Modal Test and Analysis of a Bridge under the Varying Temperature Condition

2010 ◽  
Vol 456 ◽  
pp. 1-12
Author(s):  
Yang Liu
Keyword(s):  
Confidence Interval ◽  
Ambient Temperature ◽  
Dynamic Properties ◽  
Damping Ratio ◽  
Modal Parameter ◽  
Modal Parameter Identification ◽  
Modal Test ◽  
Bridge Model ◽  
Bridge Structures ◽  
Relationship Model

To consider the effect of varying temperature on dynamic properties of bridge structures, a continuous modal test for a suspender bridge was carried out. Firstly, a long-term modal test is conducted, and the first five modes (frequencies, damping ratio and modal shapes) under different temperature are identified by modal parameter identification. Secondly, the comparison between the analytical dynamic properties and measured results are analyzed, and the changing regularity of this structure under varying temperature is summarized. The results show that the frequencies of this bridge increase as the ambient temperature decrease, and that the damping ratio and modal shapes are not sensitive with the ambient temperature. Finally, the relationship model between the environmental temperature and frequencies of this bridge model is obtained by regression analysis. The confidence interval of undamaged structure is obtained, and then this confidence interval is applied to assess the condition of this bridge.

scholarly journals Noise Reduction for Modal Parameter Identification of the Measured FRFs Using the Modal Peak-Based Hankel-SVD Method

2020 ◽  
Vol 2020 ◽  
pp. 1-21
Author(s):  
Tianxu Zhu ◽  
Chaoping Zang ◽  
Gengbei Zhang
Keyword(s):  
Parameter Identification ◽  
Noise Reduction ◽  
Flat Plate ◽  
Modal Identification ◽  
Modal Parameters ◽  
Modal Parameter ◽  
Noise Elimination ◽  
Modal Parameter Identification ◽  
Modal Test ◽  
Svd Method

The measured frequency response functions (FRFs) in the modal test are usually contaminated with noise that significantly affects the modal parameter identification. In this paper, a modal peak-based Hankel-SVD (MPHSVD) method is proposed to eliminate the noise contaminated in the measured FRFs in order to improve the accuracy of the identification of modal parameters. This method is divided into four steps. Firstly, the measured FRF signal is transferred to the impulse response function (IRF), and the Hankel-SVD method that works better in the time domain rather than in the frequency domain is further applied for the decomposition of component signals. Secondly, the iteration of the component signal accumulation is conducted to select the component signals that cover the concerned modal features, but some component signals of the residue noise may also be selected. Thirdly, another iteration considering the narrow frequency bands near the modal peak frequencies is conducted to further eliminate the residue noise and get the noise-reduced FRF signal. Finally, the modal identification method is conducted on the noise-reduced FRF to extract the modal parameters. A simulation of the FRF of a flat plate artificially contaminated with the random Gaussian noise and the random harmonic noise is implemented to verify the proposed method. Afterwards, a modal test of a flat plate under the high-temperature condition was undertaken using scanning laser Doppler vibrometry (SLDV). The noise reduction and modal parameter identification were exploited to the measured FRFs. Results show that the reconstructed FRFs retained all of the modal features we concerned about after the noise elimination, and the modal parameters are precisely identified. It demonstrates the superiority and effectiveness of the approach.

Dynamic Characteristics of a Wood Frame Structure: (II) the Effect of Artificial Damage

2013 ◽  
Vol 671-674 ◽  
pp. 921-926
Author(s):  
Hai Ling Xing ◽  
Dong Sheng Yao ◽  
Song Tao Xue
Keyword(s):  
Dynamic Properties ◽  
Damping Ratio ◽  
Frame Structure ◽  
Modal Parameter ◽  
Hilbert Huang Transform ◽  
Artificial Damage ◽  
Identification Technique ◽  
Wood Frame ◽  
Frequency Changes ◽  
Vibration Tests

A full-scale, three-storey wood frame structure had been tested in-situ to investigate the changes of dynamic properties due to artificial damage. Beams and braces of the test structure were removed, to simulate damage, and then reassembled, to simulate rehabilitation. Free vibration tests were performed during every stage of the tests. The natural frequencies and damping ratios were obtained using modal parameter identification technique based on the Hilbert-Huang Transform. It is shown that, when the structure is damaged or rehabilitated, the natural frequency changes in accord with the structural stiffness in general while the damping ratio varies irregularly.

scholarly journals Active Mass Damper for Reducing Wind and Earthquake Vibrations of a Long-Period Bridge

Actuators ◽  
2020 ◽  
Vol 9 (3) ◽  
pp. 66
Author(s):  
Seongkyu Chang
Keyword(s):  
Dynamic Properties ◽  
Damping Ratio ◽  
Harmonic Load ◽  
Control Effect ◽  
Linear Quadratic ◽  
Active Mass ◽  
Long Period ◽  
Bridge Model ◽  
Mass Damper ◽  
Active Mass Damper

