TUBULAR GIBDEK BRIDGES. 195 



service after being submitted to the heaviest rolling load, 

 or one-sixth of the hf.eaking weight. 



In closing these remarks, I would observe that, after 

 these experiments, I came to the conclusion that the tests 

 for bridges of this kind should not exceed the greatest roll- 

 ing load, and that load to be one-sixth of the breaking 

 weight of the bridge. I may be wrong in this conclusion, 

 which, with great deference, I submit for correction ; but 

 in this I am fully persuaded, that in order to give the 

 necessary security, and to provide for all the contingencies 

 consequent upon railway traffic, it will not injure the in- 

 terests of a railway proprietary to have the bridges of suf- 

 ficient strength to resist six times the greatest load. 



TORKSEY BRIDGE OVER THE RIVER TRENT. 

 The two main girders extpnd over the middle pier, on which they rest, 

 ■with expansion rollers on each abutment. 



Feet Inches. 



Total length of each girder 282 



Clear span of each opening 130 



Depth of main girder 10 



Breadth 2 9 



Depth of cross girders 1 2 



Spsin of „ 25 



Distance of „ from centre to centre 2 



Total length of bridge, including masonry 342 



Tona. owt. 



Total weight of iron in main and cross girders ... 252 14 



PERMANENT I.0AD FOB ONE OPENING. 



Tona. cwt 



Weight of main girders 91 12 



Weight of cross girders 27 1 



Timber 18 6 



Ballast (2 inches thick) 19 10 



Rails, chairs, and fastenings 7 18 



164 6 



laches. 



Sectional area of top, in inches 60*24 



„ „ bottom „ 49-68 



The bridge has been tested with six locomotive engines in steam, 



equally distributed over one opening, of the aggregate weight of 222 tons, 



when the deflection was found to be 1*26 inch in the middle. On the 



removal of the load the bridge returned to its original level. 



