44 PROBLEMS 



PROBLEM 14. WIND AND CEILING LOAD STRESSES IN AN UNSYM- 

 METRICAL TRUSS, BY GRAPHIC RESOLUTION. 



(a) Problem. Given the unsymmetrical triangular truss, span 

 5o'-o", height i6'-o", rollers leeward, wind joint load 4000 Ibs., 

 ceiling joint load 3000 Ibs. Calculate the stresses due to both systems 

 of loading by graphic resolution. Scale of truss, i" = 8'-o". Scale 

 of loads, i" : = 4000 Ibs. 



(b) Methods. Calculate the reactions due to the wind loads, 

 using the method of Fig. 33. Calculate the reactions due to ceiling 

 loads. Then place the y point of the wind load line on the point separat- 

 ing the ceiling load reactions (the x point). The wind loads are laid off 

 in order downwards, while the ceiling loads are laid off in order upwards. 

 The left reaction, R lt is the resultant of R lw and 7^ D while the right reac- 

 tion, R 2 , is the resultant of R 2W and R 2 v. The calculation of the 

 stresses is begun at R lf as in Problem 10. The stresses are then 

 calculated by passing to joint C lt then to joint F 2 , then to C 2 , etc., until 

 the stress diagram is checked up at R 2 . 



(c) Results. The members 1-2 and 7-8 are simply hangers to 

 carry the ceiling loads. The triangular truss in this problem is of the 

 Howe type, the verticals being in tension, while the diagonal web mem- 

 bers are in compression. This truss is expensive to build of iron or 

 steel but is quite a satisfactory type where iron is expensive and wood 

 is cheap, and is used for the struts. 



PROBLEM I4a. WIND AND CEILING LOAD STRESSES IN AN UNSYM- 

 METRICAL TRUSS, BY GRAPHIC RESOLUTION. 

 (a) Problem. Given the unsymmetrical triangular truss span 

 5o'-o", height, i6'-o", rollers windward, wind joint load 4000 Ibs., 

 ceiling joint load 3000 Ibs. Calculate the stresses due to both systems 

 of loading by graphic resolution. Scale of truss, i" = 8'-o". Scale 

 of loads, i " = 4000 Ibs. 



