• Earthquakes and Structures
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• 제1권1호
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• pp.69-91
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• 2010

Current seismic design codes do not contemplate explicitly some variables that are relevant for the design of structures subjected to ground motions exhibiting large energy content. Particularly, the lack of explicit consideration of the cumulative plastic demands and of the degradation of the hysteretic cycle may result in a significant underestimation of the lateral strength of reinforced concrete structures built on soft soils. This paper introduces and illustrates the use of a numerical performance-based methodology for the predesign of standard-occupation reinforced concrete ductile structures. The methodology takes into account two limit states, the performance of the non-structural system, and in the case of the life safety limit state, the effect of cumulative plastic demands and of the degradation of the hysteretic cycle on the assessment of structural performance.

• 국제강구조저널
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• 제18권4호
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• pp.1464-1469
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• 2018

Steel frames with ductile connections have good seismic performance under strong earthquake, they are now popular for high seismic design. In order to simplify the process of numerical analysis of the steel frames with ductile connections, simplified connection models are introduced, two types of springs are placed in the simplified connection model, which can simulate deformation of the panel zone and members. 6-story-3-bay steel frames with ductile connections are simplified and carried out modal analysis, fundamental periods of the frames predicted by finite-element analysis for simplified steel frame models were compared to the results for actual frame models. 2-story steel frame with reduced beam section connections is simplified and carried out pseudo-static analysis, hysteretic curves and skeleton curves of the frame obtained by finite-element analysis for simplified steel frame model are compared to test results. The comparison show that the difference between them is small, it is reliable and effective to predict mechanical properties of the steel frame with ductile connection by finite-element analysis of simplified steel frame model.

• Structural Engineering and Mechanics
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• 제73권3호
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• pp.239-257
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• 2020

In the present study, an innovative steel bracket and haunch hybrid scheme is devised, for retrofitting of earthquake damaged deficient beam-column sub-assemblages. Formulations are presented for evaluating haunch force factor under combined load case of lateral and gravity loads for the design of double haunch retrofit. The strength hierarchies of control and retrofitted beam-column sub-assemblages are established to showcase the efficacy of the retrofit in reversing the undesirable strength hierarchy. Further, the efficacy of the proposed retrofit scheme is demonstrated through experimental investigations carried out on gravity load designed (GLD), non-ductile and ductile detailed beam-column sub-assemblages which were damaged under reverse cyclic loading. The maximum load carried by repaired and retrofitted GLD specimen in positive and negative cycle is 12% and 28% respectively higher than that of the control GLD specimen. Further, the retrofitted GLD specimen sustained load up to drift ratio of 5.88% compared with 2.94% drift sustained by control GLD specimen. Repaired and retrofitted non-ductile specimen, could attain the displacement ductility of three during positive cycle of loading and showed improved ductility well above the expected displacement ductility of three during negative cycle. The hybrid haunch retrofit restored the load carrying capacity of damaged ductile specimen to the original level of control specimen and improved the ductility closer to the expected displacement ductility of five. The total cumulative energy dissipated by repaired and retrofitted GLD, non-ductile and ductile specimens are respectively 6.5 times, 2.31 times, 1.21 times that of the corresponding undamaged control specimens. Further, the damage indices of the repaired and retrofitted specimens are found to be lower than that of the corresponding control specimens. The novel and innovative steel bracket and haunch hybrid retrofit scheme proposed in the present study demonstrated its effectiveness by attaining the required displacement ductility and load carrying capacity and would be an excellent candidate for post-earthquake retrofit of damaged existing RC structures designed according to different design evolutions.

