• Earthquakes and Structures
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• 제17권1호
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• pp.39-48
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• 2019

This paper presents an experimental study on a 1/2 scale steel frame with archaized-style under the pseudo-dynamic loading. Four seismic waves, including El Centro wave, Taft wave, Lanzhou wave and Wenchuan wave, were input during the test. The hysteresis characteristic, energy dissipation acceleration response, displacement response, strength, stiffness and strain were analyzed. Based on the experiment, the elastoplastic dynamic time-history analysis was carried out with the software ABAQUS. The stress distribution and failure mode were obtained. The results indicate that the steel frame with archaized-style was in elastic stage when the peak acceleration of input wave was no more than 400 gal. Under Wenchuan wave with peak acceleration of 620 gal, the steel frame enters into the elastoplastic stage, the maximum inter-story drift was 1/203 and the bearing capacity still tended to increase. During the loading process, Dou-Gong yielded first and played the role of the first seismic fortification line, and then beam ends and column bottom ends yielded in turn. The steel frame with archaized-style has good seismic performance and meets the seismic design requirement of Chinese code.

• Earthquakes and Structures
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• 제16권1호
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• pp.83-96
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• 2019

The seismic behavior of PRC coupling beam-hybrid coupled shear wall system is analyzed by using the finite element software ABAQUS. The stress distribution of steel plate, reinforcing bar in coupling beam, reinforcing bar in slab and concrete is investigated. Meanwhile, the plastic hinges developing law of this hybrid coupled shear wall system is also studied. Further, the effect of coupling ratio, section dimensions of coupling beam, aspect ratio of single shear wall, total height of structure and the role of slab on the seismic behavior of the new structural system. A fitting formula of plate characteristic values for PRC coupling beams based on different displacement requirements is proposed through the experimental date regression analysis of PRC coupling beams at home and abroad. The seismic behavior control method for PRC coupling beam-hybrid coupled shear wall system is proposed based on the continuous connection method and through controlling the coupling ratio, the roof displacement, story drift angle of hybrid coupled shear wall system, displacement ductility of coupling beam.

• Earthquakes and Structures
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• 제16권5호
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• pp.589-599
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• 2019

Conventional buckling restrained braces used in concentrically braced frames are expected to yield in both tension and compression without major degradation of capacity under severe seismic ground motions. One of the weakness points of a standard buckling restrained braced frame is the low post-yield stiffness and thus large residual deformation under moderate to severe ground motions. This phenomenon can be attributed to low post-yield stiffness of core member in a BRB. This paper introduces a multi-core buckling restrained brace. The multi-core term arises from the use of more than one core component with different steel materials, including high-performance steel (HPS-70W) and stainless steel (304L) with high strain hardening properties. Nonlinear dynamic time history analyses were conducted on variety of diagonally braced frames with different heights, in order to compare the seismic performance of regular and multi-core buckling restrained braced frames. The results exhibited that the proposed multi-core buckling restrained braces reduce inter-story and especially residual drift demands in BRBFs. In addition, the results of seismic fragility analysis designated that the probability of exceedance of residual drifts in multi-core buckling restrained braced frames is significantly lower in comparison to standard BRBFs.

• 한국지진공학회논문집
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• 제25권6호
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• pp.251-259
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• 2021

Current seismic fragility functions for buildings were developed by defining damage state threshold based on story drift concerning foreign references and using the capacity spectrum method based on spectral displacement. In this study, insufficient details and dependence on the core location of piloti-type buildings were not reflected in the fragility function because it was developed before the Pohang earthquake. In order to develop an improved one for piloti-type buildings, several types of core were selected, damage state threshold was determined based on the capacity of structural members, and three-dimensional analyses were utilized. As a result, seismic fragility functions based on spectral acceleration were developed for various core locations and different shear strengths of the column stirrup. The fragility of piloti-type buildings significantly varied according to core location, an additional single wall, and whether the contribution of column stirrup was included or not. To estimate fragility more reasonably, it is necessary to prepare the parameters to reflect actual state well.

• Earthquakes and Structures
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• 제20권2호
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• pp.175-185
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• 2021

This study strives to highlight the importance of considering the vertical ground motions (VGM) in the seismic evaluation of RC buildings. To this aim, IDA (Incremental Dynamic Analysis) is conducted on three code-based designed high-rise RC frame-core wall buildings using a suite of earthquake records comprising of significant VGMs. To unravel the significance of the VGM inclusion on the performance of the buildings, IDAs are conducted in two states (with and without the vertical component), and subsequently based on each analysis, fragility curves are developed. Non-simulated collapse criteria are used to determine the collapse state drift ratio and the area under the velocity spectrum (SIm) is taken into account as the intensity measure. The outcome of this study delineates that the inclusion of VGM leads to the increase in the collapse vulnerability of the structures as well as to the change in the pattern of inter-story drifts and failure mode of the buildings. The results suggested that it would be more conservative if the VGM is included in the seismic assessment and the fragility analysis of RC buildings.

