164 ANNUAL REPORT 
less than 13-32 inch. Two hundred and fifty soldiers crossed, march- 
ing in quick step, and recrossed at “double time” in order to test the 
bridge for vibration, which it was found to stand remarkably well, 
Figure tot shows the method of construction and figure 102 shows the 
complete bridge. 
A seven span concrete bridge at Dayton, Ohio, completed in 1903, 
which is 56 feet wide and 588 feet long, cost $140,000. 
Fig. 102.—Chatellerault Bridge, Vienne, France. 
RETAINING WALLS. 
In the construction of the Paris Exposition of 1900, it was found 
necessary to depress one of the-streets near the exposition grounds to 
better accommodate the visitors. This street was to be depressed about 
t8 feet below the surface levels; and because of the character of the 
debris and filled ground through which the cut was to be made would 
have required expensive, heavy masonry for retaining walls if the ordi- 
many eravity section were used; hence the engineers decided to use 
“armored concrete.” 
The retaining. walls are listed into panels 19.7 feet in length, 
and extending back into the ground from the back of each panel, are 
three concrete buttresses. Connecting these buttresses at a point midway 
from the top to the bottom is a horizontal concrete beam from 4 to 9 
inches thick and about 4 feet wide. The face wall rests upon another 
