• Steel and Composite Structures
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• 제26권6호
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• pp.793-808
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• 2018

In this study, the seismic performance of the connections between L-shaped columns composed of concrete-filled steel tubes (L-CFST columns) and H-beams used in high-rise steel frame structures was investigated. Seven full-scale specimens were tested under quasi-static cyclic loading. The variables studied in the tests included the joint type, the axial compression ratio, the presence of concrete, the width-to-thickness ratio and the internal extension length of the side plates. The hysteretic response, strength degradation, stiffness degradation, ductility, plastic rotation capacity, energy dissipation capacity and the strain distribution were evaluated at different load cycles. The test results indicated that both the corner and exterior joint specimens failed due to local buckling and crack within the beam flange adjacent to the end of the side plates. However, the failure modes of the interior joint specimens primarily included local buckling and crack at the end plates and curved corners of the beam flange. A design method was proposed for the flexural capacity of the end plate connection in the interior joint. Good agreement was observed between the theoretical and test results of both the yield and ultimate flexural capacity of the end plate connection.

• Steel and Composite Structures
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• 제23권4호
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• pp.453-464
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• 2017

The square tubed-reinforced concrete (TRC) column is a kind of special concrete-filled steel tube (CFST) columns, in which the outer thin-walled steel tube does not pass through the beam-column joint, so that the longitudinal steel reinforcing bars in the RC beam are continuous through the connection zone. However, there is a possible decrease of the axial bearing capacity at the TRC column to RC beam connection due to the discontinuity of the column tube, which is a concern to engineers. 24 connections and 7 square TRC columns were tested under axial compression. The primary parameters considered in the tests are: (1) connection location (corner, exterior and interior); (2) dimensions of RC beam cross section; (3) RC beam type (with or without horizontal haunches); (4) tube type (with or without stiffening ribs). The test results show that all specimens have relatively high load-carrying capacity and satisfactory ductility. With a proper design, the connections exhibit higher axial resistance and better ductility performance than the TRC column. The feasibility of this type of connections is verified.

• 한국지진공학회논문집
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• 제18권4호
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• pp.201-212
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• 2014

The plastic hinge region of RC pier ensures its nonlinear behavior during strong earthquake events. It is assumed that the piers secure sufficient strength and ductility in order to prevent the collapse of the bridge during strong earthquake. However, the presence of a lap-splice of longitudinal bars in the plastic hinge region may lead to the occurrence of early bond failure in the lap-splice zone and result in significant loss of the seismic performance. The current regulations for seismic performance evaluation limit the ultimate strain and displacement ductility considering the eventual presence of lap-splice, but do not consider the lap-splice length. In this study, seismic performance test and analysis are performed according to the cross-sectional size and the lap-splice length in the case of longitudinal bars with lap-splice located in the plastic hinge region of existing RC bridge columns with circular cross-section. The seismic behavioral characteristics of the piers are also analyzed. Based upon the results, this paper presents a more reasonable seismic performance evaluation method considering the lap-splice length and the cross-sectional size of the column.

• Steel and Composite Structures
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• 제44권3호
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• pp.295-307
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• 2022

The objective of this research is to study experimentally the behavior of stiffened steel tubes (CFSTs). Considered parameters are stiffening methods by through-bolts or shear connectors with different configurations. In addition, the effect of global (ratio between length to diameter) and local (proportion between diameter to thickness) slenderness ratios are investigated. Load application either applied on steel only or both steel and concrete is studied as well. Case of loading on steel only happens when concrete inside the column shrinks. The purpose of the research is to improve the behavior of CFSTs by load transfer between them and different stiffening methods. A parametric experimental study that incorporates thirty-three specimens is carried out to highlight the impact of those parameters. Different outputs are recorded for every specimen such as load capacities, vertical deflections, longitudinal strains, and hoop strains. Two modes of failure occur, yielding and global buckling. Shear connectors and through-bolts improve the ultimate load by up to 5% for sections loaded at steel with different studied global slenderness and local slenderness equal 63.5. Meanwhile, shear connectors or through bolts increase the ultimate load by up to 6% for global slenderness up to 15.75 for sections loaded on composite with local slenderness equals 63.50. Recommendations for future design code development are outlined.

