Khac-Duy Nguyen

Multiscale Acceleration-Dynamic Strain-Impedance Sensor System for Structural Health Monitoring

A multiscale wireless sensor system is designed for vibration- and impedance-based structural health monitoring. In order to achieve the objective, the following approaches are implemented. Firstly, smart sensor nodes for vibration and impedance monitoring are designed. In the design, Imote2 platform which has high performance microcontroller, large amount of memory, and flexible radio communication is implemented to acceleration and impedance sensor nodes. Acceleration sensor node is modified to measure PZTs dynamic strain along with acceleration. A solar-power harvesting unit is implemented for power supply to the sensor system. Secondly, operation logics of the multi-scale sensor nodes are programmed based on the concept of the decentralized sensor network. Finally, the performance of the multi-scale sensor system is evaluated on a lab-scale beam to examine the long-term monitoring capacities under various weather conditions.

Temperature-Compensated Damage Monitoring by Using Wireless Acceleration-Impedance Sensor Nodes in Steel Girder Connection

Temperature-compensated damage monitoring in steel girder connections by using wireless acceleration-impedance sensor nodes is experimentally examined. To achieve the objective, the following approaches are implemented. Firstly, wireless acceleration-impedance sensor nodes are described on the design of hardware components to operate. Secondly, temperature-compensated damage monitoring scheme for steel girder connections is designed by using the temperature compensation model and acceleration-impedance-based structural health monitoring methods. Finally, the feasibility of temperature-compensated damage monitoring scheme by using wireless acceleration-impedance sensor nodes is experimentally evaluated from damage monitoring in a lab-scaled steel girder with bolted connection joints.

Long-Term Vibration Monitoring of Cable-Stayed Bridge Using Wireless Sensor Network

Wireless sensor networks provide a lot of advantages for vibration monitoring of bridges. The installation time and implementation cost of the monitoring system are greatly reduced by the adoption of this innovative technology. This paper presents a long-term vibration monitoring of the Hwamyung cable-stayed bridge in Korea using an Imote2-platformed wireless sensor network. First, the wireless vibration monitoring system of the bridge is briefly described by outlining the test history, the design of wireless sensor system, and the sensor deployment. Next, the vibration behaviors of the bridge are experimentally examined with respect to the variation of temperature, the wind loads induced by typhoons, and the change of bridge deck mass caused by pavement.

Wireless Impedance Sensor Node and Interface Washer for Damage Monitoring in Structural Connections

In this study, a technique using wireless impedance sensor node and interface washer is proposed for monitoring damage in structural connections of bridges. In order to achieve the objective, the following approaches are implemented. First, a wireless impedance sensor node is designed for automated and cost-efficient monitoring in structural connections. Second, impedance-based algorithms are embedded in the wireless impedance sensor node for autonomous monitoring of structural connections. Third, a tensile-force monitoring technique using an interface washer is proposed to overcome limitations of the wireless impedance sensor node such as measureable ranges with narrow frequency band, and the proposed technique is numerically validated. Finally, the performance of the wireless impedance sensor node and the interface washer is experimentally evaluated in cable-anchor connection and bolted connection models.

Multi-scale hybrid sensor nodes for acceleration-impedance monitoring for steel structural connections

This paper presents hybrid structural health monitoring of steel girder connections using wireless acceleration and impedance sensor nodes based on Imote2-platform. To achieve the research objective, the feasibility of the sensor nodes is examined about its performance for vibration-based global monitoring and impedance-based local monitoring in the structural systems as the following approaches. First, a damage monitoring scheme is described in parallel with global vibration-based methods and local impedance-based methods. Second, multi-scale sensor nodes that enable combined acceleration-impedance monitoring are described on the design of hardware components and embedded software to operate. Third, the performances of the multi-scale sensor nodes are experimentally evaluated from damage monitoring in a lab-scaled steel girder with bolted connection joints.