• 대한건축학회논문집:구조계
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• 제35권3호
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• pp.3-10
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• 2019

On November 15, 2017, an earthquake($M_L5.4$) occurred in Pohang. Pohang earthquake was the second largest earthquake since earthquake was observed in Korea, but structural damage caused by earthquake was biggest. Structural damage caused by Pohang earthquake was mainly caused by schools and pilotis, above all damage to pilotis was outstanding. This is because area where pilotis structures are concentrated is located near epicenter, and seismic performance of pilotis structures is not excellent compared with general structures. In this study, described results of damage investigation and analysis of damage causes through analysis of pilotis Structures on 131 buildings that were investigated immediately after Pohang earthquake. In addition, cause of damage was analyzed through analysis of seismic wave. Investigation site was selected to Jangseong-dong, where damage occurred in large numbers. Damage level was classified into A, B, and C level by measuring residual crack width and story drift of structural members.

• Steel and Composite Structures
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• 제38권6호
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• pp.671-690
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• 2021

Seismic responses of RC core wall with two outriggers are investigated in this study. In the models analyzed here, one of the outriggers is fixed at the top of the building and the second is placed at different levels along the height of the system. Each of the systems resulting from the placement of the outrigger at different locations is designed according to the prescriptive codes. The location of the outrigger changes along the height. Linear design of all the structures is accomplished by using prescriptive codes. Buckling restrained braces (BRBs) are used in the outriggers and forward directivity near fault and far fault earthquake record sets are used at maximum considered earthquake (MCE) level. Results from nonlinear time history analysis demonstrate that BRB outriggers can change the seismic responses like force distribution and deformation demand of the RC core-walls over the height and lead to the new plastic hinge arrangement over the core-wall height. Plasticity extension in the RC core wall occurs at the base as well as adjacent to the outrigger levels. Considering the maximum inter-story drift ratio (IDR) demand as an engineering parameter, the best location for the second outrigger is at 0.75H, in which the maximum IDR at the region upper the second outrigger level is approximately equal to the corresponding value in the lower region.

• Structural Engineering and Mechanics
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• 제83권1호
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• pp.45-51
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• 2022

The need to account for accidental torsion in seismic design is no longer debatable, however, the seismic codes' requirement for accidental eccentricity has recently faced criticism. In order to get as close to real conditions as possible, this study investigated the impact of accidental torsion in symmetric RC multistory buildings caused by one of its many sources, the torsional earthquake component, and compared the results to those obtained by using the accidental eccentricity recommended by the codes (shifting the center of mass). To cover a wide range of frequencies and site conditions, two types of torsion seismic components were used: a recorded torsion accelerogram and five others generated using translation accelerograms. The main parameters that govern seismic responses, such as the number of stories (to account for the influence of all modes of vibration) and the frequency ratio (Ω) variation, were studied in terms of inter-story drift and displacement responses, as well as torsional moment. The results show that the eccentricity ratio of 5% required by most codes for accidental torsion should be reexamined and that it is prudent for computer analysis to use the static moment approach to implement the accidental eccentricity while waiting for new seismic code recommendations on the subject.

• Structural Engineering and Mechanics
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• 제83권1호
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• pp.1-17
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• 2022

The static design approach in the current code implies that the inherent torsional moment represents the state of zero inertial torsional moments at the center of mass (CM). However, both experimental and analytical results prove the existence of a large amount of the inertial torsional moment at the CM. Also, the definition of eccentricity by engineers, which is referred to as the resistance eccentricity, is defined as the distance between the center of mass and the center of resistance, which is conceptually different from the static eccentricity in the current codes, defined as the arm length about the center of rotation. The difference in the definitions of eccentricity should be made clear to avoid confusion about the torsion design. This study proposed prediction equations as a function of resistance eccentricity based on a resistance eccentricity model with advantages of (1) the recognition of the existence of torsional moment at the CM, (2) the avoidance of the confusion by using resistance eccentricity instead of the design eccentricity, and (3) a clear relationship of applied inertial forces at the CM and resisting forces. These predictions are compared with the seismic responses obtained from time-history analyses of a five-story building structure under moderate and severe earthquakes. Then, the trend of the resistance eccentricity corresponding to the maximum edge drift is investigated for elastic and inelastic responses. The comparison given in this study shows that these prediction equations can serve as a useful reference for the prediction in both the elastic and the inelastic ranges.

• Earthquakes and Structures
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• 제23권1호
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• pp.87-100
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• 2022

Limiting the displacement of seismic isolators causes a pounding phenomenon under severe earthquakes. Therefore, the ASCE 7-16 has provided minimum criteria for the design of the isolated building. In this research the seismic response of isolated buildings by Triple Friction Pendulum Isolator (TFPI) under the impact, expected, and unexpected mass eccentricity was evaluated. Also, the effect of different design parameters on the seismic behavior of structural and nonstructural elements was found. For this, a special steel moment frame structure with a surrounding moat wall was designed according to the criteria, by considering different response modification coefficients (RI), and 20% mass eccentricity in one direction. Then, different values of these parameters and the damping of the base isolation were evaluated. The results show that the structural elements have acceptable behavior after impact, but the nonstructural components are placed in a moderate damage range after impact and the used improved methods could not ameliorate the level of damage. The reduction in the RI and the enhancement of the isolator's damping are beneficial up to a certain point for improving the seismic response after impact. The moat wall reduces torque and maximum absolute acceleration (MAA) due to unexpected enhancement of mass eccentricity. However, drifts of some stories increase. Also, the difference between the response of story drift by expected and unexpected mass eccentricity is less. This indicates that the minimum requirement displacement according to ASCE 7-16 criteria lead to acceptable results under the unexpected enhancement of mass eccentricity.