Developments on the CENS Structural Health Monitoring Front (2009)

CENS research related to developing and implementing structural health monitoring (SHM) systems is advancing on two distinct but related fronts; ShakeNet, a portable wireless sensor network for instrumenting civil structures and SHMnet, for monitoring of tall buildings in Los Angeles. \t SHM is the process of assessing the state of health (e.g., damage) of instrumented structures from measurements. The goal of SHM is to improve safety and reliability of infrastructure systems by detecting damage before it reaches a critical state, or to allow rapid post-event assessment. The primary objective of the SHMnet research is the development of a robust SHM system along with the associated hardware and software, using tall and special buildings in Los Angeles as a testbed. To manage this large-scale, multi-disciplinary goal, the work tasks are divided into several key focus areas, each with specific objectives, including the development of; a robust wireless Data Acquisition (DAQ) toolbox suitable for rapid urban deployments, a suite of state-of-the-art sensors for monitoring key structural responses including an innovative laser/photodiode for directly measuring interstory drift, and probabilistic post-event assessment algorithms based on experimental motion-damage relationships. A confluence of events, namely the local boom in tall building design and construction, the LA-DBS instrumentation requirements for tall buildings, the technology and experience of CENS and nees@UCLA, coupled with the active participation of key industrial partners, provides the synergy required to enable the proposed research.ShakeNet is a vibration sensor network designed for use in civil structures such as buildings and bridges for system identification and for identifying potential locations of damage due to earthquake motions. ShakeNet can also be used in test structures loaded to failure to characterize damage signals in waveform data such as those produced by moment-frame weld fractures. ShakeNet is a multi-tier wireless sensing system of 75 wireless nodes that can be rapidly deployed by 2-3 people on, for example, multiple floors of a large building. It will be designed to collect structural vibration measurements for up to a week from each node within the network. This portable system can be used to instrument large structures within hours immediately after an earthquake. Significant aftershocks of even moderate-size earthquakes occur for up to a week after the earthquake. What makes ShakeNet application-realistic is careful attention to the design of its data-acquisition hardware, the ShakeBoard. The ShakeBoard is a 24-bit high resolution acceleration data acquisition system that uses commercial low-noise MEMS accelerometers and conforms to specifications currently being established by the US Geological Survey for their Advanced National Seismic System (ANSS). ShakeNet’s software subsystem will be built upon Tenet; programmable wireless sensing software designed for multi-tier sensor networks. The strength of ShakeNet lies in the planned field tests in order to make it application-realistic. Future tests of ShakeNet, pending project funding, include deployments in moment-frame steel and reinforced concrete buildings, a bridge, and a dam near the San Andreas Fault.