Essentials in the theory of framed structures . 18) j-^ + j{e + l)::NV:b therefore NV:c::i:a -\- c -\ e or NV:VO:?a-\-c + - e whence NV:NV + VO:?a + b + c+ - e or Pit -h P NV b e or NO I e + asubstituting in criterion (i) N0^If the criterion is expressed as an equation, then NV NOThus it is clear that when the right portion of the truss isloaded for maximum tensile stress in U2L3, the load in thepanel divided by the length NV equals the total load on thespan divided by the length NO. Likewise it may be shownthat for a maximum compressive stress in U2L3, the left portion l82 THEORY OF FRAMED ST
Essentials in the theory of framed structures . 18) j-^ + j{e + l)::NV:b therefore NV:c::i:a -\- c -\ e or NV:VO:?a-\-c + - e whence NV:NV + VO:?a + b + c+ - e or Pit -h P NV b e or NO I e + asubstituting in criterion (i) N0^If the criterion is expressed as an equation, then NV NOThus it is clear that when the right portion of the truss isloaded for maximum tensile stress in U2L3, the load in thepanel divided by the length NV equals the total load on thespan divided by the length NO. Likewise it may be shownthat for a maximum compressive stress in U2L3, the left portion l82 THEORY OF FRAMED STRUCTURES Chap. IV of the truss is loaded so that the load in the panel divided byNU equals the total load on the span divided by NQ. Compute the lengths NV andNUm Fig. 117 and show thatthe criterions developed therefrom are the same as previouslygiven. 115. Tension in a Vertical when Counters are Used.—Themaximum tensile stress in UiLi (Fig. 117) for an E-40 trainwith wheel 4 at L2 is The conditions are different if the. Fig. 119. diagonal web members are designed to take tensile stressesonly, as in Fig. 119, and the use of counters becomes dimensions of the truss are the same as in Fig. 117. Weshall assume that total dead load for the bridge is 2,600 lb. perlinear foot, or 1,300 lb. to be carried by each truss; of which 950lb. will be considered as acting at the bottom chord and 350 lb. atthe top chord. The panel loads are 28,500 lb. for the bottomchord and 10,500 lb. for the lop chord. The resulting deadload stresses for UiLi and C/2L3 are. shown in the figure. Let the train advance on the span at io until wheel 7 is atio- The live load compressive stress in C/2L3 is 2,155 240 X 420216 174s Sec. IV BRIDGES 183 and the impact compressive stress is _ X g? = . The live-load and impact compressive stresses in U2L3 balanceapproximately the dead-load tensile stress, and the total stressin the member is zero. Let the train advance upon the span. Durin
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectstructu, bookyear1922
