• Earthquakes and Structures
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• v.18 no.2
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• pp.171-184
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• 2020

The potential of using the roof water tanks as a mitigation measure to minimize the required separation gap and induced pounding forces due to collisions is investigated. The investigation is carried out using nonlinear dynamic analysis for two adjacent 3-story buildings with different dynamic characteristics under two real earthquake motions. For such analysis, nonlinear viscoelastic model is used to simulate forces due to impact. The sloshing force due to water movement is modelled in terms of width of the water tank and the instantaneous wave heights at the end wall. The effect of roof water tanks on the story's responses, separation gap, and magnitude and number of induced pounding forces are investigated. The influence of structural stiffness and storey mass are investigated as well. It is found that pounding causes instantaneous acceleration pulses in the colliding buildings, but the existence of roof water tanks eliminates such acceleration pulses. At the same time the water tanks effectively reduce the number of collisions as well as the magnitude of the induced impact forces. Moreover, buildings without constructed water tanks require wider separation gap to prevent pounding as compared to those with water tanks attached to top floor under seismic excitations.

• Structural Engineering and Mechanics
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• v.23 no.3
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• pp.233-247
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• 2006

Most codes of practice state that for large in-plane structures it is necessary to account for the spatial variability of earthquake ground motion. There are essentially three effects that contribute for this variation: (i) wave passage effect, due to finite propagation velocity; (ii) incoherence effect, due to differences in superposition of waves; and (iii) the local site amplification due to spatial variation in geological conditions. This paper discusses the procedures to be undertaken in the time domain analysis of a cable-stayed bridge under spatial variability of earthquake ground motion. The artificial synthesis of correlated displacements series that simulate the earthquake load is discussed first. Next, it is described the 3D model of the International Guadiana Bridge used for running tests with seismic analysis. A comparison of the effects produced by seismic waves with different apparent propagation velocities and different geological conditions is undertaken. The results in this study show that the differences between the analysis with and without spatial variability of earthquake ground motion can be important for some displacements and internal forces, especially those influenced by symmetric modes.

• Earthquakes and Structures
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• v.15 no.1
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• pp.45-65
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• 2018

Over the last three decades, Performance-based Earthquake Engineering (PBEE) has been mainly developed for high seismicity regions. Although information is abundant for PBEE throughout the world, the application of PBEE to lower-seismicity regions, such as those where the magnitude of the maximum considered earthquake (MCE) is less than 6.5, is not always straightforward because some portions of PBEE may not be appropriate for such regions due to geological differences between high- and low-seismicity regions. This paper presents a brief review of state-of-art PBEE methodologies and introduces the seismic hazard of lower-seismicity regions, including those of the Korean Peninsula, with their unique characteristics. With this seismic hazard, representative low-rise RC MRF structures and high-rise RC wall residential structures are evaluated using PBEE. Also, the range of the forces and deformations of the representative building structures under the design earthquake (DE) and the MCE of South Korea are presented. These reviews are used to propose some ideas to improve the practice of state-of-art PBEE in lower-seismicity regions.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 1997.10a
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• pp.201-208
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• 1997

In most seismic codes such as the Uniform Building Code(UBC), the response modification factor(or the force reduction factor)is used to reflect the capability of a structure in dissipating energy through inelastic behavior. The response modification factor is assigned according to structural system type. Ductile systems such as special moment-resisting steel frames are assigned larger values of the response modification factor, and are consequently designed for smaller seismic design forces. Therefore, structural damage may occur during a severe earthquake. To ensure safety of the structures, the suitability of the response modification factor used in aseismic design procedures shall be evaluated. The object of this study is to develop a method for the evaluating of the response modification factor. The validity of the evaluating method has been examined for several cases of different structures and different earthquake excitations.

• Journal of the Earthquake Engineering Society of Korea
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• v.20 no.5
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• pp.319-329
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• 2016

The Eradi Quake System (EQS) is a seismic isolation bearing system designed to minimize forces and displacements experienced by structures subjected to ground motion. The EQS dissipates seismic energy through friction of Poly Tetra Fluoro Ethylene (PTFE) disk pad. In general, a force-displacement relationship of EQS has post yield stiffness hardening during large inelastic displacement. In this study, seismic responses of seismically isolated nuclear power plant (NPP) subjected to design basis earthquake (DBE) and beyond design basis earthquakes (150% DBE and 167% DBE) are compared considering the post yield stiffness hardening effect of EQS. From the results, it can be observed that if the post-yield stiffness hardening effect of EQS is increased, the displacement response of EQS is reduced, and the acceleration and shear responses of containment structures of NPP is increased.

