Essentials in the theory of framed structures . n Fig. 104, to illustratethe manner in which the wheel loads of a train are carried toand supported by the piers at either end. The wheels restupon the rails which are supported by cross-ties. The tiesrest on longitudinal stringers which are supported by cross-beams, more often called floor beams. The floor beams aresupported by the truss at the bottom chord panel points. Itshould be thoroughly understood, and constantly kept in mind,that the truss does not directly support any wheel loads. Thetruss receives the weight of the train only in the fo
Essentials in the theory of framed structures . n Fig. 104, to illustratethe manner in which the wheel loads of a train are carried toand supported by the piers at either end. The wheels restupon the rails which are supported by cross-ties. The tiesrest on longitudinal stringers which are supported by cross-beams, more often called floor beams. The floor beams aresupported by the truss at the bottom chord panel points. Itshould be thoroughly understood, and constantly kept in mind,that the truss does not directly support any wheel loads. Thetruss receives the weight of the train only in the form of flsor beamloads, delivered to the truss at the panel points. 97. Influence Line for Maximum Stress in a Chord the truss in Fig. 105 be loaded in any manner, and letMi represent the algebraic sum of the moments about L2 Sec. Ill BRIDGES 147 of all the external forces acting on one side (either side) of thesection through the panel 1-2. Since the stress in UiUi. variesas Mi, it is clear that the stress in U1U2 is a maximum, when. Pig. 104. Mi is a maximum. For this reason we shall draw the influenceline for Mi as a load of i lb. moves across the span. When the load of i lb. is between Z4 and Li, the only forceacting on the left of the section is the left reaction Ro, and Mi= 50R0. As the load moves fromLi to Lo, Ro increases uniformlyfrom o to I- lb., and 5oi?o increasesuniformly from o to 50 f Hencethe line ON is the influence line forMi when the load of i lb. is betweenLi and L2. When the load of i lb. is betweenLo and Li, the only force acting onthe light of the section is the right reaction Ri, and Mi =Soi?4. When the load is between Li and Li, there are twoforces acting on the right of the section—a floor beam load atLi and the truss reaction Ri; and the moment of these twoforces about Li is also Mi = ^oRi. As the load moves fromLo to Li, Ri increases uniformly from o to i lb.; and $oRiincreases uniformly from o to 50 Hence, the line QN
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectstructu, bookyear1922
