Essentials in the theory of framed structures . is not the same as the criterion for maximum compres-sion. In this respect, members U1L2, and C/2Z-2 are in thesame category as U^Ls. The criterions are not the same for anytwo members, neither are the criterions for maximum tensionand compression the same for any one member. The center ofmoments for UiLs and U^Li is at the same point, but the sec-tion is not the same for both members. The center of momentsfor U1L2 and C/a^z is not at the same point as for U2L3 and U3L3. 113. Problems. Draw the influence line, develop the criterion, and compute S
Essentials in the theory of framed structures . is not the same as the criterion for maximum compres-sion. In this respect, members U1L2, and C/2Z-2 are in thesame category as U^Ls. The criterions are not the same for anytwo members, neither are the criterions for maximum tensionand compression the same for any one member. The center ofmoments for UiLs and U^Li is at the same point, but the sec-tion is not the same for both members. The center of momentsfor U1L2 and C/a^z is not at the same point as for U2L3 and U3L3. 113. Problems. Draw the influence line, develop the criterion, and compute Sec. IV BRIDGES 177 the maximum tensile and compressive stresses in UiLi, U1L2,Uil^, U3L3 and UiLi (Fig. 117), using an E-40 train. Computethe impact stress in each case, using the formula of Article General Criterion for Maximum Stress in Web Memberof a Parker Truss.—^Let Mi represent the algebraic sum of themoments of all the forces acting on one side (either side) of thesection through the panel 2-3 (Fig. 118). Since the stress in. -(e^lj Fig. 118. U2L3 equals Mj -^ h, it is clear that the stress is a maximumwhen Mj is a maximum. Let a equal the length of the seg-ment LoLi, b equal the length of the panel, c equal the length ofthe segment LsLs, and e equal the length /Lo; then a + b + c = influence line OTNSQ for Mi is drawn in the same manneras described in Article no. The value of Mi may be deter-mined by taking the sum of the products of each load andits corresponding ordinate in the influence line. The loads willbe combined into three groups. Pi, Pz and P3, corresponding 178 THEORY OF FRAMED STRUCTURES Chap. IV to the three portions of the influence line QS, ST and yi, yi and 313 represent respectively the three ordinates underthe centers of gravity of Pi, Pi and P3, thenMj = Fzji ± Piyi — Piyi Let the loads move a small distance d to the left in such a waythat no loads cross the panel points Lo, L2, is and ig. Or, inother words. Pi, P2 and P3 ar
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