. Concrete bridges and culverts, for both railroads and highways . rches havebeen designed with no provision for tension in anypart of the arch section, and consequently no needfor reinforcing metal to resist direct stresses. The table is not intended to be comprehensive orcomplete, but gives some details of a few of thelargest concrete spans, the main arches of whichare designed without reinforcement. In referenceto the Hudson ]\Iemorial Bridge, noted in this table,and illustrated on page 77, the design calls for alarge amount of metal reinforcement, not for thepurpose of resisting any tensil
. Concrete bridges and culverts, for both railroads and highways . rches havebeen designed with no provision for tension in anypart of the arch section, and consequently no needfor reinforcing metal to resist direct stresses. The table is not intended to be comprehensive orcomplete, but gives some details of a few of thelargest concrete spans, the main arches of whichare designed without reinforcement. In referenceto the Hudson ]\Iemorial Bridge, noted in this table,and illustrated on page 77, the design calls for alarge amount of metal reinforcement, not for thepurpose of resisting any tensile stresses in the arch,but rather to supplement the concrete in resistingdirect compression. This is a new principle in archconstruction, not previously used. Illustrations and descriptions of two old Romanbridges are also given for the purpose of callin^^attention to the superiority and permanence cf ma-sonry bridges over those of any other known typeor material. They have existed for centuries, andsuch bridges should endure after metal bridges 74 CONCRETE BRIDGES .WD CUIJ-ERTS. Ponte Rotto, Rome. As it stands to-day, this old bridge lias three stonearch spans, and a suspension bridge, spanning thegap where other arches originally stood. The pres-ent bridge stands on the site of the old Pons Aemil-ius, built B. C. 178-1-1:2, -which was the first stonebridge over the Tiber at Rome. The three remain-ing arches date from Julius III, and are richly orna-mented. Two arches were carried away by a floodin 1598, and have never been replaced. The bridgeseems to be unfortunately located, as it has beencarried away at least four times, the first time in 280. It was erected by Caius Flavins, and isprobably the first appearance of the arch in bridgeconstruction. It has semicircular arches and alevel roadway. The two end arches were shorterthan the three intermediate ones. It is called alsoPons Palatinus, Senators Pridge, and Pons Lapi-deus. The bridge is similar in c
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