# Temperature Effects on Vibration-Based Damage Detection of a Reinforced Concrete Slab
## 1 Introduction  
Actual civil structures are susceptible to the influence of varying environmental factors and operational conditions such as humidity, wind and moving vehicles, however the most important factor has proven to be temperature [1; 2; 3]. In recent years, structural health monitoring under environmental variations has become a popular research topic in the field of civil engineering [4; 5; 6]. [PERSON] and [PERSON] [7] investigated the effects of changing ambient temperatures on finite element (FE) model updating of the Dowling Hall Footbridge. [PERSON] and [PERSON] [8] studied temperature-dependent bridge movements and stress development in bridges. [PERSON] et al. [9] proposed a new data normalization technique based on the improved restoring force model (IRFM) to distinguish the effect of damage from those caused by environmental and operational variations. [PERSON] and [PERSON] [10] conducted a static continuous monitoring experiment to assess the validity of some damage detection algorithms. [PERSON] et al. [11] proposed a damage identification approach in bridge structures under moving vehicular loads without knowledge of the vehicle properties and the time-histories of moving interaction forces. [PERSON] and [PERSON] [12] utilized the relationship between temperature changes and the resulting strains and displacements of the structure to create a unique numerical and graphical baseline within an structural health monitoring (SHM) framework and found the temperature-based approach was more sensitive for the scenarios examined. [PERSON] et al. [13] investigated the feasibility of the pseudo-static damage identification method derived from a bridge-vehicle interaction system through a moving vehicle laboratory experiment. For structural damage identification, damage is generally identified through the dynamic characteristics test of the structures by analyzing the change of structural modal parameters, such as natural frequencies, mode shapes, and damping ratios. [PERSON] et al. [14; 15] provided an overview of methods to detect, locate, and characterize damage in structural and mechanical systems by examining changes in measured vibration response. [PERSON] and [PERSON] [16] proposed a genetic algorithm (GA) with real number encoding to identify the structural damage by minimizing the objective function, which directly compares the changes in the measurements before and after damage occurs. [PERSON] and [PERSON] [17] introduced a novel approach for vibration-based damage detection, which is based on the use of a large network of sensors' frequency response function (FRF). [PERSON] [18] performed a vibration-based damage detection of a beam based on a cooperative co evolutionary GA. However, dynamic characteristics such as natural frequencies, mode shapes and damping ratios are inherently susceptible not only to structural damage but also environmental variations and operational conditions, and it is the variation of temperature that induces major fluctuation of structural dynamic parameters [19]. Among the many factors that affect the modal frequency of the bridge structure, the change of the modal frequency caused by temperature may be larger than that caused by structural damage, and the change caused by small damage to the structure is even submerged or masked. Therefore, it is of great significance to study the effect of temperature on modal properties. [PERSON] [20] took an experiment for one small steel truss bridge and found that the influence of temperature on frequency exceeds the influence of simulated fault on frequency. [PERSON] et al. [21] carried out a 10-month dynamic test on Z24 Bridge and found that the fluctuation range of the 1 st to 4 th natural frequencies of the bridge was 14%, 18%, 16% and 17%, respectively. [PERSON] and [PERSON] [22] monitored a steel plate girder bridge for 2 years and it is shown that the natural frequency change at the lowest temperature (\(-\)15.6 \({}^{\circ}\)C) compared with the reference temperature (12.8 \({}^{\circ}\)C) could be up to 15.4%.