Observed Natural Frequencies, Damping Ratios, and Mode Shapes of Vibration of a 30-Story Building Excited by a Major Earthquake and Typhoon

2010 ◽  
Vol 26 (2) ◽  
pp. 371-397 ◽  
Author(s):  
Kun-Sung Liu ◽  
Yi-Ben Tsai
Keyword(s):  
Natural Frequencies ◽  
Transfer Functions ◽  
Measurement Data ◽  
Spectral Ratio ◽  
Transverse Mode ◽  
Structural Vibration ◽  
Mode Shapes ◽  
Building Structures ◽  
Ambient Vibrations ◽  
Frequency Changes

The safety of building structures and contents, as well as the comfort of occupants, under such strong forces as earthquakes and typhoons remain major engineering concerns. In order to improve our understanding of building structural responses, records of a structural array in the 30-story PS Building in Taipei from the M7.6 Chi-Chi earthquake and Typhoon Aere are analyzed. In addition, wind data measured at the Taipei Meteorological Station are also used. First, the field measurement data clearly demonstrate that serviceability of the PS Building met the criteria for occupant comfort during Typhoon Aere. Secondly, several structural vibration parameters of this highrise building, including the transfer functions, natural frequencies, damping ratios and mode shapes, excited by the Chi-Chi earthquake, Typhoon Aere, and ambient vibrations are also determined and compared. The results show the frequency of the first mode for the longitudinal components is approximately 8.6% lower for the earthquake than the ambient vibrations. The transverse mode frequencies behave similarly. In contrast, frequency changes from the typhoon to ambient vibrations are in the third decimal (1.3% and 0.9% lower in the longitudinal and transverse directions, respectively), indicating little nonlinearity. The damping ratios of the PS Building apparently increase with vibration amplitudes. Finally, results of a spectral ratio analysis of the Chi-Chi earthquake data do not indicate significant SSI effects in the longitudinal and transverse directions.

Role of Dynamic Testing in Assessment of Bridges

1997 ◽  
Vol 1594 (1) ◽  
pp. 115-124 ◽  
Author(s):  
P. C. Das ◽  
J. S. Owen ◽  
B. J. Eccles ◽  
M. A. Woodings ◽  
B. S. Choo
Keyword(s):  
Reinforced Concrete ◽  
Natural Frequencies ◽  
Concrete Beams ◽  
Dynamic Testing ◽  
Reinforced Concrete Beams ◽  
Mode Shapes ◽  
Ambient Conditions ◽  
Frequency Changes ◽  
Frequency Ratios

Six reinforced concrete beams were loaded incrementally up to failure. After each increment the load was removed and measurements of the modal properties of the beams were made by impulse testing. The variation of the natural frequencies, frequency ratios, mode shapes, and the level of damage were investigated. It was found that on completion of the tests the natural frequencies of the beams had been reduced by an average of 25 percent in each mode. However, changes in mode shape were very small, and appreciable differences were only observed when the damage was highly localized. Modeling of the beam by using finite elements predicted trends that compared well with experimental observations. It is concluded that if dynamic testing were used in monitoring reinforced concrete structures, then the changes in frequency due to initial concrete cracking or yield of the reinforcement could be detected. More useful information associated with the spread and type of cracking through a structure may be detectable, although the level of the frequency changes is of the same order as those due to changes in ambient conditions.

Structural vibration design of a pod structure including an optical system of a fighter aircraft

2021 ◽  
Vol 263 (1) ◽  
pp. 5555-5561
Author(s):  
Taeyoung Yoon ◽  
Jaemyung Cho ◽  
Sungsoo Na ◽  
Seongho Yoon
Keyword(s):  
Structural Dynamics ◽  
Optical System ◽  
Natural Frequencies ◽  
Free Vibration Analysis ◽  
Structural Vibration ◽  
Mode Shapes ◽  
Element Analysis ◽  
Fighter Aircraft ◽  
Frequency Responses ◽  
Improving Accuracy

