• Structural Engineering and Mechanics
• /
• 제67권1호
• /
• pp.1-8
• /
• 2018

Shake table tests performed on five 1:3 reduced scale two story RC moment resisting frames having construction defects, have shown severe joint damageability in deficient RC frames, resulting in joint panels' cover spalling and core concrete crushing. Haunch retrofitting technique was adopted herein to upgrade the seismic resistance of the deficient RC frames. Additional four deficient RC frames were built and retrofitted with steel haunch; both axially stiffer and deformable with energy dissipation, fixed to the beam-column connections to reduce shear demand on joint panels. The as-built and retrofitted frames' seismic response parameters are calculated and compared to evaluate the viability of haunch retrofitting technique. The haunch retrofitting technique increased the lateral stiffness and strength of the structure, resulting in the increase of structure's overstrength. The retrofitting increased response modification factor R by 60% to 100%. Further, the input excitation PGA was correlated with the lateral roof displacement to derive structure response curve that have shown significant resistance of retrofitted models against input excitations. The technique can significantly enhance the seismic performance of deficient RC frames, particularly against the frequent and rare earthquake events, hence, promising for seismic risk mitigation.

• Structural Engineering and Mechanics
• /
• 제62권2호
• /
• pp.209-224
• /
• 2017

Elevated water tanks are considered as important structures due to its post-earthquake requirements. Elevated water tank on reinforced concrete frame staging is widely used in India. Different response reduction factors depending on ductility of frame members are used in seismic design of frame staging. The study on appropriateness of response reduction factor for reinforced concrete tank staging is sparse in literature. In the present paper a systematic study on estimation of key components of response reduction factors is presented. By considering the various combinations of tank capacity, height of staging, seismic design level and design response reduction factors, forty-eight analytical models are developed and designed using relevant Indian codes. The minimum specified design cross section of column as per Indian code is found to be sufficient to accommodate the design steel. The strength factor and ductility factor are estimated using results of nonlinear static pushover analysis. It was observed that for seismic design category 'high' the strength factor has lesser contribution than ductility factor, whereas, opposite trend is observed for seismic design category 'low'. Further, the effects of staging height and tank capacity on strength and ductility factors for two different seismic design categories are studied. For both seismic design categories, the response reduction factors obtained from the nonlinear static analysis is higher than the code specified response reduction factors. The minimum dimension restriction of column is observed as key parameter in achieving the desired performance of the elevated water tank on frame staging.

• Earthquakes and Structures
• /
• 제1권2호
• /
• pp.215-230
• /
• 2010

The main objectives of this work were to investigate the effects of the nonlinear behavior of the isolation pads on the seismic response of bridges with rubber bearings, and to identify when base isolation improved their seismic performance. To achieve these objectives a parametric study was conducted designing a set of bridges for three different soil types and varying the number of spans, span lengths, and pier heights. The seismic responses (accelerations, displacements and pier seismic forces) were evaluated for three different structural models subjected to three earthquakes with different dynamic characteristics. The first represented bridges without base isolation; the second corresponded to the same bridges including now rubber bearings as an isolation system, with linear elastic behavior that shifted the natural period of the bridge by a factor of 2 to 4. In the third model the seismic response of bridges supported on lead-Rubber bearings was studied accounting for the nonlinear behavior of the lead. The results show clearly the importance of the nonlinear behavior on the seismic performance of the bridges.

• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 2004년도 추계 학술발표회 제16권2호
• /
• pp.65-68
• /
• 2004

In the seismical capacity evaluation for RC structure wall-slab joint is very important factor. Because lateral load is resistance element and gravity load resistance element are acted mutually in the wall-slab joint. In this paper, to improve the seismic capacity of the wall-slab joint in the existing wall type apartments experiment which improve and retrofit a seismic capacity by unequal angle bracing and carbon sheet attachment are carried out. These methods are also economic and simple in mitigating seismic hazard, improve earthquake-resistance performance, and reduce risk level of building occupants. From the experimental results, the change of strength, degration of stiffness, and energy dissipation are evaluated. It can be concluded that these methods are effective in improving the seismic performance.

• 한국지진공학회:학술대회논문집
• /
• 한국지진공학회 2003년도 춘계 학술발표회논문집
• /
• pp.377-384
• /
• 2003

Recently, there are much concerns about new and innovative transverse materials which could be used instead of conventional transverse steel in reinforced concrete bridge piers. FRP materials could be substituted for conventional transverse steel because of their sufficient strength, light weight, easy fabrication, and useful applicability to any shapes of pier sections, such as rectangular or circular sections. The objective of this research is to evaluate the seismic performance of reinforced concrete bridge pier specimens with FRP transverse reinforcement by means of the Quasi-Static test. In the first task, test columns were made using FRP rope, but these specimens appeared to fail at low displacement ductility levels due to insufficient confinement of strand extension itself. Therefore, the second task was to evaluate the seismic performance of test specimens transversely confined with FRP band. Although FRP banded specimens showed lower seismic performance than the specimen with spiral reinforcing steel, it satisfied with the response modification factor, 3, required for the single column of Korea bridge roadway design code. It was concluded that FRP band could be efficiently substituted for conventional reinforcing steel.

