260 



STRESSES IN A BALTIMORE TRUSS. 



Art. 136. 



136. Stresses in a Baltimore Truss. Fig. 190 shows 

 three ways in which sub-trussing may be put in. Heavy lines 

 indicate compression members and light lines tension mem- 

 bers. By horizontal and vertical resolutions at the junction 

 of the diagonals the stress in the sub-diagonal may be found in 

 any case. The stress in the sub-vertical, V s , is evidently equal 



+*/ ! 



A h 



IP 



(c') 



to the load at its lower extremity unity. Assuming com- 

 pression in each of the three diagonals in Fig. 190 (a), we get, 



DI sin D 2 sin D S sin = 0, 

 D l cos 0-D 2 cos +D S cos =P. 



Dividing the first equation by sin and the second by cos 6 

 and subtracting, we get 



2D S = P sec or D,~ IP sec 0. 



Thus we get the coefficient for D s to be J. By a similar process 

 the coefficient for D s may be shown to be J in any case where 

 the inclinations of the diagonals are equal and the loads ver- 

 tical. Figs. 190 (a'), (b') and (c') show diagrammatically tlie 

 paths of the stresses from the sub-panel loads. 



Fig. 191 shows a Baltimore truss of sixteen panels with the 

 sub-diagonals in tension. The top chord is usually supported 

 at the sub-panel points by vertical struts V s ', as this reduces 