• Earthquakes and Structures
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• 제13권2호
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• pp.177-191
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• 2017

In the present study, exterior beam column sub-assemblages are designed in accordance with the codal stipulations prevailed at different times prior to the introduction of modern seismic provisions, viz., i) Gravity load designed with straight bar anchorage (SP1), ii) Gravity load designed with compression anchorage (SP1-D), iii) designed for seismic load but not detailed for ductility (SP2), and iv) designed for seismic load and detailed for ductility (SP3). Comparative seismic performance of these exterior beam-column sub-assemblages are evaluated through experimental investigations carried out under repeated reverse cyclic loading. Seismic performance parameters like load-displacement hysteresis behavior, energy dissipation, strength and stiffness degradation, and joint shear deformation of the specimens are evaluated. It is found from the experimental studies that with the evolution of the design methods, from gravity load designed to non-ductile and then to ductile detailed specimens, a marked improvement in damage resilience is observed. The gravity load designed specimens SP1 and SP1-D respectively dissipated only one-tenth and one-sixth of the energy dissipated by SP3. The specimen SP3 showcased tremendous improvement in the energy dissipation capacity of nearly 2.56 times that of SP2. Irrespective of the level of design and detailing, energy dissipation is finally manifested through the damage in the joint region. The present study underlines the seismic deficiency of beam-column sub-assemblages of different design evolutions and highlights the need for their strengthening/retrofit to make them fit for seismic event.

• 한국지진공학회논문집
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• 제25권4호
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• pp.161-168
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• 2021

Existing old reinforced concrete buildings could be vulnerable to earthquakes because they were constructed without satisfying seismic design and detail requirements. In current seismic design standards, the target collapse probability for a given Maximum Considered Earthquake (MCE) ground-shaking hazard is defined as 10% for ordinary buildings. This study aims to estimate the collapse probabilities of a three-story, old, reinforced concrete building designed by only considering gravity loads. Four different seismic design categories (SDC), A, B, C, and D, are considered. This study reveals that the RC building located in the SDC A region satisfies the target collapse probability. However, buildings located in SDC B, C, and D regions do not meet the target collapse probability. Since the degree of exceedance of the target probability increases with an increase in the SDC level, it is imminent to retrofit non-ductile RC buildings similar to the model building. It can be confirmed that repair and reinforcement of old reinforced concrete buildings are required.

• 한국지진공학회논문집
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• 제15권1호
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• pp.11-18
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• 2011

현재 국내 철골 모멘트골조 접합부는 대부분 공장제작으로 품질관리가 잘 이루어져 연성능력이 상당한 수준이다. 문헌에 의하면 국내 접합부는 미국 철강협회에서 철골 중간모멘트골조에 대해 제시한 성능 기준을 충분히 만족하고 있다. 그런데 이전 설계기준인 KBC2005에서는 철골모멘트골조에 연성모멘트골조 하나만을 제공하였으나 현 KBC2009 기준은 보통, 중간, 특수모멘트골조로 다양하게 제공하고 있다. 여기서 국내 접합부 형식을 그대로 사용했을 때 어떤 시스템이 적합한지 조사할 필요성이 있다. 따라서 본 연구에서는 KBC2005의 연성모멘트골조와 KBC2009의 중간모멘트골조의 거동을 비교하여 국내에 적합한 설계 방법을 찾고자 하였다. 연구 결과 기존 연성모멘트골조의 설계 계수를 따르더라도 성능목표를 충분히 만족하는 것으로 나타났다.

• 소성∙가공
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• 제23권4호
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• pp.238-243
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• 2014

Recently, magnesium alloys have been widely used in the automotive, aerospace and electronics industries with the advantages of high specific strength, excellent machinability, high electrical conductivity, and high thermal conductivity. Deep drawn magnesium alloys not only meet the demands environmentally and the need for lighter products, but also can lead to remarkably improved productivity and more rapid qualification of the product The current study reports on a failure prediction procedure using finite element modeling (FEM) and a ductile fracture criterion and applies this procedure to the design of a deep drawing process. Critical damage values were determined from a series of uniaxial tensile tests and FEM simulations. They were then expressed as a function of strain rate and temperature. Based on the plastic deformation histories obtained from the FEM analyses of the warm drawing process and the critical damage value curves, the initiation time and location of fracture were predicted. The proposed method was applied to the process design for fabrication of a Mg automotive compressor case and verified with experimental results. The final results indicate that a Mg case part 39% lighter than an Al die casting part can be produced without any defects.

