Art. 170. 



PLATE GIRDER PORTAL. 



343 



When x=Q, BB'=y 2 R+H 



When x=y 2 l>, BB'=y>R. 



When s=&, BB'=y 2 R-H f 1+% -^ 



55' has therefore a uniform compressive stress equal to y 2 R 

 and a uniformly varying stress. The latter equals zero at the 

 center, is compressive on the windward side and tensile on the 

 leeward side. 



With the center of moments at I 



FF'd=H 



-Vx 



d d 



When x=0, FF'=H ( l-fi/o ~ 

 When 0^1/06, FF'=Q. 



When x=b, FF'=H ( 1-f y 2 -%- 



\ a , 



FF' has therefore a uniformly varying stress from compres- 

 sion on the leeward side through zero at the center to tension on 

 the windward side. 



The difference in stress between BB' and FF' is y 2 R. 



The vertical shear in the web at any section is V. 



The moment at the middle of the girder at any section 

 l<y i v=y 2 (R+y 2 P)d+y 2 H(a+d)-Vx. 



For the connection BF the moment is %(.R-f%'P)<M- 

 %fl"(rt+d), and the shear is V. 



All stresses are reversed when the direction of the wind is 

 reversed. 



Case No. 2b. Posts Fixed at the Top and Partially Fixed 

 at the Bottom. (See Fig. 220.) In this case from equations 

 (121) and (122) y 2 Jc 1 D^y s (R+P)a and y 2 M><% (R+P) a, 

 tut on account of the construction the posts may always be con- 

 sidered fixed at the top, so the latter condition is the only one 

 that need be tested. 



An approximate mean value of x t and #/ is determined from 



the equation x m = TTTTT^. v is neglected in this value of D. 



