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Mechanics of Materials: StressM. VableJanuary, 2010EXAMPLE 1.3All members of the truss shown in Figure 1.12 have a cross-sectional area of 500 mm2 and all pins have a diameter of 20 mm. Determine: (a) The axial stresses in members BCand DE, (b) The shear stress in the pin at A, assuming the pin is in double shear. PLAN(a) The free-body diagram of joint D can be used to find the internal axial force in member DE. The free body diagram drawn after an imaginary cut through BC, CF, and EF can be used to find the internal force in member BC. (b) The free-body diagram of the entire truss can be used to find the support reaction at A, from which the shear stress in the pin at A can be found. P21 kNABFEDGC2 m2 m2 m2 mFigure 1.12 Truss.ANS.
19Printed from: Mechanics of Materials: StressM. VableJanuary, 2010COMMENTS1. We calculated the internal forces in each member before calculating the axial stresses, emphasizing the two steps Figure 1.2 of relat-ing stresses to external forces.2. In part (a) we could have solved for the force in BCby noting that ECis a zero force member and by drawing the free-body diagram of joint C.PROBLEM SET 1.1Tensile stress