**2. Time-Lag E** ff**ect**

In this section, the time-lag e ffect is demonstrated through the field measured data of a real bridge. Firstly, the general situation of the Lieshihe Bridge and its SHM systems will be introduced. Then the collected data is illustrated and the time-lag e ffect is put forward. Finally, the character of the time-lag effect in di fferent seasons is discussed.

#### *2.1. Introduction of Lieshihe Bridge*

Concrete small box-girder are commonly used in medium and small span bridges. Thanks to the stability and the structural characteristics suitable for both positive and negative bending moments, the cross-section form (concrete small box-girder) is becoming more and more popular in designing small and medium span bridges. This study focuses on the temperature e ffects on small concrete box-girders.

Lieshihe Bridge is a typical small box-girder bridge, located in Jiangsu province, China. This case study is used as an example to illustrate the thermal load on a bridge and the time-lag e ffect of temperature-induced strains on the bridge. The superstructure of Lieshihe Bridge is a 5-span continuous box-girder, as shown in Figure 1a. Each of the spans has a length of 25 m, with the total length of the bridge reaching 125 m. The main beams are small box-girder with a height of 1.5 m, as shown in Figure 1b. On the longitudinal axis, the locations for temperature and strain sensors are arranged in the middle section of the second span, while their positions on the lateral axis are illustrated in Figure 1b.

(**a**) Photo of Lieshihe River Bridge 

**Figure 1.** Photo of Lieshihe River Bridge and deployment locations of sensors.
