Art. 169. 



PORTAL WITH SIMPLE X BRACING 



335 



the letter c that both ends of the posts are only partially fixed. 

 (The case of one or both ends not fixed cannot occur in practice.) 



In all the cases which follow we take the supports on a level 

 and assume the posts to be alike. Therefore 

 a'=a, c'=c, l f =l 



It may happen, in any particular portal, that all three cases 

 a, 6, and c, occur, depending upon whether we are considering 

 the windward or leeward post, or whether the posts are under 

 dead load stress only or both dead and live loads are acting. 



169. Case No. 1. Simple X Bracing. 



Case No. la. Portal with Posts Fixed Top and Bottom. 



In this case a? 1 =a? 1 / and 



from equation (118) a; 1 =o :r 

 from equation (106) H=H'=y[R+P] 

 from equation (128) E 1 = 

 From equation (126) 

 y=-T"= - 



from equation (130) 



Stress in BB'=R+y 2 P+%(R+P) 







from equation (132) 



Horiz. Comp. B'*M#+P)( 1+ ^" 



from equation (134) 



Stress in FP'=y 2 (7?+P) 1+^f^) 



from equation (136) Maximum stress per sq. in. in 



DL+LL+V y>(R+P)XiXwidth of of 

 ' B '= ~~ 



From equation (138) Maximum stress per sq. in. in 



DL-^-LL V y 2 (R+P)x 1 'Xwidth of aB 

 aB= -r - + 27" 



