2i6 FRAMEWORK 



Tension Members. 



Member 1-2. - Maximum stress = 24,900 Ibs. 



The net area required is 24,900 -=- 16,000 = 1.56 sq. in. The 

 gross area of the section must be such, that there will be a net area of 

 not less than 1 . 56 sq. in. after the area of the rivet holes in any section 

 has been deducted. 



Try two 3" x 3" x *4" angles. It will be necessary to deduct the 

 area of one rivet hole from each angle. The diameter of the rivet hole 

 deducted is taken */ inch larger than the diameter of the rivet before 

 driving. Assuming the rivets as y% inch, it will be necessary to deduct 

 o. 19 sq. in. from each angle (page 310 Cambria). The net area of two 

 3" x 3" x /4" angles is 2.88 0.38 = 2.50 sq. in. The section is 

 somewhat large, but will be used, for the reason that angles much 

 smaller than these will be deficient in rigidity. 



The angles will be riveted together about every 3 feet to make them 

 act as one member. 



Member 5-6. Maximum stress = 5,ooo Ibs. 



The net area required is 5,000 -f- 16,000 = 0.32 sq. in. The gross 

 area of the section must be such that there will be a net area of at least 

 0.32 sq. in. after the area of the rivet holes in any section has been 

 deducted. 



Try two 2" x 2" x y^" angles the minimum angles that can be 

 used under the specifications. Deducting the area of one rivet the net 

 area is 1 . 88 o . 38 = 1 . 50 sq. in. The section appears to be exces- 

 sively large and one 2" x 2" x J4" angle will be tried. Where angles 

 in tension are fastened by one leg the specifications require that (para- 

 graph 35) only one leg shall be counted as effective, or the eccentric stress 

 shall be calculated. The net area of the one 2" x 2" x J4 " angle when 

 fastened by one leg, will then be y 2 0.94 o. 19 = 0.28 sq. ins., which 

 is insufficient. One 2^" x 2^" x %" angle will have a net area of 0.40 

 sq. in., which will be sufficient. However, since it is preferable to make 

 tension members of symmetrical sections, the member will be made 

 of two 2" x 2" x y 4 " angles. 



