concentric loading, experiments show that the allowable unit stress may 

 be represented by the straight line formula, p = 16,000 70 llr Ib. per sq. in., where p = allow- 

 able unit stress in the member; / = length of the member, c. to c. of end connections, and r = 

 radius of gyration of the column, both in inches. Now the allowable unit stress on a short block 

 is 16,000 Ib. per sq. in., and the 70 llr represents the increase in the fiber stress in the column. 



\Y -I 

 Now if we assume that this fiber stress is caused by a uniform horizontal load, W, then - 



701-1 



, where I = moment of inertia of the cross-section of the column = A -r z , where A = the 



