• Earthquakes and Structures
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• 제24권3호
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• pp.183-192
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• 2023

It is essential to properly understand the seismic behavior of reinforced concrete (RC) columns confined by stirrups that experience different corrosion rates. The current study investigated the effect of seismic performance indicators such as strength loss, energy dissipation rate, ductility and hysteresis damping on specimens and models for different stirrup corrosion rates. Analysis revealed the adverse effects of corrosion on the bond performance between the concrete and steel bars which affected the seismic performance of the columns. It was found that with increasing corrosion rate, ductility and energy dissipation of the specimens decreased. Compared with the uncorroded specimen, the ductility factor and energy dissipation decreased observably, by 22.89% and 60.64%, respectively. An attenuation relationship is proposed for the corrosion rate of the stirrups for different stirrup yield strengths, concrete compressive strengths, concrete covers and stirrup spacing.

• Steel and Composite Structures
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• 제50권6호
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• pp.643-658
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• 2024

The main aim of this study is to quantify the code seismic design coefficients of the RCS system, which consisted of reinforced concrete columns and steel beams, based on the FEMA P-695 methodology. The underlying intention is to evaluate the seismic performance of the RCS system at the system level rather than the connection level. A set of 24 archetype buildings with a various number of stories, beam span lengths, gravity load levels, and seismic load levels are selected and designed based on the prevailing code requirements. Nonlinear analytical models are developed and validated by experimental tests. The pushover and response history dynamic analyses are conducted to evaluate the required data in the performance quantification process. The results show that the design coefficients suggested by the code are acceptable. However, the level of conservatism is very high. Thus, it is possible to use a larger R-factor in the design process or make some relaxations in the design requirements related to this structural system.

• 한국지진공학회논문집
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• 제21권2호
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• pp.105-114
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• 2017

Nonlinear analysis for seismic performance evaluation of existing building usually takes 4~5 times more than linear analysis based on KBC code. To obtain accurate results from the nonlinear analysis, there are a lot of things to be considered for nonlinear analysis modeling. For example, reinforcing layout, applied load and seismic details affect behavior of structural members for the existing building. Engineer-oriented computerized system was developed for engineers to evaluate effective seismic performance of existing buildings with abiding by seismic design principles. Using the engineer-oriented program, seismic performance evaluation of reinforced concrete building was performed. Nonlinear hinge properties were applied with real time multiple consideration such as section layout, section analysis result, applied load and performance levels. As a result, the building was evaluated to satisfy LS(Life Safety) performance level. A comparison between engineer-oriented and program-oriented results is presented to show how important the role of structural engineer is for seismic performance evaluation of existing buildings.

• 한국지진공학회논문집
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• 제21권2호
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• pp.95-103
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• 2017

In order to modeling seismic isolation system such as lead-rubber bearing (LRB), bilinear model is widely used by many researchers. In general, an actual force-displacement relationship for LRB has a smooth hysteretic shape. So, Bouc-Wen model with smooth hysteretic shape represents more accurately actual hysteretic shape than bilinear model. In this study, seismic responses for seismically isolated nuclear power plant (NPP) with LRB modelled by Bouc-Wen and bilinear models are compared with those of NPP without seismic isolation system. To evaluate effect of earthquake characteristics for seismic responses of NPP isolated by LRB, 5 different site class earthquakes distinguished by Geomatrix 3rd Letter Site Classification and artificially generated earthquakes corresponding to standard design spectrum by Reg. Guide 1.60 are used as input earthquakes. From the seismic response results of seismically isolated NPP, it can be observed that maximum displacements of seismic isolation modelled by Bouc-Wen model are larger than those by bilinear model. Seismic responses of NPP with LRB is significantly reduced than those without LRB. This reduction effect for seismic responses of NPP subjected to Site A (rock) earthquakes is larger than that to Site E (soft soil) earthquakes.

• Structural Engineering and Mechanics
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• 제40권3호
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• pp.315-334
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• 2011

Seismic isolated building structures are examined in this study. The triple concave friction pendulum (TCFP) is used as a seismic isolation system which is easy to be manufactured and enduring more than traditional seismic isolation systems. In the TCFP, take advantage of weight which pendulum carrying and it's geometry in order to obtain desirable result of seismic isolation systems. These systems offer advantage to buildings which subject to severe earthquake. This is result of damping force of earthquake by means of their internal constructions, which consists of multiple surfaces. As the combinations of surfaces upon which sliding is occurring change, the stiffness and effective friction change accordingly. Additionally, the mentioned the TCFP is modeled as of a series arrangement of the three single concave friction pendulum (SCFP) bearings. A two dimensional- and eight- story of a building with and without isolation system are used in the time history analysis in order to investigate of the effectiveness of the seismic isolation systems on the buildings. Results are compared with each other to emphasize efficiency of the TCFP as a seismic isolation device against the other friction type isolation system like single and double concave surfaces. The values of the acceleration, floor displacement and isolator displacement obtained from the results by using different types of the isolation bearings are compared each other. As a result, the findings show that the TCFP bearings are more effective devices for isolation of the buildings against severe earthquakes.