Structural vibration design of a pod structure including an optical system installed on a fighter aircraft is very significant in improving accuracy of targeting system to the target objects. To reduce and isolate the vibration generated during the flight, it is crucial to properly design the rubber mount between the pod and the aircraft. In this study, free vibration analysis of the pod is conducted through finite element analysis (FEA) and experiments. Correlations are performed with reasonably acceptable accuracy about the natural frequencies, mode shapes, and frequency response functions obtained by FEA and experiment. Then to optimize the structural dynamics of the pod, three variables are considered, which are mass of the dummies, the numbers of and positions of rubber mounts, and hyperelastic property of rubber mounts. In addition, the position of the pod on the fighter is analysed by FEM to estimate the possibility of further enhancement of its structural dynamics. Finally, forced vibration was undertaken using random signals of a shaker with 1Grms, 2Grms and 2.65Grms considering the test standard. It is found out that frequency responses of the pod are sensitive below 100 Hz to the values of the excitation signals. It is thus indeed to design appropriately the rubber mounts to improve structural dynamics of the pod, which results in the accuracy of targeting system.

Experimental and Numerical Modal Analysis of Gearbox Casing in a Polishing Machinery

2009 ◽  
Vol 69-70 ◽  
pp. 560-564
Author(s):  
Yang Yu Wang ◽  
Shi Ming Ji ◽  
Dong Hui Wen ◽  
Xian Zhang
Keyword(s):  
Modal Analysis ◽  
Natural Frequencies ◽  
Test System ◽  
Structural Vibration ◽  
Mode Shapes ◽  
Modal Parameters ◽  
Vibration Test ◽  
3D Fem ◽  
Fem Model

Vibrations in polishing machinery may affect the manual or automatic controls and reduce the efficiency of the operations to be carried out. In this article, an experimental and numerical analysis on the dynamic characteristic of a gearbox casing in polishing machinery have been carried out. The numerical investigation was achieved with NASTRAN based on a 3D FEM model and the experimental modal analysis for the determination of the natural frequencies and the associated eigenmodes of the gearbox casing with LMS structural vibration test system was performed. The fundamental modal parameters including the first 10-order natural frequencies, damping ratios and mode shapes were estimated and identified. Analytical and experimental results have been compared and discussed. Agreement between measurements and calculations is satisfactory and the results can be used as reliable reference for improving the dynamic behavior of the gearbox casing.

INTEGRATED STRUCTURAL OPTIMIZATION AND VIBRATION CONTROL FOR IMPROVING WIND-INDUCED DYNAMIC PERFORMANCE OF TALL BUILDINGS

2011 ◽  
Vol 11 (06) ◽  
pp. 1139-1161 ◽  
Author(s):  
M. F. HUANG ◽  
K. T. TSE ◽  
C. M. CHAN ◽  
W. J. LOU
Keyword(s):  
Structural Optimization ◽  
Vibration Control ◽  
Structural Design ◽  
Structural Control ◽  
Integrated Design ◽  
Tall Buildings ◽  
Optimality Criteria ◽  
Structural Vibration ◽  
Mode Shapes ◽  
Building Structures

Structural optimization and vibration control have long been recognized as effective approaches to obtain the optimal structural design and to mitigate excessive responses of tall building structures. However, the combined effects of both techniques in the structural design of wind-sensitive tall buildings with excessive responses have not been revealed. Therefore, this paper develops an integrated design technique making use of both the advantages of structural optimization and vibration control with an empirical cost model of the control devices. While the structural optimization is based on a very efficient optimality criteria (OC) method, a smart tuned mass damper (STMD) is used for the structural control purposes. Utilizing data obtained from synchronous pressure measurements in the wind tunnel, a 60-story building of mixed steel and concrete construction with three-dimensional (3D) mode shapes was employed as an illustrative example to demonstrate the effectiveness of the proposed optimal performance-based design framework integrating with structural vibration control.

