CAMBRIA STEEL. 



EXAMPLE OF THE USE OF THE TABLES OF RADII 

 OF GYRATION FOR TWO ANGLES PLACED BACK 

 TO BACK AND THE TABLES OF STRENGTH OF 

 STEEL COLUMNS OR STRUTS. 



PAGES 215 TO 221 INCLUSIVE 



What is the size of truss member required to safely sustain 50 000 

 pounds in compression, the safety factor being 4, the unsupported 

 length 8 feet, the gusset plates at each end being y%" thick? 



Assume for trial two 4" x 3" x s /f s " angles with the long legs together. 

 Referring to page 216, the least Radius of Gyration, comparing values 

 in columns r and r 3 is found to be 1.27. The ratio of the length of the 



column in feet to the Least Radius of Gyration in inches, - is, there- 

 fore, ^- =6.3. 

 1.27 



Referring to the table of Strength of Steel Columns or Struts for 

 medium steel, page 220, the ultimate strength of a column in which 



=6.3 is found by interpolation between the values for 6.2 and 6.4 



to be 43 149 pounds per square inch, which, divided by the safety 

 factor 4, gives 10 787 pounds as the safe unit stress per square inch. 

 Multiplying the safe unit stress per square inch, 10 787 pounds, by 

 4.18, the area of the two angles in square inches, gives 45 090 pounds 

 as the total safe load. This is slightly less than the specified load of 

 50 000 pounds, and, therefore, it will be necessary to increase the 

 assumed section . Assume the angles to be 4" x 3" x %", for which the 

 Least Radius of Gyration is found by interpolation to be 1.26, and, by 



the same process used above, is found to be 6.35, which corre- 

 sponds to an ultimate strength of 43 055 pounds per square inch, or a 

 safe unit stress of 10 764 pounds per square inch, which, if multiplied 

 by the area of the two angles, 4.96 square inches, gives a safe total 

 load of 53 389 pounds, which is ample to meet the conditions stated. 



EXPLANATION OF TABLES RELATING TO DIMEN- 

 SIONS AND SAFE LOADS OF STEEL COLUMNS 

 OF VARIOUS SECTIONS. 



PAGES 224 TO 301 INCLUSIVE 



Tables of Dimensions for Plate and Angle Columns are given on 

 pages 224 and 225, the Moments of Inertia and Section Moduli about 

 two rectangular axes are given on pages 226 to 228 and the Safe Loads 

 for various lengths, calculated for the Radius of Gyration about each 

 of the two rectangular axes, are given on pages 248 to 267 inclusive. 



Tables of Dimensions for Latticed Channel Columns are given on 

 pages 230, the Moments of Inertia and Section Moduli about two rec- 

 tangular axes are given on page 231 , the Safe Loads for various lengths 



