DISTRIBUTION AND GENERA I. 3 



neeewary. Many valuable compilation* of 



.f .-iniet u:, an- t<> bo had, hut they are not usually 



accompanied by fui eDgineer must be sure 



of the quantities which go into hi- Mrm-tun-. an. I they 



therefore should be estimated as the computations are 



d along and all computations based on wrong at* 



i load- - .1. 



16 design of a Mm.- tun- .-hould always begin with 

 - tin load an<l follow with ea *sive 



part in the path of the l>ad a> it travel- t tl rt. 



in an ordinary through j ; i.-r rail- 



road I'M :.: . tin- design of tin- various parts shoul<l U- 

 made in tin- following onh-r: HaiU, 

 beams, latnal hracing, and main gird> 



In making a i of th- Wright of any gir 



(i.ini.ut. th live-load stress at the center of tin- 1* 

 flange ami inm-a.-<- impact if : to !>< a.l.h-il, 



add t< thi- Mini \^ cf c for th.- >tn-ss due to the weight of 

 then determine the net area of thi- innnl>er in 

 ><iuaiv iiirlir>. This net area in square inch.- iindtij.li.-d 

 I will give a weight per foot of girder \\hieh may U- 

 used as a fir.M eMin . 



Thi> estimate is baaed on e<|iial gross areas 1 

 than tli :ea of the bottom flange, for top flange, 



bottom flange, and \\ l. and their Mini in I.". 1 f.-r 



details. An error oi al stress due to a wrong 



:i>Mimed dead load should require : 

 load to be u 



It ditlieult to give a good general rule for < 



mating the weight of irirders. as tl i>lv is a 



