436 PROBLEMS 



PROBLEM 12. WIND LOAD STRESSES IN A FINK TRUSS ROLLERS LEE- 

 WARD BY GRAPHIC RESOLUTION. 



(a) Problem. Given the same truss as in Problem n. Wind 

 load to be the normal component of a horizontal wind load of 30 Ibs. per 

 sq. ft. The truss is assumed to have frictionless rollers under the lee- 

 ward side. Calculate the reactions by means of force and equilibrium 

 polygons. Calculate the stresses by graphic resolution. Scale of truss, 

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



(b) Methods. Start stress diagram at (4.7$", 6.55"). The 

 reaction R 2 will be vertical, while the direction of R will be 

 unknown. Use the method of calculating the reactions described on 

 page 51, and in Fig. 33; noting that the vertical components of the 

 reactions are independent of the conditions of the ends of the truss. 

 In calculating the stresses the ambiguity of stresses at point 3-4-7-4-^ 

 is removed by substituting the dotted member shown, for members 

 4-5 and 5-6. The calculation of the stresses is begun at R lt and is 

 checked up at R 2 . 



(c) Results. The load P has no effect on the stresses in the 

 truss. The stresses in the members are of the same kind as for dead 

 loads as given in Problem n, except that there are no stresses in the 

 web members on the leeward side. 



PROBLEM I2a. WIND LOAD STRESSES IN A FINK TRUSS ROLLERS 

 LEEWARD BY GRAPHIC RESOLUTION. 



(a) Problem. Given the same truss as in Problem na. Wind 

 load to be the normal component of a horizontal wind load of 30 Ibs. 

 per sq. ft. The truss is assumed to have frictionless rollers under the 

 leeward side. Calculate the reactions by means of force and equili- 

 brium polygons. Calculate the stresses by graphic resolution. Scale 

 of truss, i" == IO'-G". Scale of loads, i" = 3000 Ibs. 



