Art. 166. 



PORTAL POSTS PARTIALLY FIXED. 



329 



V produces no stress in BF. V produces a uniform stress in 

 a'B'. 



When the wind blows from the opposite direction the condi- 

 tions in the posts are reversed. Both cases must therefore be con- 

 sidered in order to find the maximum stresses. The same is true 

 of BE' and FF', the stresses' in which will, in general, change, as 

 can be seen from (130) and (134). The stress in BF' will be the 

 same as in B'F. See Eq. (131). 



The connection at B should be designed to take the stress in 

 BB' and the vertical component of B'F=V, although these 

 stresses do not act simultaneously. The connection at B' must 

 take the horizontal component of B'F, an amount equal to the 

 stress in BB' going to BB', and an amount equal to y 2 P+.E/- 

 going to the post. The connection at F' takes the stress in FF' 

 while at F, this much of the horizontal component of B'F goes to 

 FF' and the balance into the post. At F the vertical component 

 of B'F=V goes to the post. 



166. General Case of Portal with Posts Fixed at Top 

 and Partially Fixed at the Bottom. Assuming as in the 

 previous case (see Fig. 217), that F deflects as much as B, the 

 distribution of the load between H and H' may be found as 

 follows : 



For x greater than a (See Fig. 218). 



ax 2 



(139) 



El =M 2 x-y 2 R 2 x*+Q(y 2 x*-ax)+C l 



^i-^rO when x=c, whence C 1 =y 2 R 2 c- M 2 c Q(y 2 c 2 ac) 

 ax 



EI^=M 2 (x-c) -y 2 R 2 (x 2 ~c 2 )+Q(y 2 x 2 -ax-y 2 c 2 +ac) (140) 

 For x less than a 



(141) 



El = 



(142) 



men*=a, ^-from (140)=^- from (142) 



