一 112 — 
corresponding to a 40 pound channel, which is far greater than would ever bo used 
in practice. Hence we may conclude that it will be necessary to assume that the 
trusses deflect independently in all cases where their depth is not great enough to 
permit of the use of vertical sway bracing. 
It might be well however to increase the sectional area of the upper lateral 
struts in order to resist the racking effect which the vibration of passing loads pro- 
duces in these members. It is difficult to say what the amount of increase should 
be, but the author considers that if six inch channels weighing eight or ten pounds 
per lineal foot and spaced ten or twelve inches apart be employed, the struts will bo 
strong enough. 
It is obvious that no unequal distribution of moving load can affect the portal 
bracing, for tlio loads at the feet of tlio batter braces rest directly upon the foantla- 
tions, and those at tlio first panel points produce an inconsiderable shortening 
of the batter braces. 
