260 M. Mehrkash and E. Santini-Bell Table 26.4 Analytical, experimental and updated frequencies obtained by two-parameter estimation Mode no. Anal. freq. (Hz) Updated freq. (Hz) Exper. freq. (Hz) 1 22.63 22.17 22.25 2 28.44 27.86 26.81 3 33.87 33.05 33.31 4 43.76 42.64 40.63 5 62.38 61.65 64.56 6 65.63 64.92 67.56 7 73.20 73.20 – 8 73.20 73.20 – 9 73.38 73.38 – 10 96.33 96.33 94.06 11 99.50 99.34 96.38 12 109.62 107.07 102.40 Fig. 26.11 MAC value plot of the two-parameter estimation analysis Table 26.5 Initial and updated values of two-parameter estimation Stiffness parameter Initial stiffness value (kN m/rad) Updated value (kN m/rad) Lower bound (kN m/rad) Upper bound (kN m/rad) Group 1 8000 11,307 4000 16,000 Group 2 8000 16,000 4000 16,000 26.7 Conclusion In this paper, the stiffness parameters of the joints of an experimental structure were verified with respect to laboratory collected model response data. The capability of SAP2000 ® software package for incorporating partial fixities at the connection regions as well as the OAPI was employed. It was shown how the joints stiffness of the experimental structure could affect its modal behavior. The parameter estimation operation presented in this paper was limited to updating the rigidity of the joints. Obviously, there are some uncertainties in terms of stiffness, mass and damping of the structure members. In a more comprehensive model updating procedure, those uncertain structural parameters need to be incorporated in the parameter estimation and model updating protocol. Also, it was demonstrated that updating the partial fixity springs
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