340 PORTAL WITH SIMPLE X BRACING. Art. 169 



V 2 7j 1 'Z)'==4.5X(93,200+12,600)==476,000 in. Ibs. at B' with 



LL. on. 

 or r=4.5X f 26,400+12,600)=175,500 in. ibs. at B' with 



DL only. 



These values are greater for live load stress and less for 

 dead load only acting, in each post, than the value of M v . There- 

 fore the posts are partially fixed at the tops under dead load 

 only. 



Bottom: i/U 2 =4.75 (93,200 12,600)=383 ? 000 in. Ibs. at a 

 or -=4.75(26,40012,600)= 65,500 in. Ibs. at a 



%V#'=4.75(93,200+12,600)=502,000 in. Ibs. at a' 

 or =4.75(26,400+12,600)=185,200 in. Ibs. at a' 



Since all of these are less than M 2 , the bottom ends of the 

 posts are not fully fixed under either condition. For maximum 

 moment in the posts, this problem comes under case No. Ib. Here 

 we shall consider the other case, that is, dead load only acting. 

 We have from equation (174) 



From equation (180) approx. mean value of x^ and xj 



4.75X26400 



=2o in. =2.1 ft. 

 5000 



From equation (175) 



M l =4.5X26,400 = 119,000 in. Ibs. =9,900 ft. Ibs. 

 Before we can get Af /, we must know V. 



For an approximate MJ we will assume V = 13,600. (V 

 will be larger than 12,600 determined from equation (126) be- 

 cause x l will be smaller.) 



1st. Approx. MS =4.5(26,400 + 13,600) = 180,000 in Ibs. 



= 15,000 ft. Ibs. 



From equation (174) 



1st. Approx. V =^^[10,000(28 -2.1) +9,900 + 15,000] = 16,700 



1st Trial: 



D =26,400 -16, 700= 9,700 



