Structural Health Monitoring (SHM) of buildings using Wireless Sensor Network (WSN) includes sensor selection, sensor placement & optimisation on a selected building. The monitoring of selected building is to be carried out for a period of two years to detect changes in dynamic behaviour if any. For this, the changes in dynamic properties of buildings, theoretically for a common type of damages in Reinforced Concrete (RC) framed building using Finite Element (FE) technique, has been carried out. It has been attempted to establish the sensitivity of wireless sensor network system under ambient and forced conditions. The approach is highly useful in timely warning /information system in a disaster situation for rapid condition screening and provides reliable information regarding the integrity of the building. The building response system is shown in Fig. 1 using Accelerometer sensor. This data is communicated to the system from coordinator using UART protocol and the signal is plotted in frequency and time domain for calculating the frequencies of structure or building. The present work is supported by CSIR.
- PCB Piezotronics PCB393B12 Accelerometer sensor (Sensitivity-10V/g, Frequency range 0-1000Hz, Range-+/- 1g and 1-axis)
- TI-MSP430F5438A Microcontroller
- CC2520 RF Transreceiver (IEEE802.15.4, 2.4GHz)
Fig. 1: WSN setup for building SHM
A Graphical User Interface (GUI) has been developed for demonstrating the visual outputs of WSN system as shown in Fig. 2. The developed GUI represents each sensor response in time domain as well as frequency domain and first three dominant frequency modes. LabVIEW tool is used for GUI implementation. The following framework of the software tools has been used for this development:
- Z-stack Energy ZigBee protocol
- IAR Workbench 5.52 version
- Embedded C and Python scripting
Fig. 2: GUI for representing the Accelerometer sensor response in time and frequency domains
Developed WSN System incorporates following main features to achieve the Structural Health Monitoring objectives:
- Accelerometer Sensor interfaced with C-WSN node. After data acquisition wireless transmission has been achieved from 0.5 Hz to 200 Hz (0.5 Hz to 50 Hz is practically required for SHM of Buildings)
- GUI for real-time data monitoring and analysis using Python language
- Supports multi-hopping, solar powered and (4 Analog and 4 Digital channels) customized interface
- Experimental Testing has been conducted on 6-storey test structure at CSIR-CBRI, Roorkee
Experimental Results achieved so far are at par with the theory. We have been able to match the natural frequencies till 3rd order for a 6-storey test structure using the developed WSN system. The approximate natural frequencies of an RC building are 4Hz, 13Hz, and 24Hz for 1st, 2nd and 3rd order respectively.