STABII.H Y OF BRIDGE ABUTMENTS. 



247 



ached the point 2 in (b), Fig. 2. The weight of the girders and the live load was assumed as 

 uniformly distributed over a length of the abutment equal to the distance between track centers, 

 and one lineal foot of wall was investigated. 



Case (a). The pressure of the filling on the plane 5-2 was calculated as in Chapter V, 

 Fig. 9, and is P' = 14,700 lb., acting through the center of gravity of the trapczoid 2-3-4-5. 

 The weight of the filling and surcharge is Wt + Wi = 14,900 lb., which when combined with P' 

 t he resultant pressure of the filling on the wall = P = 20,900 lb. The pressure P is then 

 combine-el with the weight of the wall, W\ = 29,800 lb.. and with the dead load and live load 

 from the girder = 12,820 lb., giving the resultant pressure on the foundation, E 59,400 lb., 

 and acting, b = 1.4 ft. from the center of the wall, and F = 57,500 lb. 



i. Stability Against Overturning. The resultant E is nearly vertical and well within the 

 middle third, so that the wall is amply safe against overturning. 



/=" "Fill 

 Wj-" Surcharge 

 Concrete /50 Ibs/cu.ft. 

 Far/h 100"-" 



f=>=?0900 



(b) 



FIG. 2. ABUTMENT FOR WEST ALAMEDA AVENUE SUBWAY, DENVER, COLO. 



2. Stability Against Sliding. Assuming that <' = 30, then the coefficient of friction will 

 be tan <j>' 0.57. Using the definition of factor of safety given in equation (27) Chapter V. the 

 resistance of the wall against sliding will be 57.500 X 0.57 = 32,765 lb. The sliding force is 

 P' = 14,700 lb., and the factor of safety is 32,765/14,700 = 2.23, which is ample. 



3. Pressure on Foundation. The pressure on the foundation will be p = F/d * 6F-b/d* 

 = + 5>74 a d + 1,700 lb. per sq. ft., which is safe. 



4. Upward Pressure on Front Projection of Foundation. The base will be investigated on 

 the plane 7-8 to see that the upward pressure .will not break off the front projection of the founda- 

 tion. The bending moment of the upward pressure about the front face of the wall in (a), Fig. 2, 

 will be 



