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.

Identification of modal parameters from non-stationary responses of high-rise buildings

2021 ◽  
pp. 136943322110339
Author(s):  
Lunhai Zhi ◽  
Feng Hu ◽  
Qiusheng Li ◽  
Zhixiang Hu
Keyword(s):  
Damping Ratio ◽  
Modal Identification ◽  
Frame Structure ◽  
Modal Parameters ◽  
Strong Wind ◽  
Modal Parameter ◽  
Civil Structures ◽  
High Rise ◽  
Random Decrement Technique ◽  
Structural Responses

A key issue in the control, health monitoring, and condition assessment of civil structures is the estimation of structural modal parameters based on measured structural responses. However, field measurements of structural responses from civil structures under strong wind or earthquake excitations usually exhibit non-stationary feature and therefore cannot be adequately deal with by traditional modal identification methods. In this study, a novel procedure is integrated for modal parameter identification of civil structures from non-stationary structural responses on the basis of the variational mode decomposition (VMD) technique. First, the VMD algorithm is applied to decompose measured vibration signals into individual mode components. Then, the random decrement technique (RDT) is employed to obtain free vibration response of each mono component. Next, normalized Hilbert transform (NHT) is used to estimate modal natural frequency and damping ratio. The performance of the developed approach is evaluated using simulated non-stationary responses of a frame structure, and the identified results are validated. The effects of crucial factors such as levels of noise involved in structural response and data length on the modal parameter estimations are examined through detailed parametric study. Furthermore, the approach is applied to modal identification based on field measured non-stationary responses of a high-rise building during Typhoon Nida. The case study illustrates that the integrated method is an efficient tool for estimating the modal parameters of civil structures from non-stationary structural responses.

Experimental Study on Lateral Stiffness and Dynamic Properties of Steel Drive-in Storage Racks

2013 ◽  
Vol 351-352 ◽  
pp. 730-733
Author(s):  
Bo Cheng ◽  
Zhen Yu Wu
Keyword(s):  
Load Transfer ◽  
Dynamic Properties ◽  
Damping Ratio ◽  
Single Point ◽  
Lateral Stiffness ◽  
Test Results ◽  
Static Test ◽  
Vibration Tests ◽  
Storage Racks ◽  
Deformation Modes

The static and free vibration tests were carried out to investigate the initial lateral stiffness and dynamic properties of steel drive-in storage racks. The bracing configuration and friction between pallets and rail beams were taken into consideration. The static test results indicate that the tested storage racks show sideways and torsional deformation modes under the single-point horizontal force. Both top plan bracings and back spine bracings can change the load transfer through the rack framework, strengthen the initial lateral stiffness of racks, but only back spine bracings can affect the natural frequency and damping ratio of racks. The friction force between pallets and rail beams makes pallets act as links to connect adjacent rack columns, so the pallets are beneficial factors to increase the lateral stiffness of storage racks. Compared with unload racks, the natural frequencies of loaded racks are smaller.

EFFECTS OF HUMAN-STRUCTURE INTERACTIONS ON THE DYNAMIC PROPERTIES OF BUILDING FLOORS SUSCEPTIBLE TO VIBRATIONS

2019 ◽  
Vol 6 (1) ◽  
Author(s):  
Mehdi Setareh ◽  
Stephanie Renard
Keyword(s):  
Dynamic System ◽  
Dynamic Models ◽  
Dynamic Properties ◽  
Damping Ratio ◽  
Human Movements ◽  
Vibration Serviceability ◽  
Dimensional Parameters ◽  
Vibration Tests ◽  
Floor System ◽  
Two Degree Of Freedom

Excessive vibrations of building floors due to human movements have become an important vibration serviceability problem for building designers and owners. A series of vibration tests on a full-scale laboratory floor with different numbers of humans in various postures were conducted. Using this data, the dynamic properties of a two-degree-of-freedom (2-DOF) dynamic system representing groups of people in different postures were computed. A 3-DOF model representing the floor and humans was developed and its dynamic properties were defined in terms of non-dimensional parameters. The dynamic properties of the floor were measured when occupied by groups of people in different postures and compared to those predicted using the 3-DOF dynamic model considering the identified human models. The results showed that the predicted properties were within the range of those found from the measurements, which validated the identified human dynamic models. This study also showed how the presence of humans can affect the natural frequency and damping ratio of a floor system.

