• Earthquakes and Structures
• /
• v.16 no.5
• /
• pp.523-532
• /
• 2019

Different types of gas reservoir such as Liquid Natural Gas (LNG) are among the strategic infrastructures, and have great importance for any government or their private owners. To keep the tank and its contents safe during earthquakes especially if the contents are of hazardous or flammable materials; using seismic protection systems such as base isolator can be considered as an effective solution. However, the major deficiency of this system can be the large deformation in the isolation level which may lead to the failure of bearing system. In this paper, as a solution, the efficacy of an optimally designed combined vibration control system, the combined laminated rubber isolator and rotational friction damper, is investigated to evaluate the enhancement of an existing metal tank response under both far- and near-field earthquakes. Responses like impulsive and convective accelerations, base shear, and sloshing height are studied herein. The probabilistic framework is used to consider the uncertainties in the structural modeling, as well as record-to-record variability. Due to the high calculation cost of probabilistic methods, a simplified structural model is used. By using the Mont-Carlo simulation approach, it is revealed that this combined isolation system is a highly reliable system which provides considerable enhancement in the performance of reservoir, not only leads to the reduction of probability of catastrophic failure of the tank but also decrease the reservoir damage during the earthquake. Moreover, the relative displacement of the isolation level is controlled very well by this combined system.

• Earthquakes and Structures
• /
• v.24 no.5
• /
• pp.333-343
• /
• 2023

Various seismic isolation and reduction devices have been applied to suppress the longitudinal vibration of continuous girder bridges. As representative devices, lead rubber bearing (LRB) and fluid viscous damper (FVD) might suffer from deterioration during the long-term service. This study aims to evaluate the impact of device deterioration on the seismic responses of continuous girder bridges and investigate the seismic behavior of deteriorated LRBs and FVDs. Seismic performance of a simplified bridge model was investigated, and the influence of device deterioration was evaluated by the coefficient of variation method. The contribution of LRB and FVD was assessed by the Sobol global sensitivity analysis method. Finally, the seismic behaviors of deteriorated LRBs and FVDs were discussed. The result shows that (i) the girder-pier relative displacement is the most sensitive to the changes in the deterioration level, (ii) the deterioration of FVD has a greater effect on the structural responses than that of LRB, (iii) FVD plays a major role in energy dissipation with a low degradation level while LRB is more essential in dissipating energy when suffering from high degradation level, (iv) the deteriorated devices are more likely to reach the ultimate state and thus be damaged.

• Earthquakes and Structures
• /
• v.23 no.4
• /
• pp.373-384
• /
• 2022

To improve the seismic performance of suspended ceiling structures, various vibration-damping devices have been developed. However, the devices made of metals have a limit in that they cause large deformation and seriously damages the exterior of the suspended ceiling structure from the wall. As a results, their strengthening effect of the suspended ceiling structure was minimal. Thus, this study employed a spring and vibration-proof rubber effectively controlled vibrations without increasing horizontal seismic loads on the ceiling to enhance the seismic resistance of suspended ceiling structures. The objective of the study is to examine the dynamic properties of a seismic damping-isolation unit (SDI) with various details developed. The developed SDI was composed of a spring, embossed rubbers, and prestressed bolts, which were the main factors enhancing the damping effect. The shaking table tests were performed on eight SDI specimens produced with the number of layers of embossed rubber (n_s), presence or absence of a spring, prestressed force magnitude introduced in bolts (f_ps), and mass weight (W_m) as the main parameters. To identify the enhancement effect of the SDI, the dynamic properties of the control specimen with a conventional hanger bolt were compared to those of the SDI specimens. The SDI specimens were effective in reducing the maximum acceleration (A_{c max}), acceleration amplification factor (α_p), relative displacement (δ_R), and increasing the damping ratio (ξ) when compared to the control specimen. The A_{c max}, α_p, and δ_R of the SDI specimens with two rubbers, spring, and f_ps of 0.1f_by, where f_by is the yielding strength of the screw bolt were 57.8%, 58.0%, and 61.9% lower than those of the conventional hanger bolt specimens, respectively, resulting in the highest ξ (=0.127). In addition, the α_p of the SDI specimens was 50.8% lower than those specified in ASCE 7 and FEMA 356. Consequently, to accurately estimate the α_p of the SDI specimens, a simple model was proposed based on the functions of f_ps, stiffness constant of the spring (K), W_m, and n_s.

• Journal of KSNVE
• /
• v.8 no.2
• /
• pp.260-266
• /
• 1998

According to the conventional method of analysis for the seismic sliding of equipment submerged in a pool, in general, only the initial condition of fluid gap is used to estimate the hydrodynamic effect between the two structures throughout the seismic analysis. This is based on the assumption of small displacement relative to the fluid gap thickness during earthquakes. In a narrow fluid gap condition, however, this method may lead to a result of unconservative side. Through example seismic analyses for equipment submerged in a pool of a building, in this paper, it is studied when and how much the sliding response can be underestimated. And method of updating the hydrodynamic effect in each step of time integration is proposed to avoid excessive error in estimation of peak sliding response in such a case.

