•— 94 — — 
span, is given by the formula 
；r = セニ 1 」 十 — 1 V 〃 tan の 
n f having tho same value as in tlie last formula. For the end panel, tlie stress is 
the same as for tlie second panel. 
substitution in these formulas is a very simple matter. 
The stress in the hip verticals of any through or pony truss is equal to one 
half of tlie floor beam load including its own weight plus tlie weight of a panel 
length of the lower cliord. It is not necessary to calculate this stress for singlo 
track bridges, as the sections required for and sizes of liip verticals for all practical 
cases are given in Table VII. 
In deck bridges tlie hip verticals sustain only the weight of a panel length of 
the bottom chord and lower lateral system so that two one inch rods will bo suffi- 
cient. 
Tlie only other difference between tlio stresses iu a dcok bridge and those in a 
corresponding through bridge will be in tlie posts, the stresses for wliicli are to bo 
found by letting the live load extend from the farthest end of tho bridge to the top 
of tho post; so that tlie post will no longer take its greatest stress with the main 
diagonal attached to its top, but with tlie one attached to its foot. 
Tho formula for post stresses iu single-intersection deck bridges is, therefore, 
Some engineers may object to using formulas for figuring stresses: if so, tlio 
following method will give the same results for single- intersection bridges. 
Pass a vertical plane through the middle point of the bottom chord : all the dead 
loads to the right of this plane may be considered to go to the rigbt-lianil pier, and 
all to tlie left of tlie plane to tlio left- hand pier. Should there be a post at tlie micl- 
clle of the bridge, the weight at the foot is to be considered as halved, one-half going 
* In “ The Designing of Ordinary Iron Highway Bridges ” this formula is given as 
n> (n 1 一 1) + 2/i 
2 
This was obtained under the supposition that the load W on top of the post passes down the post 
before being separated into the portions which go to the right and left, but the author has come 
to the conclusion that the portion, which passes to tho farther end of the span, goes down the 
main diagonals as compression or in reality as a reduction of tension. The error in the last for- 
mula is upon the side of safety and varies between zero and moreover its greatest effect is 
upon the posts at and near the middle of the span, which posts in many cases have necessarily 
greater sections than the stresses call for. 
Besides the load comes more quickly upon the posts of deck bridges than upon those of 
through bridges, so some engineers might prefer to use the less correct formula. 
