scholarly journals Investigation of Dynamic Responses and Vibration Serviceability of Temporary Grandstands by a 3 DOF Interaction Model due to Swaying Motion

2022 ◽  
Vol 2022 ◽  
pp. 1-32
Author(s):  
Jian Yuan ◽  
Suhui Yu ◽  
Cong Liu ◽  
Chengqiang Gao ◽  
Wei Wang ◽  
...  
Keyword(s):  
Damping Ratio ◽  
Force Plate ◽  
Interaction Model ◽  
Reference Value ◽  
Experimental Results ◽  
Shaking Table ◽  
Dynamic Responses ◽  
Random Waves ◽  
Lateral Direction ◽  
Structural Dynamic

Excessive vibration of temporary grandstand by the crowd has lateral rhythmic motions, which attracted increasing attention in the recent years. This paper focuses on experiments where a temporary grandstand occupied by 20 participants is oscillated by a shaking table with a series of random waves and the crowd-induced rhythmic swaying motions at lateral direction, respectively. The dynamic forces that were induced by participants who have swayed at 0.5–1.8 Hz are recorded by a tri-axial human biomechanics force plate. A new relationship between the annoyance rate and structural acceleration at logarithmic coordinate is investigated and proposed, and the swaying load model is given. Based on these experimental results, a simplified three-degree-of-freedom lumped dynamic model of the joint human–structure system is reinterpreted. Afterwards, combined with a feasible range of crowd/structural dynamic parameters, a series of interaction models are analyzed, the vibration dose value (VDV) of the structure is obtained and discussed, and the notable parameters for interaction model are predicted. The experimental results show that the lateral serviceability limit is 1.29 m/s1.75 and the upper boundary is 2.32 m/s1.75. The dynamic response of model indicated that the VDV of structure will be decreased with increasing the mass of static crowd and damping ratio of the dynamic crowd. The max response of the model is α ≤ 0.6, f2 = 1.8 Hz or α > 0.6, f2 = 1.5 Hz or f1 = 2.5–3.5 Hz. It may be used as a reference value in vibration safety and serviceability assessment of TDGs, to estimate realistically the vibration response on the occasions when the crowds are swaying.

scholarly journals THE DYNAMIC PARAMETERS OF PASSIVE HUMAN AT TEMPORARY DEMOUNTABLE GRANDSTANDS DURING EXPOSURE TO LATERAL VIBRATION

2018 ◽  
Vol 24 (4) ◽  
pp. 265-283 ◽  
Author(s):  
Jian Yuan ◽  
Lin He ◽  
Feng Fan ◽  
Cong Liu
Keyword(s):  
Natural Frequency ◽  
Dynamic Properties ◽  
Damping Ratio ◽  
Reference Value ◽  
Shaking Table ◽  
Model Parameters ◽  
Dynamic Parameters ◽  
Random Waves ◽  
Mass Ratio ◽  
Dynamic Features

Modelling the interaction between crowds and temporary demountable grandstands with identifying the human dynamic properties are challenges for structure optimal design. In this paper, for investigating and understanding the human and structural lateral dynamic features. A demountable grandstand was tested to obtain its model parameters firstly. Then it is tested at amplitudes between 0.16 m/s2 to 1.54 m/s2 with 75 random waves through a shaking table when occupied by twenty persons. Afterword a simplified two-degree of freedom lumped dynamic model of the joint human-structure system is reinterpreted. Utilizing the state-space model, the passive crowd dynamic parameters are obtained, based on root mean square accumulation error analysis. Statistical analysis of the predictive results concludes that seated crowd model damping ratio is 0.5, and the probable natural frequency is 2.0 Hz with the model mass ratio 0.7. For standing crowd model, the probable natural frequency is 1.5 Hz with the model mass damping ratio 0.4, and the model mass ratio is 0.7. It may have ability to serve as a reference value that can be utilized in vibration safety and serviceability assessment of TDGs, to estimate realistically the vibration response on the occasions when crowd are seated or standing.

scholarly journals Influence of Structure on the Aseismic Stability and Dynamic Responses of Liquefiable Soil

2021 ◽  
Author(s):  
Pengfei Dou ◽  
Chengshun Xu ◽  
Xiuli Du ◽  
Su Chen
Keyword(s):  
Earthquake Engineering ◽  
Damping Ratio ◽  
Free Field ◽  
Shaking Table ◽  
Dynamic Responses ◽  
Seismic Stability ◽  
Geotechnical Earthquake Engineering ◽  
Liquefiable Soil ◽  
Porewater Pressure ◽  
Lateral Displacements

