Van Nostrand's engineering magazine . m impeded deflections. In certain mechanical structures, as,for instance, in swing bridges with shorttail ends, the action of high winds maystop or impede their motion withoutactually producing any dangerous amountof damage. High timber stagings, owing to theirlightness and the broad surface presentedby their planks, are exposed to considerablerisks of damage by wind. An excellentmethod for strengthening them wasadopted at the Chaumont viaduct, whichis 164 feet high, and has three tiers of arches, each of which was provided witha temporary platform for the
Van Nostrand's engineering magazine . m impeded deflections. In certain mechanical structures, as,for instance, in swing bridges with shorttail ends, the action of high winds maystop or impede their motion withoutactually producing any dangerous amountof damage. High timber stagings, owing to theirlightness and the broad surface presentedby their planks, are exposed to considerablerisks of damage by wind. An excellentmethod for strengthening them wasadopted at the Chaumont viaduct, whichis 164 feet high, and has three tiers of arches, each of which was provided witha temporary platform for the supply ofmaterials. The staging was braced invarious directions by iron wire cables,very tightly stretched and firmly an-chored. When a structure rests without suf-ficient adherence on a fixed base, alateral thrust would turn it over by de-taching it from its support; but if itsfall cannot be effected without some in-determinate or chance cleavage, the rup-ture will take place in an oblique anddownward direction B A, Fig. 6, because. a certain triangular prism, BAC, pos-sesses a stable position, on account of theleverage of the weight being great, andthat of the impact of the wind small, inrelation to the axis of rotation. In reality, so long as the solid is notbroken, the pivoting does not tend totake place on the extreme edge A, butupon some neutral axis of the section ofrupture AB; as in every prismatic body,subjected to a bending strain, fracture re-sults from the crushing of some por-tions and the tearing of others. The direction AB being defined by theindeterminate CB=£C, the external forcesacting are, the weight of the prismABEF, and the pressure of the wind onBE. In calculating the combined effectsof pressure and flexure exerted on AB,the chance of fracture would be investi-gated from the position of the criticalpoint A or B. The first of these the place of maximum compression ;assuming that it reaches the limit of im-minent crushing, an equation of ultimate
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectenginee, bookyear1879
