. The railroad engineer's practice . , the abutment at A has to sustain, in addition, theload on \ A J5, which, added to the resolved component ofthe strain on A (7, produces a vertical strain of a W, as itought. If only the point B is loaded with ^ W, the portionwhich is transferred to the abutment F will produce amoment about D tending to break the joint across, if it isrigid. If, however, it is flexible, there will be a tendency 54 for the joint to rise which is resisted by the rod D E (pro-ducing a strain upon it of \ W) and the strain transferredto E, must be resisted by the transverse st
. The railroad engineer's practice . , the abutment at A has to sustain, in addition, theload on \ A J5, which, added to the resolved component ofthe strain on A (7, produces a vertical strain of a W, as itought. If only the point B is loaded with ^ W, the portionwhich is transferred to the abutment F will produce amoment about D tending to break the joint across, if it isrigid. If, however, it is flexible, there will be a tendency 54 for the joint to rise which is resisted by the rod D E (pro-ducing a strain upon it of \ W) and the strain transferredto E, must be resisted by the transverse strength of thebeam B F, calculated in the same way as the first case ofthe simple beam loaded in the middle (of a length B F,not A F). If braces are introduced in the directionsB D and (J E, the bridge becomes a Howe Strains are the same in this case as in the king-post truss,the tension on the straining beam, however, being con-verted into thrust against the abutments. Strains are the same as in the queen-post C _§ D. This is a combination of the king and queen postsystems. To prevent the point B from rising on the application ofa weight at 1), braces are often introduced at A E andC F. The force W^ acting upward at B, produces a forceequal to TFsin. a in the diiection of C jP ( C-F being atright angles to F B) and acting at B, which has a tend- 00 cncy to break the beam transversely at F. The form-ula for the breaking weight of a beam fixed at one end and loaded at the other is W— \ S—-—. The pressure on C i^ is also W sin. a, which produces a transverse strainin yl J> at C, which can be calculated in like manner. The trussed girders of the following forms may belooked upon as king and queen post trusses inverted :
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Keywords: ., bo, bookcentury1800, bookdecade1880, bookidrailroadengineer00clee
