CAMBRIA STEEL. 179 



EXAMPLES OF APPLICATION OF THE TABLES 

 OF PROPERTIES. 



EXAMPLE I. 



What is the proper size of I-Beam to carry a load of 35 000 

 pounds concentrated at the center of a span of 25 feet, the fibre 

 stress not to exceed 16 000 pounds per square inch? 



In the Tables of Properties of Standard I-Beams, the column 

 headed F gives the coefficient of strength for a uniform load cor- 

 responding to a fibre stress of 16 000 pounds per square inch. 



The coefficient of strength for a concentrated load at the center 

 is twice that for the same load uniformly distributed, hence the 

 coefficient necessary to meet the conditions is 35 000 X 25 X 2 

 = 1 750 000. From the Table of Properties of Standard 

 I-Beams, page 185, column 13, the coefficient F for a 24-inch 

 80-pound beam is found to be 1 855 310. The weight of the 

 beam itself is 80 X 25 = 2000 pounds, which corresponds to a 

 coefficient of 2000 X 25 = 50 000, which deducted from 1 855 310 

 gives a net coefficient of 1 805 310. A 24-inch beam weighing 

 80 pounds per foot is, therefore, the proper size. 



EXAMPLE II. 



What is the deflection of the beam in the preceding example 

 under the given load? 



In the Table of Properties of Standard I-Beams, pages 182 to 

 185 inclusive, the coefficient of deflection for beams with center 

 loads is given in column 16. To obtain the required deflection it 

 is only necessary to multiply the coefficient by the cube of the span 

 and the number of 1 000 pounds units contained in the load. 



Thus for the given example the deflection in inches = 



.0000006 X 25 s X = .328 inch. 



1000 



