• Smart Structures and Systems
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• v.20 no.6
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• pp.641-656
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• 2017

The effects of vertical component of earthquakes on torsional amplification due to mass eccentricity in seismic responses of base-isolated structures subjected to near-field ground motions are studied in this paper. 3-, 6- and 9-story superstructures and aspect ratios of 1, 2 and 3 have been modeled as steel special moment frames mounted on Triple Concave Friction Pendulum (TCFP) bearings considering different period and damping ratios. Three-dimensional linear superstructures resting on nonlinear isolators are subjected to both 2 and 3 component near-field ground motions. Effects of mass eccentricity and vertical component of 25 near-field earthquakes on the seismic responses including maximum isolator displacement and base shear as well as peak superstructure acceleration are studied. The results indicate that the effect of vertical component on the responses of asymmetric structures, especially on the base shear is significant. Therefore, it can be claimed that in the absence of the vertical component, mass eccentricity has a little effect on the base shear increase. Additionally, the impact of this component on acceleration is remarkable so the roof acceleration of a nine-story structure has been increased 1.67 times, compared to the case that the structure is subjected to only horizontal components of earthquakes.

• Structural Engineering and Mechanics
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• v.73 no.5
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• pp.599-612
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• 2020

A combination of a gravity wall and an anchor beam is widely used to support the high soil deposit on rock mass. In this study, two groups of shaking table test were performed to investigate the responses of such combined retaining structure, where the rock masses were shaped with a flat surface and a curved surface, respectively. Meanwhile, the dynamic numerical analysis was carried out for a comparison or an extensive study. The results were studied and compared between the combined retaining structures with different shaped rock masses with regard to the acceleration response, the earth pressure response, and the axial anchor force. The acceleration response is not significantly influenced by the surface shape of rock mass. The earth pressure response on the combined retaining structure with a flat rock surface is more intensive than the one with a curved rock surface. The anchor force is significantly enlarged by seismic excitation with a main earthquake-induced increment at the first intensive pulse of Wenchuan motion. The value of anchor force in the combined retaining structure with a flat rock surface is generally larger than the one with a curved rock surface. Generally, the combined retaining structure with a curved rock surface presents a better seismic performance.

• Smart Structures and Systems
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• v.24 no.4
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• pp.447-457
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• 2019

The use of Tuned mass dampers (TMD) has proved to be effective in reducing the effects of vibrations caused by wind loads and far-field seismic action. However, its effectiveness in controlling the dynamic response of structures under near-fault earthquakes is still under discussion. In this case, the uncertainty about the TMD performance arises from the short significant duration of near-fault ground motions. In this work, the TMD effectiveness for increasing the safety margin against collapse of structures subjected to near-fault earthquakes is investigated. In order to evaluate the TMD performance in the proposed scenario, the nonlinear dynamic response of two reinforced concrete (RC) frames was analyzed. TMDs with different mass values were added to these structures, and a set of near-fault records with frequency content close to the fundamental frequency of the structure was employed. Through a series of nonlinear dynamic analysis, the minimum amplitude of each seismic record that causes the structural collapse was found. By comparing this value, called collapse acceleration, for the case of the structures with and without TMD, the benefit produced by the addition of the control device was established.

• Structural Engineering and Mechanics
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• v.77 no.6
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• pp.721-734
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• 2021

The seismic analysis of structures without applying the effects of soil can undermine functional objectives of structure so that it can affect all the desired purposes at the design and control stages of the structure. In this research, employing OpenSees and MATLAB software simultaneously and developing a definite three-dimensional finite element model of a high-rise concrete structure, designed using performance-based plastic design approach, the performance of Tuned Mass Damper (TMD) and Active Mass Damper (AMD) is both examined and compared. Moreover some less noted aspects such as nonlinear interaction of soil and structure, uplift, nonlinear behavior of structure and structural torsion have received more attention. For this purpose, the analysis of time history on the structural model has been performed under 22 far-field accelerogram records. Examining a full range of all structural seismic responses, including lateral displacement, acceleration, inter-story drift, lost plastic energy, number of plastic hinges, story shear force and uplift. The results indicate that TMD performs better than AMD except for lateral displacement and inter-story drift to control other structural responses. Because on the one hand, nonlinear structural parameters and soil-structure interaction have been added and on the other hand, the restriction on the control force applied that leads up to saturation phenomenon in the active control system affect the performance of AMD. Moreover, the control force applied by structural control system has created undesirable acceleration and shear force in the structure.

