80 



will keop the unit presstire the same all along the base and 

 the seulement uniform. 



Internal Stresses: To prevent internal failure the con- 

 crete steel beams are figured by the usual methods of 

 concrete steel design. In the inverted T or L type of wall 

 the trunk, the -heel and the toe are simply cantilever 

 beams. The moment on the trunk is produced by the earth 

 thrust. The moment on the toe is produced by the re- 

 action of the foundation acting upward. This reaction is 

 represented by the part of the triangle mno (see Fig.) 

 directly under the toe. The. moment in the heel is pro- 

 duced by the weight of the earth on the heel, the force 

 due to friction in the plane a a' and the reaction, if any, 

 on the foundation, acting negatively. This reaction is 

 represented by the part of the triangle mno directly under 

 the heel. . The distribution of the stresses in the heel and 

 toe vary greatly under different loads. So the stresses 

 in the base should be considered for the various possible 

 loadings. 



Internal Stresses of Counterfort Walls: In counterfort 

 walls the counterforts or ribs are reinforced sufficiently 

 to carry the load of an entire panel length. The stresses 

 caused by the pressures in the face and base must be 

 carried from their points of application to the counter- 

 forts, by a slab construction. Th ese slabs act as con- 

 tinuous beams, and must be reinforced on each side of 

 the slab at proper places. The variation of the position 

 of the stresses in the base under different loads necessi- 

 tates an analysis of the stresses for all of the possible 

 loading. In some parts of the slab the tension may some- 

 times be on one side and sometimes on the other, requir- 

 ing rods on both sides of the slab, and the pressure may 

 be concentrated on one part or it may be distributed. 

 The action of continuity which occurs at the juncture of 

 the face with the floor slab requires vertical rods in the 

 back part of the face slab, continuing down along the top 

 of the base. The positions of the shearing stresses under 

 the various loads must be determined and resisted. A 

 larger factor of safety should be allowed a counterfort 

 v, all than a T wall, in regard to internal stresses, because 

 in a T wall the rods act strictly in series, and, being 

 numerous, a defect or failure in one would be of little im- 

 portance, while in a counterfort wall a defect in one 

 member might endanger the wall for an entire panel 

 length. Also, in the thin slabs that are used in counter- 

 fort walls a slight displacement in a rod makes' consider- 