• 한국전산구조공학회논문집
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• 제29권2호
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• pp.187-192
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• 2016

일반설계에서 탄성거동을 전제로 구조물을 설계하는 것과 달리 내진설계는 구조물의 소성거동을 규명하고 조정하여 붕괴를 방지하는 것이 목적이다. 일반교량의 경우에 요구되는 붕괴방지수준은 교량의 특정한 구조부재의 소성거동으로 낙교를 방지하여 지진발생 이후에 긴급차량의 통과를 가능하게 하는 것이다. 이러한 소성거동은 연결부분 또는 교각기둥에 제한되고 각 경우에 적절한 조치가 요구된다. 도로교설계기준은 교각기둥에서 소성힌지를 형성하여 연성붕괴기구를 구성하는 설계방식과 함께 철근콘크리트 교각을 하부구조로 하는 교량을 대상으로 연결부분의 항복을 이용하여 취성붕괴기구를 구성하는 연성도 내진설계를 부록으로 제시하고 있다. 이 연구에서는 철근콘크리트 교각기둥과 강재받침으로 설계된 일반교량을 선정하고 연성붕괴기구와 취성붕괴기구를 모두 고려한 붕괴방지 설계절차 및 도로교설계기준에 요구되는 수정사항을 제안하였다.

• 한국지진공학회논문집
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• 제6권4호
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• pp.1-6
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• 2002

일반설계에서 요구하는 구조물의 안전성은 탄성영역에서 일정수준의 안전계수를 확보하여 만족된다. 그러나 내진설계에서의 안전성은 소성영역에서 구조물의 형상에 따라 특정한 연성파괴메카니즘을 유도하여 확보하도록 요구하고 있다. 그러므로 이러한 안전성은 구조물의 기본설계단계에서 여러 개의 대안을 가지고 비교, 검토를 수행하여 확보되어야 하며 실시설계단계에서 이를 확인하는 작업이 이루어져야 한다. 이 연구에서는 일반도로교량을 대상으로 하여 기본설계와 실시설계에 사용하는 모델을 설정하였으며 양 모델의 동적거동특성인 주기와 모드형상을 비교하고 다중모드스펙트럼해석을 적용하여 파괴메카니즘을 규명하였다. 기본설계와 실시설계에 사용하는 모델로 각각 확인한 파괴메카니즘을 비교하여 기본설계모델의 타당성을 입증하고 실무에 적용할 수 있는 내진해석모델로 제시하였다.

• Computers and Concrete
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• 제7권3호
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• pp.203-220
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• 2010

In the present study, exterior beam-column sub-assemblage from a regular reinforced concrete (RC) building has been considered. Two different types of beam-column sub-assemblages from existing RC building have been considered, i.e., gravity load designed ('GLD'), and seismically designed but without any ductile detailing ('NonDuctile'). Hence, both the cases represent the under-designed structure at different time frame span before the introduction of ductile detailing. For designing 'NonDuctile' structure, Eurocode and Indian Standard were considered. Non-linear finite element (FE) program has been employed for analysing the sub-assemblages under cyclic loading. FE models were developed using quadratic concrete brick elements with embedded truss elements to represent reinforcements. It has been found that the results obtained from the numerical analysis are well corroborated with that of experimental results. Using the validated numerical models, it was proposed to correlate the energy dissipation from numerical analysis to that from experimental analysis. Numerical models would be helpful in practice to evaluate the seismic performance of the critical sub-assemblages prior to design decisions. Further, using the numerical studies, performance of the sub-assemblages with variation of axial load ratios (ratio is defined by applied axial load divided by axial strength) has been studied since many researchers have brought out inconsistent observations on role of axial load in changing strength and energy dissipation under cyclic load.