• Journal of the Earthquake Engineering Society of Korea
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• v.10 no.3 s.49
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• pp.125-134
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• 2006

Conventional methods for the assessment of liquefaction potential were primary for severe earthquake regions $(M{\geq}7.5)$ such as North America and Japan. In Korea, an earthquake related research has started in 1997, but most contents in the guidelines were still quoted from literature reviews of North America and Japan, which are located in strong earthquake region. Those are not proper in a moderate earthquake regions including Korea. Also the equivalent uniform stress concept (Seed & Idriss, 1971) using regular sinusoidal loading which is used, in a conventional method for the assessment of liquefaction potential, can't reflect correctly the dynamic characteristics of real irregular earthquake motions. In this study, cyclic triaxial tests using irregular earthquake motions are performed with different earthquake magnitudes, relative densities, and fines contents. Assessment of liquefaction potential in moderate earthquake regions is discussed based on various laboratory test results. From the results, screening limits in seismic design were re-investigated and proposed using normalized maximum stress ratios under real irregular earthquake motions. Also from the tests using constant wedge loading and incremental wedge loading, the characteristics of liquefaction resistance of saturated sand under irregular ground motions are investigated.

• Journal of the Korean Geotechnical Society
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• v.20 no.7
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• pp.127-140
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• 2004

Conventional methods for the assessment of liquefaction potential were primarily for areas of severe earthquake zones (M=7.5) such as North America and Japan. Detailed earthquake related researches in Korea started in 1997, including development of the seismic design standards for port and harbour structures, which was later completed in 1999. Because most contents in the guidelines were quoted through literature reviews from North America and Japan, which are located in strong earthquake region, those are not proper in Korea, a moderate earthquake region. This requires further improvement of the present guidelines. Considering earthquake hazard data in Korea, use of laboratory tests based on irregular earthquake motion appears to be effective to reflect the dynamic characteristics of soil more realistically than those using simplified regular loading. In this study, cyclic triaxial tests using irregular earthquake motions are performed with different earthquake magnitudes, relative densities, and fines contents. Assessment of liquefaction potential in moderate earthquake regions is discussed based on various laboratory test results. Effects of these components on dynamic behavior of soils are discussed as well. From the test results, screening limits and magnitude scaling factors to determine the soil liquefaction resistance strength in seismic design were re-investigated and proposed using normalized maximum stress ratios under real irregular earthquake motions.

• Structural Engineering and Mechanics
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• v.49 no.6
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• pp.687-703
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• 2014

This paper develops a new nonlinear model for active control of three-dimensional (3D) irregular building structures. Both geometrical and material nonlinearities with a neuro-controller training algorithm are applied to a multi-degree-of-freedom 3D system. Two dynamic assembling motions are considered simultaneously in the control model such as coupling between torsional and lateral responses of the structure and interaction between the structural system and the actuators. The proposed control system and training algorithm of the structural system are evaluated by simulating the responses of the structure under the El-Centro 1940 earthquake excitation. In the numerical example, the 3D three-story structure with linear and nonlinear stiffness is controlled by a trained neural network. The actuator dynamics, control time delay and incident angle of earthquake are also considered in the simulation. Results show that the proposed control algorithm for 3D buildings is effective in structural control.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.66-71
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• 2003

The semi-active TLCD system is investigated for control of responses of 3D irregular buildings under seismic excitations. The TLCD system is a special type of TMD system providing a performance similar to a TMD system but offers a number of practical advantages over the traditional TMD system. The equations of motion for the combined building and TLCD system are derived for multistory building structures with rigid floors and plan and elevation irregularities. Simulation results for control of two multistory moment-resisting space structures with vertical and plan irregularities show clearly that the semi-active TLCD control system reduces the responses of 3D irregular buildings subjected to earthquake ground motions efficiently.

• Ocean Systems Engineering
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• v.7 no.1
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• pp.1-19
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• 2017

This paper presents the numerical simulation results for the dynamic responses of two types of submerged floating tunnels (SFT) under wave and/or seismic excitations. Time domain simulations are conducted by the commercial program OrcaFlex (OF) and in-house CHARM3D program (CP). The dynamic performances of a short/rigid/free-end SFT section with vertical and inclined mooring lines are evaluated. The SFT numerical models were validated against Oh et al.'s (2013) model test results under regular wave conditions. Then the numerical models were further applied to the cases of irregular waves or seismic motions. The main results presented are SFT surge/heave motions and mooring tensions. The general trends and magnitudes obtained by the two different software packages reasonably agree to each other along with experimental results. When seabed seismic motions are applied to the SFT system, the dynamic responses of SFTs are small but dynamic mooring tension can significantly be amplified. In particular, horizontal earthquakes greatly increase the dynamic tension of the inclined mooring system, while vertical earthquakes cause similar effect on vertical mooring system.