• International Journal of Railway
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• 제1권2호
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• pp.72-81
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• 2008

This paper introduces a new steel jacketing method for reinforced concrete columns with lap splice and evaluates its performance by a series of axial tests of concrete cylinders. At first, 45 concrete cylinders were fabricated with varying the design compressive strengths of 21, 27 and 35 MPa and, then, the part of them was jacketed with two-split-steel jackets under lateral confining pressure. The parameters in the first test were the steel jacket's thickness and the existence of adhesive between steel and concrete surface. In the second test, whole steel jackets were used to wrap cylinders with lateral pressure. Also, a double-layer jacket consisted of two steel plates was introduced; a cylinder was jacketed by two steel plates one after another. The effect of the new method was verified through comparing the results of the compressive tests for plain and jacketed cylinders. The steel jacket built following the new method showed good results of increasing the compressive strength and ductility of the jacketed cylinders with respect to the plain cylinders. The thicker steel jackets showed the more increased compressive strength, and the ductility at failure depended on the welding quality on steel jackets. The adhesive between steel and concrete surface reduced the confining effect of the steel jackets. The whole jacket showed more ductile behavior than the two-split jackets. The double-layered jackets were estimated to possess an equal performance to that of a single steel jacket having the same thickness of the double-layered jacket. Finally, the experimental results were compared with the constitutive model of steel-jacketed concrete; which showed a good agreement between the experimental results and the models.

• Earthquakes and Structures
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• 제17권2호
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• pp.163-173
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• 2019

For Special Concentrically Braced Frame (SCBF), it is common that the damage concentrates at a certain story instead of spreading over all stories. Once the damage occurs, the soft-story mechanism is likely to take place and possibly to result in the failure of the whole system with more damage accumulation. In this study, we use a strongback column which is an additional structural component extending along the height of the building, to redistribute the excessive deformation of SCBF and activate more structural members to dissipate energy and thus avoid damage concentration and improve the seismic performance of SCBF. We tested one-third-scaled, three-story, double-story X SCBF specimens with static cyclic loading procedure. Three specimens, namely S73, S42 and S0, which represent different combinations of stiffness and strength factors ${\alpha}$ and ${\beta}$ for the strongback columns, were designed based on results of numerical simulations. Specimens S73 and S42 were the specimens with the strongback columns, and S0 is the specimen without the strongback column. Test results show that the deformation distribution of Specimen S73 is more uniform and more brace members in three stories perform nonlinearly. Comparing Drift Concentration Factor (DCF), we can observe 29% and 11% improvement in Specimen S73 and S42, respectively. This improvement increases the nonlinear demand of the third-story braces and reduces that of the first-story braces where the demand used to be excessive, and, therefore, postpones the rupture of the first-story braces and enhances the ductility and energy dissipation capacity of the whole SCBF system.

• Steel and Composite Structures
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• 제39권1호
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• pp.65-80
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• 2021

Irregularities of a building in plan and elevation, which results in the change in stiffness on different floors highly affect the seismic performance and resistance of a structure. This study motivated to investigate the seismic responses of high-rise steel-frame buildings of twelve stories with various stiffness irregularities. The building has five spans of 3200 mm distance in both X- and Z-directions in the plan. The design package SAP2000 was adopted for the design of beams and columns and resulted in the profile IPE500 for the beams of all floors and box sections for columns. The column cross-section dimensions vary concerning the number of the story; one to three: 0.50×0.50×0.05m, four to seven: 0.45×0.45×0.05 m, and eight to twelve: 0.40×0.40×0.05 m. Real recorded ground accelerations obtained from the Vrancea earthquake in Romania together with dead and live loads corresponding to each story were considered for the applied load. The model was validated by comparing the results of the current method and literature considering a three-bay steel moment-resisting frame of eight-story height subject to seismic load. To investigate the seismic performance of the buildings, the time-history analysis was performed using ABAQUS. Deformed shapes corresponding to negative and positive peaks were provided followed by the story drifts and fragility curves which were used to examine the probability of collapse of the building. From the results, it was concluded that regular buildings provided a seismic performance much better than irregular buildings. Furthermore, it was observed that building with torsional irregularity was more vulnerable to seismic failure.

