• Journal of Korean Tunnelling and Underground Space Association
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• v.19 no.6
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• pp.959-972
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• 2017

In evaluation of blast-induced vibration, peak particle velocity (PPV) is generally calculated by using attenuation relation curve. Calculated velocity is compared with the value in legal requirements or the standards to determine the stability. Attenuation relation curve varies depending on frequency of test blasting, geological structure of the site and blasting condition, so it is difficult to predict accurately using such an equation. Since PPV is response value from the ground, direct evaluation of the structure is impractical. Because of such a limit, engineers tend to use the commercial numerical analysis program in evaluating the stability of the structure more accurately. However, when simulate the explosion process using existing numerical analysis program, it's never easy to accurately simulate the complex conditions (fracture, crushing, cracks and plastic deformation) around blasting hole. For simulating such a process, the range for modelling will be limited due to the maximum node count and it requires extended calculation time as well. Thus, this study is intended to simulate the elastic energy after fractured zone only, instead of simulating the complex conditions of the rock that results from the blast, and the analysis of response characteristics of the velocity depending on shape and size of the fractured zone was conducted. As a result, difference in velocity and attenuation character were calculated depending on fractured zone around the blast source appeared. Propagation of vibration tended to spread spherically as it is distanced farther from the blast source.

• KIEAE Journal
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• v.7 no.4
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• pp.147-152
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• 2007

Numerous non-destructive tests(NDT) to assess the safety of real structures have been developed. System identification(SI) techniques using dynamic responses and behaviors of structural systems become an outstanding issue of researchers. However the conventional SI techniques are identified to be non-practical to the complex and tall buildings, due to limitation of the availability of an accurate data that is magnitude or location of external loads. In most SI approaches, the information on input loading and output responses must be known. In many cases, measuring the input information may take most of the resources, and it is very difficult to accurately measure the input information during actual vibrations of practical importance, e.g., earthquakes, winds, micro seismic tremors, and mechanical vibration. However, the desirability and application potential of SI to real structures could be highly improved if an algorithm is available that can estimate structural parameters based on the response data alone without the input information. Thus a technique to estimate structural properties of building without input measurement data and using limited response is essential in structural health monitoring. In this study, shaking table tests on three-story plane frame steel structures were performed. Out-put only model analysis on the measured data was performed, and the dynamic properties were inverse analyzed using least square method in time domain. In results damage detection was performed in each member level, which was performed at story level in conventional SI techniques of frequency domain.

• The Journal of the Acoustical Society of Korea
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• v.21 no.1
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• pp.73-81
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• 2002

The transmission of vibration energy through beam-plate junctions in vibration intensity analysis called power new analysis (PFA) has been studied. PFA is an analytic tool for the prediction of frequency averaged vibration response of built-up structures at medium to high frequency ranges. The power transmission and reflection coefficients between the semi-infinite beam and plate are estimated using the wave transmission approach. For the application of the power coefficients to practical complex structures, the numerical methods, such as finite element method are needed to be adapted to the power flow governing equation. To solve the discontinuity of energy density at the joint, joint matrix is developed using energy flow coupling relationships at the beam-plate joint. Using the joint matrix developed in this paper, an idealized ship stem part is modeled with finite element program, and vibration energy density and intensity are calculated.

• Journal of Korean Tunnelling and Underground Space Association
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• v.22 no.4
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• pp.337-346
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• 2020

Traffic jam and congestion in urban areas has caused the need to improve the utility of underground space. In response, research on underground structures is increasingly being conducted. Notably, a double-deck tunnel is one of the most widely used of all those underground structures. This double-deck tunnel is separated by the middle slab into the upper and lower roadways. Both vehicle load and earthquake load cause the middle slab to exhibit dynamic behavior. Earthquake-related response characteristics, in particular, are highly complex and difficult to interpret in a theoretical context, and thus experimental research is required. The aim of the present study is to assess the stability of a double-deck tunnel's middle slab of the Collapse Prevention Level and Seismic Category 1 with regard to the presence of vibration-damping Rubber Bearings. In vibration table tests, the ratio of similitude was set to 1/4. Linings and vibrating platforms were fixed during scaled model tests to represent the integrated behavior of the ground and the applied models. In doing so, it was possible to minimize relative behavior. The standard TBM cross-section for the virtual double-deck tunnel was selected as a test subject. The level of ground motion exerted on the bedrock was set to 0.154 g (artificial seismic wave, Collapse Prevention Level and Seismic Category 1). A seismic wave with the maximum acceleration of 0.154 g was applied to the vibration table input (bedrock) to analyze resultant amplification in the models. As a result, the seismic stability of the middle slab was evaluated and analyzed with respect to the presence of vibration-damping rubber bearings. It was confirmed that the presence of vibration-damping rubber bearings improved its earthquake acceleration damping performance by up to 40%.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.4
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• pp.1-8
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• 2016

Recently, buildings tend to be large size, complex shape and functional. As the size of buildings is becoming massive, the need for structural health monitoring(SHM) technique is ever-increasing. Various SHM techniques have been studied for buildings which have different dynamic characteristics and are influenced by various external loads. Generally, the visual inspection and non-destructive test for an accessible point of structures are performed by experts. But nowadays, the system is required which is online measurement and detect risk elements automatically without blind spots on structures. In this study, in order to consider the response of non-linear structures, proposed a signal feature extraction and the adaptive threshold setting algorithm utilized to determine the abnormal behavior by using statistical methods such as control chart, root mean square deviation, generalized extremely distribution. And the performance of that was validated by using the acceleration response of structures during earthquakes measuring system of forced vibration tests and actual operation.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.11 s.176
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• pp.111-117
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• 2005

