Essentials in the theory of framed structures . forces acting on the right of the section ,the truss reaction at L4 and the floor beam load at Li. Wheel6 is I ft. on the span. 1,640 103 X I = 103 100)1,743 = right reaction — = = floor beam load at L22: ^ 14-23 = negative shear in the X —- = = the maximum compression in member U1L2 may have a maximum tension of , Sec. Ill BRIDGES 157 or a maximum compression of It is clear that, if themember C/1L2 were removed and a member L1C/2 substituted,the member LiUt would have a maximum tension of
Essentials in the theory of framed structures . forces acting on the right of the section ,the truss reaction at L4 and the floor beam load at Li. Wheel6 is I ft. on the span. 1,640 103 X I = 103 100)1,743 = right reaction — = = floor beam load at L22: ^ 14-23 = negative shear in the X —- = = the maximum compression in member U1L2 may have a maximum tension of , Sec. Ill BRIDGES 157 or a maximum compression of It is clear that, if themember C/1L2 were removed and a member L1C/2 substituted,the member LiUt would have a maximum tension of a maximum compression of UiL\.—This member supports the floor beam load at Li,consequently the stress is a maximum when the floor beam loadis a maximum. As a load of i lb. moves from Li to L^, thefloor beam load is zero. The floor beam load increases uni-formly from o to I lb. as the load moves from L^ to Li, anddecreases uniformly from i lb. to o as the load moves from iito Lo. The influence line diagram for the stress in U\L\ is. Fig. I10. an isosceles triangle having a base 50 ft. long, and an altitudeof I lb. under L\. The criterion for maximum stress in Z7i£i,developed from this influence line, shows that the panelsZ0L2 should be loaded with one-half the load in each wheel 4 or wheel 13 atZ,i satisfies this criterion; the stressbeing the same in either case. When wheel 4 is at L\, wheel 8is at Li and wheel i is 7 ft. from Lo- The stress in f/iLi whichequals the floor beam load at Li is tension. 104. General Criterion for Maximtun Shear in a Panel.—Let F represent the shear in panel 2-3 of the parallel chordtruss in Fig. no, when the truss supports any system ofvertical loads. Since F represents also the vertical componentof the stress in UiLi, it is clear that the stress is a maximum IS8 THEORY OF FRAMED STRUCTURES Chap. IV when the shear in the panel is a maximum. The influence forshear in panel 2-3 has been drawn as in Article loi. If Pir
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