## 3 Field Application
### Installation of Sensors and Wireless Nodes  
The location of sensors to be installed is generally planned in consideration of the floor plan and elevation of the structure. The basic principle of elevation plan is to select floors from which long-term monitoring of shortening is possible. In this application, sensors were installed on the 10 th and 25 th floors in tower 1 and on the 10 th and 25 th floors in tower 2, as shown in Figure 6. The number of installed sensors and nodes is shown in Table 1. Taking into account the locations of the sensors and partitions that could obstruct wireless communication, the locations of sensor nodes and master nodes for both towers are shown in Figure 7. Sensor nodes, which were connected by short wires to sensors, automatically collected measured data and sent the information to master node installed on the same floor through wireless communication. Master node sent the data from numerous sensor nodes to the server through long-distance wireless communication. The data stored in the server were available in real-time from any place with an internet connection through a web-based managing program.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Type**} & \multicolumn{2}{c}{**Tower 1**} & \multicolumn{2}{c}{**Tower 2**} \\ \cline{2-5}  & **10F** & **25F** & **10F** & **25F** \\ \hline Sensor & 14 & 5 & 15 & 5 \\ Sensor node & 7 & 5 & 6 & 5 \\ Master node & 1 & 1 & 1 & 1 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Number of sensors, sensor nodes, and master nodes deployed for measurement of column shortenings.  
Figure 6: Conceptual diagram of WSNs for tower 1 and tower 2.  
The installation of the sensor and sensor node was performed in the manner shown in Figure 8. First, a sensor is affixed to the steel reinforcement before filling the concrete in the form, and cable is organized and sealed in order to be connected to the sensor node after filling the concrete. After removal of the form, the procedure to connect the sealed cable to the sensor node is performed. The wireless nodes used in this study are basically operated with a small-capacity battery (2,700 mAh), but in actual practice, the problem of power consumption should be considered when conducting  
Figure 8: Installation of sensor and sensor node. (**a**) Installation of sensor; (**b**) Sensor and sensor node; (**c**) Installation of sensor node.  
Figure 7: Location of sensor nodes and master nodes for field measurement of column shortenings in tower 1 and tower 2.  
long-term automatic measurement during construction. To address this issue, sensor nodes used at this site were programmed to perform measurements for one minute and then go into sleep mode for the next 30 min. This strategy can extend the duration of the battery for approximately six months or more.  
In this study, the automatic measurements were obtained using the proposed automatic sensing system over a limited period because of a client's financial demands. Thus, the measurement period and the quantities of sensing members and wireless sensing units were limited. The cost of the sensing nodes (sensor nodes, repeater nodes, and master nodes) and the monitoring software are approximately 1,400 USD and 280 USD, respectively, per month.