344 LATTICED PORTAL. Art. 171. 



Approx. F=-i (R+P) (a+d-x m ) 



D=DL(+LL)-V D'=DL(+LL)+V 



M 2 =y 2 k. 2 D M 2 '=y 2 k. 2 D' 



From equation (156) fl'=%[K+p+JL(Af 2 ' J|f 2 )] 

 H=R+PH' 



x- M > x'- M * 



H ~H~' 



T=-i- [(B+P) (a+d-aO-irto'-*,)] 



If this value of V is near enough to the value given above, 

 we need not again determine H, H', x^ and a?/. 



The bending in the posts at a=Hx ) at a'=H'x- i ', at ^= 

 H(ax 1 ) and at F f =H f (ax^). 



The maximum stress in the posts will occur at a' or F'. 

 Other stresses are gotten in a manner exactly similar to the pre- 

 vious case (No. 2 a). 



d d 



Shear in the girder web at any section=F. 

 The moment at the middle of the girder at any section 

 lm= y 2 (R+y 2 p)d+H(a 

 For the connection BF 



the moment= l / 2 (R + l / 2 P)d+Ha-Xi+- and the shear=F. 



All stresses are reversed when the direction of the wind is 

 reversed. 



Case No. 2c with the posts only partially fixed at both the 

 top and bottom, can never occur because by the construction the 

 tops of the posts are always fixed regardless of the direct stresses. 

 Of course the connection BF must be properly designated. 



171. Case No. 3. Latticed Portal. 



Case No. 3a. Posts Fixed Top and Bottom. (See Fig. 221.) 

 The stresses for this case are the same as for No. 2a excepting, 

 of course, that the stresses in BB' and FF', in place of varying 

 uniformly, increase at intervals equal to the distance between 

 connections of web members. 



The shear at any section may be taken as equally distributed 

 over the web members cut. The connection at F must take the 



