• 한국지진공학회논문집
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• 제24권1호
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• pp.39-47
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• 2020

Lightly reinforced concrete (RC) moment frames may suffer significant damage during large earthquake events. Most buildings with RC moment frames were designed without considering seismic loads. The load-displacement response of gravity load designed frames could be altered by masonry infill walls. The objective of this study is to investigate the load-displacement response of gravity load designed frames with masonry infill walls. For this purpose, three-story gravity load designed frames with masonry infill walls were considered. The masonry infilled RC frames demonstrated larger lateral strength and stiffness than bare RC frames, whereas their drift capacity was less than that of bare frames. A specimen with a partial-height infill wall showed the least drift capacity and energy dissipation capacity. This specimen failed in shear, whereas other specimens experienced a relatively ductile failure mode (flexure-shear failure).

• 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.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 1997년도 추계 학술발표회 논문집 Proceedings of EESK Conference-Fall 1997
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• pp.209-216
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• 1997

The seismic performance of R/C frame structure designed for gravity load investigated in this paper. The investigation shows a satisfactory seismic performance against moderate earthquakes but column sway failure mechanism against severe earthquakes. Capacity design method is employed to redesign the R/C frame to improve seismic performance. This study provides an insight an insight into seismic upgrading methodology for medium rise R/C frame structures designed gravity load.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1991년도 봄 학술발표회 논문집
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• pp.72-78
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• 1991

An improved procedure for earthquake resistant design of multistory building structures is proposed in this study. The effect of gravity load on seismic response of structures is evaluated through nonlinear dynamic analyses of a single story example structure. The presence of gravity load tends to initiate plastic hinge formation in earlier stage of a strong earthquake. However, the effect of gravity load seems to disapper as ground motion is getting stronger. And one of shortcomings in current earthquake resistant codes is overestimation of gravity load effects when earthquake load is applied at the same time so that it may leads to less inelastic deformation or structural damage in upper stories, and inelastic deformation is increased in lower stories. Based on these observation, an improved procedure for earthquake resistant design is derived by reducing the factor for gravity load and inceasing that for seismic load. Structures designed by the proposed design procedure turned out to have increased safety and stability against strong earthquakes.

• Steel and Composite Structures
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• 제28권6호
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• pp.719-734
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• 2018

Prior to the introduction of modern seismic guidelines, it was a common practice to provide straight bar anchorage for beam bottom reinforcement of gravity load designed building. Exterior joints with straight bar anchorages for beam bottom reinforcements are susceptible to sudden anchorage failure under load reversals and hence require systematic seismic upgradation. Hence in the present study, an attempt is made to upgrade exterior beam-column sub-assemblage of a three storied gravity load designed (GLD) building with single steel haunch. Analytical formulations are presented for evaluating the haunch forces in single steel haunch retrofit. Influence of parameters that affect the efficacy and effectiveness of the single haunch retrofit are also discussed. The effectiveness of the single haunch retrofit for enhancing seismic performance of GLD beam-column specimen is evaluated through experimental investigation under reverse cyclic loading. The single steel haunch retrofit had succeeded in preventing the anchorage failure of beam bottom bars of GLD specimen, delaying the joint shear damage and partially directing the damage towards the beam. A remarkable improvement in the load carrying capacity of the upgraded GLD beam-column sub-assemblage is observed. Further, a tremendous improvement in the energy dissipation of about 2.63 times that of GLD specimen is observed in the case of upgraded GLD specimen. The study also underlines the efficacy of single steel haunch retrofit for seismic upgradation of deficient GLD structures.

• 한국지진공학회논문집
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• 제23권5호
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• pp.249-259
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• 2019

To study the seismic resistance of the shear capacity of the RC beam-column joints of two-story and four-story RC buildings, sample buildings are designed with ordinary moment resisting frame. For the shear capacity of joints, the equations of FEMA 356 and NZ seismic assessment are selected and compared. For comparison, one group of buildings is designed only for gravity loads and the other group is designed for seismic and gravity loads. For 16 cases of the designed buildings, seismic performance point is evaluated through push-over analysis and the capacity of joint shear strength is checked. Not only for the gravity designed buildings but also for seismic designed buildings, the demand of joint shear is exceeding the capacity at exterior joints. However, for interior joint, the demand of joint shear exceeds the capacity only for one case. At exterior joints, the axial load stress ratio is lower than 0.21 for gravity designed buildings and 0.13 for seismic designed buildings.