• Journal of the Earthquake Engineering Society of Korea
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• v.22 no.7
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• pp.369-378
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• 2018

Full-scale seismic retrofit of old and deteriorated masonry buildings requires a lot of cost and time. In such buildings, installing an emergency evacuation space can be considered as an alternative. In this study, requirements of the earthquake-proof table used as an emergency evacuation space for buildings hit by earthquake are investigated. Load conditions required for the table, including the impact effects due to building debris drop, are explained. To investigate the impact effects in more detail, weight drop test is performed for an prototype earthquake-proof table. In the test, the weight of the falling object and free fall height were considered as the main test parameters. The results showed that the duration of impact is very short (0.0226~0.0779sec), and thus the impact forces increase to 15.8~45.2 times the weight of the falling object. Based on these results, design considerations and performance verification criteria of the earthquake-proof table as an emergency evacuation space are given.

• Earthquakes and Structures
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• v.3 no.5
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• pp.749-766
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• 2012

Structural control through integration of passive damping devices within the building structure has been increasingly implemented internationally in the last years and has proven to be a most promising strategy for earthquake safety. In the present paper an alternative configuration of an innovative energy dissipation mechanism that consists of slender tension only bracing members with closed loop and a hysteretic damper is investigated in its dynamic behavior. The implementation of the adaptable dual control system, ADCS, in frame structures enables a dual function of the component members, leading to two practically uncoupled systems, i.e., the primary frame, responsible for the normal vertical and horizontal forces and the closed bracing-damper mechanism, for the earthquake forces and the necessary energy dissipation. Three representative international earthquake motions of differing frequency contents, duration and peak ground acceleration have been considered for the numerical verification of the effectiveness and properties of the SDOF systems with the proposed ADCS-configuration. The control mechanism may result in significant energy dissipation, when the geometrical and mechanical properties, i.e., stiffness and yield force of the integrated damper, are predefined. An optimum damper ratio, DR, defined as the ratio of the stiffness to the yield force of the hysteretic damper, is proposed to be used along with the stiffness factor of the damper's- to the primary frame's stiffness, in order for the control mechanism to achieve high energy dissipation and at the same time to prevent any increase of the system's maximum base shear and relative displacements. The results are summarized in a preliminary design methodology for ADCS.

• Structural Engineering and Mechanics
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• v.62 no.4
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• pp.455-464
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• 2017

Rayleigh damping model is recommended in the recently developed Performance-Based Earthquake Engineering (PBEE) methodology, but this methodology does not provide sufficient information due to the complexity of the damping mechanism. Furthermore, each Rayleigh-type damping model may have its individual limitations. In this study, Rayleigh-type damping models that are used widely in engineering practice are discussed. The seismic performance of a large-span single-layer latticed dome subjected to earthquake ground motions is investigated using different Rayleigh damping models. Herein a simulation technique is developed considering low cycle fatigue (LCF) in steel material. In the simulation technique, Ramberg-Osgood steel material model with the low cycle fatigue effect is used to simulate the non-uniformly distributed material damping and low cycle fatigue damage in the structure. Subsequently, the damping forces of the structure generated by different damping models are compared and discussed; the effects of the damping ratio and roof load on the damping forces are evaluated. Finally, the low cycle fatigue damage values in sections of members are given using these damping models. Through a comparative analysis, an appropriate Rayleigh-type damping model used for a large span single-layer latticed dome subjected to earthquake ground motions is determined in terms of the existing damping models.

• Structural Engineering and Mechanics
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• v.23 no.5
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• pp.543-562
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• 2006

Base isolation technology has been accepted as a feasible and attractive way in improving seismic resistance of structures. The seismic design of new seismically isolated structures is mainly governed by the Uniform Building Code (UBC-97) published by the International Conference of Building Officials. In the UBC code, the distribution formula of the inertial (or lateral) forces leads to an inverted triangular shape in the vertical direction. It has been found to be too conservative for most isolated structures through experimental, computational and real earthquake examinations. In this paper, four simple and reasonable design formulae, based on the first mode of the base-isolated structures, for the lateral force distribution on isolated structures have been validated by a multiple-bay three-story base-isolated steel structure tested on the shaking table. Moreover, to obtain more accurate results for base-isolated structures in which higher mode contributions are more likely expected during earthquakes, another four inertial force distribution formulae are also proposed to include higher mode effects. Besides the experimental verification through shaking table tests, the vertical distributions of peak accelerations computed by the proposed design formulae are in good agreement with the recorded floor accelerations of the USC University Hospital during the Northridge earthquake.

• Journal of the Korea institute for structural maintenance and inspection
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• v.8 no.1
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• pp.139-146
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• 2004

In this paper, the seismic analysis and the modeling techniques have been introduced for seismic performances assessment, when seismic isolation bearings are applied to a real bridge. Nonlinear time-history analysis is carried out using finite element analysis program. El Centro earthquake(1940, N00W) used as earthquake ground excitations. The seismic response of seismically isolated bridge is compared with that of a bridge using conventional Pot Bearings, after obtaining the displacements of the deck, the deformations of the piers, shear forces and moments of the bottoms of the piers. The analytical analysis results show that seismic isolation bearing, especially seismic isolation bearings with sliding mechanism, could reduce earthquake forces.