scholarly journals Experimental and Analytical Study on the Vibration Performance of U-Shaped Steel-Concrete Composite Hollow Waffle Slab

2020 ◽  
Vol 2020 ◽  
pp. 1-15 ◽  
Author(s):  
Xi Zhang ◽  
Qiming Wang ◽  
Yousan Wang ◽  
Qing Li
Keyword(s):  
Damping Ratio ◽  
Low Frequency ◽  
Field Testing ◽  
Mode Shapes ◽  
Large Span ◽  
Human Perceptions ◽  
Vibration Responses ◽  
Activity Types ◽  
Floor System ◽  
Vibration Performance

The large-span floor system being lightweight with low frequency and low damping is prone to suffer severe vibration under human excitations. In this research, the vibration performance of an innovative large-span U-shaped steel-concrete composite hollow waffle (CHW) slab was studied based on field testing and theoretical analysis. First, the modal properties of CHW slab including mode shapes, frequencies, and damping ratio were captured by on-site tests and validated by the finite element method, indicating the CHW slab is a low-frequency floor system with a low damping ratio. Second, the vibration responses of CHW slab under heel-drop and jumping excitations were studied considering the impacts of spatial position, tester number, and activity types. Third, the CHW slab shows excellent vibration serviceability proved by the frequency, accelerations, and human perceptions threshold with the current codes. Meanwhile, the paper gives appropriate threshold values for the CHW slab under impulsive excitation. Finally, the natural frequency formula for the CHW slab derived by the Rayleigh–Ritz energy method agrees well with the measurements.

Vibration of a U-shaped steel–concrete composite hollow waffle floor under human-induced excitations

2020 ◽  
Vol 23 (14) ◽  
pp. 2996-3008
Author(s):  
Xi Zhang ◽  
Qing Li ◽  
Yousan Wang ◽  
Qiming Wang
Keyword(s):  
Plate Theory ◽  
Experimental Testing ◽  
Damping Ratio ◽  
Low Frequency ◽  
Threshold Values ◽  
Thin Plate Theory ◽  
Orthotropic Thin Plate ◽  
Floor System ◽  
Vibration Performance ◽  
Position Group

The U-shaped steel–concrete composite hollow waffle floor is an innovative slender large-span floor system, where severe vibration may occur under human-induced excitations. In this research, a theoretical analysis and experimental testing are performed to explore the vibration behaviour of the composite hollow waffle floor. First, the natural frequency formula is proposed based on orthotropic thin plate theory, and the main rigidity calculation for the composite hollow waffle floor is given. Second, the mode shape, frequency and damping ratio of the composite hollow waffle floor are captured by on-site tests and validated by analytical and numerical methods, indicating that the floor has a low-frequency with a low damping ratio. Third, the vibration response of the composite hollow waffle floor is obtained by walking and running tests considering the influence of the frequency, spatial position, group size and route; in addition, the relationships between the values involved in the vibration evaluation are discussed. Finally, the composite hollow waffle floor presents satisfactory vibration performance evaluated by the threshold values among the current codes.

scholarly journals Spatially Resolved Experimental Modal Analysis on High-Speed Composite Rotors Using a Non-Contact, Non-Rotating Sensor

Sensors ◽  
2021 ◽  
Vol 21 (14) ◽  
pp. 4705
Author(s):  
Julian Lich ◽  
Tino Wollmann ◽  
Angelos Filippatos ◽  
Maik Gude ◽  
Juergen Czarske ◽  
...  
Keyword(s):  
High Speed ◽  
Natural Frequencies ◽  
Mode Shapes ◽  
Fiber Reinforced ◽  
Structural Dynamic ◽  
Spatially Resolved ◽  
Glass Fiber Reinforced ◽  
Vibration Responses ◽  
And Performance

Due to their lightweight properties, fiber-reinforced composites are well suited for large and fast rotating structures, such as fan blades in turbomachines. To investigate rotor safety and performance, in situ measurements of the structural dynamic behaviour must be performed during rotating conditions. An approach to measuring spatially resolved vibration responses of a rotating structure with a non-contact, non-rotating sensor is investigated here. The resulting spectra can be assigned to specific locations on the structure and have similar properties to the spectra measured with co-rotating sensors, such as strain gauges. The sampling frequency is increased by performing consecutive measurements with a constant excitation function and varying time delays. The method allows for a paradigm shift to unambiguous identification of natural frequencies and mode shapes with arbitrary rotor shapes and excitation functions without the need for co-rotating sensors. Deflection measurements on a glass fiber-reinforced polymer disk were performed with a diffraction grating-based sensor system at 40 measurement points with an uncertainty below 15 μrad and a commercial triangulation sensor at 200 measurement points at surface speeds up to 300 m/s. A rotation-induced increase of two natural frequencies was measured, and their mode shapes were derived at the corresponding rotational speeds. A strain gauge was used for validation.

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.

