Semi-Active Structural Control of a 2-Story Shear Building

With continuing urban development across the world, it is becoming ever more important to provide increased structural safety against events such as earthquakes and strong winds. The field of structural control has recently been growing to meet these challenges through the use of semi-active control methods, such as the Magnetorheological (MR) Damper. However, due to the non-linearity of the device, the knowledge base surrounding the MR Damper and its various control algorithms still needs to be strengthened before large-scale implementation of this control method can occur. To address these issues, this study will examine a two story benchmark structure using MR Dampers controlled by the Clipped Optimal, Lyapunov, and Viscous Damping Negative Stiffness (VDNS) control algorithms. In preliminary simulation, these algorithms have been noted to significantly reduce vibrational effects over both the uncontrolled and passive cases. To prepare for small scale experimentation, both the prototype MR Damper and the structure were numerically identified. This preparation was performed with sufficient accuracy as to facilitate the implementation of the control algorithm in both precise simulation and physical experimentation. Using the information obtained in these preliminary tests it is the hope that better controllers can be developed, thus keeping our societies better protected from natural disasters

Structural Damage Detection Robust Against Time Synchronization Errors

Structural Damage Detection based on Wireless Sensor Networks Can Be Affected Significantly by Time Synchronization Errors among Sensors. Precise Time Synchronization of Sensor Nodes Has Been Viewed as Crucial for Addressing This Issue. However, Precise Time Synchronization over a Long Period of Time is Often Impractical in Large Wireless Sensor Networks Due to Two Inherent Challenges. First, Time Synchronization Needs to Be Performed Periodically, Requiring Frequent Wireless Communication among Sensors at Significant Energy Cost. Second, Significant Time Synchronization Errors May Result from Node Failures Which Are Likely to Occur during Long-Term Deployment over Civil Infrastructures. in This Paper, a Damage Detection Approach is Proposed that is Robust Against Time Synchronization Errors in Wireless Sensor Networks. the Paper First Examines the Ways in Which Time Synchronization Errors Distort Identified Mode Shapes, and Then Proposes a Strategy for Reducing Distortion in the Identified Mode Shapes. Modified Values for These Identified Mode Shapes Are Then Used in Conjunction with Flexibility-Based Damage Detection Methods to Localize Damage. This Alternative Approach Relaxes the Need for Frequent Sensor Synchronization and Can Tolerate Significant Time Synchronization Errors Caused by Node Failures. the Proposed Approach is Successfully Demonstrated through Numerical Simulations and Experimental Tests in a Lab. © 2010 IOP Publishing Ltd

The Development of a Vision-Based Vibration Measurement System for Characterizing Civil Structures

Photogrammetry is one of the most promising non-contact, vision-based measuring techniques. It became commercially available as a result of the development of digital cameras and computer processing technology. Vision-based technique has wide applications in civil engineering such as deflection measurement or condition inspection. However, these applications focus more on static measurements because of the limitations of the acquisition frame rate and the resolution of the image sensor. Developing measurement systems using newly developed equipments and software can enable this technique to be applied to more fields. In this project, a vision-based vibration measurement system for characterizing civil structures is developed under LabVIEW environment. The major apparatus include two recently released machine vision cameras (Basler acA2040-180kc) with high resolution (4M pixels) and frame rate (180Hz), and a Camera Link image acquisition board (NI PXIe-1435). First, the test structure is modeled in 3-D by a photogrammetric software called PhotoModeler. Second, the measurement locations are determined by the dynamic characteristic of the structure. Then consecutive pictures of the test structure are taken and sent to the LabVIEW program to obtain the vibration data. At last the measured parameters are compared to the measurements of contact sensors. The results show that the obtained parameters are comparable to the contact measurements. In conclusion, photogrammetry is a considerably accurate non-contact measuring method. This project mainly focuses on the measurement part and the analysis of the acquired data is left for future study

Controlling errors and improving performance of transient simulations using multitime-step integration

A key aspect of simulating the dynamic response of structures is judging how accurate the solution is and how much error it may contain. Errors are primarily introduced into the solution due to the underlying assumptions of the model and due to numerical solution procedures. Inherent problem characteristics, such as geometry, loading, and boundary conditions also affect error and can lead to local regions in the problem domain with high error. In the past, such locations, or problem features, have been dealt with by refining the spatial discretization in these areas. However, location-specific temporal discretization is not possible with methods that use a uniform time-step for the entire problem domain. Thus, one is forced to use a small time-step for the entire problem domain to achieve a low level of error. Multitime-step methods, on the other hand, allow one to choose different time-steps for different regions in the problem domain so that local error can be reduced where needed although still keeping the computational cost low. The aim of this article is to investigate how changing local temporal discretization affects local error, global error, and computational cost for transient problems that contain regions of high error. A method is presented for determining how to best decompose a given problem domain into subdomains, and how to select the time step for each subdomain to minimize the total computational cost and a measure of global error. For a given problem, numerous different combinations of spatial and temporal discretizations were studied to characterize the error in these solutions and their corresponding computational cost. The space of possible multitime-step decompositions was examined to find an optimal spatial decomposition and corresponding time-steps to meet predetermined criteria of cost and error. Recommendations are also made for finding such optimal decompositions for general problems in structural dynamics. Numerical examples for truss and frame structures are presented to show how choosing a finer temporal discretization around local problem features can reduce not only the local error, but also the error throughout the entire problem domain while still minimizing the computational cost of the simulation

Cyber-Physical Codesign of Distributed Structural Health Monitoring with Wireless Sensor Networks

Our Deteriorating Civil Infrastructure Faces the Critical Challenge of Long-Term Structural Health Monitoring for Damage Detection and Localization. in Contrast to Existing Research that Often Separates the Designs of Wireless Sensor Networks and Structural Engineering Algorithms, This Paper Proposes a Cyber-Physical Co-Design Approach to Structural Health Monitoring based on Wireless Sensor Networks. Our Approach Closely Integrates (1) Flexibility-Based Damage Localization Methods that Allow a Tradeoff between the Number of Sensors and the Resolution of Damage Localization, and (2) an Energy-Efficient, Multi-Level Computing Architecture Specifically Designed to Leverage the Multi-Resolution Feature of the Flexibility-Based Approach. the Proposed Approach Has Been Implemented on the Intel Imote2 Platform. Experiments on a Physical Beam and Simulations of a Truss Structure Demonstrate the System\u27s Efficacy in Damage Localization and Energy Efficiency. © 2010 ACM

Cyber-Physical Codesign of Distributed Structural Health Monitoring with Wireless Sensor Networks

Our Deteriorating Civil Infrastructure Faces the Critical Challenge of Long-Term Structural Health Monitoring for Damage Detection and Localization. in Contrast to Existing Research that Often Separates the Designs of Wireless Sensor Networks and Structural Engineering Algorithms, This Paper Proposes a Cyber-Physical Codesign Approach to Structural Health Monitoring based on Wireless Sensor Networks. Our Approach Closely Integrates 1) Flexibility-Based Damage Localization Methods that Allow a Tradeoff between the Number of Sensors and the Resolution of Damage Localization, and 2) an Energy-Efficient, Multilevel Computing Architecture Specifically Designed to Leverage the Multiresolution Feature of the Flexibility-Based Approach. the Proposed Approach Has Been Implemented on the Intel Imote2 Platform. Experiments on a Simulated Truss Structure and a Real Full-Scale Truss Structure Demonstrate the System\u27s Efficacy in Damage Localization and Energy Efficiency