REINFORCED CONCRETE. 59 



VI., but only the stress curves on the compression side of 

 the neutral axis are shown ; they are very similar to the 

 stress curves on the compression side of Fig. 6. The neutral 

 axis moves from the centre of the depth of the beam in all 

 four cases, to more than 2 inches towards the extreme fibre 

 in compression, also the curves 1 are practically straight 

 lines, whereas 2, 3, and 4 are approximately parabolic. 



The form of the curve of compressive stress in a reinforced 

 concrete beam tested to the breaking point is therefore 

 fairly represented by a parabolic curve, having its origin 

 in tbe neutral axis, and its maximum ordinate at the extreme 

 fibre in compression, and the equations given in a former 

 paper, 1 express fairly well the conditions of stress in such 

 beams. In applying the foregoing results to the practical 

 design of reinforced concrete beams, we must remember 

 that the curve of stress on the compression side, for work- 

 ing stresses, is more nearly represented by a straight 

 line than a parabola, and that the tensile resistance of 

 the concrete should be neglected for the sake of safety, 

 more especially as it contributes very little to the moment 

 of resistance of the beam. 



c. The safe working stresses and the fundamental 

 equations recommended to be used in the design of 

 reinforced concrete. 



Pounds per 

 square inch 



The extreme fibre stresses in concrete compression = 500 

 The shearing stress in concrete and the adhesion 



of the concrete to the steel ... ... ... 50 



The direct compression stress ... ... ... 350 



The tensile stress in the steel reinforcement ... 16000 



The compressive stress ,, „ ... 12000 



The shearing stress ,, „ ... 10000 



1 Further Experiments on Eeinforced Concrete — Proc. Eoy. Soc. N. S. 

 Wales, Sept. 7, 1904. 



