FIRE-BOX GIRDER STAYS. 239 



Note that the "Moment of Rupture" = If in this case is 

 the same as in the previous case ; so that, provided that the 

 length of the girder and the total load upon the bolts remain 

 the same in the two cases, then the " Moment of Rupture " 

 at the centre of the girder is the same whether two or three 

 supporting bolts are employed. 



But as before 



M=R 

 so that 



_ __ _ 



and in consideration that the length of the girder is ex- 

 pressed in feet and that the " Factor of Safety " = 6, the 

 equation becomes 



6~"" 6x12x6 ~ 



, , 7 GXCXCP Xt r, 



or 31 = IV X I = = it 



6 X 12 X 6 



and substituting the proper " Modulus of Rupture " for C. 



,, , 6xb4000xd^xt „ 



6x12x6 



,, , 324000 xcZ~x^ „ 

 or M = ivxl = = li 



432 

 or M = iuxl = 150xd^xt = R 

 750 xd^xt 



and w 



I 



But as before to = the total load on the supporting bolts 

 and 



to = {W-P)xDx WP 