An active mass damper (AMD) was developed that uses a linear motor and coil spring to reduce the vertical vibration of a long-period cable-stayed bridge subjected to wind and earthquake loads. A scaled-down bridge model and AMD were fabricated, and the control effect of the AMD was investigated experimentally and analytically. The AMD was controlled via a linear quadratic Gaussian algorithm, which combines a linear quadratic regulator and Kalman filter. The dynamic properties were investigated using a 1/10 scale indoor experimental model, and the results confirmed that the measured and analytical accelerations were consistent. A vibrator was used to simulate the wind-induced vibration, and the experimental and analytical results were consistent. The proposed AMD was confirmed to damp the free vibration and harmonic load and increase the damping ratio of the bridge model from 0.17% to 9.2%. Finally, the control performance of the proposed AMD was numerically investigated with the scaled-down bridge model subjected to the El Centro and Imperial Valley-02 earthquakes. These results were compared with those of a TMD, and they confirmed that the proposed AMD could reduce excessive vertical vibrations of long-period cable-stayed bridges subjected to wind and earthquakes.

scholarly journals Application of Improved Combined Deterministic-Stochastic Subspace Algorithm in Bridge Modal Parameter Identification

2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Peng Wen ◽  
Inamullah Khan ◽  
Jie He ◽  
Qiaofeng Chen
Keyword(s):  
Parameter Identification ◽  
Clustering Algorithm ◽  
Identification Algorithm ◽  
Modal Parameter ◽  
Modal Parameter Identification ◽  
Fuzzy C Means ◽  
Subspace Algorithm ◽  
Bridge Structures ◽  
Fuzzy C Means Clustering ◽  
Online Tracking

Modal parameter identification is considered to be one of the most important tasks in structural health monitoring because it provides a reliable reference for structural vibration control, damage severity, and operational state. Moreover, at present, the combined deterministic-stochastic subspace algorithm is cogitated as one of the key algorithms in the modal parameter identification, which is why it is widely used in the modal parameter identification of bridge structures. In this paper, a novel method is proposed, which is a time-domain identification algorithm, based on sliding window-fuzzy C-means clustering algorithm-combined with deterministic-stochastic subspace identification (SC-CDSI), to achieve online intelligent tracking and identification of modal parameters for nonlinear time-varying structures. First of all, to realize the online tracking and identification process, it is necessary to divide the input and output signal of the nonlinear time-varying structure by windowing; for that, to determine the window function, window size and window step length according to the characteristics of the signal are analyzed. Secondly, in order to satisfy the intelligent identification of effective modals in stability diagram, the fuzzy C-means clustering algorithm is kept as a base, whereas frequency, damping ratio, and modal shapes serve as clustering elements, applied to fuzzy C-means clustering algorithm, and then the intelligent selection of effective modals is achieved. Finally, a shaking table test bridge is used as a modal parameter identification in lab, and its results are compared with the MIDAS finite element results. The compared results show that the proposed SC-CDSI identification algorithm can accurately achieve the intelligent identification of online tracking of the structural frequency, and the identification results are reliable to be used in real-life bridge structures.

Modal Parameter Identification of Concrete Filled Steel Tube Arch Bridge Based on Stochastic Subspace Method

2014 ◽  
Vol 919-921 ◽  
pp. 325-328 ◽  
Author(s):  
Li Xian Wang ◽  
Sheng Kui Di
Keyword(s):  
Finite Element ◽  
Parameter Identification ◽  
Model Updating ◽  
Dynamic Properties ◽  
Steel Tube ◽  
Subspace Method ◽  
Modal Parameter ◽  
Arch Bridge ◽  
Modal Parameter Identification ◽  
Finite Element Software

Based on stochastic subspace method, the natural frequency of the bridge arch rib, damping ratios and vibration mold parameter was obtained by modal parameter identification of a concrete filled steel tubular arch bridge under ambient excitation, and the Midas Civil finite element software was used to establish a computational model of the bridge. Measured results and calculated results were compared, and the reliability of the identification results have been verified, the identified dynamic properties can be served as the basis in the finite element model updating, damage detection, condition assessment and health monitoring of the bridge.

scholarly journals Modal parameters identification of bridge by improved stochastic subspace identification method with Grubbs criterion

2021 ◽  
Vol 54 (3-4) ◽  
pp. 457-464
Author(s):  
Yulin Zhou ◽  
Xulei Jiang ◽  
Mingjin Zhang ◽  
Jinxiang Zhang ◽  
Hao Sun ◽  
...  
Keyword(s):  
Wind Tunnel ◽  
Parameter Identification ◽  
Damping Ratio ◽  
Wind Tunnel Test ◽  
Modal Parameters ◽  
Subspace Identification ◽  
Identification Algorithm ◽  
Modal Parameter ◽  
Modal Parameter Identification ◽  
Stochastic Subspace Identification