Detection of Cracks in Stationary Rotors via the Modal Frequency Changes Induced by a Roving Disc

2014 ◽  
Author(s):  
Z. N. Haji ◽  
S. O. Oyadiji
Keyword(s):  
Natural Frequencies ◽  
Crack Depth ◽  
Mode Shapes ◽  
Crack Identification ◽  
Open Crack ◽  
Suggested Approach ◽  
Rotor Systems ◽  
Crack Location ◽  
High Crack ◽  
Frequency Changes

In this study, a crack identification approach based on a finite element cracked model is presented to identify the location and depth ratios of a crack in rotor systems. A Bernoulli-Euler rotor carrying an auxiliary roving disc has been used to model the cracked rotor, in which the effect of a transverse open crack is modelled as a time-varying stiffness matrix. In order to predict the crack location in the rotor-disc-bearing system, the suggested approach utilises the variation of the normalized natural frequency curves versus the non-dimensional location of a roving disc which traverses along the rotor span. The merit of the suggested approach is to identify the location and sizes of a crack in a rotor by determining only the natural frequencies of the stationary rotor system. The first four natural frequencies are employed for the identification and localisation of a crack in the stationary rotor. Furthermore, this approach is not only efficient and practicable for high crack depth ratios but also for small crack depth ratios and for a crack close to or at the node of mode shapes, where natural frequencies are unaffected.

scholarly journals Changes in the Dynamic Characteristics of a Small-Scale Gymnasium Model Due to Simulated Earthquake Damage

2021 ◽  
Vol 16 (7) ◽  
pp. 1074-1085
Author(s):  
Jun Fujiwara ◽  
Akiko Kishida ◽  
Takashi Aoki ◽  
Ryuta Enokida ◽  
Koichi Kajiwara ◽  
...  
Keyword(s):  
Structural Damage ◽  
Natural Frequencies ◽  
Mode Shapes ◽  
Modal Parameters ◽  
Small Scale ◽  
Building Structures ◽  
Shake Table Tests ◽  
Large Span ◽  
Similarity Rule ◽  
Measured Response

In this study, the authors used shake-table tests to assess the modal parameters of a small-scale gymnasium model with simulated damage, the feasibility of estimating the damage to large-span building structures was studied. In Japan, large-span structures, such as gymnasiums, are expected to be used as evacuation shelters when a natural disaster occurs. As the shelter itself may be damaged in case of an earthquake, it is critical to determine whether damage has occurred, where it occurred, and how serious it is, before the shelter is used. The small-scale gymnasium was designed based on the similarity rule. Observed earthquake ground motions scaled to aftershock levels were applied to the model. The natural frequencies and mode shapes were obtained from the measured response accelerations. To study the influence of structural damage on the modal parameters, a gymnasium model with simulated damage was also tested. The results indicate that the modal parameters, e.g., natural frequencies and mode shapes, can be obtained from the response accelerations, and the damage patterns can be estimated from the changes in these modal parameters.

Full-Scale Measurements on Vibrations of a 51-Story Tall Building Due to a Major Earthquake and Typhoon

2013 ◽  
Vol 284-287 ◽  
pp. 1259-1263 ◽  
Author(s):  
Kun Sung Liu ◽  
Yi Ben Tsai
Keyword(s):  
Transfer Functions ◽  
Tall Building ◽  
Building Structures ◽  
Ambient Vibrations ◽  
Structural Dynamic ◽  
High Rise ◽  
Taipei City ◽  
Structural Dynamic Characteristics ◽  
Strong Winds ◽  
Northern Taiwan

The Shin Kong Tower located in Taipei City has a height of 244.15 m. It was the tallest building in northern Taiwan when it was built in 1993. This super tall building is susceptible to severe vibrations induced by strong winds or earthquakes. Safety of the building structures and its contents as well as the comfort of its occupants under such strong forces remains a significant engineering concern. Records by a structural array in the 51-story SK Building of the 1999 M7.6 Chi-Chi earthquake and 2004 Typhoon Aere are analyzed in this study. As a result, the structural dynamic characteristics of the high-rise building, including the transfer functions and natural frequencies, excited by the Chi-Chi earthquake, Typhoon Aere, and ambient vibrations are also determined and compared.

