DOUBLE; PORTAL 



119 



H = H = H = = 1000 Ibs. 



and 



Rh 



2s 



= 2250 Ibs. 



The vertical reaction of the middle column is zero. By substitut- 

 ing the dotted members as shown, the stresses can be calculated as in the 

 case of the simple portal. The full lines represent stresses in the portal 

 members. The shear in the columns is equal and is H below, and 

 above the foot of the knee brace. 



H d 



CASE I 



Columns Hinged 



Stress Diagram 



1000 2000 3000 



Compression 

 Tension 



10 



The maximum bending moment occurs at the foot of the knee 



brace and is 



M = H d = 192,000 inch-lbs. 