In the wind tunnel test of a long-span bridge model, to ensure that the dynamic characteristics of the model can satisfy the test design requirements, it is particularly important to accurately identify the modal parameters of the model. First, the stochastic subspace identification algorithm was used to analyze the modal parameters of the model in the wind tunnel test; then, Grubbs criterion was introduced to effectively eliminate outliers in the damping ratio matrix. Stochastic subspace identification algorithm with Grubbs criterion improved the accuracy of the modal parameter identification and the ability to determine system matrix order and prevented the modal omissions caused by determining the stable condition of the damping ratio in the stability diagram. Finally, Oujiang Bridge was used as an example to verify the stochastic subspace identification algorithm with Grubbs criterion and compare with the results of the finite element method. The example shows that the improved method can be effectively applied to the modal parameter identification of bridges.

scholarly journals Instantaneous Modal Parameter Identification of Linear Time-Varying Systems Based on Chirplet Adaptive Decomposition

2019 ◽  
Vol 2019 ◽  
pp. 1-13 ◽  
Author(s):  
Jie Zhang ◽  
Zhiyu Shi
Keyword(s):  
Parameter Identification ◽  
Energy Analysis ◽  
Linear Time ◽  
Damping Ratio ◽  
Energy Concentration ◽  
Time Varying ◽  
Modal Parameter ◽  
Modal Parameter Identification ◽  
Time Frequency ◽  
Time Varying Systems

Instantaneous modal parameter identification of time-varying dynamic systems is a useful but challenging task, especially in the identification of damping ratio. This paper presents a method for modal parameter identification of linear time-varying systems by combining adaptive time-frequency decomposition and signal energy analysis. In this framework, the adaptive linear chirplet transform is applied in time-frequency analysis of acceleration response for its higher energy concentration, and the response of each mode can be adaptively decomposed via an adaptive Kalman filter. Then, the damping ratio of the time-varying systems is identified based on energy analysis of component response signal. The proposed method can not only improve the accuracy of instantaneous frequency extraction but also ensure the antinoise ability in identifying the damping ratio. The efficiency of the method is first verified through a numerical simulation of a three-degree-of-freedom time-varying structure. Then, the method is demonstrated by comparing with the traditional wavelet and time-domain peak method. The identified results illustrate that the proposed method can obtain more accurate modal parameters in low signal-to-noise ratio (SNR) scenarios.

Modal Parameter Identification of Time-Varying Systems Using the Time-Varying Multivariate Autoregressive Model

2005 ◽  
Author(s):  
Lilan Liu ◽  
Hongzhao Liu ◽  
Ziying Wu ◽  
Daning Yuan ◽  
Pengfei Li
Keyword(s):  
Parameter Identification ◽  
Linear Time ◽  
Damping Ratio ◽  
Least Square Method ◽  
Least Square ◽  
Time Varying ◽  
Recursive Least Square ◽  
Modal Parameter ◽  
Modal Parameter Identification ◽  
Multivariate Autoregressive

A new time-varying multivariate autoregressive (TVMAR) model method for modal parameter identification of linear time-varying (TV) systems with multi-output is introduced. Besides, a modified recursive least square method based on the traditional one is presented to determine the coefficient matrices of the TVMAR model. In the proposed method, multi-dimensional nonstationary response signals of the vibrating system can be processed simultaneously. Not only the TV modal frequency and damping ratio of the system, but also the changing behavior of the mode shape in the course of vibration are identified by the proposed procedure. Numerical simulations, in which a three-degree-of-freedom system with TV stiffness is respectively subjected to impulse excitation and white noise excitation, are presented. The validity and accuracy of the method are demonstrated by the good simulation results.

ANALYSIS OF DYNAMIC STRESS-STRAIN RELATIONSHIP OF LOESS

2008 ◽  
Vol 22 (31n32) ◽  
pp. 5559-5565
Author(s):  
HONGJIAN LIAO ◽  
ZHIGANG ZHANG ◽  
CHUNMING NING ◽  
JIAN LIU ◽  
LI SONG
Keyword(s):  
Residual Strain ◽  
Dynamic Stress ◽  
Dynamic Properties ◽  
Damping Ratio ◽  
Constitutive Relationship ◽  
Triaxial Tests ◽  
Stress And Strain ◽  
Test Results ◽  
Relationship Model ◽  
Strain Relationship

This paper aims to study dynamic properties of loess. This study is helpful to the subject on how to avoid or decrease the seismic disasters on loess ground. Dynamic triaxial tests are carried out with saturated remoulded soil samples taken form loess sites in Xi'an, China. Dynamic stress and strain relationship as well as the rule of the accumulated residual strain are obtained from the test results. Linear relationship between accumulated residual strain and vibration circle under constant amplitude circular loading is presented. A hypothesis about the accumulated residual strain is proposed. 1D dynamic constitutive relationship model which can well describe the real relationship between dynamic stress and strain under irregular dynamic loading is established. Numerical program with this model is developed and an example is tested. Numerical results of hysteresis loop, accumulated residual strain, amplitude of dynamic stress and damping ratio show good agreement with test results. It is indicated that the hypothesis of accumulated residual strain and the 1D dynamic constitutive relationship model can accurately simulate the dynamic triaxial tests of saturated remoulded loess.

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