Duc-Duy Ho

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.

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.

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.

Field vibration tests-based model update for system identification of railway bridge

In this study, a multi-phase model update approach for system identification of real railway bridge using vibration test results is present. First, a multi-phase system identification scheme designed on the basis of eigenvalue sensitivity concept is proposed. Next, the proposed multi-phase approach is evaluated from field vibration tests on Wondongcheon bridge which is a steel girder railway bridge located in Yangsan, South Korea. On the bridge, a few natural frequencies and mode shapes are experimentally measured under the excitation of trains, ambient vibration and free vibration. The corresponding modal parameters are numerically calculated from a three-dimensional finite element (FE) model which is established for the target bridge. Eigenvalue sensitivities are analyzed for potential model-updating parameters of the FE model. Then, structural subsystems are identified phase-by-phase using the proposed model update procedure. Based on model update results, a baseline model of the Wondongcheon railway bridge is identified.

Damage Detection Algorithm-Embedded Smart Sensor Node System for Bridge Structural Health Monitoring

In this study, a system using autonomous smart sensor nodes is developed for bridge structural health monitoring (SHM). In order to achieve the research goal, the following tasks are implemented. Firstly, acceleration-based and impedancebased smart sensor nodes are designed. Secondly, an autonomous operation system using smart sensor nodes is designed for hybrid health monitoring using global and local health monitoring methods. Finally, the feasibility and applicability of the proposed system are experimentally evaluated in a lab-scaled prestressed concrete (PSC) girder for which a set of damage scenarios are experimentally monitored by wireless sensor nodes and embedded software.

Modal Strain Energy-based Damage Monitoring in Beam Structures using PZT's Direct Piezoelectric Response

The main objective of this study is to examine the feasibility of using lead zirconate titanate (PZT)`s direct piezoelectric response as vibrational feature for damage monitoring in beam structures. For the purpose, modal strain energy (MSE)-based damage monitoring in beam structures using dynamic strain response based on the direct piezoelectric effect of PZT sensor is proposed in this paper. The following approaches are used to achieve the objective. First, the theoretical background of PZT`s direct piezoelectric effect for dynamic strain response is presented. Next, the damage monitoring method that utilizes the change in MSE to locate of damage in beam structures is outlined. For validation, forced vibration tests are carried out on lab-scale cantilever beam. For several damage scenarios, dynamic responses are measured by three different sensor types (accelerometer, PZT sensor and electrical strain gage) and damage monitoring tasks are performed thereafter. The performance of PZT`s direct piezoelectric response for MSE-based damage monitoring is evaluated by comparing the damage localization results from the three sensor types.