43 2 PROBLEMS 



PROBLEM 10. WIND LOAD STRESSES IN A TRIANGULAR TRUSS No 

 ROLLERS BY GRAPHIC RESOLUTION. 



(a) Problem. Given a triangular truss, span 6o'-o", pitch y$, 

 camber of lower chord 3'-o", trusses spaced i4'-o", wind load normal 

 component of a horizontal wind load of 30 Ibs. per sq. ft., no rollers. 

 Calculate the reactions by means of force and equilibrium polygons. 

 Calculate the stresses by graphic resolution. Take P as 3300 Ibs. Scale 

 of truss, i"= lo'-o". Scale of loads, i" = 3ooo Ibs. 



(b) Methods. Start stress diagram at (4.65", 6.6"). The reac- 

 tions will be parallel to each other and to the resultant of the external 

 loads. The equilibrium polygon may be started at any convenient 

 point in one reaction, closing up on the other one. The closing line 

 of the equilibrium polygon will always have its end in the reactions. 

 The calculation of stresses is begun a R^, and is checked up at R 2 . 



(c) Results. The stresses are of the same kind in the chords 

 as for dead loads as given in Problem 9, while the webs on the leeward 

 side are not stressed. The load P has no effect on the stresses in the 

 truss. Calculate the vertical component of the wind load by means of 

 Duchemin's formula (5), as plotted in Fig. 6 (page 15). The normal 

 wind joint load will be equal to 14 X 9 X 26 = 3276, which is taken 

 as 3300 Ibs. For a discussion on the different conditions of the ends 

 of trusses, see Chapter VII. 



PROBLEM loa. WIND LOAD STRESSES IN A TRIANGULAR TRUSS No 



ROLLERS BY GRAPHIC RESOLUTION. 



(a) Problem. Given a triangular truss, span 6o'-o", pitch J^, 

 camber of lower chord 2'-o", trusses spaced i6'-o", wind load normal 

 component of a horizontal wind load of 30 Ibs. per sq. ft., no rollers. 

 Calculate the reactions by means of force and equilibrium polygons. 

 Calculate the stresses by graphic resolution. Take P as 3800 Ibs. 

 Scale of truss, i" = lo'-o". Scale of loads, i" = 3000 Ibs. 