Abstract In previous major earthquakes, the damage and collapse of structures located in liquefied field which caused by site failure a common occurrence, and the problem of evaluation and disscusion on site liquefaction and the seismic stability is still a key topic in geotechnical earthquake engineering. To study the influence of the presence of structure on the seismic stability of liquefiable sites, a series of shaking table tests on liquefiable free field and non-free field with the same soil sample was carried out. It can be summarized from experimental results as following. The natural frequency of non-free field is larger and the damping ratio is smaller than that of free field. For the weak seismic loading condition, the dynamic response of sites show similar rules and trend. For the strong ground motion condition, soils in both experiments all liquefied obviously and the depth of liquefaction soil in the free field is significantly greater than that in the non-free field, besides, porewater pressure in the non-free field accumulated relately slow and the dissapited quikly from analysis of porewater pressure ratios(PPRs) in both experiments. The amplitudes of lateral displacements and acceleration of soil in the non-free field is obviously smaller than that in the free field caused by the effect of presence of the structure. In a word, the presence of structures will lead to the increase of site stiffness, site more difficult to liquefy, and the seismic stability of the non-free site is higher than that of the free site due to soil-structure interaction.

Damage Diagnosis of a Structure in Time-Frequency Domain

2015 ◽  
Vol 764-765 ◽  
pp. 1051-1057
Author(s):  
Wei Chih Su ◽  
Chiung Shiann Huang ◽  
Liane Jye Chen
Keyword(s):  
Life Cycle ◽  
Damping Ratio ◽  
Dynamic Responses ◽  
Short Time Fourier Transform ◽  
Structural Dynamic ◽  
Damage Diagnosis ◽  
Time Frequency ◽  
Input Model ◽  
Short Time ◽  
Vector Approach

This work proposes a simple and efficient approach to locating the storeys whose stiffness change in the life cycle of a structure. The storeys that may be damaged are determined by comparing the unitary stiffness matrix in different stages in the life cycle of a building. An appropriate ARX (autoregressive with exogenous input) model of structure in established from the structural dynamic responses in terms of acceleration or velocity. The parameters in an ARX model are identified through the short time Fourier transform, and the natural frequency and damping ratio of structure are estimated directly through these identified parameters. The effectiveness of the proposed procedure is verified using the numerically simulated earthquake acceleration responses of a six-storey structure that is damaged at one or two storeys. The proposed scheme is compared to the DLV approach (flexibility-based damage locating vector approach) in identifying damage storeys.

Vibration Characteristic Evaluation of Nonlinear Vibration Systems With Gaps Considering Energy Dissipation by Collision

2005 ◽  
Author(s):  
Masanori Shintani ◽  
Hiroyuki Ikuta ◽  
Hiroyuki Shume
Keyword(s):  
Nonlinear Vibration ◽  
Analytical Model ◽  
Damping Ratio ◽  
Experimental Results ◽  
Experimental Result ◽  
Vibration Characteristic ◽  
Random Waves ◽  
Restoring Force ◽  
Dissipation Energy ◽  
Experimental Apparatus

This paper deals with nonlinear vibration of a continuum system with gaps under random waves considered collision phenomena. In order to investigate this nonlinear vibration characteristic, experiments are made with an experimental apparatus consisting of a nonlinear vibration system. A 2.3mm thick plate is used for the collision phenomena experiments. Moreover, an analytical model of the cubic equation is proposed based on the restoring force characteristics in the experiments. This analytical model is used for the simulation analysis, and the results are compared with the experimental results. However, the Root- Mean- Square (R.M.S.) values of the response acceleration of the analytical results are larger than R.M.S. values of the response acceleration of the experimental result. The difference of these results indicates that energy is dissipated in the collision phenomena. Then, the coefficient of restitution by the collision phenomenon between mass and plate is measured from the experiments. In the analysis, the dissipation energy is replaced with an equivalent damping ratio. The simulations are calculated by using this modified analysis. Consequently, the simulation results agree well with the experimental results.

