92 CONSOLIDATED STEEL CORPORATION 



EXPLANATION OF TABLES OF SAFE LOADS 



FOR BETHLEHEM ROLLED STEEL 



H-COLUMNS 



The superiority of steel columns over columns of any other material is 

 so well understood and recognized as to need no comment. Cast iron columns 

 are sometimes used solely on the score of cheapness because of the relatively 

 greater cost of riveted steel columns the only kind of steel columns heretofore 

 obtainable; but in buildings of anything more than the most moderate height, 

 or wherever stiffness of frame and absolute security are essential, steel columns 

 are employed exclusively. 



Rethlehem Rolled Steel H-Sections reduce the cost of steel columns to such 

 an extent that they can be used for all purposes with economy. These rolled 

 steel columns provide all the desired qualities of safety and reliability at a cost 

 less than that of any other form of steel column and at a cost as low or even less 

 than cast iron. 



For very short lengths the compressive strength of structural steel of 

 .standard quality is the same as its tensile strength. As the length increases the 

 compressive strength diminishes. A short column has a practically uniform 

 compressive strength for all lengths less than about fifteen times its least diam- 

 eter; but for greater lengths the strength decreases, the decrease being a func- 

 tion of the length of the column and the radius of gyration of the section in the 

 direction of its least resistance to bending. Conforming to these conditions, 

 the safe allowable stress, in pounds per square inch, on square ended columns 

 of medium steel used for buildings is given by the following formula: 



13,000 pounds for lengths under 55 radii of gyration, 

 16,000 55 for lengths over 55 radii of gyration, 



in which / = unsupported length of column and r = least radius of gyration, 

 both in inches. 



The safe strength of steel columns given by this formula agrees in a satis- 

 factory manner with the available experimental data on the subject. In addi- 

 tion it is of correct theoretical form. It represents a straight line which be- 

 comes tangent to the curve of Euler's Formula for very long columns and fixes 

 a maximum limit of stress for columns of relatively short length. The safe 

 stress allowed on steel columns by this rule corresponds to the safe stress usu- 

 ally allowed for beams and girders in buildings. Columns proportioned in 

 accordance with this formula have the same proper degree of safety as the 

 beams and girders which they support, thus maintaining a symmetrical propor- 

 tion of all parts of the structure. 



