The portion of the illustration at (a), Fig. 7, shows the arrangement of a pile bent trestle, while that at (b) shows the arrangement of a framing bent trestle. In case the trestle is not very high and piles are used, they may be driven vertically, but it is always best to have the outer piles driven at an angle so as to form batter braces. VEL AK 19 FIG. 8 Fig. 9 illustrates a pile having a tenon formed on the upper end to receive the cap. When this method of securing caps is used, a hole is drilled through the cheeks of the mortise in the cap and through the tenon. It is well to have the hole in the cheeks of the mortise so placed that when the pin is driven through two holes it will tend to draw the cap down on to the top of the pile. The pin used for this purpose is commonly called a treenail, and should be made of hardwood, locust wood if possible, and slightly tapered, as shown in the lower part of the illustration. Sometimes the caps are not mortised and tenoned on to the piles, but may be secured by means of drift bolts, as shown in Fig. 10, or by means of dowels, as shown in Fig. 11. 42. Split Caps.-Another arrangement is shown in Fig. 12. This is called the "split " cap; in place of using one 10" x 10" timber, two 5" X 10" timbers are employed and the top of the pile d is cut as shown in the illustration. The timbers can be seen at a and b, while c is a tenon, the full width of the pile, that is allowed to project up between the timbers. No notches are cut in the timbers where they rest on top of the piles, but they are secured in place by means of a bolt d, which passes through both timbers and the tenon. Some of the advantages of this method of framing the caps are as follows: FIG. 12 1. On account of the smaller size of the cap pieces, it is possible to obtain better timber. 2. Repairs can be made with greater ease than where caps are mortised and tenoned or fastened with drift bolts to the top of the piles, for either of the caps can be removed and replaced without interfering with traffic or cutting any portion of the timber work. 43. Framed Bents.— Where it is not possible to drive piles and form pile bents, framed bents are used. Fig. 13 illustrates a framed bent in which all the timbers are timbers are simply secured by means of drift bolts. 44. T FIG. 13 Foundations for Sills.-The sill of the bent should always be placed upon some form of foundation. This may be composed of timber mudsills, as shown at 10, Fig. 7, but it is a better practice to construct stone or masonry walls under the sills and to see that the latter are well bedded. When masonry is used as a foundation for sills, care must be taken to see that the stones are well laid; it is never good practice to construct these foundations of round stones laid up like rubblework, for the constant passage of trains over the trestle is liable to break up such a foundation. 45. Placing Timbers. The batter braces should have a uniform angle of 3 inches per foot. Fig. 14 illustrates the method of framing on the ends of batter braces TIT FIG. 14 FIG. 15 and posts in framed bents and also shows a drainage hole bored in such a manner that any water collecting under the jointing will immediately flow out through the drain and 46. Illustration of a Framed Bent.-Fig. 16 is a dimensioned drawing showing a timber bent as used on one 5"x 8" Guard Timber. 4-86 6"X8"x12. 12x12 x14 line of railroad. The gauge of the track is the standard for the United States, that is, 4 feet 8 inches, and the dimensions on the drawing fully explain the various parts. 47. Elevation of Outer Rail.-Where the trestle comes in a curve on the railroad track, if it is intended that the cars should move at any considerable speed, it is necessary that the outer rail be elevated. This may be accomplished by wedge blocks placed on the top of the cap and under the stringers; usually, however, the cross-ties are cut wedge-shaped to give the desired elevation. 48. Framing Buildings.-Small buildings about mills can be framed of small stuff, without any special framing, the pieces simply being spiked together to form a balloon frame, which is covered with either siding or corrugated iron. FIG. 17 When it becomes necessary to build somewhat heavier structures, some form of framing may be used. The different joints used in framing are all similar to those illustrated in connection with trestle work and consist mainly in the use a FIG. 18 of tenons or notching the timbers together. When timbers must be joined in the direction of their length, special joints or a different method may be necessary. When two timbers are joined without an increase of size, it is called a "scarfed " joint. Fig. 17 illustrates one form of scarfed joint in which the timbers a and b are joined as illustrated, and are held in place by means of the key c. Fig. 18 illustrates another form of. scarfed joint, which is better adapted for resisting end N. M. III.-3 |