Litchfield enquirer., 1879-02-06
THE RAILROADS OF C0NNECTI-
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aspendent
 THE RAILROADS OF C0NNECTI-s r.~ @ CUT. I ~"#szE"H '.a.
 In the Beth annual Report of the Railroad Commissioners of tis state, which has just Deen presented to the legislature, there is much inforll. ation of importance to the public, not only concerning the condition of each railroad, out in relation to the true principles and laws of safety in the construction of railways and railway b ,es. This latter point-the causes of weaknes in some bridges-is made the sub Iect of an exhaustive and very capable paper, introduced in the first part of the report, on the es e ial topic of the Tariffyille bridge dis aster That saster, which happened on the 18th of last January is still subject of disa -sreement on the part of the people who have
 discussed it's cause and the prolonged session of the jury of inquest resulted in division of the iurv After session which lasted from the 22d of January to the 12 h of Febuary, eight of their number returned q report say ing: =
 We are of opinion that if the materialsof the bridge at the time of it's construction were of suitable quality, quantity, and proportion to fulfill all of it's requirements they had at the time of the disaster become dcteriorated, that the iron suspension rods from being over-strain, )r from some other cause, had lost their tensile and sustaining power, that the tinibel of the chords from many years exposure to the ac- tion of the eleme its without covering or paint, had become weekend by decay to such an ex- tent as to reuder the bridge unsafe and unfit for the purpose for which it was constructeI and that the disaster was Occasloned by the heavy train passing over abridge thus rendered dangerously weak and defective" e oF fhA i1rv
 "In our opinion, from the evidence, the bridge at the time of the disaster was in safe condition for the passage of trains, whether consisting of one or more engines. And we further believe that the same was constructed upon thorough scientific principles, and we do not believe that it had become deteriorated by exposure to the elements sufficiently to weaken the to q point of danger We also be- lieve by the numerous tests of the iron that it is of good quality, and that the same had not been Overstrained sufficiently to cause any weakening or danger therefrom. We have had sufficient evidence to believe that there was derailnent of some portion of the train, and if so, by falling upon the timbers of the brids or comiag in con act with the same, would in either case, il our opinion, cause d severe shock, sufficient to cause the structure to fall"
 To determine which of these two reports corresponds most with the facts and to en-
 eavor to ascertain Tn the light of this accident what can be done to prevent similar calamitles in future this paper on the Tariffville disaster IS presented. The authorship of it we think we cannot be wrong in attriOuting to Commis siuner BacOn whose practical eng gincering a. Jlty is justification of Governor Hubbard's $ good sense ill appointing him member of the oOard He first states the results Ot q careful examination of the fatal fridge itself; an ex animation which decides, in the opinion of the board of railroad commissioners, these facts |: First, that the fracture of the chord timbers could not have occurred before the breaking of .he suspension rods and that the condition of the timber generally, was remarkably sound, and the timber itself capable of snstainsng q coupreSgive resstanoe4six to seven times grea ger, per square inch, than anything to which il Vas subjected t; and, second, that the real cause ,f the disaster was the breahiag Cf kte suSpe~- si0n-90ds whic fractured, six of them in all, 5n the west end of the south truss, aud in ev
 .ry instance Gt hte Screto -ttre0d just above the lower nut.
 In these woden bridges, built on the Howe truss plan, most of the weight of the bridge ana my pasSlns tram cJ.neS practically rSht up)h these wrought-iron rods. Moreover, the strain is greatest at each end of the bridge. Ol this point we quote the language of this report =
 line strain on these rods is least iD tine center ,f the bridge, and gradually accunulates tow ards eac end until the total Welght finally reach 1s the abut.nents. The end sets of rods there lore support the greater part Con the lanttvllie bridge about 94 per cent. of the whole weight of the bridge and train. Bridge builde.s seldom make sufficient allowance for this increase Ot strain>in proportioning the sizes of their rods
 in this bridge, for example, although the strain on each end set more than seven times f fi,a ju,r Qaf effective area of the former is less than three times that of the latter. 4.+
 .'Examination disclosed the fact that the actual strain at the time of the accident the dead weight of the bridge and train, allowing equal tension on all the rods, was on the first set 1O.8 tons per square inch, measuring area at bottom of screw-threads. Now there were tests made of the iron, soon after the accident, at Colts works Hartford, at the Stevens In, sttute, Hobokcn, and at Richie Brothers, Philadelphia and these tests show all average tensile strength of over p tons per square i,eh- 's-
 ''fhese tests seem to show that if the rods were all free from imperfection, and under e Iual tension, they might Oe expected to sus tain more than double the dead weight actua . ly upon them, and that some sudden slOck, like the thumping of cars off the track, Or other additional strain, would be necessary to Cause their rupture"
 But it is just here that the value of supe io. practical engineering knowledge, and a knowl- edge of the structure of iron itself is favorably revealed. The principles of bridge cons:ruc- tion seem, says the report to have been Ovtr looked Or disregarded. even by railroad man. a.,ers, in the construction of very many of the wooden railroad bridges in thlS state What is called the ''elastic limit" of iron is the point to be regarded. A change occurs in the molecular character of the iron itself, ii sub jecteu to a strain too great-if the "elastlc limit" is exceeded That is although the .ldn sation of these bridge rods. which is c used by the passage of every train is chang ed as soon as the load has passed, and the rod recovcrs it's atc lsloa.eL length, yet if the elastic Ii nit" is ,Ac led, the iron under goes permanent Change, and is less safe. There seems to bt almost paradox ill the statement of the case, as It is made by this Report namely, that after such strain (which is usual ly not quite half the breaking load) the iron btco .nes brittle, hard, unelastic, and unit to sustain shocks and vibrations; while, never theless, owing 10 it's increased hardntss, ''iis tensile strength and elIstic limit are both con- siderably increased" We doubt not this is strictly true-yet it seems to involve some ob scure molecular law of iron, which this state ulent of the case does not quite cover. This is the language of the Report :- s,.. -..,.. ..,
 ..Ath0ugn iron used for bridge rods will gen orally endure a tensile strain of 9 to % tons per square inch before breaking, yet strains very much less than this will greatly damage it, and unit it for railroad use. Within cer ta liuts, iron is an elastic substance, and if its original elasticity is not impaired by too heavy strains, it is not injured by use. Every train which passes over Howe truss bridge elongates each suspension rod in proportion to the stain per square inch upon such rod, but the original length of all is substantially re- gained on removal of the load, unless the 'elasic limit is exceeded, whi:h is usually less than half the breaking load. and, for pres ent purposes, may be assu,ned at 10 tons per square inch Strains above this limit produce an elongatior which is permanent, or in other ,0rds :s f, ,.laiI,!, tl., ;,a.,.a =. !.