378 



NOTE TO ART. 128. 



[APPENDIX. 



NOTE TO ART. 128, CHAPTER XII. 



IT. "We wish here to call more particular attention to the 

 relative economy of the continuous as compared with the 

 simple girder. This, we think, is greater than is generally sup- 

 posed. It may reach from 18 to 25, and even as high as 50 

 per cent. 



Take the example worked out in Art. 128, Fig. 88. We 

 have obtained the maximum strains in that Art. upon every 

 piece. 



We give them below, compared with the strains in the same 

 pieces for a simple girder of same dimensions anb load : 



Aa Ac Ae Ag Ak Bf> Bd B/ BA 

 Continuous.. -203.6 +63.6 +115.3 +63.6 203.5 +89.3 115.9 115.9 +89.3 



Simple +180 +240 +180 90 210 210 90 



06 b<s cA de ef fg gh hk 

 Continuous. .+ 189.3 109.9 +109.9 +45.5 +45.5 +109.9 +109.9 +189.3 

 Simple +127.8 127.3 +56.5 +56.6 56.5 +56.5 127.3 +127.3 



It will be seen at once that there is a saving in the flanges 

 about 11 per cent, in all but the bracing is heavier, giving lit- 

 tle or no saving. The span is too short to properly represent 

 the relative economy of the two systems. 



If we take a truss such as represented in PI. 2, Fig. VII., 

 Appendix, by the full lines only, omitting the dotted verticals and 

 diagonals height 6 ft., span 50 ft., panel length 10 ft., dead 

 load 5 tons per panel, live load 7 tons per panel and calculate 

 the strains in the pieces for a simple girder, and then as a con- 

 tinuous girder of two spans and three spans, we have the fol- 

 lowing results : 



