. Concrete bridges and culverts, for both railroads and highways . e end abutments may sometimes bekept down lower than the corresponding s]>rings onthe pier, or if abutments nuist be high, it may beeconomical to use rilibed abutments, cored out andreinforced with metal bars, if necessary. The use of pavenu^nt ties of either Avood av metal,will cause the arch thrusts to counteract each other,and thereby greatly reduce the size of expedient has not been used to any great ex=-tent until recent years, and even now is used chieflyfor bridges of reinforced concrete. A wide and sha
. Concrete bridges and culverts, for both railroads and highways . e end abutments may sometimes bekept down lower than the corresponding s]>rings onthe pier, or if abutments nuist be high, it may beeconomical to use rilibed abutments, cored out andreinforced with metal bars, if necessary. The use of pavenu^nt ties of either Avood av metal,will cause the arch thrusts to counteract each other,and thereby greatly reduce the size of expedient has not been used to any great ex=-tent until recent years, and even now is used chieflyfor bridges of reinforced concrete. A wide and shallow waterway is more effectivethan a narrow but higher one of the same area. Fig-ure 11 shows some possible abutment forms. AtA and C are shoAvn almtments where the concretein front of dotted line, not only is of no se-rvice orbenefit, but actually decreases the area of waterway PLAIN COXCRRTR ARCII BRIDGES. 57 and at the same time adds to tlie cost of the striic-tnre. It Avill be seen, however, that the abutmentA is one of tlie most common fomns used in nearly. Fig. 11ARCH ABUTMENTS. all old arch bridges. If for any sufficient reason,vertical sides are desirable or necessary, it vvill beeconomy to build independent side walls, as shown 58 COXCRETE BRIDGES AXD CFUERTS. at B, rather than ^ iDaterial In^ making thewhole alnitment solid. At E are shown old and neAv methods of construc-tion. The dotted lines showing an abutment builton level foundation is the method given ])y Traut-wine and the one generally used until recent will be seen, however, that the forms shown at Ein full lines is equally effective in transmittingthrusts to the soil, and requires somewhat less ma-terial. If vertical sides are not required, some ad-ditional iiuiterial may be saved by using the methodshown liy dotted line at C. D is suitable for archeswith considerable rise on hard soil or loose rock,and F sliows a form of a])utment in which the arciitlirusts against solid rock. In designing a
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