CHAPTER VI. 



STRESSES IN FRAMED STRUCTURES. 



Methods of Calculation. The determination of the reactions of 

 simple framed structures usually requires the use of the three funda- 

 mental equations of equilibrium 



2 horizontal components of forces = (a) 



3 vertical components of forces = (b) 

 2 moments of forces about any point = (c) 



Having completely determined the external forces, the internal 

 stresses may be obtained by either equations (a) and (b) (resolution), 

 or equation (c) (moments). These equations may be solved by 

 graphics or by algebra. There are, therefore, four methods of calcu- 

 lating stresses: 



_, . ^ ( Algebraic Method 



Resolution of Forces < - , . ,, , , 

 { Graphic Method 



,.. r -^ ( Algebraic Method 



Moments of Forces < 



( Graphic Method 



The stresses in any simple framed structure can be calculated by 

 using any one of the four methods. However, all the methods are 

 not equally well suited to all problems, and there is in general one 

 method that is best suited to each particular problem. 



The common practice of dividing methods of calculation of 

 stresses into analytic and graphic methods is meaningless and mis- 

 leading for the reason that both algebraic and graphic methods are 

 analytical, i. e. capable of analysis. 



The loads on trusses are usually considered as concentrated at the 

 joints in the plane of the loaded chord. 



