333 PORTAL WITH SIMPLE X BRACING. Art. 169. 



Neglecting V and calling HII', we get nearly a mean value 

 of *, and tf from = =167 in.=13.9 ft. 



From (158), Rj= |/I - ^ Taking H as above 



RI approx.=f X G,30C ~ - =13,800=12 1 / approx. 



From equation (125) 

 1 



= - [12,600(43.5-13.9)+ - 27,600] =29,300 

 lo. o 



1st Trial 



D= 100,000 29,300= 70,700 Ibs. 

 #'-=100,000+29,300= 129,300 Ibs. 

 M^= 70,700X10.5 = 742,500 in. lbs.= 61,900 ft. Ibs. 

 M/=129,300X10.5 =1,358,000 in. lbs.=113,200 ft. Ibs. 



:J/ 2 '-M 2 = 51,300 ft. Ibs. 

 From equation (156) 



H'=%(12,600+ 3L5 3 ( 1 10 5 +g 4 5 3 . 5) 51,300)^7,430 . 

 5=12,600-7,430=5,170 



61,900 113,200 



"5T70 ' 12 ' "' % ~ " ' 



2nd Trial 



X 5,170 31 5 ~ 12 =12,600 



' =15,100 



F= = [12,600(43.5-12) -7,430X3.2+-VX27,700]=29,300 

 I o.o 



Since this is exactly what was used in the first trial we need 

 not again calculate E and x r 



In any case V will not vary much from the first approximate 

 determination, and it is readily seen what effect a change in V 

 will have upon M 2 , M 2 ' and H'. 



Now we have ^=32.0 ft, z/=15.2 ft., #=5,170, #'=7,430 

 ^=12,600, #i'=15,100 



