216 



ME ANGUS R. FULTON ON 



(2) A direct uniformly distributed stress due to the force W acting at the centroid 

 of the section AB. 



Thus if the strain produced was entirely elastic, the stress diagram of (l), when 

 the material has approximately the same ultimate strengths in compression and in 

 tension, would be as represented by AaN&B in fig. 3, Aa being the tensile stress 

 of the extreme fibres AA, and Bb being the compressive stress of the extreme fibres 

 BB of the section shown in fig. 2. 



The neutral axis NN passes through the centroid of the section. This diagram 

 would be modified by the direct tensile stress AA X of (2) to the form AaiN^iB, this 



Fig 2. a 



r, gS 



having the effect of changing the neutral axis from N to N a . If NN X = x, this 

 increases the external bending moment to the extent of Wx, and correspondingly 

 the resisting moment of the section must be increased to the same extent. 



If t and c represent the values of the extreme stresses, then, by the ordinary 

 elastic formula for determining these stresses, 



.... (2a) 



t = 



My W 

 I + A 



,wp$+l 



,_My 



A V I 



I 



W 



Therefore the ratio of - = constant and the line a-fri, though its slope varies, passes 



through a fixed point N x so long as the condition of elastic stress is maintained. 



