. Concrete bridges and culverts, for both railroads and highways . dvantages of beam bridges are asollows:—(1) It is possible in a beam bridge tooeate the grade of the bridge floor much lower andlearer to the high water level or other clearanceine than can be done when an arch is used; (2)oundations for beam bridges may be built on soilhat is more or less yielding, which cannot be doneivitli arch bridges, unless hinges are used at the^enter and spring. The lateral thrust of arches on>oft foundations is liable to cause serious injury to:he structure, Avhile the corresponding amount ofsettlem
. Concrete bridges and culverts, for both railroads and highways . dvantages of beam bridges are asollows:—(1) It is possible in a beam bridge tooeate the grade of the bridge floor much lower andlearer to the high water level or other clearanceine than can be done when an arch is used; (2)oundations for beam bridges may be built on soilhat is more or less yielding, which cannot be doneivitli arch bridges, unless hinges are used at the^enter and spring. The lateral thrust of arches on>oft foundations is liable to cause serious injury to:he structure, Avhile the corresponding amount ofsettlement under the abutments of beam bridgesproduces no injurious effect. A frequent objection to the use of beam bridgesis that they are not susceptible to artistic treatment,[t will be seen, however, by referring to Figures 37,38 and 39, that beam bridges may be designed thatare equally pleasing in appearance to arch bridges,and for many locations are more suitable. In making a selection between an arch and abeam design, the chief consideration will generally X8X. IIIGHUAV BRIDGES. 18c he their relative cost. The cost of concrete archhridges has already been given bj the formulaereferred to above, and for the purpose of compar-ison, the costs of concrete beam bridges, in spansranging from 4 to 40 feet in length, are given inthe tables on bigures 38 and 39. The estimatedcosts of these beam bridges include the filling, pave-ment and tM-o lines of railing, but do not includelamps or other purely ornamental features. OnFigure 38 is given also a table of approximate costsfor concrete abutments of various heights, whichestimates also include railing and pavement to-gether with earth excavation and back filling in theabutments. These estimates will enable the de-signer to compare the relative cost of arch andbeam bridges, and to select the form which he findsmost economical. TABLE IV Span 2 Abutments SlabThick Rods Eslimalp Length SteelLbs. Yds. Cost Ft. In. In. Sq. In.
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