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  • Title/Summary/Keyword: seismic inelastic response

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Seismic performance evaluation of coupled core walls with concrete and steel coupling beams

  • Fortney, Patrick J.;Shahrooz, Bahram M.;Rassati, Gian A.
    • Steel and Composite Structures
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    • v.7 no.4
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    • pp.279-301
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    • 2007
  • When coupling beams are proportioned appropriately in coupled core wall (CCW) systems, the input energy from ground motions is dissipated primarily through inelastic deformations in plastic hinge regions at the ends of the coupling beams. It is desirable that the plastic hinges form at the beam ends while the base wall piers remain elastic. The strength and stiffness of the coupling beams are, therefore, crucial if the desired global behavior of the CCW system is to be achieved. This paper presents the results of nonlinear response history analysis of two 20-story CCW buildings. Both buildings have the same geometric dimensions, and the components of the buildings are designed based on the equivalent lateral force procedure. However, one building is fitted with steel coupling beams while the other is fitted with diagonally reinforced concrete coupling beams. The force-deflection relationships of both beams are based on experimental data, while the moment-curvature and axial load-moment relationships of the wall piers are analytically generated from cross-sectional fiber analyses. Using the aforementioned beam and wall properties, nonlinear response history analyses are performed. Superiority of the steel coupling beams is demonstrated through detailed evaluations of local and global responses computed for a number of recorded and artificially generated ground motions.

Multimode pushover analysis based on energy-equivalent SDOF systems

  • Manoukas, Grigorios E.;Athanatopoulou, Asimina M.;Avramidis, Ioannis E.
    • Structural Engineering and Mechanics
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    • v.51 no.4
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    • pp.531-546
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    • 2014
  • In this paper the extension of a recently established energy-based pushover procedure in order to include the higher mode contributions to the seismic response of structures is presented and preliminary evaluated. The steps of the proposed methodology in its new formulation are quite similar to those of the well-known Modal Pushover Analysis. However, the determination of the properties of the 'modal' equivalent single-degree-of-freedom systems is achieved by a rationally founded energy-based concept. Firstly, the theoretical background and the assumptions of the proposed methodology are presented and briefly discussed. Secondly, the sequence of steps to be followed for its implementation along with the necessary equations is systematically presented. The accuracy of the methodology is evaluated by an extensive parametric study which shows that, in general, it provides better results compared to those produced by other similar procedures. In addition, the main shortcoming of the initial version of the methodology now seems to be mitigated to a large extent.

ATC-55 Based Friction Damper Design Procedure for Controlling Inelastic Seismic Responses (비탄성 지진응답 제어를 위한 ATC-55에 기반한 마찰감쇠기 설계절차)

  • Kim, Hyoung-Seop;Min, Kyung-Won;Lee, Sang-Hyun;Park, Ji-Hun
    • Journal of the Earthquake Engineering Society of Korea
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    • v.9 no.1 s.41
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    • pp.9-16
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    • 2005
  • The purpose of this paper is to present a design procedure of a friction damper for controlling elastic and inelastic responses of building structures under earthquake excitation. The equivalent damping and period increased by the friction damper are estimated using ATC-40 and ATC-55 procedures which provide equivalent linear system for bilinear one, and then a design formula to achieve target performance response level by the friction damper is presented. It is identified that there exists error between the responses obtained by this formula and by performing nonlinear analysis and the features of the error vary according to the hardening ratio, yield strength ratio, and structural period. Equations for compensating the error are proposed based on the least square method, and the results from numerical analysis indicate that the error is significantly reduced. The proposed formula can be used without much error for designing a friction damper for retrofitting a structure showing elastic or inelastic behavior.

