PART II 



THE THEORY AND DESIGN OF SLABS, BEAMS, 

 AND COLUMNS. 



CHAPTER IV 

 RECTANGULAR BEAMS 



[Reinforced concrete is not used .for plain tension members 

 so that the stresses to be resisted in this type of construction 

 come from simple compression, simple bending, or combined 

 compression and bending. The simple beam supported at its two 

 ends will be studied first and the stresses which must be provided 

 for will be analyzed. The student should know how to determine 

 the outer forces (loads and reactions) which are applied to a beam. 

 Before taking up reinforced concrete beams it will be desirable to 

 consider the nature of the stresses in a plain concrete or homo- 

 geneous beam of any material.] 



29. Inner Forces in a Homogeneous Beam. The ymer forces 

 in a beam are tension, compression, and shear. The following 

 principles concerning homogeneous beams should be familiar 

 to the student: 



1. At any cross-section the internal forces, or stresses, may 

 be resolved into normal and tangential components. The com- 

 ponents normal to the section are stresses of tension and com- 

 pression, while the tangential components add together and 

 form a stress known as the resisting shear. 



2. The shear at any cross-section is borne by the tangential 

 stresses in that section. The moment at any section is borne by 

 the component stresses normal to that section. 



3. The neutral axis passes through the center of gravity of 

 the cross-section. 



4. The intensity of stress normal to the section increases 

 directly with the distance from the neutral axis and is a maximum 

 at the extreme fiber. The intensity of this stress at any given 



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