Review of piezoelectric impedance based structural health monitoring: Physics-based and data-driven methods

2021 ◽  
pp. 136943322110384
Author(s):  
Xingyu Fan ◽  
Jun Li ◽  
Hong Hao
Keyword(s):  
Structural Health Monitoring ◽  
Health Monitoring ◽  
Structural Damage ◽  
Low Frequency ◽  
Data Driven ◽  
Mode Shapes ◽  
Monitoring Methods ◽  
Destructive Testing ◽  
Electromechanical Impedance ◽  
Structural Health

Vibration based structural health monitoring methods are usually dependent on the first several orders of modal information, such as natural frequencies, mode shapes and the related derived features. These information are usually in a low frequency range. These global vibration characteristics may not be sufficiently sensitive to minor structural damage. The alternative non-destructive testing method using piezoelectric transducers, called as electromechanical impedance (EMI) technique, has been developed for more than two decades. Numerous studies on the EMI based structural health monitoring have been carried out based on representing impedance signatures in frequency domain by statistical indicators, which can be used for damage detection. On the other hand, damage quantification and localization remain a great challenge for EMI based methods. Physics-based EMI methods have been developed for quantifying the structural damage, by using the impedance responses and an accurate numerical model. This article provides a comprehensive review of the exciting researches and sorts out these approaches into two categories: data-driven based and physics-based EMI techniques. The merits and limitations of these methods are discussed. In addition, practical issues and research gaps for EMI based structural health monitoring methods are summarized.

Free Vibration Analysis of a Carbon Nanotube Reinforced Composite Beam

2014 ◽  
Vol 592-594 ◽  
pp. 2041-2045 ◽  
Author(s):  
B. Naresh ◽  
A. Ananda Babu ◽  
P. Edwin Sudhagar ◽  
A. Anisa Thaslim ◽  
R. Vasudevan
Keyword(s):  
Carbon Nanotube ◽  
Free Vibration ◽  
Composite Beam ◽  
Natural Frequencies ◽  
Equations Of Motion ◽  
Free Vibration Analysis ◽  
Mode Shapes ◽  
Element Formulation ◽  
Reinforced Composite ◽  
Vibration Responses

In this study, free vibration responses of a carbon nanotube reinforced composite beam are investigated. The governing differential equations of motion of a carbon nanotube (CNT) reinforced composite beam are presented in finite element formulation. The validity of the developed formulation is demonstrated by comparing the natural frequencies evaluated using present FEM with those of available literature. Various parametric studies are also performed to investigate the effect of aspect ratio and percentage of CNT content and boundary conditions on natural frequencies and mode shapes of a carbon nanotube reinforced composite beam. It is shown that the addition of carbon nanotube in fiber reinforced composite beam increases the stiffness of the structure and consequently increases the natural frequencies and alter the mode shapes.

scholarly journals Long-Term Vibration Monitoring of the Effects of Temperature and Humidity on PC Girders with and without Fly Ash considering ASR Deterioration

2017 ◽  
Vol 2017 ◽  
pp. 1-23
Author(s):  
Tuan Minh Ha ◽  
Saiji Fukada ◽  
Kazuyuki Torii
Keyword(s):  
Fly Ash ◽  
Prestressed Concrete ◽  
Weather Conditions ◽  
Element Model ◽  
Vibration Monitoring ◽  
Mode Shapes ◽  
Numerical Verification ◽  
Evaluation Procedures ◽  
Temperature And Humidity ◽  
Vibration Responses

Structural responses have been used as inputs in the evaluation procedures of civil structures for years. Apart from the degradation of a structure itself, changes in the environmental conditions affect its characteristics. For adequate maintenance, it is necessary to quantify the environment-induced changes and discriminate them from the effects due to damage. This study investigates the variation in the vibration responses of prestressed concrete (PC) girders, which were deteriorated because of the alkali–silica reaction (ASR), concerning ambient temperature and humidity. Three PC girders were exposed to outdoor weather conditions outside the laboratory, one of which had a selected amount of fly ash in its mixture to mitigate the ASR. The girders were periodically vibration tested for one and a half years. It was found that when the temperature and humidity increased, the frequencies and damping ratios decreased in proportion. No apparent variation in the mode shapes could be identified. A finite element model was proposed for numerical verification, the results of which were in good agreement with the measured changes in the natural frequencies. Moreover, the different dynamic performances of the three specimens indicated that the fly ash significantly affected the vibrations of the PC girders under ASR deterioration.

scholarly journals A Comparison on Numerical Simulation Models for Vibrational Performances of the Wood Truss Joist Floor System

2021 ◽  
Vol 2021 ◽  
pp. 1-18
Author(s):  
Yinlan Shen ◽  
Haibin Zhou ◽  
Shuo Xue ◽  
Jinchuan Zhang
Keyword(s):  
Simulation Models ◽  
Metal Plate ◽  
Modeling Methods ◽  
Time Period ◽  
Long Time ◽  
Flexible Metal ◽  
Plate Connections ◽  
Simplified Modeling ◽  
Floor System ◽  
Vibration Performance

