MECHANICS 99 



The moments of the areas of the separate sections, with 

 respect to the line ab, are as follows: 



Flange plate, 4.5 X A = .84 



Two angles, 2X3.75X1*1 = 11.70 



Web-plate, 6X8| =50.25 



Total, 62.79 



The distance c from the top edge of the flange plate to the 

 neutral axis de of the section is therefore 62.79-1-18 = 3.48 in. 



FORCES ACTING ON BEAMS 



STYLES OF BEAMS 



A beam that has two points of support, one at each end, 

 as shown in Fig. 1 , is known as a simple beam. The distance 

 between the points of sup- 

 port is called the span. 



A beam that has more 

 than two supports, as 

 shown in Fig 2, is known 

 as a continuous beam. The 

 point of support of the 

 middle support is con- 

 sidered to be at its cen- 

 ter, as at a. Continuous 

 beams, except in rein- 

 forced-concrete work, have 

 not found much favor 

 among engineers in the 

 last few years. 



A cantilever beam is 

 one with only one sup- 

 port, which is at the 

 middle, or any part of 

 a beam that projects 



out beyond its support. A common form of cantilever is 

 shown in Fig. 3. This beam projects from a wall or some 

 other solid structure and has no support at its outer end. 



FIG. 2 



FIG. 3 



