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Thicknesses of arches
Rule for Determining the Thicknesses of.arches.
79
ature, that drops which required but one second of time to disappear at the temperature of maximum vaporization~ required 152 seconds when the metal was heated to 395 ° of Fahrenheit. The committee goes on to state that--"One ounce of water introdued into an iron bowl three-sixteenths of an inch thick, aud supplied with heat by an oil-bath at the temperature of 546 °, was vaporized in fifteen seconds, while at the initial temperature of 507°~ that of the most rapid evaporization was thirteen seconds." The cooling effect of the metal is here strikingly exemplified by. the increased rapidity of the evaporization, which, at a reduced temperature of 38 °, is effected in thirteen instead of fifteen seconds. This does not, however, hold good in every case, as an increased quantity of water, say fi'om one-eighth of an ounce to two ounces, thrown upon heated plates; raised lhe temperature of its vaporation from 460 ° to 600 ° Fahrenheit; thus clearly showing that the time required for the generation of explosive steam, under these circumstances, is attended with danger, and it may be doubted whether the ordinary safety-valves may not be wholly inadequate for its escape. Numerous examples may be quoted to show that explosions from deficiency Of water~ although less fi'equent than those arising from undue pressure~ are by no means uncommon; they are~ nevertheless~ comparatively fewer in number, and the preventives are good pumps, self-acting feeders (when they can be applied), and all those conveniences, such as water-cocks, water-gauges, floats, alarms, and other indicators of the loss and reduction of water in tim boiler. To be Continued. '
For the Journal of the Franklin Institute. By CHARLESELLET, JR., Cir. Eng. In some investigations on the equilibrium of arches, made many years ago, I deduded the foUowing simple and convenient rule for determining t h e proper depth or thickness of the voussoirs of a cut stone arch at the crown. I am not sure that I ever published the formula, though I have applied it in numerous works. Let s represent the span of the arch~ and T the thickness at the crown.
Thicknesses of Jtrches.
Then T
=-~3 ~ s _
or~ the depth of the voussoir at the crown~ will be three-eighlhs the square root of the span. This simple rule is applicable to all arches, however great or however small the span~ from a semi-circ]e~ to the flatest segments ever attempted on public works. It is always safe. I communicate the formula for the convenience of those who have no better rule to guide them. Bath ./tlum~ Va, June 28~ 1853.
79
ature, that drops which required but one second of time to disappear at the temperature of maximum vaporization~ required 152 seconds when the metal was heated to 395 ° of Fahrenheit. The committee goes on to state that--"One ounce of water introdued into an iron bowl three-sixteenths of an inch thick, aud supplied with heat by an oil-bath at the temperature of 546 °, was vaporized in fifteen seconds, while at the initial temperature of 507°~ that of the most rapid evaporization was thirteen seconds." The cooling effect of the metal is here strikingly exemplified by. the increased rapidity of the evaporization, which, at a reduced temperature of 38 °, is effected in thirteen instead of fifteen seconds. This does not, however, hold good in every case, as an increased quantity of water, say fi'om one-eighth of an ounce to two ounces, thrown upon heated plates; raised lhe temperature of its vaporation from 460 ° to 600 ° Fahrenheit; thus clearly showing that the time required for the generation of explosive steam, under these circumstances, is attended with danger, and it may be doubted whether the ordinary safety-valves may not be wholly inadequate for its escape. Numerous examples may be quoted to show that explosions from deficiency Of water~ although less fi'equent than those arising from undue pressure~ are by no means uncommon; they are~ nevertheless~ comparatively fewer in number, and the preventives are good pumps, self-acting feeders (when they can be applied), and all those conveniences, such as water-cocks, water-gauges, floats, alarms, and other indicators of the loss and reduction of water in tim boiler. To be Continued. '
For the Journal of the Franklin Institute. By CHARLESELLET, JR., Cir. Eng. In some investigations on the equilibrium of arches, made many years ago, I deduded the foUowing simple and convenient rule for determining t h e proper depth or thickness of the voussoirs of a cut stone arch at the crown. I am not sure that I ever published the formula, though I have applied it in numerous works. Let s represent the span of the arch~ and T the thickness at the crown.
Thicknesses of Jtrches.
Then T
=-~3 ~ s _
or~ the depth of the voussoir at the crown~ will be three-eighlhs the square root of the span. This simple rule is applicable to all arches, however great or however small the span~ from a semi-circ]e~ to the flatest segments ever attempted on public works. It is always safe. I communicate the formula for the convenience of those who have no better rule to guide them. Bath ./tlum~ Va, June 28~ 1853.