• 대한기계학회논문집A
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• 제37권1호
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• pp.83-88
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• 2013

연쇄붕괴는 충격이나 폭발 등의 비정상 하중에 의하여 구조물의 하중 전달요소가 제거됨으로써 구조물의 일부 또는 전체가 연쇄적으로 붕괴되는 형상을 말한다. 예상외의 하중이 기둥부재에 작용할 경우, 좌굴이 발생하며 내력저하가 급격히 진행되어 붕괴에까지 이르게 된다. 하지만 좌굴 후 에너지를 흡수할 수 있는 잔존내력이 충분하면 붕괴를 막을 수 있다. 따라서, 구조물이 최종 붕괴상태에 도달되는 전 과정에 대한 기둥부재의 하중-변형관계를 명확히 파악할 필요가 있다. 본 논문에서는 비선형유한요소해석을 실시하여 H 형 강재기둥의 단부 구속조건이 고정일 경우 잔존내력의 변화추이를 파악하였다. 또한, 처짐이론을 기반으로 이론식을 도출하여 해석값과의 적합성을 검토하였다.

• 한국지진공학회논문집
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• 제6권3호
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• pp.11-21
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• 2002

유연도법 섬유요소모델을 통하여 반복하중을 받는 철근콘크리트 교각의 비탄성 이력 거동을 추적하고 직접적인 방법에 의해 변위연성도 평가를 수행하였다. 철근 콘크리트 교각의 극한상태까지의 비탄성 거동을 합리적으로 추적하기 위해 인장강성거동, 기둥-기초면의 불연속 변위 등을 고려하여 철근과 콘크리트의 평균응력-평균변형률 관계, 접촉면요소 등을 실험과 잘 일치하는 기존의 해석 모델을 수정, 적용하였다. 또한 수치해석시 간편하게 적용할 수 있는 직접적인 방법에 의하여 교각의 연성능력을 평가하였으며, 항복변위 및 극한변위의 산출에 영향을 미치는 적분점의 위치, 콘크리트 압쇄 후 강루 철근의 low-cycle fatigue에 의한 파단 시점 등에 대하여 유연도법 섬유요소모델에 적용할 수 있는 값들을 제시하였다. 해석에 의한 변위연성도는 10%이내의 오차를 보이므로, 적용한 해석기법 및 모델에 의한 항복변위 및 극한변위의 평가는 타당하다고 할 수 있다.

• 한국구조물진단유지관리공학회 논문집
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• 제12권3호
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• pp.119-126
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• 2008

국내에서 공동주택이 대량으로 공급되었던 1980~1990년대에는 콘크리트의 설계기준강도가 약 18MPa로 낮았으며 또한 대부분의 기둥은 수직하중만을 고려하여 설계되었다. 본 연구에서는 수명이 오래된 콘크리트 기둥의 성능을 향상시키기 위하여 시공이 간편하고 내식성이 우수하며 인장성능이 매우 뛰어난 탄소섬유시트로 보강된 RC 기둥의 압축강도 성능평가 실험을 수행하였다. 기둥을 구속하는 탄소섬유시트의 wrapping 각도는 수직하중과 수평하중에 저항할 수 있도록 기둥의 재축방향에 대하여 ${\pm}60^{\circ}$ 각도로 보강하였다. 실험을 수행한 후 압축강도 및 변형률의 증가양상과 시험체의 파괴양상을 분석하였으며 실험결과의 회귀분석을 수행하여 향상된 압축강도를 예측할 수 있는 회귀식을 작성하였다.