• Earthquakes and Structures
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• v.11 no.1
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• pp.109-127
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• 2016

This paper examines the contribution of three sources of uncertainties to probabilistic seismic behaviour of wood frame buildings, including ground motions, intensity and seismic mass. This sensitivity analysis is performed using three methods, including the traditional method based on the conditional distributions of ground motions at given intensity measures, a method using the summation of conditional distributions at given ground motion records, and the Monte Carlo simulation. FEMA P-695 ground motions and its scaling methods are used in the analysis. Two archetype buildings are used in the sensitivity analysis, including a two-storey building and a four-storey building. The results of these analyses indicate that using data-fitting techniques to obtain probability distributions may cause some errors. Linear interpolation combined with data-fitting technique may be employed to improve the accuracy of the calculated exceeding probability. The procedures can be used to quantify the risk of wood frame buildings in seismic events and to calibrate seismic design provisions towards design code improvement.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.34 no.12
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• pp.27-34
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• 2018

This paper considers the seismic performance of lever-type tuned mass damper(TMD). The lever-type TMD is designed utilizing the seismic-performance of TMD and the control force required for constraining story drift. The TMD is basically designed by tuning the frequency of primary structure. Thus, the TMD plays an important role to reduce the dynamic responses. The lever-type TMD has a merit to control more displacement responses than the existing TMD due to the control forces. It is shown that the optimum design of lever-type TMD is affected by the ratio of the TMD mass with respect to the mass of the primary structure, the damping ration of the primary structure, and the length ratio of the lever. A numerical example exhibits the effectiveness of the dynamic control by the lever-type TMD and its validity is illustrated in a three-story building structure subjected to earthquake.

• Earthquakes and Structures
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• v.24 no.1
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• pp.21-36
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• 2023

Structural vibrations generated by earthquakes and wind loads can be controlled by varying the structural parameters such as mass, stiffness, damping ratio, and geometry and providing a certain amount of passive or active reaction forces. A Double-Tuned Mass Dampers (DTMDs) system, which is simple and more effective than the conventional single tuned mass damper (TMD) system for vibration mitigation is presented. Two TMDs tuned to the first two natural frequencies were used to control vibrations. Experimental investigations were carried out on a three degrees-of-freedom frame model to investigate the effectiveness of DTMDs systems in controlling displacements, accelerations, and base shear. Numerical models were developed and validated against the experimental results. The validation showed a good match between the experimental and numerical results. The validated model was employed to investigate the behavior of a five degrees-of-freedom shear building structure, wherein mass dampers with different mass ratios were considered. The effectiveness of the DTMDs system was investigated for harmonic, seismic, and white noise base excitations. The proposed system was capable of significantly reducing the story displacements, accelerations, and base shears at the first and second natural frequencies, as compared to conventional single TMD.

• Earthquakes and Structures
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• v.25 no.6
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• pp.455-467
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• 2023

This study focuses on demonstrating the effectiveness of vibration control of tuned rotary mass damper (TRMD) for reducing the bidirectional and torsional response of the irregular asymmetric structure with voided slabs under earthquake excitations. The TRMD arranged in plane of one-story eccentric structure is proposed as a distributed tuned rotary mass damper (DTRMD) system. Lagrange's equation is used to derive the equations of motion of the controlled system. The optimum position and number of TRMD are numerically investigated under harmonic excitation and the control effects of different distributions are discussed. Furthermore, a shaking table test is conducted under different excitation cases, including free vibration, forced vibration and seismic wave to investigate the absorption performance of the device. The numerical simulations of different distributions of the TRMDs show that the DTRMDs are more effective in reduction of the displacement response of the asymmetric structure under the same mass ratio, even when the degree of eccentricity becomes large. However, with small degree of eccentricity, the unreasonable asymmetrical arrangement may cause the increase of the peak value of the rotational angular displacement. Finally, the experimental investigations exhibit similar results of translational displacement of the structure. It is concluded that the vibration of the irregular asymmetric structure can be controlled more economically and effectively by reducing the mass ratio through reducing the quantity of TRMDs at the high stiffness end.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1997.04a
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• pp.128-132
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• 1997

This paper deals with the optimization of pipe-support allocation using the genetic algorithm, and shows the feasibility of the optimization method to actual design problems and also the convergence characteristics of optimization calculation with respect to the various seismic waves. The piping system was modeled as mass-spring system with 5 degrees of freedom and the support was as spring-damper. The support allocation problem was formulated to minimize the response of the piping system to seismic excitation.

• Coupled systems mechanics
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• v.2 no.4
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• pp.389-410
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• 2013

Three-dimensional Lagrangian fluid finite element is applied to seismic response analysis of an oil storage tank with a floating roof. The fluid element utilized in the present analysis is formulated based on the displacement finite element method considering only volumetric elasticity and its element stiffness matrix is derived by using one-point integration method in order to avoid volumetric locking. The method usually adds a rotational penalty stiffness to satisfy the irrotational condition for fluid motion and modifies element mass matrices through the projected mass method to suppress spurious hourglass-mode appeared in compensation for one-point integration. In the fluid element utilized in the present paper, a small hourglass stiffness is employed. The fluid and structure domains for the objective oil storage tank are modeled by eight-node solid elements and four-node shell elements, respectively, and the transient response of the floating roof structure or the free surface are evaluated by implicit direct time integration method. The results of seismic response analyses are compared with those by other method and the validation of the present analysis using three-dimensional Lagrangian fluid finite elements is shown.