Application of Modal Identification Methods to Spatial Structure Using Field Measurement Data

2009 ◽  
Vol 131 (3) ◽  
Author(s):  
Wei Liu ◽  
Wei-cheng Gao ◽  
Yi Sun
Keyword(s):  
Finite Element ◽  
System Identification ◽  
Spatial Structure ◽  
Measurement Data ◽  
Element Model ◽  
Modal Identification ◽  
Modal Parameters ◽  
Identification Methods ◽  
Output Only ◽  
Leakage Error

Modal identification with output-only measurements plays a key role in vibration-based damage detection, model updating, and structural health monitoring in civil engineering. This paper addresses the application of modal identification method to a triangle steel tube truss natatorium using the field measurement data. To obtain dynamic characteristics of the spatial structure, four different output-only system identification methods are employed. They are natural excitation technique–eigensystem realization algorithm, data-driven stochastic subspace identification method, frequency-domain decomposition/frequency-spatial domain decomposition method, and half spectra/rational fractional orthogonal polynomial method. First an analytical modal analysis was performed on the three-dimensional finite element model according to the factual layout design to obtain the calculated frequencies and mode shapes. Then the whole procedure of the field vibration tests on the natatorium was presented. Finally, practical issues and efficiency of the four output-only modal identification techniques are investigated, and compared with the results from a finite element model. The system identification results demonstrate that both methods can provide reliable information on dynamic characteristics of the spatial structure. The frequency-domain methods, however, can quickly identify the modal parameters, but the leakage error introduced by power-spectral density estimation is existent due to the limited length of data. And the time-domain methods can avoid the leakage error, but the computational modes and the computational cost are the main two drawbacks in application. The conclusion is that several system identification methods should be consulted to ensure the accuracy of the estimated modal parameters.

Weak-Points Diagnosis and Optimization of Shield Machine Cutter Tool Based on Characteristic Parameters

2016 ◽  
Vol 693 ◽  
pp. 1479-1485 ◽  
Author(s):  
Jian Zhao ◽  
Xue Wu Hong ◽  
Ming Yu ◽  
Zhi Peng Gao ◽  
Wen Jin Wang
Keyword(s):  
Finite Element ◽  
Dynamic Characteristics ◽  
Optimization Design ◽  
Weak Link ◽  
Human Life ◽  
Element Model ◽  
Ring Structure ◽  
Modal Parameters ◽  
Underground Engineering ◽  
Shield Machine

Shield machine plays an indispensable role in the mining, transportation, underground engineering, hydraulic engineering and municipal construction. Shield cutters of shield construction process often appears serious deformation, damage that leads to engineering accident, or even a threat to human life and safety. In order to provide high precise data for shield machine cutter tool dynamic modification and to diagnose the shield machine cutter tool fault, the dynamic characteristic of the shield machine cutter tool system, which is the main component of a shield machine cutter tool, has to be obtained precisely. The compute modal parameters identification method base on the finite element method is proposed to identify the modal parameters of the shield machine cutter tool. By means of Solidwords software, the knife ring structure of the shield machine tool and the tool is designed; then build the tool the finite element model, modal analysis, obtained the dynamic characteristics, and find out the weak link, put forward the improvement measures and prolong its life. Therefore, the study on dynamic characteristics of shield machine cutter, for the optimization design of domestic tool, has an important significance improve tool life.

scholarly journals Case Study and Numerical Simulation of Excavation beneath Existing Buildings

2020 ◽  
Vol 2020 ◽  
pp. 1-14
Author(s):  
Hua-feng Shan ◽  
Shao-heng He ◽  
Yu-hua Lu ◽  
Wei-jian Jiang
Keyword(s):  
Finite Element ◽  
Case Reports ◽  
Measurement Data ◽  
Element Model ◽  
Existing Buildings ◽  
Related Case ◽  
Finite Element Software ◽  
Curing Period ◽  
Cutting Sequences ◽  
Bearing Behavior