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 Effect of architectural components on the dynamic properties of a long-span floor system

1987 ◽  
Vol 14 (4) ◽  
pp. 461-467 ◽  
Author(s):  
G. Pernica
Keyword(s):  
Fundamental Mode ◽  
Composite Structures ◽  
Dynamic Properties ◽  
Damping Ratio ◽  
Long Span ◽  
Modal Damping Ratio ◽  
Modal Damping ◽  
Vibration Tests ◽  
Comparison Of The Results ◽  
Floor System

Vibration measurements were taken to determine the effects of architectural components on the dynamic properties (modal frequency, modal damping ratio, and mode shape) of a long-span floor system. The floor was located above a two-storey gymnasium in a recently constructed three-storey elementary school. The dynamic properties of the bare floor system were measured during the construction phase, immediately after the main structural components and the exterior masonry walls were in place. Six months later, with construction completed and the school ready for occupancy, the properties of the finished floor system, complete with internal partitions, mechanical ducts, furnishings, and carpeting, were again obtained.A comparison of the results of the two test series indicated that the dynamic properties of the floor system were altered by the addition of the architectural components. The fundamental frequency rose by 3% and the frequencies of the higher modes by 23%, even though the static load on the floor increased by about 26%. The substantial stiffening of the floor system necessary to precipitate these increases in frequency was linked to the presence of the internal partitions. A full-span partition was also found to behave as a floor support, creating an additional set of modes which were not previously present. Except for the fundamental mode, damping ratios increased by about 2% of critical, from 1.5% to 3.5% of critical. For the fundamental mode, the negligible increase in damping from 4.1 to 4.2% of critical could not be explained. Key words: floors, composite structures, vibration tests, spectrum analysis, resonant frequency, vibration damping.

Effect of Crack Orientation on Laminated CFRP Composites Using Vibration and Numerical Analysis

2021 ◽  
Vol 79 (11) ◽  
pp. 1081-1093
Author(s):  
Essam Moustafa ◽  
Khalid Almitani ◽  
Hossameldin Hussein
Keyword(s):  
Composite Structures ◽  
Dynamic Properties ◽  
Damping Ratio ◽  
Composite Plates ◽  
Mode Shapes ◽  
Crack Orientation ◽  
Test Plate ◽  
Cfrp Composites ◽  
Cfrp Composite ◽  
Vibration Tests

Crack orientation, a critical parameter, significantly affects the dynamic properties of composite structures. Experimental free vibration tests were conducted on carbon fiber–reinforced polymer (CFRP) composite plates at room temperature with different crack orientations. Dynamic properties such as damping ratio, natural frequency, and storage modulus were measured using a four-channel dynamic pulse analyzer. Multi-sensors were mounted on the test plate to pick up the vibration signals. Experimental modal analysis was performed to identify the first three mode shapes of the defective plates. A numerical model using ANSYS software was developed via parametric investigation to predict the correlation between crack orientation and resonant frequencies with corresponding mode shapes. The orientation of the introduced cracks had a significant effect on the dynamic properties of CFRP composites. Vertical cracks had the most significant influence on the eigenvalues of the mode shape frequencies. Furthermore, the damping ratio was an effective method to detect the cracks in CFRP composites.

scholarly journals Evaluation of Dynamic Properties of Sodium-Alginate-Reinforced Soil Using A Resonant-Column Test

Materials ◽  
2021 ◽  
Vol 14 (11) ◽  
pp. 2743
Author(s):  
Seongnoh Ahn ◽  
Jae-Eun Ryou ◽  
Kwangkuk Ahn ◽  
Changho Lee ◽  
Jun-Dae Lee ◽  
...  
Keyword(s):  
Shear Modulus ◽  
Sodium Alginate ◽  
Shear Failure ◽  
Dynamic Properties ◽  
Damping Ratio ◽  
Reinforced Soil ◽  
Resonant Column ◽  
Column Test ◽  
Alginate Solution ◽  
Resonant Column Test

