• 240 — 
ADDENDA. 
Since the preceding pages were written the author lias seen in an otherwise very 
favourable review of liis keatiae 011 “ Tlie Designing of Ordinary Iron Highway 
Bridges .' 5 by tlie American Engineer a serious objection to the usual attachment of a 
floor beam by four hangers. 
I11 tlie words of the review “ tlie inner loop will take nearly, if nofe quite, all tbc 
load at the panel point ; when the bridge is first adjusted ; and this not only become 只 
constrained itse]t. but also overstrains the inner tension brace. - ：: The number of 
inner hangers wliicli arc constantly working loose, presumably by stretching» 
railroad bridges in which this detail is usecl, demonstrates its iui 8 atisfiicfcoO , 
character. 5, 
Tlie author has long recoguizecl the inequality of diatribukion of floor beam 
between tho inner and outer liaugers, but considered that the low intensity 
working stress on tlieso members would compensate for the objectionable iueqi 以 1 办* 
buch has been also in all probability the opinion of most American eugiucers ; 
beams, when not rivetted to the posts, are nearly always suspended by four liange l，s， 
丄 lie fact of the inner hangers working loose can have been only lately discovered ： ^ 
shows, however, that this detail needs improvement ; and as the aim of this treatise 
is to design structures not only equal but in some respects superior to the best America 11 
bridges, it bocorues necessary, even at this late hour, to correct tlie newly discovered 
fault. 
Tlie simple method of using singlo beam hangers will no fc always work, 〇、咖轻 
to the great bending moments which they produce upon tlie pius. For instanco 
tlie case of a double track bridge with panels twenty-four feet in length. The weigU 
supported by each single hanger would bo about forty tons, and the distance betwe e，i 
centres of main diagonals would not be far from twelve inclies. Those data give Ä 
vertical bending moment upon the pin equal to one hundred and twenty inch to が’ 
whicli alone would require an iron pin five and a half inches iu diameter, or a 
one of four and three quarter inches ; but when combined with the horizontal mon 1011 ^ 
would call for a pin much larger than any intelligent designer would think f 01 ' a 
moment of using. 
Tlie double hangers iu such a case are a necessity, but tlie connection must be 
such as to distribute the load equally upon them. Such a distribution can be assured 
by using the following detail. 
On tlie under side ol the beam at ^eacli end is attached by four rivets a が ポ 
about five eighths of an inch thick, six inches long and as wide as or a life tic wi み 1 
than tho beam flange. This plate is placed symmetrically to the plane of tlio ti’u# 
and the middle of the under side is grooved so as to receive one sixth of tlie 
of a pin about two inches in diameter, which rests in a similar groove on the top 
the beam hanger plate. The lateral dimensions of tliis plate will be slightly gi*e^ ter 
than usual, but the thickness need not exceed one inch. To prevent the plate む 〇 似 
^ Main diagonal. 