• Structural Engineering and Mechanics
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• 제82권1호
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• pp.55-67
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• 2022

The precast reinforced concrete frame system is a method for industrialization of construction. However, the seismic performance factor of this structural system is not explicitly clarified in some existing building codes. In this paper, the seismic performance factor for the existing precast concrete building frame systems with cast-in-situ reinforced shear walls were evaluated. Nonlinear behavior of the precast beam-column joints and cast-in-situ reinforced shear walls were considered in the modeling of the structures. The ATC-19's coefficient method was used for calculating the seismic performance factor and the FEMA P-695's approach was adopted for evaluating the accuracy of the computed seismic performance factor. The results showed that the over-strength factor varies from 2 to 2.63 and the seismic performance factor (R factor) varies from 5.1 to 8.95 concerning the height of the structure. Also, it was proved that all of the examined buildings have adequate safety against the collapse at the MCE level of earthquake, so the validity of R factors was confirmed. The obtained incremental dynamic analysis (IDA) results indicated that the minimum adjusted collapse margin ratio (ACMR) of the precast buildings representing the seismic vulnerability of the structures approximately equaled to 2.7, and pass the requirements of FEMA P-695.

• International Journal of Concrete Structures and Materials
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• 제9권1호
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• pp.89-118
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• 2015

The geometric nonlinearity of off-diagonal bracing system (ODBS) could be a complementary system to covering and extending the nonlinearity of reinforced concrete material. Finite element modeling is performed for flexural frame, x-braced frame and the ODBS braced frame system at the initial phase. Then the different models are investigated along various analyses. According to the experimental results of flexural and x-braced frame, the verification is done. Analytical assessments are performed in according to three dimensional finite element modeling. Nonlinear static analysis is considered to obtain performance level and seismic behaviour, and then the response modification factors calculated from each model's pushover curve. In the next phase, the evaluation of cracks observed in the finite element models, especially for RC members of all three systems is performed. The finite element assessment is performed on engendered cracks in ODBS braced frame for various time steps. The nonlinear dynamic time history analysis accomplished in different stories models for three records of Elcentro, Naghan and Tabas earthquake accelerograms. Dynamic analysis is performed after scaling accelerogram on each type of flexural frame, x-braced frame and ODBS braced frame one by one. The base-point on RC frame is considered to investigate proportional displacement under each record. Hysteresis curves are assessed along continuing this study. The equivalent viscous damping for ODBS system is estimated in according to references. Results in each section show the ODBS system has an acceptable seismic behaviour and their conclusions have been converged when the ODBS system is utilized in reinforced concrete frame.

• Earthquakes and Structures
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• 제17권4호
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• pp.373-385
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• 2019

In this article, different frequently adopted modeling aspects of linear and nonlinear dynamic soil-structure interaction (SSI) are studied on a pile-supported integral abutment bridge structure using the open-source platform OpenSees (McKenna et al. 2000, Mazzoni et al. 2007, McKenna and Fenves 2008) for a 2D domain. Analyzed approaches are as follows: (i) free field input at the base of fixed base bridge; (ii) SSI input at the base of fixed base bridge; (iii) SSI model with two dimensional quadrilateral soil elements interacting with bridge and incident input motion propagating upwards at model bottom boundary (with and without considering the effect of abutment backfill response); (iv) simplified SSI model by idealizing the interaction between structural and soil elements through nonlinear springs (with and without considering the effect of abutment backfill response). Salient conclusions of this paper include: (i) free-field motions may differ significantly from those computed at the base of the bridge foundations, thus put a significant bias on the inertial component of SSI; (ii) conventional modeling of SSI through series of soil springs and dashpot system seems to stay on the safer side under dynamic conditions when one considers the seismic actions on the structure by considering a fully coupled SSI model; (iii) consideration of abutment-backfill in the SSI model positively affects the general response of the bridge, as a result of large passive resistance that may develop behind the abutments.

• 한국강구조학회 논문집
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• 제12권5호통권48호
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• pp.559-568
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• 2000

본 논문에서는 용접 수평헌치로 보강된 내진 철골모멘트접합부를 간단히 해석적으로 모형화하는 새로운 방안을 제시하였다. 1994년 노스리지 및 1995년 효고현 남부 지진피해 이후 철골모멘트접합부의 새로운 내진상세가 다양하게 제시되어 왔다. 이 가운데 보의 하부를 헌치로서 보강하는 방안도 유망한 대안의 하나로 평가되고 있다. 삼각헌치 대신 수평헌치를 도입하면 보강작업이 용이하고 경제적으로도 유리하나 아직 응력전달 메카니즘이 규명되지 않고 있어서 정립된 설계방안이 존재하지 않는다. 본 연구에서는 보와 헌치의 상호작용 및 변형의 적합조건을 고려하여 이 문제의 해결방안을 제시하였다. 본 연구의 방안에 의해 설계에 필요한 보-헌치의 상호작용력 및 보와 헌치 플랜지 용접부의 휨응력도를 만족스럽게 예측할 수 있다.

• 한국구조물진단유지관리공학회 논문집
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• 제17권4호
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• pp.1-8
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• 2013

철근콘크리트 구성요소에 대한 비탄성 거동 모델 개발은 철근콘크리트 구조물에 대한 성능기반 내진평가의 정밀도 향상에 있어 매우 중요한 요소로 본 연구에서는 지진과 같은 불규칙 반복 하중에 대한 철근콘크리트 구조물의 비선형 동적응답을 예측함에 있어 콘크리트 구성모델의 특성에 따른 민감도를 고찰하고자 하였다. 해석결과에 따르면 구속된 코어 콘크리트 모델과 일반 콘크리트의 구성모델은 동적응답에 큰 영향을 끼치지 않았으나 철근의 경우에 층간변위와 관련하여 구성모델에 따른 동적거동은 매우 민감하게 응답하는 것으로 나타났으며, 몇 개 층에서의 층간변위는 그 차이가 철근 구성모델 선택에 따라 2배 이상 차이 나는 것으로 나타났다. 따라서 Non-ductile과 Ductile 골조 공히 비선형 동적해석을 수행하는데 있어 정밀한 철근 구성모델의 선택은 매우 중요한 것으로 사료된다.