58 



RESISTANCE OF MATERIALS 



119. Find the required size of a square wooden beam of 14-ft. span to carry 

 an axial tension of 2 tons and a uniform load of 100 Ib./f t. 



120. A floor designed to carry a uniform load of 200 lb./ft. 2 is supported by 

 10-in. steel I-beams weighing 30 lb./ft. How far apart may they be placed for 

 a span of 16 ft. and a working stress of 16,000 lb./in. 2 ? 



PLAN 



END ELEVATION 



FIG. 56 



121. A floor is supported by wooden joists 2 in. x 12 in. in section and 16 ft. 

 span, spaced 16 in. apart on centers. Find the safe load per sq. ft. of floor area 

 for a working stress of 800 lb./in. 2 



122. A floor is required to support a uniform load of 150 lb./ft. 2 and is supported 

 by steel I-beams, 18 ft. span and spaced 5 ft. apart on centers. What size I-beam 



is required for a working 

 stress of 16,000 lb./in. 2 ? 



123. A structural-steel 

 built beam is 20 ft. long and 

 has the cross section shown 

 in Fig. 53. Compute its mo- 

 ment of resistance and find 

 the safe uniform load it can 

 carry per linear foot for a 

 factor of safety of 5. 



124. The cast-iron bracket 

 shown in Fig. 54 has at the 

 dangerous section the dimen- 

 sions shown in the figure. 

 Find the maximum concen- 

 trated load it can carry with a factor of safety of 15. 



125. Find the proper dimensions for a wrought-iron crank of dimensions shown 

 in Fig. 55 for a crank thrust of 1500 Ib. and a factor of safety of 6. 



126. A wrought-iron pipe 1 in. in external diameter and T ! ff in. thick projects 

 6 ft. from a wall. Find the maximum load it can support at the outer end. 



FIG. 57 



