348 



PLATE GIRDER PORTAL KNEE BRACED. Art. 174. 



GG'=y 2 (R+P)=H. 

 Taking the center of moments at G, 



CD=H 



a 



-F - + 1 +R+V 2 P=-CD'. 



Vert. Comp. of GC=V= Vert. Comp. of CG'. 

 Taking the section rs and the center of moments at B 



c x 3/1 

 Horiz. Comp. of GF=H - - + - r =R 1 +H. 



e. e 



BF=Vert. Comp. of GFV=B'F'. 



Vert. Comp. of Z)JB=Vert. Comp. of DG=BF. 



&B=Horiz. Comp. of DBR^=G'B'. 



DE--=--R-\-y 2 P and D'E'=y 2 P. 



When the direction of the wind is reversed the stresses are 

 reversed. 



Case No. 5b. Posts Fixed at the Top and Partially Fixed 

 at the Bottom. H, V, R l} and x l are found exactly as under 

 case No. 4b, and then the stresses are found as in the preceding 

 case, No. 5a. 



Case No. 5c. Posts Partially Fixed at Both Ends. The 

 external forces are found in exactly the same manner as under 

 case No. 4c, and then the stresses as in case No. 5a. 



174. Case. No. 6. Plate Girder Portal, Knee Braced. 

 Case No. 6a. Posts . , , r 



Fixed Top and Bottom. * ^ ^ 



In Fig. 224 if the plate 

 girder BEE'B' is rigid- 

 ly connected to the post 

 at EB, we may take the 

 post as fixed at B in all 

 cases, as with the Case 

 No. 2, Art. 170. H, V, 

 x 1 and R! may be gotten 

 as for the case No. 4a, 



With a section Im and 

 a center of moments at 



<? 

 **"=*'= 



Fig. 224. (Case No. 6) 



