Y. F. Duan

Cable Vibration Control using Magnetorheological Dampers

As the worlds first implementation of magnetorheological (MR) smart damping technique in bridge structures, a total of 312 semi-active MR dampers (RD-1005, Lord Corporation) have recently been installed for rain–wind-induced cable vibration control on the cable-stayed Dongting Lake Bridge, China. This project has undergone several stages of in situ experiments and tests: (i) modal tests of undamped cables, (ii) forced vibration tests of MR-damped trial cables, (iii) monitoring of MR-damped and undamped cable responses under rain–wind excitations, (iv) comparative tests using different damper setups, (v) full installation, and (vi) field measurements and real-time control tests after the installation. After outlining the above six stages of the whole project and addressing the experience and lessons learned from both open-loop control and closed-loop control practices, this study focuses on the design considerations of implementing MR dampers for cable vibration control, taking into account the effects of the damper stiffness, damper mass, stiffness of damper support, nonlinearity of the damper, and sag and inclination of the cable. The research efforts make it possible to develop elaborate MR dampers specific for application to bridge stay cables.

Steel stress monitoring sensor based on elasto-magnetic effect and using magneto-electric laminated composite

Monitoring of stresses in in-service steel structural components is challenging, but crucial to structural safety and health evaluation. Elasto-magnetic (EM) sensors are promising for stress monitoring of steel structural components, because of their great capabilities for actual stress measurement, noncontact monitoring, and long service life. However, the low sensitivity, low signal-to-noise ratio, slow response, and complicated installation of the EM sensors limit their application flexibility. This paper presents a steel stress monitoring sensor (SSMS) using a magneto-electric (ME) sensing unit to overcome the drawbacks intrinsic in the conventional EM sensors. The ME sensing unit is made of a ME-laminated composite of Terfenol-D magnetostrictive alloy and 0.7Pb_Mg1/3Nb2/3_O3−0.3PbTiO3 (PMN-PT) piezoelectric crystal. The theoretical analysis and experimental characterization conducted on the ME sensing unit show high sensitivity, real-time response, and good linearity. Stress monitoring of a steel bar under tension is implemented for the SSMS with a pulse excitation of magnetization. The results demonstrate that the SSMS is feasible for real-time stress monitoring of steel structural components with high sensitivity, fast response, and ease of installation.

Smart Elasto-Magneto-Electric (EME) Sensors for Stress Monitoring of Steel Cables: Design Theory and Experimental Validation

An elasto-magnetic (EM) and magneto-electric (ME) effect based elasto-magneto-electric (EME) sensor has been proposed recently by the authors for stress monitoring of steel cables with obvious superiorities over traditional elasto-magnetic sensors. For design optimization and engineering application of the EME sensor, the design theory is interpreted with a developed model taking into account the EM coupling effect and ME coupling effect. This model is able to approximate the magnetization changes that a steel structural component undergoes when subjected to excitation magnetic field and external stress, and to simulate the induced ME voltages of the ME sensing unit located in the magnetization area. A full-scale experiment is then carried out to verify the model and to calibrate the EME sensor as a non-destructive evaluation (NDE) tool to monitor the cable stress. The experimental results agree well with the simulation results using the developed model. The proposed EME sensor proves to be feasible for stress monitoring of steel cables with high sensitivity, fast response, and ease of installation.

Development of Magnetorheological Dampers with Embedded Piezoelectric Force Sensors for Structural Vibration Control

Magnetorheological (MR) dampers with embedded piezoelectric force sensors are developed to enable real-time, closed-loop vibration control of civil and mechanical structures. In this study, a prestress-type piezoelectric force sensor is fabricated and integrated with an actuation-only MR damper to form a smart MR damper possessing the attractive functionality of force sensing-while-damping with a high degree of sensor—damper collocation. Calibration of the piezoelectric force sensor is performed in a servohydraulic material testing system operating in force-controlled excitations of sine and ramp waveforms at different combinations of amplitude and frequency. The sensing and damping performance of the smart MR damper is evaluated by operating the material testing system in displacement-controlled sine and ramp excitations while adjusting different DC control currents to the damper. A good agreement between the piezoelectric force sensor outputs and the material testing system force inputs is observed, besides the highly controllable force—displacement and force—velocity hysteretic characteristics. The results show great promise of deploying the smart MR damper in intelligent structural vibration control systems.

Damping identification of MR-damped bridge cables from in-situ monitoring under wind-rain-excited conditions

The newly built cable-stayed Dongting Lake Bridge in Hunan, China has experienced wind-rain-induced cable vibration several times during the past months. A research/implementation project on using semi-active magneto-rheological (MR) dampers for cable vibration control of the bridge is in progress. As part of this ongoing project, one typical stay cable with 115 m length was installed with two MR dampers near the lower anchorage, and accelerometers were deployed on the damped cable and its two neighboring cables for long-term monitoring. After installing the dampers and sensors, wind-rain-induced cable oscillations were observed two times. This paper aims to investigate the vibration characteristics and to identify the equivalent modal damping of the cables with and without MR dampers in one wind-rain-excited event based on in-situ monitoring. In this wind-rain-excited event, the in-plane and out-of-plane responses of the damped cable and its two neighboring free cables were monitored. Equivalent modal damping ratios of the cables in both in-plane and out-of-plane motions are identified by means of spectral analysis of the measured data in conjunction with a curve-fitting technique. Such observed and identified results are beneficial to understanding the coupled motion of cables in wind-rain-excited conditions and the damping contribution of MR dampers to both in-plane and out-of-plane motions. The frequency-domain analysis of the wind-rain-excited responses of the damped and undamped cables also reveals the response characteristics under wind-rain excitation and the damping mechanism of MR dampers in suppressing such oscillation.

