**4. Case Study**

This section includes two parts. First, the processing of separating temperature-induced strain from the field measured data is given. Then, according to the above data, the phase subtraction method based on the Fourier fitting method is described in detail and its effectiveness is verified.

### *4.1. Separation of Temperature-Induced Strain*

The measured strain data includes the interaction of live load and temperature effects. Therefore, the separation of temperature strain is a prerequisite for thermal strain response studies. The measured data of the S6 strain measuring point of the bridge on 9 June 2017 is shown in Figure 6.

(**a**) Raw strain and temperature-induced strain.

**Figure 6.** *Cont*.

**Figure 6.** Strain time history of the raw data and the processed data.

In Figure 6, the separation of temperature effects is achieved by the wavelet decomposition and reconstruction method [20]. As shown in Figure 6, this method can separate temperature strain effectively. The raw strain data is finally decomposed into temperature-induced strain (Figure 6a, the red line) and live load strain (Figure 6b). It is worth noting that the live load-induced strain in Figure 6b is larger than that in Figure 2b. The reason is the location of sensor S6 is in the center of the bridge where the girder will withstand more vehicle loads.