Imote2-based multi-channel wireless impedance sensor nodes for local SHM of structural connections

This paper presents a technique for local structural health monitoring (SHM) of multiple structural connections by using multi-channel wireless impedance sensor nodes based on Imote2 platform. To achieve the objective, following approaches are implemented. Firstly, an Imote2-based multi-channel wireless impedance sensor node is designed for automated and cost-efficient impedance-based SHM of structural connections. Secondly, an interface washer associate with impedance measurements is designed to monitor bearing stress which is considered as main effect on structural connections. Finally, performances of the multi-channel wireless impedance sensor node and the interface washer are experimentally validated for a bolted connection model. A damage monitoring method using RMSD index of electro-mechanical impedance signatures is used to examine the strength of each individual bolted connection.

Multiscale Structural Health Monitoring of Cable-Anchorage System Using Piezoelectric PZT Sensors

Structural health monitoring of the cable-anchorage system is very important to secure the integrity of the cable-stayed bridge. The cable-anchorage system carries most of the self-weight, so that any damage in the system may significantly reduce the load carrying capacity of the bridge. This study presents a multiscale structural health monitoring of the cable-anchorage system using piezoelectric PZT sensors. Firstly, the electromechanical impedance response is utilized for alerting the change in anchorage zone caused by the loss of cable force or local anchorage damage. Secondly, the dynamic strain of cable is utilized for classifying the damage type. Thirdly, the loss of cable force and the anchorage damage are quantified by a frequency-based cable force model and an impedance-based damage estimation model, respectively. The feasibility of the approach is evaluated from the experiment on a lab-scale cable-anchorage model for which several damage scenarios are simulated about cable damage and anchorage damage.

Wireless structural health monitoring of cable-stayed bridge using Imote2-platformed smart sensors

In this study, wireless structural health monitoring (SHM) system of cable-stayed bridge is developed using Imote2- platformed smart sensors. In order to achieve the objective, the following approaches are proposed. Firstly, vibrationand impedance-based SHM methods suitable for the pylon-cable-deck system in cable-stayed bridge are briefly described. Secondly, the multi-scale vibration-impedance sensor node on Imote2-platform is presented on the design of hardware components and embedded software for vibration- and impedance-based SHM. In this approach, a solarpowered energy harvesting is implemented for autonomous operation of the smart sensor node. Finally, the feasibility and practicality of the multi-scale sensor system is experimentally evaluated on a real cable-stayed bridge, Hwamyung Bridge in Korea. Successful level of wireless communication and solar-power supply for smart sensor nodes are verified. Also, vibration and impedance responses measured from the target bridge which experiences various weather conditions are examined for the robust long-term monitoring capability of the smart sensor system.

Smart PZT-interface for SHM in tendon-anchorage of cable-stayed bridge

For the safety of cable-stayed bridges, it is very important to ensure the tensile forces of cables. The loss of cable force could significantly reduce load carrying capacity of the structure and even results in structural collapse. This study presents a smart PZT-interface associated with wireless sensing device for tendon force-loss monitoring in cable-stayed bridge. The following approaches are carried out to achieve the objective. Firstly, a smart PZT-interface is designed to monitor the cable force-loss by using electromechanical impedance-based method. Secondly, wireless impedance sensor node is designed for impedance monitoring. The sensor node is mounted on the high-performance Imote2 sensor platform to fulfill high operating speed, low power requirement and large storage memory. Finally, a system of smart PZT-interface and wireless sensor node is evaluated for its performance on a lab-scale cable-anchorage model.

Hybrid SHM of cable-anchorage system in cable-stayed bridge using smart sensor and interface

Cable force is one of the most important parameters of cable-stayed bridge. Since cable system carries most of selfweight of the bridge, the loss of cable force could significantly reduce load carrying capacity of the bridge. This study presents a hybrid structural health monitoring (SHM) method for cable-anchorage system of cable-stayed bridge using smart sensor and interface. The following approaches are carried out to achieve the objective. Firstly, a hybrid SHM method is newly designed for tension force monitoring in cable-anchorage system. In the method, vibration response of cable is utilized for tension force monitoring of global cable, and impedance response of anchorage is utilized to detect tension force change of local tendon. A smart PZT-interface is also designed for sensitively monitoring of electromechanical impedance changes in tendon-anchorage subsystem. Secondly, wireless vibration and impedance sensor network working on Imote2 platform are outlined with regarding to hardware design and embedded software. Finally, an experiment on lab-scale cable-anchorage system is performed to evaluate the feasibility of the proposed SHM method.