A quantitative investigation on vibration durability of viscoelastic relaxation in bolted composite joints

2016 ◽  
Vol 50 (29) ◽  
pp. 4041-4056 ◽  
Author(s):  
Z Zhang ◽  
Y Xiao ◽  
YQ Liu ◽  
ZQ Su
Keyword(s):  
Polymer Matrix Composites ◽  
Damping Ratio ◽  
Viscoelastic Behavior ◽  
Bolted Joints ◽  
Dynamic Responses ◽  
Matrix Composites ◽  
Structural Dynamic ◽  
Factors Affecting ◽  
Exciting Frequency ◽  
Vibration Fatigue

Time-dependent behavior and factors affecting preload relaxation in a carbon/epoxy composite bolted joint under resonance were studied. The effect of viscoelasticity of composite material on bolt relaxation was studied quantitatively through modal analysis from the perspective of energy dissipation and stiffness degradation. Damping ratio and resonance frequency were utilized to characterize the effects of preload relaxation on structural dynamic response. The loss of preload was found to decrease with increasing initial preloads over a 10 h vibration fatigue. However, an increase in preload loss occurred as exciting frequency increases. Vibration fatigue damage was found to result in decaying stiffness and amplitude responses of the bolted joints, along with an increase in damping ratio. As a proof-of-concept study, a beam-like specimens with and without bolted joints were comparatively excited to ascertain their respective dynamic responses; results revealed that relaxation in bolted joints could be attributed to the conjunct mechanisms between viscoelastic behavior of polymer matrix composites and interface friction for different contact surfaces, where such relaxation behavior was mainly due to viscoelasticity of the joint materials.

Structural Seismic Damage Detection Using Fractal Dimension of Time-Frequency Feature

2013 ◽  
Vol 558 ◽  
pp. 554-560 ◽  
Author(s):  
Dong Wang Tao ◽  
Dong Yu Zhang ◽  
Hui Li
Keyword(s):  
Fractal Dimension ◽  
Structural Damage ◽  
Nonlinear Behavior ◽  
Fractal Dimensions ◽  
Seismic Damage ◽  
Shaking Table ◽  
Dynamic Responses ◽  
Structural Dynamic ◽  
Time Frequency ◽  
Frequency Feature

In this paper, a data-driven approach to localizing structural damage subjected to ground motion is proposed by using the fractal dimension of the time-frequency features of structural dynamic responses. The time-frequency feature is defined as the real part of wavelet coefficient and the fractal dimension adopts the box-counting method. It is shown that the proposed fractal dimensions at each story of linear system are identical, while the fractal dimension at the stories with nonlinearity is different from those at the stories with linearity. Therefore, the nonlinear behavior of structural damage caused by strong ground motions can be detected and localized through comparing the fractal dimensions of structural responses at different stories. Shaking table test on a uniform 16-story 3-bay steel frame with added friction dampers modelling interstory nonlinear behavior was conducted. The experiment results validate the effectiveness of the proposed method to localize single and multi seismic damage of structures.

scholarly journals Dynamic Forces of Swaying Human and Responses of Temporary Demountable Grandstand Based on Experiment and Simulation

2018 ◽  
Vol 2018 ◽  
pp. 1-22
Author(s):  
Lin He ◽  
Jian Yuan ◽  
Feng Fan ◽  
Cong Liu
Keyword(s):  
Force Plate ◽  
Dynamic Responses ◽  
Experimental Program ◽  
Force Model ◽  
Lateral Vibration ◽  
Structural Dynamic ◽  
Important Research Topic ◽  
Dynamic Forces ◽  
Semiempirical Formula ◽  
Stiffness And Damping

Modern temporary demountable structures must be designed to withstand the dynamic forces which generated by crowd occupants. The human forces and that cause the dynamic responses of structure have become an important research topic. In this paper, the human swaying forces and responses of temporary demountable grandstand are studied through an experimental program. The dynamic forces that were induced by participants who have swayed 0.5–1.8 Hz are recorded by a triaxial human biomechanics force plate, and the structural dynamic responses of a temporary grandstand occupied twenty swaying human are investigated. The constraint parameters of swaying force model which derives from a semiempirical formula are developed and can be represented for crowd. Crowd can able to induce excessive lateral vibration of structure due to the lower frequency of temporary grandstand and make them in panic. The dynamic responses of a large temporary grandstand are predicted by finite element method, and the results show that a person was considered as a load with stiffness and damping, and the structural lateral dynamic responses are higher than the model of person just only considered as load.

scholarly journals Experimental Studies of Single-Layer Reticulated Domes with Isolated Supports

