432 



TERENCE T. QUIRKE 



member yielding to tension parts in a plane at right angles to its 

 axis. Figure 7 illustrates the rupture of flexed wooden columns 

 by tension and shear. Examples j£ and B have ruptured by ten- 

 sion and by shear, whereas example C has ruptured by a com- 

 bination of tension and shear. Applying these illustrations to 

 conditions in the earth's crust, it is probable that rock is so weak 

 to resist tension that under continued straight compression its 

 folds are likely to rupture at the arches by tension. In the case 



Fig. 6. — A illustrates the character of rupture of a short block under highly 

 rotational compression. The surface abed represents the break. The planes marked 

 X represent the distributed shear due to the unequally distributed forces F. B illus- 

 trates the character of rupture of a long column or of a flexible sheet by rotational 

 compression. The plane marked 5 is ,the plane of maximum shear due to flexure; 

 the planes marked x indicate the planes of distributed shear and the action of the 

 unequally distributed forces F. The place of maximum tension is marked I and 

 the place of maximum compression is marked k. The rupture abed ideally follows 

 the plane 5-5 partly and emerges near /. 



of major terrestrial deformations, however, straight compression 

 is thought to give place to rotatiojial forces, and the situation 

 is changed. 



Analysis of the rupture of sheets and columns under rotational 

 forces. — Any compressive force unequally distributed in its appH- 

 cation gives rise to shearing stresses within the member affected. 

 The case of members folded by rotational forces includes tension 

 due to bending, shear due to bending, and shear due to rotational 

 stress. The plane of maximum shear is somewhere near the middle 



I 



