3.3.1. Working Condition without Damage

Under the conditions without damage, *k*<sup>1</sup> ∼ *k*3, α and β are obtained as shown in Figure 5 when the proposed recognition algorithm is used in the situation.

It can be seen from Figure 5 that structural damage can be identified based on the algorithm in the paper. The computation converges very quickly so that, *k*<sup>1</sup> ∼ *k*<sup>3</sup> reaches the steady values within 14.5 s. Moreover, α and β converge to steady values within the 20 s. The differences between the recognition results and the initial values show that the initial estimation of the structure parameters is not accurate. However, by using the UKF it can give a more accurate structural parameter identification even under the condition with observation noises.

**Figure 5.** *Cont.*

**Figure 5.** Identification results of the system parameters under the nondestructive working conditions: (**a**) recognition results of *k*1, (**b**) recognition results of *k*2, (**c**) recognition results of *k*3, (**d**) recognition results of α and (**e**) recognition results of β.