Seismic torsional vibration in elevated tanks

  • Dutta, Sekhar Chandra;Murty, C.V.R.;Jain, Sudhir K.
    • Structural Engineering and Mechanics
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    • v.9 no.6
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    • pp.615-636
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    • 2000
  • Some elevated water tanks have failed due to torsional vibrations in past earthquakes. The overall axisymmetric structural geometry and mass distribution of such structures may leave only a small accidental eccentricity between centre of stiffness and centre of mass. Such a small accidental eccentricity is not expected to cause a torsional failure. This paper studies the possibility of amplified torsional behaviour of elevated water tanks due to such small accidental eccentricity in the elastic as well as inelastic range; using two simple idealized systems with two coupled lateral-torsional degrees of freedom. The systems are capable of retaining the characteristics of two extreme categories of water tanks namely, a) tanks on staging with less number of columns and panels and b) tanks on staging with large number of columns and panels. The study shows that the presence of a small eccentricity may lead to large displacement of the staging edge in the elastic range, if the torsional-to-lateral time period ratio (τ) of the elevated tanks lies within a critical range of 0.7< τ <1.25. Inelastic behaviour study reveals that such excessive displacement in some of the reinforced concrete staging elements may cause unsymmetric yielding. This may lead to progressive strength deterioration through successive yielding in same elements under cyclic loading during earthquakes. Such localized strength drop progressively develop large strength eccentricity resulting in large localized inelastic displacement and ductility demand, leading to failure. So, elevated water tanks should have τ outside the said critical range to avoid amplified torsional response. The tanks supported on staging with less number of columns and panels are found to have greater torsional vulnerability. Tanks located near faults seem to have torsional vulnerability for large τ.

Seismic Fragility Analysis by Key Components of a Two-pylon Concrete Cable-stayed Bridge (2주탑 콘크리트 사장교의 주요 부재 지진 취약도 분석)

  • Shin, Yeon-Woo;Hong, Ki-Nam;Kwon, Yong-Min;Yeon, Yeong-Mo
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.24 no.4
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    • pp.26-37
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    • 2020
  • This study intends to present a fragility analysis method suitable for concrete cable-stayed bridges by performing an analysis reflecting design criteria and material characteristics from the results of inelastic time-history analysis. In order to obtain the fragility curve of the cable-stayed bridge, the limit state of the main component of the cable-stayed bridge is determined, and the damage state is classified by comparing it with the response value based on inelastic time history analysis. The seismic fragility curve of the cable-stayed bridge was made by obtaining the probability of damage to PGA that the dynamic response of the vulnerable parts to input ground motion would exceed the limit state of each structural member. According to the pylon's fragility curve, the probability of moderate damage at 0.5g is 32% for the longitudinal direction, while 7% for the transversal direction, indicating that the probability of damage in the longitudinal direction is higher in the same PGA than in the transversal direction. The seismic fragility curve of the connections showed a very high probability of damage, meaning that damage to the connections caused by earthquakes is very sensitive compared to damage to the pylon and cables. The cable's seismic fragility curve also showed that the probability of complete damage state after moderate damage state gradually decreased, resulting in less than 30% probability of complete damage at 2.0g.

Comparison between uniform deformation method and Genetic Algorithm for optimizing mechanical properties of dampers

  • Mohammadi, Reza Karami;Mirjalaly, Maryam;Mirtaheri, Masoud;Nazeryan, Meissam
    • Earthquakes and Structures
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    • v.14 no.1
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    • pp.1-10
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    • 2018
  • Seismic retrofitting of existing buildings and design of earth-quake resistant buildings are important issues associated with earthquake-prone zones. Use of metallic-yielding dampers as an energy dissipation system is an acceptable method for controlling damages in structures and improving their seismic performance. In this study, the optimal distribution of dampers for reducing the seismic response of steel frames with multi-degrees freedom is presented utilizing the uniform distribution of deformations. This has been done in a way that, the final configuration of dampers in the frames lead to minimum weight while satisfying the performance criteria. It is shown that such a structure has an optimum seismic performance, in which the maximum structure capacity is used. Then the genetic algorithm which is an evolutionary optimization method is used for optimal arrangement of the steel dampers in the structure. In continuation for specifying the optimal accurate response, the local search algorithm based on the gradient concept has been selected. In this research the introduced optimization methods are used for optimal retrofitting in the moment-resisting frame with inelastic behavior and initial weakness in design. Ultimately the optimal configuration of dampers over the height of building specified and by comparing the results of the uniform deformation method with those of the genetic algorithm, the validity of the uniform deformation method in terms of accuracy, Time Speed Optimization and the simplicity of the theory have been proven.