• Earthquakes and Structures
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• 제16권2호
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• pp.235-251
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• 2019

Corrosion of reinforcement is the greatest threat to the safety of existing reinforced concrete (RC) structures. Most of the olden structures are gravity load designed (GLD) and are seismically deficient. In present study, investigations are carried out on corrosion damaged GLD beam-column sub-assemblages under reverse cyclic loading, in order to evaluate their seismic performance. Five GLD beam-column sub-assemblage specimens comprising of i) One uncorroded ii) Two corroded iii) One uncorroded strengthened with steel bracket and haunch iv) One corroded strengthened with steel bracket and haunch, are tested under reverse cyclic loading. The performances of these specimens are assessed in terms of hysteretic behaviour, energy dissipation and strength degradation. It is noted that the nature of corrosion i.e. uniform or pitting corrosion and its location have significant influence on the behaviour of corrosion damaged GLD beam-column sub-assemblages. The corroded specimens with localised corrosion pits showed in-cyclic strength degradation. The study also reveals that external strengthening which provides an alternate force path but depends on the strength of the existing reinforcement bars, is able to mitigate the seismic risk of corroded GLD beam-column sub-assemblages to the level of control uncorroded GLD specimen.

• 전산구조공학
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• 제6권3호
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• pp.67-80
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• 1993

본 연구에서는 지진에 대한 고층건물의 응답특성, 그리고 지진응답에 미치는 중력하중의 영향과 중력하중의 영향이 내진설계에 미치는 중요성을 산정하였다. 이를 위해서 예제 구조물에 대한 정적해석 및 지진하중에 대한 동적해석을 하였다. 지진에 대한 고층건물의 지진응답 특성을 파악하기 위하여 비탄성 변형의 건물 높이에 따른 분포를 알아보았다. 지진이 발생하면 휨모멘트 요구도가 건물의 상부층보다 하부층에서 상대적으로 더 많이 증가해서 설계모멘트와의 차이가 건물의 하부층으로 갈수록 더 커진다. 그 결과 현재 쓰이는 내진설계방법에 따라 설계된 예제 건물들은 지진에 대하여 비탄성 응답이 건물의 각 층마다 서로 다르게 발생하는데 주로 건물의 하부층에서 큰 비탄성 응답이 발생한다. 또한 설계시에 고려된 중력하중 때문에 구조적 손상이 건물의 꼭대기 층에서 아래로 갈수록 크게 증가한다. 구조물의 지진응답에 관하여 중력하중은 보의 항복시간을 앞당기며, 보의 양단의 소성힌지에 각기 다른 비탄성 거동을 유발시킨다. 그러나 중력하중에 의한 초기 휨모멘트의 영향은 보가 비탄성 거동을 계속함에 따라 재분배되어 보의 양단에서 그 영향이 감소되며 비탄성 변형이 계속되면 크게 감소한다. 중력하중에 의한 초기 휨모멘트의 영향이 감소는 고층건물의 내진설계에 있어서 중력하중의 영향이 주는 의미는 기둥과 보의 휨강도를 결정할 때 현재의 방법보다 중력하중의 영향을 줄이고 지진하중의 영향을 증가시켜야 한다는 것이다.

• 대한전기학회논문지:시스템및제어부문D
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• 제49권5호
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• pp.257-263
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• 2000

One of the basic assumptions in the static gait design for a walking robot is that the weight of leg should be negligible compared to that of body, so that the total gravity center is not affected by swing of a leg. Based on the ideal assumption of zero leg-weight, conventional static gait has been simply designed for the gravity center of body to be inside the support polygon, consisting of each support leg's tip position. In case that the weight of leg is relatively heavy, however, while the gravity center of body is kept inside the support polygon, the total gravity center of walking robot can be out of the polygon due to weight of a swinging leg, which causes instability in walking. Thus, it is necessary in the static gait design of a real robot a compensation scheme for the fluctuation in the gravity center. In this paper, a body impedance control is proposed to obtain the total gravity center based on foot forces measured from load cells of a real walking robot and to adjust its position to track the pre-designed trajectory of the corresponding ideal robot's body center. Therefore, the walking stability is secured even in case that the weight of leg has serious influence on the total gravity center of robot.

• Wind and Structures
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• 제12권5호
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• pp.425-439
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• 2009

The expediency of revising universal rules for the combination of gravity and lateral actions of wind force-resisting steel structures recommended by the Standards EN 1990 and ASCE/SEI 7-05 is discussed. Extreme wind forces, gravity actions and their combinations for the limit state design of structures are considered. The effect of statistical uncertainties of extreme wind pressure and steel yield strength on the structural safety of beam-column joints of wind force-resisting multistory steel frames designed by the partial factor design (PFD) and the load and resistance factor design (LRFD) methods is demonstrated. The limit state criterion and the performance process of steel frame joints are presented and considered. Their long-term survival probability analysis is based on the unsophisticated method of transformed conditional probabilities. A numerical example illustrates some discrepancies in international design standards and the necessity to revise the rule of universal combinations of loads in wind and structural engineering.