ADVANCED FINITE ELEMENT MODEL OF TSING MA BRIDGE FOR STRUCTURAL HEALTH MONITORING

The Tsing Ma Bridge is a cable suspension bridge carrying both highway and railway. A bridge health monitoring system called wind and structural health monitoring system (WASHMS) has been installed in the Tsing Ma Bridge and operated since 1997 to monitor the structural performance and its associated loads and environments. However, there exists a possibility that the worst structural conditions may not be directly monitored due to the limited number of sensors and the complexity of structure and loading conditions. Therefore, it is an essential task to establish structural performance relationships between the critical locations/components of the bridge and those instrumented by the WASHMS. Meanwhile, to develop and validate practical and effective structural damage detection techniques and safety evaluation strategies, the conventional modeling for cable-supported bridges by approximating the bridge deck as continuous beams or grids is not applicable for simulation of real damage scenarios. To fulfil these tasks, a detailed full three-dimensional (3D) finite element model of the Tsing Ma Bridge is currently established for direct computation of the stress/strain states for all important bridge components. This paper presents the details of establishing this full 3D finite element model and its calibration. The major structural components are modeled in detail and the connections and boundary conditions are modeled properly, which results in about half million elements for the complete bridge model. The calibration of vibration modes and stresses/strains due to passing trains is carried out, and a good agreement is found between the computed and measured results.

Entire-Process Simulation of Earthquake-Induced Collapse of a Mockup Cable-Stayed Bridge by Vector Form Intrinsic Finite Element (VFIFE) Method

It is important to simulate the entire-process collapse of earthquake excited cable-stayed bridge in order to assure the damage extent under strong earthquakes and to optimize the anti-collapse seismic measures. The newly developed vector form intrinsic finite element (VFIFE) method is capable of computing large deformation, large displacement, collision, and fractures that would happen in the structural collapse. Therefore, it has the potential to simulate the entire-process collapse of earthquake excited structures. For the cable-stayed bridges, the axial forces change significantly during the earthquake excitation. The interaction between the axial forces and bending moments should be taken into account. In order to address this issue, this paper first presents the formulation for integration of VFIFE method and fiber beam-column element model. A bilinear elastic-plastic constitutive damage model is proposed for the mechanical behavior of the fiber and element. The collapse analysis of a 2D mockup bridge scaled from an actual cable-stayed bridge is then conducted. The entire process of the structural damage and collapse are successfully simulated by the proposed method VFIFE-Fiber. This study provides a foundation for seismic damage prediction and anti-collapse seismic design for cable-stayed bridges.

High magnetoelectric tuning effect in a polymer-based magnetostrictive- piezoelectric laminate under resonance drive

A polymer-based magnetoelectric (ME) laminate was fabricated by sandwiching one layer of thickness-polarized, length-stretched polyvinylidene fluoride (PVDF) piezoelectric polymer between two layers of length-magnetized, epoxy-bonded Tb0.3Dy0.7Fe1.92 (Terfenol-D) pseudo-1–3 magnetostrictive particulate composite in the thickness direction, and its resonance ME effect was investigated, both experimentally and theoretically, as a function of magnetic bias field (HBias). The laminate showed a high ME voltage coefficient (αV) of 233 mV/Oe at the fundamental resonance frequency (fr) of 60.6 kHz under a relatively low HBias of 0.6 kOe. By controlling HBias in the range of 0.02–1.5 kOe, nonlinear tunabilities as high as 1382 and 8.6% were achieved for αV and fr, respectively, as a result of the reduced eddy-current losses and enhanced non-180° domain-wall motion-induced negative-ΔE effect in the Terfenol-D composite layers as well as the increased compliance contribution from the PVDF polymer layer to allow the ...

Experimental Study and Numerical Simulation of Partially Prefabricated Laminated Composite RC Walls

This paper presents the low-cyclic reversed tests and numerical simulation on partially prefabricated laminated composite reinforced concrete (RC) walls. The specimens include 4 typical composite walls without openings, 4 with openings, and 1 common cast-in-place RC wall. The structural behaviours including failure pattern, lateral load-top drift relationship and the in-plane horizontal load carrying capacity of the composite RC walls were compared with the common cast-in-place RC walls through the experiments. Then the finite element software ABAQUS was employed to simulate the experiment scenarios. The simulation results are consistent with the experimental results. After that, further simulation was conducted on the composite walls and the common cast-in-place wall under different axial forces. Experimental and numerical study indicates that there is no obvious difference in horizontal load carrying capacity and failure pattern between the composite walls and the common cast-in-place walls under the test axial ratios, but the composite walls are more vulnerable to failure under high axial force compared with the cast-in-place wall. Though they have many advantages in rapid construction, especially in reconstruction of the earthquake-hit areas, the laminated composite walls are not suggested to apply under high axial ratio conditions.

Strain-temperature correlation analysis of a tied arch bridge using monitoring data

For the reliable assessment of bridge health and safety conditions, it is important to distinguish the abnormal changes of bridge structural responses caused by structural damage from the normal changes due to environmental fluctuations. This paper addresses the modeling of separating temperature effect from structural strain responses of a tied arch bridge in China. The bridge has been instrumented with a long-term structural health monitoring system since 2007. One-year measurement data obtained from the strain and temperature sensors are used for this study. The correlation analysis technique is applied to quantify the effect of temperature on the strain responses. The results show that the linear regression model exhibits good capabilities for mapping the strain responses with temperature. Using this model, the temperature effect can be separated from the overall responses. The variation of the model parameters (variation rate and intercept) and the residual responses after removing the temperature effect can be used for novelty detection and overload alarming.