1402

THEORY AND PRACTICE OF ENGINEERING.

Book II.

The Centres of the Bridge at Neuilly were similar to those at Mantes, and the span of thearches was equal to that of the great arch of the latter : but this is not so flat, and althoughthe thickness of the arch be less than that at Neuilly , and the principals only 6 feet 6 inchesdistant from each other, they were found to be too weak : each principal had seven or

eight timbers splitthroughout their

length, others werebent, and their extre-mities penetrated intothe faces of the bindingpieces : the settling ofthe arches being veryconsiderable, it was ne-cessary to load thecentres with a weightnearly equal to 600tons: when the archeswere ready to be closed,and only seven coursesof voussoirs remainedto be placed, the gene-ral settlement of thecentre was more thanan inch in 24 hours,and it would havebeen still greater, butfor the celerity with

RRIOOE CY NSUILLY

which the work was carriedon, and the precaution takento strengthen it by braces ex-tending from one principaltimber to the other, and byplacing struts between thecourses of the oppositevoussoirs. The openingsin the framing were causedby the timbers not bearingequally against the binding-pieces throughout the wholesurface of their extremities,and an attempt was made tocorrect this defect by cutting

Fig. 2339.which was adopted

Fig . 233ft. bridgb or necilly.

each extremity in the form of an arc of a circle: this dispositionat the bridges of St. Maxence and of Concord at Paris, was successful in preventing theinclined timbers from splitting, but they continued to penetrate into the binding-pieces;it also increased the play of the framework, and rendered the centres more susceptible