NOTES OX PLATE-GIRDER DESIGN 



.1 U' the net area of each flange; 



h be the distance o. to c. of gravity of flanges; 



5 be the allowable unit stress for tension or com- 



pression produced by flexure; 

 h i !> tin depth of the web plate; 

 / be the thickness of the web plate; 

 ^2 I*' the depth out to out of flan v 

 // be moment of inertia of each flange about its <\vn 



horizontal axis. 



Then the flexure formula becomes 



2 



Tho right half of this equation represents the moment 

 of the internal stresses; of the three terms which make 

 up this half it may be said : 



47 / 

 The term - is small in most cases, but for shallow 



fl2 



girders it Is relatively quite large, its omission from the 

 expression requires the other terms to be larger. 



The value of i i- always less than unity, and in .shallow 



"2 



girders considerably less, frequently as much as 10%. 



The value of - - is usually less than unity, for very 



/l2 



shallow girders without cover plates it is often equal to 

 unity, and for girders with two or more cover plates it 

 may be as much as 10% less than unity. 



