# Temperature Effects on Vibration-Based Damage Detection of a Reinforced Concrete Slab
## 2 RC Slab and Vibration Testing  
### Testing Setup  
A classical simply supported RC slab was constructed for this study which measures 5.4m long, 0.6 m wide, and 0.12 m thick with a 0.2 m overhang at each end, and a mass density of 2410 kg/m\({}^{3}\), as shown in Figure 1. Four laminated rubber bearings support the slab at the endpoints on the top of the brick pedestal. The main aim of this paper is to investigate the influence of varying temperature on the performance of damage detection based on long-term monitoring data.  
From July 1, 2017 to June 30, 2018, the RC slab was monitored for one year under natural environmental conditions and environmental temperature and vibration data were acquired. As shown in Figure 2, 45 measurement points were uniformly located on the top and bottom surface of the slab. A laser thermometer was utilized to measure the surface temperature, which allowed an error of 0.5 \({}^{\circ}\)C in the range of 0-100 \({}^{\circ}\)C. The temperature measurement and the vibration testing were carried out at the same time. Moreover, the time interval of the temperature measurement was about 15 min and vibration testing data from all sensors were captured almost simultaneously.  
The acceleration data was captured by a DH5922 vibration testing system which has the advantages of light mass and convenient use etc. The operation temperature of acceleration acquisition instrument ranges from 0 \({}^{\circ}\)C to 60 \({}^{\circ}\)C. It is also a universal dynamic signal test and analysis system which can complete the testing and analysis of stress, strain, vibration, shock, acoustics, temperature, pressure, flow, force, torque, voltage and current, etc. The instrument has 16 24-bit IEPE input channels which are equipped with an anti-mixing filter, and supports sampling frequency up to 51.2k Hz. The system was connected with the acceleration sensor by L5 coaxial extension wire and placed in the center of the equal dividing line to collect the acceleration signal. The operation temperature of acceleration sensor ranged from \(-40\)\({}^{\circ}\)C to \(80\)\({}^{\circ}\)C and its tolerance was \(\pm 1\%\). The acceleration sensor locations and vibration testing system are shown in Figure 3.  
Figure 1: Reinforced concrete (RC) Slab.  
Figure 2: Locations of temperature measurement points. (**a**) Top surface. (**b**) Bottom surface.  
Monitoring for one year was performed and 180 sets of data were acquired. The monitoring temperature ranged from 0 to 55 \({}^{\circ}\)C, and it was found that the temperatures on the top surface vary little and the same phenomenon occurs on the bottom surface, so the average top and bottom surface temperature were calculated based on the acquired temperatures of the top and bottom surface. Then the average temperature was calculated based on the acquired average top and bottom surface temperature. Figure 4 shows the surface temperature of the slab. Typical acceleration history in time and frequency are shown in Figure 5.  
Figure 4: Temperature variations of RC slab.  
Figure 3: Layout of acceleration sensors and vibration testing system. (**a**) Acceleration sensors. (**b**) Vibration testing system.