Ground reinforcement is a method used to reduce the damage caused by earthquakes. Usually, cement-based reinforcement methods are used because they are inexpensive and show excellent performance. Recently, however, reinforcement methods using eco-friendly materials have been proposed due to environmental issues. In this study, the cement reinforcement method and the biopolymer reinforcement method using sodium alginate were compared. The dynamic properties of the reinforced ground, including shear modulus and damping ratio, were measured through a resonant-column test. Also, the viscosity of sodium alginate solution, which is a non-Newtonian fluid, was also explored and found to increase with concentration. The maximum shear modulus and minimum damping ratio increased, and the linear range of the shear modulus curve decreased, when cement and sodium alginate solution were mixed. Addition of biopolymer showed similar reinforcing effect in a lesser amount of additive compared to the cement-reinforced ground, but the effect decreased above a certain viscosity because the biopolymer solution was not homogeneously distributed. This was examined through a shear-failure-mode test.

scholarly journals Identification of Dynamic Parameters of Pedestrian Walking Model Based on a Coupled Pedestrian–Structure System

2021 ◽  
Vol 11 (14) ◽  
pp. 6407
Author(s):  
Huiqi Liang ◽  
Wenbo Xie ◽  
Peizi Wei ◽  
Dehao Ai ◽  
Zhiqiang Zhang
Keyword(s):  
Negative Correlation ◽  
Dynamic Properties ◽  
Damping Ratio ◽  
Field Testing ◽  
The Body ◽  
Structural Vibration ◽  
Pedestrian Dynamics ◽  
Structure Interaction ◽  
Mass Spring ◽  
Stiffness And Damping

As human occupancy has an enormous effect on the dynamics of light, flexible, large-span, low-damping structures, which are sensitive to human-induced vibrations, it is essential to investigate the effects of pedestrian–structure interaction. The single-degree-of-freedom (SDOF) mass–spring–damping (MSD) model, the simplest dynamical model that considers how pedestrian mass, stiffness and damping impact the dynamic properties of structures, is widely used in civil engineering. With field testing methods and the SDOF MSD model, this study obtained pedestrian dynamics parameters from measured data of the properties of both empty structures and structures with pedestrian occupancy. The parameters identification procedure involved individuals at four walking frequencies. Body frequency is positively correlated to the walking frequency, while a negative correlation is observed between the body damping ratio and the walking frequency. The test results further show a negative correlation between the pedestrian’s frequency and his/her weight, but no significant correlation exists between one’s damping ratio and weight. The findings provide a reference for structural vibration serviceability assessments that would consider pedestrian–structure interaction effects.

scholarly journals Multi-Scale Study of The Small-Strain Damping Ratio of Fiber-Sand Composites

Polymers ◽  
2021 ◽  
Vol 13 (15) ◽  
pp. 2476
Author(s):  
Haiwen Li ◽  
Sathwik S. Kasyap ◽  
Kostas Senetakis
Keyword(s):  
Dynamic Properties ◽  
Wide Spectrum ◽  
Damping Ratio ◽  
Polypropylene Fiber ◽  
Small Strain ◽  
Treatment Method ◽  
Fiber Content ◽  
Polypropylene Fibers ◽  
Test Results ◽  
Fiber Reinforced

The use of polypropylene fibers as a geosynthetic in infrastructures is a promising ground treatment method with applications in the enhancement of the bearing capacity of foundations, slope rehabilitation, strengthening of backfills, as well as the improvement of the seismic behavior of geo-systems. Despite the large number of studies published in the literature investigating the properties of fiber-reinforced soils, less attention has been given in the evaluation of the dynamic properties of these composites, especially in examining damping characteristics and the influence of fiber inclusion and content. In the present study, the effect of polypropylene fiber inclusion on the small-strain damping ratio of sands with different gradations and various particle shapes was investigated through resonant column (macroscopic) experiments. The macroscopic test results suggested that the damping ratio of the mixtures tended to increase with increasing fiber content. Accordingly, a new expression was proposed which considers the influence of fiber content in the estimation of the small-strain damping of polypropylene fiber-sand mixtures and it can be complementary of damping modeling from small-to-medium strains based on previously developed expressions in the regime of medium strains. Additional insights were attempted to be obtained on the energy dissipation and contribution of fibers of these composite materials by performing grain-scale tests which further supported the macroscopic experimental test results. It was also attempted to interpret, based on the grain-scale tests results, the influence of fiber inclusion in a wide spectrum of properties for fiber-reinforced sands providing some general inferences on the contribution of polypropylene fibers on the constitutive behavior of granular materials.

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