Wood truss joist floors are increasingly used to replace traditional solid timber joist floors in low-rise timber houses. An understanding of the vibration performance of wood truss joist floors is critical for the design and serviceability of the floors. It is difficult to model wood truss joist floors accurately because of the complicated boundary conditions and numerous sophisticated flexible connections. This paper discusses three simplified modeling methods for the wood truss joist floor system. The modeling results were validated by a series of static deflection tests and vibration modes and frequencies tests of a full-size floor. And predictive analysis of human-induced vibration of the floor was also conducted. The vibration characteristics of the wood truss joist floor were investigated. The examination of the applicability of these modeling methods was provided. The results indicate that the point loading deflection more easily affects the deflection of the adjacent joist. However, the deflection influence on other joists that are three spaces away is minimal. Walking on the wood truss joist floor produces steep vibration acceleration fluctuations at the floor center for a relatively long time period. The sheathing-to-joist connections and the metal plate connections of the joists have significant influences on the vibration response of the wood truss joist floor. The modeling method, which considers the flexible metal plate connections and flexible sheathing-to-joist connections, performs best for predicting the vibration performance of the floor.

Nonlinear Combination Resonances in Cantilever Composite Plates

1995 ◽  
Author(s):  
Kyoyul Oh ◽  
Ali H. Nayfeh
Keyword(s):  
Natural Frequencies ◽  
Excitation Frequency ◽  
Power Spectra ◽  
Low Frequency ◽  
Composite Plates ◽  
High Amplitude ◽  
Mode Shapes ◽  
Laser Vibrometer ◽  
Combination Resonance ◽  
Response Curves

Abstract We experimentally investigated nonlinear combination resonances in a graphite-epoxy cantilever plate having the configuration (–75/75/75/ – 75/75/ – 75)s. As a first step, we compared the natural frequencies and mode shapes obtained from the finite-element and experimental modal analyses. The largest difference in the obtained frequencies was 2.6%. Then, we transversely excited the plate and obtained force-response and frequency-response curves, which were used to characterize the plate dynamics. We acquired time-domain data for specific input conditions using an A/D card and used them to generate time traces, power spectra, pseudo-state portraits, and Poincaré maps. The data were obtained with an accelerometer monitoring the excitation and a laser vibrometer monitoring the plate response. We observed the external combination resonance Ω≈12(ω2+ω5) and the internal combination resonance Ω≈ω8≈12(ω2+ω13), where the ωi are the natural frequencies of the plate and Ω is the excitation frequency. The results show that a low-amplitude high-frequency excitation can produce a high-amplitude low-frequency motion.

Fluid-Elastic Instability of Rotated Square Array U-Tubes in Air-Water Flow

2009 ◽  
Vol 131 (4) ◽  
Author(s):  
In-Cheol Chu ◽  
Heung June Chung ◽  
Chang Hee Lee
Keyword(s):  
Tube Bundle ◽  
Damping Ratio ◽  
Elastic Instability ◽  
Two Phase ◽  
Instability Constant ◽  
Out Of Plane ◽  
Vibration Responses ◽  
Mode Vibration ◽  
Square Array ◽  
Side Flow

Fluid-elastic instability characteristics of a U-tube bundle were experimentally investigated in air-water two-phase flow. A total of 39 U-tubes were arranged in a rotated square array with a pitch-to-diameter ratio of 1.633. Vibration responses of four U-tubes were measured with three-axis accelerometers. Two sets of experiments were performed to investigate the onset of fluid-elastic instability, and the damping and hydrodynamic mass of the U-tube. The experiments were performed for a void fraction of 70–95%. Fluid-elastic instability was clearly observed in an out-of-plane mode vibration. The effect of a primary side flow on the vibration of U-tube was investigated separately. The damping ratio of the present U-tube was higher than the damping ratio of the cantilever tubes in the literature. The hydrodynamic mass of the U-tube was generally in accordance with the hydrodynamic mass of the cantilever tubes in the literature. The instability constant (K) of the Connors equation was assessed with a simplified effective gap velocity, and the fluid-elastic instability constant was 8.5.

Analysis of Low Frequency Oscillation in Interconnected Power System under Hedge Operation Mode

2014 ◽  
Vol 536-537 ◽  
pp. 1542-1546
Author(s):  
Xun Gao ◽  
Jie Meng ◽  
Yi Qun Li ◽  
Ying Wang ◽  
Wen Chao Zhang
Keyword(s):  
Power System ◽  
Power Flow ◽  
Power Grid ◽  
Damping Ratio ◽  
Operation Mode ◽  
Oscillation Mode ◽  
Low Frequency ◽  
Operating Mode ◽  
Low Frequency Oscillation ◽  
Interconnected Power System

A phenomenon that the damping ratio will decrease when the power flows from both sides to the primary power grid is summarized and analyzed in the paper. Based on analysis of the damping ratio change of West Inner Mongolia-Shandong oscillation under the sequential operation mode and the hedge operation mode, a three-machine equivalent system is established to study edge to edge (ETE) oscillation mode under hedge operating mode of the power system. The influence of magnitudes and trends of power flow on damping ratio is analyzed, and the reason that why damping ratios decreases when both sides send power to the mid-side power grid is explained.

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