13th World Conference on Earthquake Engineering Vancouver, B.C., Canada August 1-6, 2004 Paper No. 1406
BUILDING RISK MONITORING USING WIRELESS SENSOR NETWORK Narito KURATA1, Billie F. SPENCER, Jr.2, Manuel RUIZ-SANDOVAL3
SUMMARY Buildings are subjected to natural hazards, such as earthquakes and winds, and man-made hazards, such as fires and crimes, during their long-term use. To mitigate these hazards, monitoring these risks by sensing certain types of physical values is necessary. Recently, a smart sensor based on the Berkeley Mote platform was introduced, and an application to the next generation of structural health monitoring and control was proposed [1, 2]. The Mote has on-board microprocessor and ready-made wireless communication capabilities. In this paper, the performance of the Mote is investigated through shaking table tests employing a two-story steel structure. The acceleration sensor is tested, and its performance for wireless measurement and specific risk monitoring applications, such as damage detection in the structure, is presented. The feasibility of risk monitoring for buildings is also discussed. INTRODUCTION “Ubiquitous sensing/computing” is expected to be realized over the next ten years. The interest in sensing technology for various uses has been growing, and new kinds of sensors have been developed by micro electro mechanical systems (MEMS) technology. Environmental information, such as brightness, temperature, sound, vibration, and a picture of a certain place in a building, is evaluated by the network to which a huge number of microcomputer chips with sensors were connected [3, 4]. Fig. 1 shows the flow towards a ubiquitous sensing/computing/networked society. A structural health monitoring technology will play an important role in this stream. A number of studies have been conducted on structural health monitoring for buildings and civil engineering structures in recent years [5, 6, 7, 8]. Some of these studies have focused on wireless sensing technology. Researchers at the Stanford University have developed a wireless sensing unit for real-time structural response measurements and conducted a series of validation tests [9, 10]. In Japan, the Mitsubishi Electric Corporation has developed energy-saving wireless sensor network as shown in Fig. 2 [11, 12]. The University of Tokyo [13] and the Oki Electric Industry [14] have devoted their effort to develop new wireless sensor networks as shown in Fig. 3. 1
Kajima Corporation, Tokyo, Japan. Email:
[email protected] University of Illinois at Urbana-Champaign, Urbana, USA. Email:
[email protected] 3 University of Notre Dame, Notre Dame, USA. (On leave from Universidad Autonoma Metropolitana) Email:
[email protected] 2
Computer with sensors are getting smaller, smarter and cheaper
Small networks of computer/ sensor will be increased
Large scale networks of computer/ sensor will appear
Ubiquitous computing/ sensing/ networked society
Figure 1. Towards a ubiquitous computing/sensing/networked society.
(a) Prototype of sensor node
(b) Small Size
(c) Wireless sensor board
Figure 2. Wireless sensor network developed by Mitsubishi Electric Corporation [11, 12].
(a) U3 developed by Univ. of Tokyo [13] (b) Sensor node developed by Oki Electric Industry [14] Figure 3. Wireless sensor networks. Recently, a commercially available wireless sensor platform called the “Berkeley Mote” with an operating system was provided by researchers at the University of California, Berkeley [15, 16], and its application to the next generation of structural health monitoring and control was recently proposed [1, 2]. Because of its open hardware and software platform, the Berkeley Mote is a useful tool for research activities. In this paper, the feasibility of monitoring of various risks for buildings using the smart sensors is discussed, and the performance of the “MICA and MICA2 Mote” as a wireless acceleration sensor is tested.
BUILDING RISK MONITORING Risk monitoring and hazard mitigation Buildings are subjected to natural hazards such as severe earthquakes and strong winds, as well as manmade hazards such as fire, crime, and terrorism, during their long-term use. To mitigate these hazards, monitoring various risks in a building employing an intelligent sensor network is necessary. The sensor network could measure acceleration, displacement, strain, etc. The risk to buildings includes degraded structural performance, fatigue, damage, gas leaks, intrusions, fires, etc. According to the risk monitoring results, appropriate risk control measures (e.g., structural control, maintenance, evacuation guidance, warnings, alarms, fire fighting, rescue, security measures, etc.) can be applied (see Fig. 4).
Risk Monitoring Degraded structural performance/Fatigue/ Damage/Fires/Gas leaks/Intrusions/etc. Sensor Network
Risk Control
Acceleration/Strain/ Displacement/Light/ Temperature/Image/ Olfactory/Smoke/ Sound/etc.
Structural control/ Maintenance/Warning /Evacuation guidance/ Fire fighting/Rescue/ Security measures/ etc.
Hazard Mitigation Natural hazard (Earthquake/Typhoon/etc.) Man-made hazard (Fire/Crime/ Terrorism/etc.)
Figure 4. Building risk monitoring and hazard mitigation.
Role of sensor networks A wireless sensor network plays an important role in such strategies and can be connected to the internet so that this information can be used to monitoring future risks. Wireless sensors are easy to install, remove, and replace at any location, and are expected to become increasingly smaller (i.e., “smart dust” [21]) by using MEMS technology. They will provide a ubiquitous, networked sensing environment in buildings. For example, the acceleration and strain at numerous locations on each beam and column, temperature and light in each room, images and sounds in desired regions can be obtained by the “smart dust” sensors, as illustrated in Fig. 5. Additionally, a single type of sensor such as a condenser microphone can be used for multiple purposes, for example, to detect earthquake, fires and intrusions [17]. Furthermore, a fiber optic network is not only utilized as infrastructure for information technology, but also as a “wired” sensor network. Table 1 shows various kinds of hazards, and possible applications/combination of sensors.
Wireless sensor network acceleration/strain/ temperature/light/ image/sound/etc. Fiber optic network acceleration/strain/etc.
Internet Main server/base station
Figure 5. Example of risk monitoring system. Table 1. Sensor Applications. Hazard Earthquake /Wind
Application observation experiment structural control health monitoring damage detection fire detection gas leak detection alarm, warning
Fire
evacuation control Crime
surveillance security alert
Sensor acceleration acceleration, strain acceleration acceleration, strain acceleration, strain, displacement temperature, smoke, acoustic, acceleration, olfactory olfactory sounder temperature, smoke, acoustic, light, olfactory acceleration, acoustic, light, camera sounder
WIRELESS SENSOR NETWORK MOTE Smart dust project This technology is based on the smart dust project supported by the Defense Advanced Research Projects Agency (DARPA [18]) under the Network Embedded Software Technology (NEST [19]) program in the Wireless Embedded Systems at the University of California, Berkeley (Berkeley WEBS [20]). The goal of this project is to explore the fundamental limits to the size of autonomous sensor platforms. Many new applications are expected to become possible when actual “smart dust” can be realized on a millimeter size scale [21]. MICA and MICA2 Mote The MICA and MICA2 Mote (see Photo. 1 and 2) have been developed by researchers at the University of California, Berkeley [22]. It is an open hardware and open software platform for smart sensing and consists of plug-in sensor boards, processor, transceiver, and attached AA battery pack as shown in Table 2.
Photograph 1. MICA.
Photograph 2. MICA2. Table 2. Specifications.
Processor/Radio CPU CPU clock Program memory Data memory AD converter Processor current draw Radio frequency Data rate Radio current draw Radio range Power External power
MICA ATmega103L 4 MHz 128 KB 512 KB 10 bit 5.5 mA