Analysis of Ring-Stiffened Cylindrical Shells

1995 ◽  
Vol 62 (4) ◽  
pp. 1005-1014 ◽  
Author(s):  
Bingen Yang ◽  
Jianping Zhout
Keyword(s):  
Natural Frequencies ◽  
Transfer Functions ◽  
Cylindrical Shells ◽  
Middle Surface ◽  
Mode Shapes ◽  
Structural Components ◽  
Modeling And Analysis ◽  
Stiffened Shells ◽  
Modeling Techniques ◽  
Stiffened Cylindrical Shells

A new analytical and numerical method is presented for modeling and analysis of cylindrical shells stiffened by circumferential rings. This method treats the shell and ring stiffeners as individual structural components, and considers the ring eccentricity with respect to the shell middle surface. Through use of the distributed transfer functions of the structural components, various static and dynamic problems of stiffened shells are systematically formulated. With this transfer function formulation, the static and dynamic response, natural frequencies and mode shapes, and buckling loads of general stiffened cylindrical shells under arbitrary external excitations and boundary conditions can be determined in exact and closed form. The proposed method is illustrated on a Donnell-Mushtari shell, and compared with finite element method and two other modeling techniques.

Modal Analysis of a Container Filled with Water

2014 ◽  
Vol 592-594 ◽  
pp. 2122-2126
Author(s):  
M.L. Chandravanshi ◽  
Alok Kumar Mukhopadhyay
Keyword(s):  
Modal Analysis ◽  
Natural Frequencies ◽  
Fem Analysis ◽  
Structural Vibration ◽  
Mode Shapes ◽  
Design Stage ◽  
Modal Parameters ◽  
Element Analysis ◽  
Empty Container ◽  
Ansys Workbench

Modal analysis plays an important role at design stage which helps in diagnosing problems related to structural vibration. This paper delineates about the experimental work to investigate the modal parameters, such as mode shapes and natural frequencies of a metallic container. The modal parameters have been experimentally determined for the empty container, the container filled with one liter of water and the container filled with two liters of water. Theoretical analysis is also carried out through finite element analysis using ANSYS workbench 14 for finding out modal parameters of the empty container only. The boundary conditions of the container in the experimental and FEM analysis have been kept same. The values of modal parameters obtained by the two methods then compared for their proximity

Multi-crack detection in general cross-section swept wings based on natural frequency changes

2020 ◽  
pp. 107754632096401
Author(s):  
Fatemeh Barzegar ◽  
Saeedreza Mohebpour ◽  
Hekmat Alighanbari
Keyword(s):  
Mathematical Model ◽  
Natural Frequency ◽  
Cross Section ◽  
Crack Detection ◽  
Natural Frequencies ◽  
Detection Method ◽  
Mode Shapes ◽  
Modal Strain Energy ◽  
Torsional Mode ◽  
Frequency Changes

In this article, a multi-crack detection method, which is based on natural frequency changes and the concept of modal strain energy, is for the first time developed for the general cross-section swept tapered wings under coupled bending-torsional vibration and applied to the solid and thin-walled airfoil cross-section wings. The presented method is able to handle the problems with an unknown number of cracks and predicts the number of existent cracks, their locations and depths by optimization of an appropriate objective function. The stress intensity factors of airfoil-shaped crack surfaces are obtained using an approximation method. Inputs of the detection method are natural frequencies of uncracked and cracked wings which are calculated by using a mathematical model and finite element method software ANSYS, respectively, and validated by comparison with former research studies. In the mathematical model, the Rayleigh–Ritz method is used to calculate the coupled bending-torsional mode shapes of the uncracked wing and their corresponding natural frequencies. Results demonstrate that the proposed method has precisely predicted the number, locations and depths of cracks in all case studies.

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