Evaluation of Seismic Performance of Mixed Building Structures by using the Nonlinear Displacement Mode Method (비선형 변위모드법을 적용한 복합구조물의 내진성능평가)

  • 김부식;송호산
    • Journal of the Earthquake Engineering Society of Korea
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    • v.7 no.6
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    • pp.71-80
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    • 2003
  • Though a nonlinear time history analysis may be provided to estimate more exactly the seismic performance of building structure, approximation methods are still needed in the aspect of practicality and simplicity, In converting a multi-story structure to an equivalent SDOF system, the mode vectors of the multi-story structure are assumed as the mode shape in elastic state regardless of elastic or elastic-plastic state. However, the characteristics of displacement mode are also changed after the yielding made in the structural elements, because the structure becomes inelastic in each incremental load step. In this research, a method of converting MDOF system to ESDOF system is presented by using nonlinear displacement mode considering the mode change of structures after the yielding. Also, the accuracy and efficiency of the method of the nonlinear displacement mode method of the estimate of seismic response of Mixed Building Structures were examined by comparing the displacements of the roof level of the multi-story building structures estimated from this converted displacement response of ESDOF with the displacement of the roof level through the nonlinear dynamic analysis of the multi-story building structures subjected to an actual earthquake excitation.

Inelastic Seismic Response Control of the RC Framed Apartment Building Structures Using Exterior-Installed Kagome Damping System (외부접합형 카고메 감쇠시스템을 사용한 철근콘크리트 라멘조 공동주택 비탄성 지진 응답 제어)

  • Hur, Moo-Won;Chun, Young-Soo;Lee, Sang-Hyun
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.20 no.3
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    • pp.58-65
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    • 2016
  • Various passive energy dissipation systems have been proposed and widely applied to real building structures under seismic load due to their high energy-dissipation potential and low cost for installation and maintenance. This paper presents nonlinear dynamic analysis results of the effectiveness of exterior-installed Kagome damping system(EKDS) in passively reducing seismic response. Kagome damping system proposed by previous studies has isotropic and bi-linear hysteretic characteristics and the installation configuration is newly presented in this study. The 15 and 20 story RC framed apartment buildings are used for verifying the effectiveness of the EKDS. The stiffness ratio of the damper supporting column to the original building, the number of the dampers, and the installed stories were considered as design parameters. Numerical results demonstrated that the EKDS were very effective in reducing both the two horizontal directional seismic responses by just using smaller number of exterior-installed damping system when compared to the traditional one-directional inter-story installed damping systems.

Experimental study on the Behavior of RC Bridge Piers with Various Aspect Ratio (철근 콘크리트 교각의 형상비에 따른 거동 특성에 관한 실험적 연구)

  • Lee, Dae-Hyoung;Kim, Hoon;Kim, Yon-Gon;Chung, Young-Soo;Lee, Jae-Hoon;Cho, Jun-Sang
    • Proceedings of the Korea Concrete Institute Conference
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    • 2001.11a
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    • pp.47-52
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    • 2001
  • Short reinforced concrete bridge piers are particularly susceptible to shear failure as a consequence of the high shear/moment ratio and conservatism in the flexural strength design of existing RC bridge pier, which were constructed before 1992. In addition, shear failure is brittle and involves rapid strength degradation. Inelastic shear deformation is thus unsuitable fur ductile seismic response. It is, however, believed that there are not many experimental research works fur shear failure of the existing RC bridge pier in Korean peninsula subjected to earthquake motions. The object of this research is to evaluate the seismic performance of existing circular RC bridge piers by the quasi-static test. Existing RC bridge piers were moderate seismically designed in accordance with the conventional provisions of Korea Highway Design Specification. This study has been performed to verify the effect of aspect ratio (column height-diameter ratio). Quasi-static test has been done to investigate the physical seismic performance of RC bridge piers, such as lateral force-displacement hysteric curve, envelope curve etc.

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Mitigation of seismic collision between adjacent structures using roof water tanks

  • Mahmoud, Sayed
    • 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.