Assignment5 - have the highest stresses c Finally you can...

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1. Problem 4.3. For sections in Figures 4.20 and 4.21 the symmetry means that we have bending only about the y-axis (same direction as the moment), so that one can use Eqs. 4.31 and 4.32. For the section in Fig. 4.22, the absence of symmetry means that you need to use Eq. 4.33. a. You first want to calculate the moments of inertia (answers: Iy=4Ah 2 , Iz=2Ah 2 , Iyz=-2Ah 2 ). b. Then you want to calculate the position of the neutral axis by setting the bending stress to zero in Eq. 4.33. This will allow you to see what point in the cross-section is furthest away from the neutral axis and therefore will
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Unformatted text preview: have the highest stresses. c. Finally you can compare the maximum stress in each one of the three sections and conclude which section is most effective (has the lowest stresses). 2. Problem 4.5. To help you know if you are getting the right answers, note that (to two digit accuracy) the three moments of inertia are 24,000, 87,000 and -15,000 all in cm 4 . The stress in stringer 1 (upper left) comes out to be -1202 N/cm 2 . Check that the sum of the forces in the four stringers is zero, and explain why it should be. 3. Problem 4.6....
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