56 



W. H. WARREN. 



Fig. 



5 — Curves showing the Extension (or Compression) of Fibres of a Eeinforced 



Concrete Beam, mp^surpd at several points ovpr the depth of the beam. 



__ ___„ ._„ . — „._^ . ,,™» 



1 < m Cu^&^s 



45 



50 



5 10 15 20 25 30 35 40 



Extension or Compression on 40 inches in Units of '001 inches. 



Reference to Curves. 

 a — Extension measured \\ inch from tension face of beam 

 b— Extension measured \\ inch from centre of beam on tension side 

 c— Compression measured \\ inch from centre of beam on compression side 

 d-~ Compression measured 1| inch from compression face of beam 

 e — Extension measured on tension face of beam 

 / — Compression measured on compression face of beam 



It will be observed that the neutral axis remains in the 

 centre of the depth up to a bending moment of one-third 

 that necessary to produce fracture, and that it gradually 

 moves towards the compression face of the beam as the 

 bending moment increases, the maximum deviation being 

 0*8 of an inch. The strain curves 1, 2, 3, and 4, Fig. 4, 

 show how nearly a plane section before flexure remains a 

 plane section after flexure. The stress curves are more 

 curved on the tension than on the compression sides, 

 where they approximate very closely to a straight line. 

 The strains obtained from testing a reinforced concrete 

 beam are recorded in Pig. 5, which gives in each case the 

 mean of tests of four beams of the same material reinforced 

 in a similar manner; the results obtained in the four beams 

 were very consistent and differed very slightly from each 

 other. Fig. 6 shows the actual lengthening or shortening 

 plotted with reference to the depth of the beam in a similar 

 manner to that employed in the strain curves 1, 2, 3, and 



55 



