8 GWYTHER, Modes of nipture of a JiemispJierical shell, 



to resist tension, the conclusion must be that 

 the " ring tension " is comparatively small. The 

 theory of the " Angle of Rupture " does not apply 

 to cases of externally applied load, and it pro- 

 bably is not applicable even to a concrete dome 

 under its own weight. 



(2) Whatever the size of the example on which the 



experiments have been carried on, the fracture 

 has occurred under the same conditions (except 

 in the case of the smallest specimens) for practi- 

 cally the same load, and not for the same stress. 

 It may be concluded that the cause of the 

 fracture is not 'shear' under which concrete is 

 supposed to be apt to break, but it breaks in 

 consequence of an excessive ' bending moment,' 

 or otherwise stated, that the resultant stress on 

 some section fails to act within the 'middle 

 third.' 



(3) The section in which the fracture takes place 



appears to be approximately on a cone of which 

 the centre of the sphere is the vertex. The mean 

 height of the fracture is about 66 of the height 

 of the shell. 



(4) The angle of the cone does not vary very greatly 



with the reinforcement given to the concrete. 



(5) The load which the specimen will bear without 



rupture is greatly increased by reinforcement at 



the lower rim, and is again greatly increased by 



reinforcement at both top and bottom. 



It is desirable that a greater number of experiments 



should be made, as it is probable that a very slight 



displacement of the reinforcing wires may make a very 



considerable difference in the load which the specimen 



can bear without fracture. 



