— (59 — 
Square or flat bars are to receive the (allowance for round rods 
of equal sectional area. 
Lateral struts are always to be attached to the chord pius. comuction for Lit- 
T “ t eral Systems. 
Lateral rods arc also to bo attaclied to tlie oliortl pms by bent 
eyes when tlie larger rod at the connectiou does not exceed one and 
tlu’ee quarter (If) inches in diameter« In other cases they are to 
be connected to special vertical pius passing through jaws on the 
lateral struts. Floor beams arc not to be used in any case as lateral 
struts. 
In figuring the stress in a lower lateral strut at tlie roller end stresses i» e»<i Lower 
f 0 • Lateral Struts. 
01 a 8 P^n, tlie stress caused by the total wind pressure on both 
uppei ： and lower lateral systems is to be added to the transverse 
component of the initial tension in the end lateral rod or rods atta- 
clied to tlie windward end of the strut, and from the sum is to be 
subtracted one fourtli (}) of the reduced pressure upon tlie windward 
shoe. 
The calculations are to be made for the case of tlie bridge 
covered by the moving load and for that of tlie bridge empty, tlie 
gi eater of tho resulting stresses being adopted. 
In any panel of a bridge where the compression on tlie bottom stiffejie.i Bottom 
chord duo to tlie wind pressure when the bridge is empty exceeds 
tlie tension there duo to tlie reduced dead load alone, tlie chord in 
tliat panel must be made to resist both tlie tension and the excess 
of compression. 
Wliei.e two channels arc employed for the lower chord, tlie 
effective areas of the webs alone are to be counted upon to resist 
tension. 
The top chord and batter brace sections, whenever large Top chord an<i Bat- 
enougli cliannels are procurable, are to consist of two clianuels with 
a above and latticing 01， lacing below. The top plates must be 
thin and of the same section throughout, the increase in sectional 
y-iea being obtained by thickening the webs of the channels. For 
heavier chords, an I beam may be inserted between the channels, or • 
chord may be built of plates and angles in channel form, care 
0111 S taken to remove tlie material as far as practicable from the 
neutral surfaces. 
Posts arc to be made of two channels latticed or laced, wlien rost sectioua. 
sumciently large channels are procurable. Otherwise they are to 
. mit of plates and angles in channel form, the same restriction 
^ le g ai ’d to a proper disposition of tlie material as iu tlie case of 
c ioid sections being observed. 
Upper lateral, lower lateral and portal struts are to be composed upper Lateral ， 
Of fwn M 、 1 1 i r ， Lateral ami Portal 
u cuail nels laced or latticed, and are to be connected by pro- strut sections. 
pcily proportioned jaws. 
