PLATE AND ANGLE COLUMN. 579 



Plate and Angle Column. Design a plate and angle column, Fig. 7, to carry an axial load of 

 340,000 lb., the unsupported length being 1 6' o". 



References 34, p. 57; 38, p. 57; 79, p. 60; 94, p. 61; 96, p. 61; 100, p. 61; 114, 

 p. 62; 9, p. 104; 12, p. 104; 17, p. 104. 



Solution. A section with a 12 in. web plate and two 14 in. flange plates will be assumed. The 

 angles will be spaced 12% in. back to back to allow for an over-run in the web plate without inter- 

 fi-riiiv; with tin- cover plates. 



The radius of gyration about the axis A -A, Fig. 7, is approximately 0.45 X 12.5 5.62 in. 

 (Table 136), and about the axis B-B is 0.23 X 14 = 3.22" (Table 136). The axis B-B will 

 control the design. The allowable unit stress is 



/ = 16,000 - 70 l/r lb. per sq. in. - 16,000 - 70 X = 11,800 lb. per sq. in. 



which requires an area of 



P 340,000 



A = r = - - = 28.8 sq. in. 

 / I i, 800 



Try a section consisting of four angles 6" X 4" X %" with long legs turned out, and 12% 

 in. back to back, one web plate 12 in. X % in. and two flange plates 14 in. X % in. The prop- 

 erties of various sections are given in Table 70. The properties of sections are calculated as 

 shown at the bottom of the table. The radius of gyration about the axis A-A is found to be 

 *A. 3 5** in., about the axis B-B is r B = 3.14 in., and the area 29.44 sq- in. 



FIG. 7. PLATE AND ANGLE COLUMN. 



For this section the ratio l/r = 16 X 12/3.14 = 61.2 which satisfies the specification that 

 the maximum value of l/r is 125. The allowable unit stress is, 



f e = 16,000 70 'X 61.2 = 11,700 lb. per sq. in., 



and the required area is, 



P 340,000 



A = 7- = - - = 29.1 sq. in. 

 fe 11,700 



The area provided by the above section is 29.44 sQ- in. 



Expansion Rollers. Design the rollers for the expansion end of a single track railway bridge 

 of 175 ft. span, the dead load stress being 110,000 lb., the live load stress being 282,000 lb., and 

 the impact 178,000 lb. Total stress = 570,000 lb. 



References. 19, p. 209; 60, p. 212; 62, p. 206; 62, p. 212. 



Solution. The span being short a 6 in. roller will be used.. The allowable stress per linear 

 inch of rollers is 600 X d, when impact is considered, giving 600 X 6 = 3,600 lb. for 6 in. rollers. 



The number of linear inches required is, 570,000/3,600 = 158 in. 



Five rollers 32 in. long provide 5 X 32 = 1 60 linear inches and occupy a space about 32 inches 

 square. 



For highway bridge expansion rollers, see 41, p. 141; 82, 83, 84, p 144. 



For roof truss expansion rollers, see 7, p. 55; 33, p. 57; 117, p. 62; 15, p. 104. 



MEMBERS IN FLEXURE. The design of structural members stressed in flexure will be shown 

 by several examples. 



I-Beam. Select an I-Beam to carry a uniform load of 1000 lb. per linear foot, the span being 

 16' o" and the ends simply supported. 



