33 



of two panels, with alternating joints in the two, three, or four .stringers 

 under each rail, as may be found necessary. 



One point to be watched in trestle construction is to prevent the 

 lodgment of cinders in the structure, which would set it on lire. The 



STBS.LONGLEAFPiNEI 



^Corbels. White Oak 1 

 Cap, White Oak. 



Posts, Red Cypress 



—.Sills, 

 \°\ [ White Oak 



Sc*L£:£- iticu=l Foot. 

 Fig. 7.— Showing construction with two vertical and two standing legs. 



cinders will usually lodge between the ties on top of the stringers or 



For this reason it is I 



rn> 



between the stringers on top of the cap. 



a good practice to cover the top of the stringers, from end to H 

 end, with a galvanized-iron sheet bent down over the edges. It will 

 not only protect the stringers against the weather, but it will also 

 largely protect the structure against lire, on account of which a large 

 amount of wooden trestlework each year has to be renewed. Another 

 method used with success against tire is planking over the stringers 

 and gravel between the ties, used by Mr. Bouscaren on a long trestle 

 near New Orleans. 



As regards longitudinal bracings between trestle bents, no general 

 rules would be applicable. It will always depend upon the local con- 

 ditions. Where the trestle is high or on a curve or on uncertain bottom, 

 special provisions of bracings will have to be made. 



It may not be amiss to say — although not directly connected with 

 the subject under discussion — that no better way of economizing timber 

 in the construction of railroads could be devised than doing away with 

 trestles altogether. 



25665— No. 12- 



