ShakeNet: A portable wireless sensor network for instrumenting large civil structures

We report our findings from a U.S. Geological Survey (USGS) National Earthquake Hazards Reduction Program-funded project to develop and test a wireless, portable, strong-motion network of up to 40 triaxial accelerometers for structural health monitoring. The overall goal of the project was to record ambient vibrations for several days from USGS-instrumented structures. Structural health monitoring has important applications in fields like civil engineering and the study of earthquakes. The emergence of wireless sensor networks provides a promising means to such applications. However, while most wireless sensor networks are still in the experimentation stage, very few take into consideration the realistic earthquake engineering application requirements. To collect comprehensive data for structural health monitoring for civil engineers, high-resolution vibration sensors and sufficient sampling rates should be adopted, which makes it challenging for current wireless sensor network technology in the following ways: processing capabilities, storage limit, and communication bandwidth. The wireless sensor network has to meet expectations set by wired sensor devices prevalent in the structural health monitoring community. For this project, we built and tested an application-realistic, commercially based, portable, wireless sensor network called ShakeNet for instrumentation of large civil structures, especially for buildings, bridges, or dams after earthquakes. Two to three people can deploy ShakeNet sensors within hours after an earthquake to measure the structural response of the building or bridge during aftershocks. ShakeNet involved the development of a new sensing platform (ShakeBox) running a software suite for networking, data collection, and monitoring. Deployments reported here on a tall building and a large dam were real-world tests of ShakeNet operation, and helped to refine both hardware and software

Preliminary estimation of seismically induced ground strains from spatially variable ground motions

A model for horizontal peak ground strain (PGS) is developed in consideration of three fundamental contributions to spatially variable ground motion (SVGM): (1) spatial incoherence effects, which contribute to phase variability in a stochastic sense; (2) wave passage effects, which contribute to phase variability in a deterministic sense; and (3) amplitude variability. Previous models for each of these effects are reviewed and compared to array data from Borrego Valley, California. Published empirical models for coherency and amplitude variability are found to represent reasonably well the Borrego data. We extend previous work by considering correlations of amplitude and phase variability (generally found to be small) and characterizing the coherency-dependent probabilistic distribution of phase variability. Using the aforementioned amplitude and phase variability models, a procedure is developed to generate simulated acceleration records from a seed record. The procedure is applied to a suite of Northridge earthquake recordings to predict ground strains, which are found to be strongly dependent on the peak ground velocity (PGV) of the seed motion and the separation distance between the seed and simulated motions. The dependence of PGS on PGV saturates for large PGV (> 50 cm/sec)

Developments on the CENS Structural Health Monitoring Front

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 rapid, post-event deployments and SHMnet, a novel SHM system for permanent monitoring of tall buildings and special structures in Los Angeles. 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 structures (e.g., bridges, port structures, dams) in Los Angeles as a testbed. More specifically, the development of a wireless Data Acquisition (DAQ) toolbox suitable for rapid urban deployments, a suite of state-of-the-art sensors for monitoring key structural responses including innovative methods for directly measuring interstory displacements, and probabilistic post-event assessment algorithms based on experimental motion-damage relationships. Progress on these fronts is highlighted. One rather unique aspect of this research stems from partnerships with strong-motion instrumentation programs (SMIPs) such as CSMIP, ANSS, and the LA-DBS. The proposed SHMnet leverages both building access and instrumentation requirements already facilitated by one or more SMIPs. However, a critical look at structural instrumentation guidelines of various SMIP agencies exposed a lack of uniformity of experience-based specifications. To this end, we sought to establish a quantitative basis for key structural instrumentation specifications, namely sample rate, resolution, and time synchronization. This was accomplished by analyzing signal errors associated with data acquisition processes and engineering sensitivity analyses of several intensity measures and engineering demand parameters. Results from these studies will be useful in updating current structural instrumentation specifications of major SMIPs as well as provide specifications for SHMnet tools. ShakeNet is a portable wireless sensor network for instrumenting large civil structures such as buildings and bridges. The focus of ShakeNet design is to take advantage of wireless technology for deployments in structural environments where power or communications infrastructure is nonexistent or unavailable. It is designed to collect structural vibration measurements for up to a week from each node within the network by deployment in large structures within hours after an earthquake. It will consist of 25 sensor nodes and 5 to 10 master-tier nodes (Stargates or other embedded computers) that provide increased communications capacity. The ShakeNet software subsystem is built upon Tenet; programmable wireless sensing software designed for multi-tier sensor networks. ShakeNet will be deployed and tested on several structures that represent a range of structure types, environments, ages, and degrees of retrofit. They include the Seven Oaks Dam in Redlands, CA, the Santa Ana River Bridge in Riverside, CA, 1100 Wilshire Blvd. in downtown Los Angeles, CA, and the Long Beach Veterans Administration Hospital in Long Beach, CA

Developments on the CENS Structural Health Monitoring Front

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 rapid, post-event deployments and SHMnet, a novel SHM system for permanent monitoring of tall buildings and special structures in Los Angeles. 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 structures (e.g., bridges, port structures, dams) in Los Angeles as a testbed. More specifically, the development of a wireless Data Acquisition (DAQ) toolbox suitable for rapid urban deployments, a suite of state-of-the-art sensors for monitoring key structural responses including innovative methods for directly measuring interstory displacements, and probabilistic post-event assessment algorithms based on experimental motion-damage relationships. Progress on these fronts is highlighted. One rather unique aspect of this research stems from partnerships with strong-motion instrumentation programs (SMIPs) such as CSMIP, ANSS, and the LA-DBS. The proposed SHMnet leverages both building access and instrumentation requirements already facilitated by one or more SMIPs. However, a critical look at structural instrumentation guidelines of various SMIP agencies exposed a lack of uniformity of experience-based specifications. To this end, we sought to establish a quantitative basis for key structural instrumentation specifications, namely sample rate, resolution, and time synchronization. This was accomplished by analyzing signal errors associated with data acquisition processes and engineering sensitivity analyses of several intensity measures and engineering demand parameters. Results from these studies will be useful in updating current structural instrumentation specifications of major SMIPs as well as provide specifications for SHMnet tools. ShakeNet is a portable wireless sensor network for instrumenting large civil structures such as buildings and bridges. The focus of ShakeNet design is to take advantage of wireless technology for deployments in structural environments where power or communications infrastructure is nonexistent or unavailable. It is designed to collect structural vibration measurements for up to a week from each node within the network by deployment in large structures within hours after an earthquake. It will consist of 25 sensor nodes and 5 to 10 master-tier nodes (Stargates or other embedded computers) that provide increased communications capacity. The ShakeNet software subsystem is built upon Tenet; programmable wireless sensing software designed for multi-tier sensor networks. ShakeNet will be deployed and tested on several structures that represent a range of structure types, environments, ages, and degrees of retrofit. They include the Seven Oaks Dam in Redlands, CA, the Santa Ana River Bridge in Riverside, CA, 1100 Wilshire Blvd. in downtown Los Angeles, CA, and the Long Beach Veterans Administration Hospital in Long Beach, CA