• Structural Engineering and Mechanics
• /
• v.61 no.5
• /
• pp.675-684
• /
• 2017

In this paper, a hybrid seismic response control (HSRC) system was developed to control bridge behavior caused by the seismic load. It was aimed at optimum vibration control, composed of a rubber bearing of passive type and MR-damper of semi-active type. Its mathematical modeling was driven and applied to a bridge model so as to prove its validity. The bridge model was built for the experiment, a two-span bridge of 8.3 meters in length with the HSRC system put up on it. Then, inflicting the EI Centro seismic load on it, shaking table tests were carried out to confirm the system's validity. The experiments were conducted under the basic structure state (without an MR-damper applied) first, and then under the state with an MR-damper applied. It was also done under the basic structure state with a reinforced rubber bearing applied, then the passive on/off state of the HSRC system, and finally the semi-active state where the control algorithm was applied to the system. From the experiments, it was observed that pounding rather increased when the MR-damper alone was applied, and also that the application of the HSRC system effectively prevented it from occurring. That is, the experiments showed that the system successfully mitigated structural behavior by 70% against the basic structure state, and, further, when control algorithm is applied for the operation of the MR-damper, relative displacement was found to be effectively mitigated by 80%. As a result, the HSRC system was proven to be effective in mitigating responses of the two-span bridge under seismic load.

• Structural Engineering and Mechanics
• /
• v.63 no.2
• /
• pp.147-160
• /
• 2017

In this study, the optimum parameters of Tuned Mass Dampers (TMDs) are proposed using Gravity Search Algorithm (GSA) and Particle Swarm Optimization (PSO) to reduce the responses of the structures. A MATLAB program is developed to apply the new approach to the benchmark 10 and 40-story structures. The obtained results are compared to those of other optimization methods used in the literature to verify the developed code. To show the efficiency and accuracy of the proposed methods, nine far-field and near-field worldwide earthquakes are applied to the structures. The results reveal that in the 40-story structure, GSA algorithm can reduce the Relative Displacement (RD) and Absolute Acceleration (AA) up to 43% and 21%, respectively while the PSO decreases them by 50% and 25%, respectively. In contrast, both GSA and PSO algorithms reduce the RD and AA about 29% and 21% for the 10-story structure. Furthermore, using the proposed approach the required TMD parameters reduce by 47% and 63% in the 40 and 10-story buildings in comparison with the referenced ones. Result evaluation and related comparison indicate that these methods are more effective even by using smaller TMD parameters resulting in the reduction of acting force from TMD, having smaller stiffness and damping factors while being more cost effective due to its decreased parameters. In other words, the TMD with optimum parameters can play a positive role in both tall and typical structures.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.26 no.2
• /
• pp.122-129
• /
• 2006

Shearography is one of optical methods that has been applied to nondestructive testing (NDT) and strain/stress analysis. The technique has the merit of the directly measuring relative displacement, which is insensitive to environmental vibration disturbance. Previous studies about the method have emphasized on extending its application to new fields and lack insufficient research on effective parameters for qualitative and quantitative evaluation of defects. In this paper, the influence of shearing amount on the detection of an internal defect is investigated. In experiment, slender defects along longitudinal direction of pipeline are artificially designed and detection results according to the change of shearing amount are analyzed. Based on the investigation, we propose the technique for the determination of defect size and accurate source location.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.35 no.2
• /
• pp.201-206
• /
• 2011

A spacer grid assembly is one of the most important structural components of the nuclear fuel assembly of a pressurized water reactor (PWR), and it affects the performance of the fuel assembly. The primary design requirement is that the mechanical integrity of the fuel rod should be maintained by the spacer grid assembly during the operation of the reactor. It was known that fretting damage to the fuel rod can be reduced by adjusting the relative moving displacement between the fuel rod and its support. In this study, we used the finite element method to evaluate the characteristics of a sliding support designed to reduce fretting damage of fuel rods.

• Structural Engineering and Mechanics
• /
• v.89 no.6
• /
• pp.589-599
• /
• 2024

This study presents the usability of the high-rate single-frequency Precise Point Positioning (SF-PPP) technique based on 20 Hz Global Positioning Systems (GPS)-only observations in detecting dynamic motions. SF-PPP solutions were obtained from post-mission and real-time GNSS corrections. These include the International GNSS Service (IGS)-Final, IGS real-time (RT), real-time MADOCA (Multi-GNSS Advanced Demonstration tool for Orbit and Clock Analysis), and real-time products from the Australian/New Zealand satellite-based augmentation systems (SBAS, known as SouthPAN). SF-PPP results were compared with LVDT (Linear Variable Differential Transformer) sensor and single-frequency relative positioning (SF-RP) solutions. The findings show that the SF-PPP technique successfully detects the harmonic motions, and the real-time products-based PPP solutions were as accurate as the final post-mission products. In the frequency domain, all GNSS-based methods evaluated in this contribution correctly detect the dominant frequency of short-term harmonic oscillations, while the differences in the amplitude values corresponding to the peak frequency do not exceed 1.1 mm. However, evaluations in the time domain show that SF-PPP needs high-pass filtering to detect accurate displacement since SF-PPP solutions include trends and low-frequency fluctuations, mainly due to atmospheric effects. Findings obtained in the time domain indicate that final, real-time, and MADOCA-based PPP results capture short-term dynamic behaviors with an accuracy ranging from 3.4 mm to 8.5 mm, and SBAS-based PPP solutions have several times higher RMSE values compared to other methods. However, after high-pass filtering, the accuracies obtained from PPP methods decreased to a few mm. The outcomes demonstrate the potential of the high-rate SF-PPP method to reliably monitor structural and earthquake-induced ground motions and vibration frequencies of structures.