2018 ◽  
Vol 2018 ◽  
pp. 1-15 ◽  
Author(s):  
Guibo Nie ◽  
Kun Liu
Keyword(s):  
Seismic Behavior ◽  
Damping Ratio ◽  
Experimental Studies ◽  
Three Dimensional ◽  
Single Layer ◽  
Shaking Table ◽  
Dynamic Responses ◽  
Shaking Table Tests ◽  
Isolation Effects ◽  
Reticulated Domes

To study the seismic behavior of a single-layer reticulated dome subjected to severe earthquakes, a series of shaking table tests were conducted for this paper. Seismic responses including the acceleration, displacement, and strains gathered at the members and nodes were discussed. The dynamic characteristics, including structure frequencies and damping ratio, were obtained through the results under the input excitation of white noise and the fast sine sweeping with different amplitudes. Various isolation devices usually installed in the upper portion of the structures have been widely used to reduce the dynamic responses for more than three decades. However, these isolation devices deal mostly with either horizontal isolation or vertical isolation, which is not applicable for synchronous isolation in both horizontal and vertical isolation. Therefore, an innovative isolated support for three-dimensional isolation was invented. In order to understand the earthquake-isolation effects of a single-layer reticulated dome with the isolated support, a series of shaking table tests were conducted. The dynamic behavior of the structure was then investigated and discussed using the acceleration and displacement responses of the tested structures with or without the isolated supports. The experimental results show that the isolated support invented in this study had a remarkable earthquake-isolation action in both horizontal and vertical isolation.

Damage Detection of Composite Structures Using Dynamic Analysis

2005 ◽  
Vol 295-296 ◽  
pp. 33-38 ◽  
Author(s):  
L.H. Yam ◽  
Li Cheng ◽  
Z. Wei ◽  
Y.J. Yan
Keyword(s):  
Damage Detection ◽  
Composite Structures ◽  
Composite Plates ◽  
Experimental Results ◽  
Parameter Analysis ◽  
Dynamic Responses ◽  
Modal Parameters ◽  
Modal Parameter ◽  
Structural Dynamic ◽  
Modal Strain Energy

A study on the use of modal parameter analysis for damage detection of structures made of composites is conducted. The damage-induced variations of modal parameters are investigated both numerically and experimentally. An appropriate finite element model is proposed to analyze the dynamic characteristics of different types of structures made of composites, such as honeycomb sandwich plates and multi-layer composite plates, with internal cracks and delamination. The numerical results are in good agreement with experimental results available in the literature. Natural frequencies, modal displacements, strains and energy are analyzed for the determination of damage severity and location. Vibration measurements are carried out using piezoelectric patch actuators and sensors for comparison and verification of the FEM model proposed in this study. Energy spectrum for wavelet packets decomposition of structural dynamic responses is used to highlight the features of damaged samples. The mechanism of mode-dependent energy dissipation of composite plates due to delamination is revealed for the first time. Experimental results clearly show the dependence of changes of modal parameters on damage size and location. The results obtained in this study show that the measured modal damping change combined with the computed modal strain energy distribution can be used to determine the location of delamination in composite structures. Both numerical and experimental findings in this study are significant to the establishment of guideline for size and location identification of damage in composite structures.

A Theoretical Treatment of Crowd–Structure Interaction

2018 ◽  
Vol 18 (01) ◽  
pp. 1871001 ◽  
Author(s):  
Yan-an Gao ◽  
Qing-shan Yang
Keyword(s):  
Damping Ratio ◽  
Three Dimensional ◽  
Interaction Model ◽  
Dynamic Interaction ◽  
Theoretical Treatment ◽  
Social Force ◽  
Structural Dynamic ◽  
Structure Interaction ◽  
Crowd Density ◽  
The Social

A vertical crowd–structure interaction model including the interaction amongst pedestrians is developed to study the structural performances of the supporting structure with social force effect. This model can be used to analyze the vibration problem of footbridge under a large crowd excitation. The social force is firstly introduced to describe the dynamic interaction amongst the bipedal models with damping-spring legs modeling pedestrian movement on a three-dimensional plate structure. The social force determines the walking direction and velocity of pedestrian. Numerical studies show that the structural dynamic performances can be remarkably changed under the crowd action. The natural frequency of structure is decreased and is time-varying with an increase in the crowd density. However, the damping ratio of structure is increased. The proposed model could well describe the crowd–structure dynamic interaction.

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