• 한국지진공학회논문집
• /
• 제26권1호
• /
• pp.31-38
• /
• 2022

Based on the nonlinear static analysis and the approximate seismic evaluation method adopted in "Guidelines for seismic performance evaluation for existing buildings, two methods to calculate strength demand for retrofitting individual structural walls in unreinforced masonry buildings are proposed." The displacement coefficient method to determine displacement demand from nonlinear static analysis results is used for the inverse calculation of overall strength demand required to reduce the displacement demand to a target value meeting the performance objective of the unreinforced masonry building to retrofit. A preliminary seismic evaluation method to screen out vulnerable buildings, of which detailed evaluation is necessary, is utilized to calculate overall strength demand without structural analysis based on the difference between the seismic demand and capacity. A system modification factor is introduced to the preliminary seismic evaluation method to reduce the strength demand considering inelastic deformation. The overall strength demand is distributed to the structural walls to retrofit based on the wall stiffness, including the remaining walls or otherwise. Four detached residential houses are modeled and analyzed using the nonlinear static and preliminary evaluation procedures to examine the proposed method.

• 한국지진공학회논문집
• /
• 제6권5호
• /
• pp.53-58
• /
• 2002

최근, 콘크리트 충전 강교각은 신속한 시공과 뛰어난 연성능력으로 인해 도심지에서 철근 콘크리트 교각의 대안이 되고 있다. 이러한 콘크리트 충전 강교각은 내진 설계에서도 훌륭한 성능을 발휘할 수 있으나 내진 설계의 가이드가 없어 내진 설계시 그 성능을 모두 반영하지 못하고 있는 상황이다. 이에 실제 적용을 위해 콘크리트 충전 강교각 실험으로부터 얻어진 실험치로부터 내진 설계에 지침이 될 수 있는 가이드를 제시하고자 한다. 콘크리트 충전 강교각과 일반 강교각의 연성 능력을 평가하기 위해 준 정적 반복 재하 실험을 수행하고, 지진 거동을 검증하기 위해 고베 지진을 입력 데이타로 한 유사 동적 실험을 수행한다. 콘크리트 충전 강교각은 일반 강교각에 비해 만족할 만한 연성도와 강도를 보이고, 동적 거동은 상대적으로 큰 이력감쇠를 증명한다. 실험으로 얻어진 데이터를 근거로 하여 콘크리트 충전 강교각의 내진 성능을 정량화 하고, 탄성응답 스펙트럼에 의한 지진응답 수정계수법과 유효 점성 감쇠를 이용한 성능 곡선 및 요구 스펙트럼에 의한 성능기초 설계법의 비교를 통하여, 콘크리트 충전 강교각과 일반 강교각의 내진 성능을 평가한다. 이러한 내진 성능 평가를 기초로 하여, 일반 강교각과 더불어 내진 설계에 적용할 수 있는 콘크리트 충전 강교각의 지진응답 수정계수를 제시한다.

• 한국강구조학회 논문집
• /
• 제22권1호
• /
• pp.75-85
• /
• 2010

최근 초고층 건물에 구조적인 측면을 고려한 Freeform Structure라는 개념이 등장하고 있다. 이 형태는 Diagrid, Cantilevered, Tilted로 대변될 수 있는데 특히 다이아 그리드 시스템은 횡저항에 하중의 흐름을 가새 프레임을 따라 분산시킴으로써 효율적인 거동을 보이기 때문에 그만큼 부재를 경량화시킬 수가 있다. 그러나 Diagrid 구조시스템의 내진성능 평가를 위한 반응수정계수에 대한 신뢰성 있는 자료가 없기 때문에 우수한 내진성능이 예상됨에도 불구하고 기타구조 등으로 설계되고 있다. 본 연구에서는 실대형 실험을 통해 Diagrid 구조의 반응수정계수를 실험적으로 규명하고자 한다.

• Earthquakes and Structures
• /
• 제17권1호
• /
• pp.75-89
• /
• 2019

The paper presents experimental and numerical studies carried out on low-rise RC frames, typically found in developing countries. Shake table tests were conducted on 1:3 reduced scaled two-story RC frames that included a code conforming SMRF model and another non-compliant model. The later was similar to the code conforming model, except, it was prepared in concrete having strength 33% lower than the design specified, which is commonly found in the region. The models were tested on shake table, through multiple excitations, using acceleration time history of 1994 Northridge earthquake, which was linearly scaled for multi-levels excitations in order to study the structures' damage mechanism and measure the structural response. A representative numerical model was prepared in finite element based program SeismoStruct, simulating the observed local damage mechanisms (bar-slip and joint shear hinging), for seismic analysis of RC frames having weaker beam-column joints. A suite of spectrum compatible acceleration records was obtained from PEER for incremental dynamic analysis of considered RC frames. The seismic performance of considered RC frames was quantified in terms of seismic response parameters (seismic response modification, overstrength and displacement amplification factors), for critical comparison.

• 한국전산구조공학회논문집
• /
• 제24권6호
• /
• pp.707-714
• /
• 2011

층간변위율은 구조물의 내진성능을 평가하는데 널리 사용되는 지표 중의 하나이다. 지진에 의해 발생하는 층간변위율이 클수록 지진에 의한 손상이 커지는 것으로 알려져 있다. 이러한 이유로 층간변위율을 감소시키는 설계기술은 내진설계분야에서 중요한 이슈이다. 그럼에도 불구하고 현재까지는 지진하중을 받는 구조물에 대한 현실적인 층간변위설계기법이 제시되고 있지 않다. 본 연구는 재분배 기법을 이용하여 철골모멘트골조의 내진성능을 향상시키기는 최적 층간변위설계기법을 제시한다. 이 기법은 층간변위율 차이를 최소화함으로써 구조물의 층별 층간변위율을 고르게 분포시키고, 최대 층간변위율을 감소시킨다. 이 기법은 단위하중법으로 계산된 변위기여도를 이용하여 구조재의 단면성능을 재설계하기 때문에 반복적인 구조해석없이 구조물의 내진성능을 향상시킬 수 있는 장점을 가진다. 이 기법의 효율성 검증을 위해 철골모멘트골조 예제 적용을 실시하였다.