The vibration problems associated with gear coupled rotors have been the focus of much engineering work. These systems are complex and difficult to analyze in that they have the problems associated with conventional rotors plus those additional problems associated with the gear couplings. This paper examines the problems peculiar to the gear mesh. Because of the meshing action of gears, the elasticity of the gear teeth introduces time-varying stiffness coefficients into the governing equations of motion. This means that system response must be thought of in terms of Mathieu-type equations, where multiple-frequency response occur due to the periodic coefficients. The meshing action of the gears also couples the lateral and torsional gear motions. Gear errors, such as tooth profile and spacing errors, produce forces and torque that excite the system at multiple frequencies, some of which are much higher than shaft rotational speed. To investigate how to the time-varying stiffness in the gear teeth and the gear errors act one the dynamic response of the gear coupled rotors, a three-dimensional dynamic model with lateral-tortional oscillation is developed. The harmonic balance technique is employed to solve this mathieu-type problem.

• Structural Engineering and Mechanics
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• v.11 no.1
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• pp.71-87
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• 2001

A frequency domain response analysis is presented for building frames passively controlled by viscoelastic dampers, under harmonic ground excitation. Three different models are used to represent the linear dynamic force-deformation characteristics of viscoelastic dampers namely, Kelvin model, Linear hysteretic model and Maxwell model. The frequency domain solution is obtained by (i) an iterative pseudo-force method, which uses undamped mode shapes and frequencies of the system, (ii) an approximate modal strain energy method, which uses an equivalent modal damping of the system in each mode of vibration, and (iii) an exact method which uses complex frequency response function of the system. The responses obtained by three different methods are compared for different combinations of viscoelastic dampers giving rise to both classically and non-classically damped cases. In addition, the effect of the modelling of viscoelastic dampers on the response is investigated for a certain frequency range of interest. The results of the study are useful in appropriate modelling of viscoelastic dampers and in understanding the implication of using modal analysis procedure for building frames which are passively controlled by viscoelastic dampers against base excitation.

• Wind and Structures
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• v.32 no.2
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• pp.143-159
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• 2021

The 246.8-m-tall Beijing Olympic Tower (BOT) is a new landmark in Beijing City, China. Its unique architectural style with five sub-towers and a large tower crown gives rise to complex dynamic characteristics. Thus, it is wind-sensitive, and a double-stage pendulum tuned mass damper (DPTMD) has been installed for vibration mitigation. In this study, a finite-element analysis of the wind-induced responses of the tower based on full-scale measurement results was performed. First, the structure of the BOT and the full-scale measurement are introduced. According to the measured dynamic characteristics of the BOT, such as the natural frequencies, modal shapes, and damping ratios, an accurate finite-element model (FEM) was established and updated. On the basis of wind measurements, as well as wind-tunnel test results, the wind load on the model was calculated. Then, the wind-induced responses of the BOT with the DPTMD were obtained and compared with the measured responses to assess the numerical wind-induced response analysis method. Finally, the wind-induced serviceability of the BOT was evaluated according to the field measurement results for the wind-induced response and was found to be satisfactory for human comfort.

• Wind and Structures
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• v.32 no.2
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• pp.89-104
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• 2021

Non-synoptic winds generated by tornadoes, downbursts or gust fronts exhibit significant non-stationarity and can cause significant wind load effect on flexible structures such as long-span bridges. However, conventional assumptions on stationarity used to evaluate the structural wind-induced vibration are inadequate. In this paper, an efficient frequency domain scheme based on fast CQC method, which can predict non-stationary buffeting random responses of long-span bridges, is presented, and then this approach is applied to evaluate the buffeting response of a long-span suspension bridge located in a complex mountainous wind environment as an example. In this study, the data-driven method based on one available measured wind speed sample is firstly presented to establish non-stationary wind models, including time-varying mean wind speed, time-varying intensity envelope function and uniformly modulated fluctuating spectrum. Then, a linear time-variant (LTV) system based on the proposed scheme can be generally applied to calculate the non-stationary buffeting responses. The effectiveness and accuracy of the proposed scheme are verified through Monte Carlo time domain simulation implemented in ANSYS platform. Also, the transient effect nature of the bridge responses is further illustrated by comparison of the non-stationary, quasistationary and steady-state cases. Finally, buffeting response analysis with traditional stationary treatment (10 min constant mean plus stationary wind fluctuation) is performed to illustrate the importance of the non-stationary characteristics embedded in original wind speed samples.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.5
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• pp.41-49
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• 2005

This paper discusses the test procedure, instrumentation, verification methodology and the results of the ground vibration test(GVT) performed on the KF-16D aircraft to estimate experimentally dynamic characteristics of the aircraft. The modal tests for 7 external store configurations were conducted to estimate effects of external stores on the aircraft vibration modes. To emulate free-free boundary conditions the test aircraft was mounted on its landing gear structure with deflated tires during the GVT. The airframe modal tests were done by burst random excitations with 6 to 8 shakers and about 200 accelerometers. Frequency response functions(FRFs) were measured for each test, and the FRFs were reduced and analyzed to identify the dynamic parameters interested. The analyses were carried out in two steps. To extract modal parameters such as, frequencies and damping ratios, the poly-reference least square complex exponential method was used in the time domain. The mode shape coefficients were estimated with the least squares frequency domain method to identify the vibration modes.