• Earthquakes and Structures
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• v.13 no.4
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• pp.377-386
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• 2017

Earthquake-induced pounding damages to building structures were repeatedly observed in many previous major earthquakes. Extensive researches have been carried out in this field. Previous studies mainly focused on the regular shaped buildings and each building was normally simplified as a single-degree-of-freedom (SDOF) system or a multi-degree-of-freedom (MDOF) system by assuming the masses of the building lumped at the floor levels. The researches on the pounding responses between irregular asymmetric buildings are rare. For the asymmetric buildings subjected to earthquake loading, torsional vibration modes of the structures are excited, which in turn may significantly change the structural responses. Moreover, contact element was normally used to consider the pounding phenomenon in previous studies, which may result in inaccurate estimations of the structural responses since this method is based on the point-to-point pounding assumption with the predetermined pounding locations. In reality, poundings may take place between any locations. In other words, the pounding locations cannot be predefined. To more realistically consider the arbitrary poundings between asymmetric structures, detailed three-dimensional (3D) finite element models (FEM) and arbitrary pounding algorithm are necessary. This paper carries out numerical simulations on the pounding responses between a symmetric rectangular-shaped building and an asymmetric L-shaped building by using the explicit finite element code LS-DYNA. The detailed 3D FEMs are developed and arbitrary 3D pounding locations between these two buildings under bi-directional earthquake ground motions are investigated. Special attention is paid to the relative locations of two adjacent buildings. The influences of the left-and-right, fore-and-aft relative locations and separation gap between the two buildings on the pounding responses are systematically investigated.

• Earthquakes and Structures
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• v.21 no.5
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• pp.551-562
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• 2021

In this study, the generalized intensity measure (IM) named I_Npg is analyzed. The recently proposed proxy of the spectral shape named N_pg is the base of this intensity measure, which is similar to the traditional N_p based on the spectral shape in terms of pseudo-acceleration; however, in this case the new generalized intensity measure can be defined through other types of spectral shapes such as those obtained with velocity, displacement, input energy, inelastic parameters and so on. It is shown that this IM is able to increase the efficiency in the prediction of nonlinear behavior of structures subjected to earthquake ground motions. For this work, the efficiency of two particular cases (based on acceleration and velocity) of the generalized I_Npg to predict the peak floor acceleration demands on steel frames under 30 earthquake ground motions with respect to the traditional spectral acceleration at first mode of vibration Sa(T₁) is compared. Additionally, a 3D reinforced concrete building and an irregular steel frame is used as a basis for comparison. It is concluded that the use of velocity and acceleration spectral shape increase the efficiency to predict peak floor accelerations in comparison with the traditional and most used around the world spectral acceleration at first mode of vibration.

• Earthquakes and Structures
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• v.9 no.1
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• pp.49-71
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• 2015

The present paper aims at evaluating damage and collapse behavior of low-rise buildings with unidirectional mass irregularities in plan (torsional buildings). In previous earthquake events, such buildings have been exposed to extensive damages and even total collapse in some cases. To investigate the performance and collapse behavior of such buildings from probabilistic points of view, three-dimensional three and six-story reinforced concrete models with unidirectional mass eccentricities ranging from 0% to 30% and designed with modern seismic design code provisions specific to intermediate ductility class were subjected to nonlinear static as well as extensive nonlinear incremental dynamic analysis (IDA) under a set of far-field real ground motions containing 21 two-component records. Performance of each model was then examined by means of calculating conventional seismic design parameters including the response reduction (R), structural overstrength (${\Omega}$) and structural ductility (${\mu}$) factors, calculation of probability distribution of maximum inter-story drift responses in two orthogonal directions and calculation collapse margin ratio (CMR) as an indicator of performance. Results demonstrate that substantial differences exist between the behavior of regular and irregular buildings in terms of lateral load capacity and collapse margin ratio. Also, results indicate that current seismic design parameters could be non-conservative for buildings with high levels of plan eccentricity and such structures do not meet the target "life safety" performance level based on safety margin against collapse. The adverse effects of plan irregularity on collapse safety of structures are more pronounced as the number of stories increases.