. Elements of railroad track and construction . lt with a plaincircular arc, three-centered, or elliptical. They arebuilt in five ways, viz., stone masonry with a stone ring,stone masonry with a brick ring,all brick masonry, concrete, andreinforced concrete, the latterbeing used for large spans. Theeconomical design of arch cul-verts is an extensive subjectand will not be given here. 319. Special Culvert Con- Fig. —^There are a num-ber of special features in culvert construction whichare economical under the proper conditions. In good masonry stone can be obtained
. Elements of railroad track and construction . lt with a plaincircular arc, three-centered, or elliptical. They arebuilt in five ways, viz., stone masonry with a stone ring,stone masonry with a brick ring,all brick masonry, concrete, andreinforced concrete, the latterbeing used for large spans. Theeconomical design of arch cul-verts is an extensive subjectand will not be given here. 319. Special Culvert Con- Fig. —^There are a num-ber of special features in culvert construction whichare economical under the proper conditions. In good masonry stone can be obtained readily,but suitable cover stones cannot be obtained. Twoforms of special covers may be used, viz., reinforced con-crete and old railroad rails. Reinforced concrete coverslabs are made by embedding one of the many forms ofreinforcing bars in the concrete. The bars are placedabout two inches from the bottom of the slab and atright angles to the length of the culvert, and at a distanceapart which is governed by the clear span, the size of the. 282 RAILROAD TRACK AND CONSTRUCTION. bars, and the thickness of the slab. The bars extend thefull width of the slab, which has a bearing of one footon each side wall. The reinforced concrete cover slabsmay be made in two ways, viz., they may be made in forms,allowed to set, and then placed in position, or the formsmay be arranged so that the slabs are made in place. Covers for culverts are made from old railroad railsby cutting them in lengths two feet greater than the clearspan of the culvert and placing them on their bases, sideby side across the culvert. The culverts that have been described indicate themethods of providing for the small or minor openings,such as are most frequently met with along a rail-road. Larger openings are spanned by arches or steel trusses. Wherever^^* possible, masonry should5 \ be used, as it ranks nextFig. 162. to a solid fill for perma- nency. 320. Wing Walls.—End walls of culverts may be plain,as descri
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