Excavation beneath existing buildings may cause the superstructure to tilt and crack, which seriously affects the normal use of the superstructure. Due to the new working conditions of excavation beneath existing buildings, related case reports are rare and limited. In the case of No. 3 section basement construction project of Ganshuixiang, we monitored the excavation construction by burying test instruments at the designated location. Afterwards, Plaxis 3D finite element software was used to establish an underpinning pile-cap-excavation model, which can analyze the influence of different pile cutting sequences on the bearing behavior of new basement structural pillars. By comparing the in situ measurement data with the finite element model, it can be concluded that when the excavation depth rises, the axial force of the underpinning pile gradually increases, and the pile skin friction is slowly exerted from top to bottom. Different cutting sequences will influence the bearing behavior of the structural pillar. Moreover, the pile cutting process also significantly impacts its bearing behavior and the settlement behavior of the superstructure. Compared with the clockwise pile cutting sequence, the symmetrical pile cutting is more advantageous. In the whole process of the storey adding and reconstruction, the superstructure settlement is related to the working condition of digging and adding layers. In the stage from soil excavation to the concrete curing period of the structural pillar, it increases slowly with time and tends to be stable in the concrete curing period. However, in the pile cutting stage, the superstructure settlement increases sharply, and after pile cutting, it becomes stable.

Photogrammetry-based structural damage detection by tracking a visible laser line

2019 ◽  
Vol 19 (1) ◽  
pp. 322-336 ◽  
Author(s):  
Yongfeng Xu
Keyword(s):  
Finite Element ◽  
Damage Detection ◽  
Structural Damage ◽  
Detection Method ◽  
Element Model ◽  
Target Line ◽  
Laser Line ◽  
Modal Parameters ◽  
Structural Damage Detection ◽  
Visible Laser

Research works on photogrammetry have received tremendous attention in the past few decades. One advantage of photogrammetry is that it can measure displacement and deformation of a structure in a fully non-contact, full-field manner. As a non-destructive evaluation method, photogrammetry can be used to detect structural damage by identifying local anomalies in measured deformation of a structure. Numerous methods have been proposed to measure deformations by tracking exterior features of structures, assuming that the features can be consistently identified and tracked on sequences of digital images captured by cameras. Such feature-tracking methods can fail if the features do not exist on captured images. One feasible solution to the potential failure is to artificially add exterior features to structures. However, painting and mounting such features can introduce unwanted permanent surficial modifications, mass loads, and stiffness changes to structures. In this article, a photogrammetry-based structural damage detection method is developed, where a visible laser line is projected to a surface of a structure, serving as an exterior feature to be tracked; the projected laser line is massless and its existence is temporary. A laser-line-tracking technique is proposed to track the projected laser line on captured digital images. Modal parameters of a target line corresponding to the projected laser line can be estimated by conducting experimental modal analysis. By identifying anomalies in curvature mode shapes of the target line and mapping the anomalies to the projected laser line, structural damage can be detected with identified positions and sizes. An experimental investigation of the damage detection method was conducted on a damaged beam. Modal parameters of a target line corresponding to a projected laser line were estimated, which compared well with those from a finite element model of the damaged beam. Experimental damage detection results were validated by numerical ones from the finite element model.

Damage detection based on system identification of concrete dams using an extended finite element–wavelet transform coupled procedure

2017 ◽  
Vol 24 (18) ◽  
pp. 4226-4246 ◽  
Author(s):  
Sajjad Pirboudaghi ◽  
Reza Tarinejad ◽  
Mohammad Taghi Alami
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Wavelet Transform ◽  
System Identification ◽  
Damage Detection ◽  
Cohesive Crack ◽  
Modal Parameters ◽  
Concrete Dams ◽  
Extended Finite Element ◽  
Element Method

The aim of the present study is to propose a procedure for seismic cracking identification of concrete dams using a coupling of the extended finite element method (XFEM) based on cohesive crack segments (XFEM-COH) and continuous wavelet transform (CWT). First, the dam is numerically modeled using the traditional finite element method (FEM). Then, cracking capability is added to the dam structure by applying the XFEM-COH for concrete material. The results of both the methods under the seismic excitation have been compared and identified to damage detection purposes. In spite of predefined damage in some of the structural health monitoring (SHM) techniques, there is an advantage in the XFEM model where the whole dam structure is potentially under damage risk without initial crack, and may not crack at all. Finally, in order to evaluate any change in the system, that is, specification of any probable crack effects and nonlinear behavior, the structural modal parameters and their variation have been investigated using system identification based on the CWT. The results show that the extended finite element–wavelet transform procedure has high ability for the online SHM of concrete dams that by analysis of its results, the history of physical changes, cracking initiation time, and exact damage localization have been performed from comparing the intact (FEM) and damaged (XFEM) modal parameters of the structural response. In addition, any small change in the system is observable while the final crack profile and performance simulation of the dam body under strong seismic excitations have obtained.

