58 



REACTIONS FOR A SINGLE FORCE. 



Art. 46. 



= Pl^. To eliminate between these equations, makes this method 

 somewhat laborious. This case is similar to that of Fig. 23. 



and 



Fig. 37. 



Fig. 37 shows a cantilever beam with supports at A 

 B } the part BC extending beyond the support B. 



Taking moment about B, R l xAB=PxBC and with A as 

 a center, R 2 XAB=PxCA. As a check, R 2 =R 1 +P. 



Graphically a string polygon is drawn beginning at D. On 

 parallel to the closing line gives the force polygon, abna. 



If the truss in Fig. 38 is fixed at both supports A and B, 

 the reactions are statically indeterminate. If they be assumed 



Fig. 38. 



parallel to the load, which is the resultant of the loads acting 

 at the joints in the line AC, we have, with center at B, 



Ritti+l*) =Plz', an d with center at A, 



Graphically the problem is the same as that of Fig. 32. 

 Usually when the ends of the truss are both fixed they are 



