A treatise on concrete, plain and reinforced : materials, construction, and design of concrete and reinforced concrete; 2nd ed. . o tension. The cost of the structure was $8000,which is equivalent to about $ 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 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 cro
A treatise on concrete, plain and reinforced : materials, construction, and design of concrete and reinforced concrete; 2nd ed. . o tension. The cost of the structure was $8000,which is equivalent to about $ 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 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-face washed off with water to reveal the aggregate. Other Notable Bridges. For references to other bridges built in recentyears, see Chapter XXXI. ELEVATION OFT. IVOf-T^I, *) Flo. lio Walnut Lane Bridge, Philadelphia. {Seep. 592.) SIDEWALKS AND BASEMENT FLOORS 593 CHAPTER XXIIISIDEWALKS, BASEMENT FLOORS AND PAVEMENTS The introduction of reliable American Portland cements has renderedconcrete available for sidewalks and other similar purposes at a price notmore than two-thirds of that previous to 1890, when German and Englishcements were used. Portland cement being thus commercially withinreach of builders, masons have become familiar with its use, and concretesidewalks, because of their economy and durabiUty, are supplanting thoseof other materials. Street pavements are also being made of concrete, and with apparentsuccess,* by methods similar to those which obtain in sidewalk construction. The essentials for a good concrete sidewalk are an artificial foundationof firm but porous material, through which the rain water may percol
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