82 CAMBBIA STEEL. 



LATERAL STRENGTH OF BEAMS, 



WITHOUT LATERAL SUPPORT. 



The Tables of Safe Loads for Cambria I-Beams and Channels 

 and Tables of Spacing of Cambria I-Beams, on pages 106 to 135, 

 are calculated on the assumption that proper provision is made 

 for preventing lateral deflection by means of tie rods or other 

 braces. In order to prevent undue strains in the compression 

 flange, considered as a column, the beams should be supported 

 laterally at distances not exceeding twenty times the flange width, 

 this ratio being determined by the following formula, which 

 gives the safe load for solid columns of soft steel: 



18000 



' SOOOb 2 

 in which 



p = allowable stress in pounds per square inch. 

 1 = length between lateral supports in inches, 

 b = width of flange in inches. 



Substituting 16 000 for p in the above formula, which is the 

 allowable unit stress of the safe load tables, it is found that the 



ratio -r = 19.37, from which it may be seen that the compression 



flange should be supported laterally at distances not exceeding 

 twenty times the flange width as stated above. 



Beams which are not thus supported laterally should not be 

 loaded to their full transverse capacity. The allowable fibre 

 stresses and proportions of their full loads which they can safely 

 carry when laterally supported at various distances is given in 

 the following table: 



