Un traité sur le béton, lisse et renforcée : les matériaux, la construction, et de la conception de béton et béton armé ; 2e éd. . em est illustré dans la Fig. 184,page 623. Ceci a été construit en 1907 par le commissaire de l'ingénierie,Washington, D. C, M. W. J. Douglas, ingénieur des ponts. L'arche centrale est de 100 pieds et à portée de 15 pieds de hauteur, et la chaussée, qui est de 16 pieds de mde et macadamized, est déposé sur un reinforcedconcrete 6 pouces dalle soutenue par des poutres en béton longitudinal qui dans turnrest sur colonnes directement pris en charge par le béton des côtes. Les trois, qui archribs sont reinforc

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A treatise on concrete, plain and reinforced : materials, construction, and design of concrete and reinforced concrete; 2nd ed. . em is illustrated in Fig. 184, page 591. This was built in 1907 by the Engineering Commissioner, Washington, D. C, Mr. W. J. Douglas, Engineer of Bridges. The central arch is 100 feet clear span and 15 feet rise, and the roadway, which is 16 feet mde and macadamized, is laid upon a 6-inch reinforcedconcrete floor slab supported by longitudinal concrete girders which in turnrest upon columns supported directly by the concrete ribs. The three archribs, which are reinforced as shown, are 2 feet wide throughout their lengthwith a thickness of 2 feet 6 inches at the crown. Each hinge consists of two steel castings, shown in detail, with a pin 4inches in diameter, and these hinges are imbedded in the concrete. Anexpansion joint is provided in the roadway deck over each springing. Thefloor of the arch was computed for a 6-ton wagon, and the ribs for a liveload of 100 pounds per square foot of roadway. The maximum compressionon the concrete of the ribs under live and dead loads is 500 pounds per. , 92 A TREATISE OX COX CRETE square inch, and there is no tension. The cost of the structure was $8000, which is equivalent to about $3.00 per square foot of the roadway. Walnut Lane Bridge, Philadelphia. A notable structure in concreteis the Walnut Lane Bridge built as it is ^vdth a clear span of 233 feet.The arch was completed in 1908 under the direction of the Bureau of Sur-veys, Mr. George S. Webster, Chief Engineer and Mr. Henry H. Quimby, Assistant Engineer. The principal arch consists of two ribs, upon whichrest cross walls connected by small longitudinal arches of 20 feet spancarrying the spandrel wall supporting the I-beams of the floor. A fine photograph of the arch is shown in Fig. 156, page 532, and crosssections illustrating the design in Fig. 185, page 592. The balustrade isentirely of concrete, the posts being molded on the ground and the sur-fa

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