Study on the Finite Element Strain Simulation Model Updating Method Based on the Real Measurement Data

2013 ◽  
Vol 444-445 ◽  
pp. 1132-1139
Author(s):  
Li Feng Xiao ◽  
Ran Duan ◽  
Hui Tian
Keyword(s):  
Finite Element ◽  
Simulation Model ◽  
Model Updating ◽  
Measurement Data ◽  
Estimation Method ◽  
Element Model ◽  
Boundary Region ◽  
Strain Data ◽  
Before And After ◽  
Kriging Estimation

When using electrometric method to measure the static strain of a structure, the results are often accurate, but the number of measuring points is limited; when using the finite element method to model and analyze the practical structures, there often exist many assumptions of uncertain factors, so the accuracy of simulation results is poor, but the strain values of all the nodes in the grid of simulation structure are available, so the number of measuring points is large. In view of this situation, this paper applied Bayes-Kriging estimation method through the measurement strain data to update the strain on the surface of finite element strain simulation model. We applied the measurement strain data at different stages of the fatigue process to update finite element model. With the comparison of the strain data between before-and after-updating, we can find that at the boundary region and fatigue crack extending direction, the updating result is inaccurate, but the updating effect is good at other position. This method can improve the accuracy of these positions' strain value and make the strain value closer to the actual strain value.

An Analysis on the Effect of External Shock Loads on Building Structure Vibration

2014 ◽  
Vol 513-517 ◽  
pp. 4135-4138
Author(s):  
Jian Wan
Keyword(s):  
Finite Element ◽  
Spatial Structure ◽  
Vibration Analysis ◽  
Element Model ◽  
Building Structure ◽  
Analysis Model ◽  
Shock Loads ◽  
Nodal Displacement ◽  
Structure Vibration ◽  
Elastic Mechanics

This paper studies how the external shock loads induces vibration, and proposes a method to analyze the effect of external shock loads on building structure vibration. On basis of elastic mechanics and dynamics theory, the method calculates pressure load on each bearing node of the building produced by finite element model in accordance with the nodal displacement equivalent principle, and takes the load as excitation to study vibration of the building structure. The accuracy of the analytical method is verified by comparing with classical theory and the analysis' results of other scholars. Experiments show that the vibration analysis model can efficiently perform analysis of vibration induced by uncoupled external shock for building with complex spatial structure.

A Method to Determine the Boundary Conditions of the Finite Element Model of a Slender Beam Using Measured Modal Parameters

1996 ◽  
Vol 118 (3) ◽  
pp. 474-478 ◽  
Author(s):  
Wang Fengquan ◽  
Chen Shiyu
Keyword(s):  
Finite Element ◽  
Boundary Conditions ◽  
Finite Element Model ◽  
Interpolation Method ◽  
Element Model ◽  
Accurate Method ◽  
Modal Parameters ◽  
Computation Method ◽  
Modal Parameter ◽  
The Finite Element Model

In this paper, a method used to determine the boundary conditions of the Finite Element Model of a slender beam with measured structure modal parameters is presented. On deriving the method, the finite element model theory for dynamic calculating is used. Combined with the modal parameters from experiment, an FEM-modal parameter equation to determine the boundary conditions is put forward. For solving the equation, three methods are given. The first is the accurate method. The second is the full mode computation method by means of generalized inverse matrix. The third is the interpolation method of frequency. A numerical simulation with computer is given and the results of calculation fully verify the effectiveness of the method offered and also verify that the accuracy of the method is satisfying. Finally, an applied example is given and the results of calculation fully verify the effectiveness of the method offered.

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