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HW7supp

# HW7supp - displacements for Joints 2 4 and 8 instead of...

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CE 573: Structural Dynamics HW#7 Supplemental Problem Problem #1 Given : Illustrative Example 13.2 in the textbook (pages 418 – 426) describes the evaluation of the dynamic response of a three dimensional space frame using SAP 2000. A careful reading of the example, however, reveals that the results printed in the textbook for this analysis (namely, Table 13.2, Table 13.3, Figure 13.5, and Table 13.5) are not related at all to the structure described by the step-by-step inputs. (For that matter, the results are not related to the structure depicted in Figure 13.4. But then again, neither are the step-by-step inputs!) The goal of this Supplemental Problem is to determine what the results of the step-by-step inputs should be. Required : (a) Following the step-by-step inputs exactly as described on pages 419 – 426, determine what the actual results should be for this problem. Specifically, determine the proper forms of Table 13.2, Table 13.3, Figure 13.5, and Table 13.5, with the following modifications: (i) For Figure 13.5, plot the X
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Unformatted text preview: displacements for Joints 2, 4, and 8 instead of Joints 2, 3, and 4 (there is no need to reproduce Table 13.4); (ii) For Table 13.5, print out the first six modes instead of the first three modes. (b) You should find that the natural frequencies of vibration for this structure “pair up” – that is to say, for every mode there is another mode whose frequency is very close to the frequency of the given mode. By examining the mode shapes, describe why this is happening in this structure. Notes : The following step-by-step inputs need to be modified in order to obtain a proper analysis: i) In the step Load Function (page 421), the second line of input should be “Enter Time=0.02, Value=1.0, then press ADD.” ii) In the step Assign Load (page 421), the first line should read “Click on joint 8 and enter – “ iii) In the step Plot Displacement Function (page 424), the seventh line of this step should read “Mode Number = Include All. Then OK, OK....
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