• 한국지진공학회논문집
• /
• 제11권2호
• /
• pp.95-104
• /
• 2007

세가지 형태의 고층 비정형 철근콘크리트 건물에 대해 OpenSees를 이용하여 비선형정적해석을 수행한 후, 해석결과와 진동대 실험결과를 비교하여 해석방법에 대한 검증을 수행하고, 해석결과 나타난 비정형 건물의 성능과 하부 필로티부분의 파괴양상을 분석하였다. 선정된 모델은 필로티층이 골조로만 이루어진 모델 (모델 1), 필로티층 내부중앙골조에 벽체가 있는 모델 (모델 2), 그리고, 필로티층의 한쪽 골조에 벽체가 있는 모델 (모델 3)이다. 철근과 콘크리트의 응력-변형률 관계를 섬유모델에 이식하여 비선형부분의 거동을 묘사하고, 벽체도 비선형모델을 이식한 트러스로 이루어진 MVLEM을 적용하였다. 그 결과 축력이 작용함에 따른 기둥의 전단강성변화, 벽체의 들뜸현상 등과 같이 진동대 실험에서 나타난 거동특성을 비교적 정확하게 묘사하였다. 초과강도 측면에서 하부골조에 벽체를 포함하고 있는 모델 2와 모델 3은 모델 1보다 2배 가까이 크다. 이와 같이 모델 2와 모델 3의 초과강도와 연성이 큰 이유는 모델 2와 모델 3의 경우 모델 1로 설계된 골조에 벽체가 낀 벽의 형태로 설계되었기 때문으로 보인다. 그리고, 연성의 측면에서 모델 1과 모델 3은 모델 2의 보다 1.17배 큰 것으로 나타났다. 모델 1과 모델 3의 경우 골조부분에 과도한 모멘트가 작용하여 파괴에 이른 반면, 모델 2는 하부전단벽의 전단파괴에 의해 파괴되었으며, 모델 1과 모델 3에 비하여 크게 작용한 전도모멘트로 인해 기둥에 작용하는 축력의 변화가 크게 발생하였다.

• 한국지진공학회논문집
• /
• 제10권1호
• /
• pp.41-49
• /
• 2006

지난 1982년 우라카와 근해지진 및 1995년 효고현 남부 지진 등에 의하여 주철근이 겹침이음된 많은 교각들이 주철근 겹침이음부의 활동에 의한 휨-전단파괴를 발생하였음을 경험하였다. 철근콘크리트 교각의 내진성능은 소성힌지구간의 변형능력에 좌우되고 있으며, 이는 곡률연성도로서 평가된다. 우리나라에서는 1992년 내진 설계가 도입된 이후 철근콘크리트 교각의 주철근겹침이음에 대한 규정이 없었으나, 2005년 도로교 설계기준에서 주철근겹침음을 50% 이내에서 허용하고 있다. 본 연구는 단면 직경이 600 mm이고 형상비가 2.5 및 3.5인 주철근 겹침이음이 있는 철근콘크리트 교각에 대하여 지진시 소성힌지부의 곡률분포 및 곡률연성도에 대하여 조사하였다. 실험은 일정한 축력 $P=0.1f{ck}A_g$가 재하된 상태에서 변위제어 방식으로 준정적실험을 실시하였다. 실험결과 반복하중에 의한 주철근 겹침이음부에 활동이 발생하면, 주철근 겹침이음 구간 내의 곡률이 주철근 겹침이음이 없는 경우와 다르게 나타났다. 다시 말하면 주철근 겹침이음 실험체의 겹침이음 구간 중의 하부 곡률은 주철근 겹침이음이 없는 실험체의 경우보다 큰 값을 보이고 있으며, 상부는 작은 값을 보였다. 이로 인하여 교각실험체의 손상은 겹침이음 구간의 하부에 집중되어 휨파괴되는 모습으로 보이는 양상을 보였다.

• 한국구조물진단유지관리공학회 논문집
• /
• 제12권2호
• /
• pp.49-58
• /
• 2008

대도시 및 지하구조물에서 주로 발생하는 탄산화는 사용기간의 증가에 따라 철근부식이 발생하며, 이러한 철근부식은 구조물의 성능저하로 진전된다. 하나의 RC 구조물이라 하더라도, 콘크리트 시공에 의해 건전부뿐 아니라 시공이음부 또는 균열부와 같은 취약부가 발생하기가 쉽지만, 진단시에는 일반적으로 건전부만을 대상으로 탄산화 거동을 분석하고 있다. 본 연구에서는 대도시에서 사용중인 고가교의 RC 교각을 대상으로 하여 건전부, 균열부, 시공이음부 콘크리트의 탄산화 실태조사를 수행하였다. 조사된 탄산화 깊이와 측정된 피복두께를 확률변수로 하여, 사용기간에 따라 증가하는 내구적 파괴확률을 도출하였다. 한편 국내 시방서에서 제시하는 목표파괴확률을 기준으로 대상구조물의 내구수명을 평가하였다. 동일한 기둥부재라 하더라도 건전부, 균열부, 시공이음부 콘크리트에 따라 도출된 내구수명은 각각 다르게 평가되었으며, 피복두께가 작고 균열폭이 큰 경우에서는 매우 빠르게 감소함을 알 수 있었다. 피복두께의 변동계수에 따라서도 내구적 파괴확률의 변화가 크므로 적절한 시공과 품질확보가 중요함을 알 수 있다.

• Structural Monitoring and Maintenance
• /
• 제7권3호
• /
• pp.215-231
• /
• 2020

In a reinforced concrete building different shapes of column are adopted depending on the structural orientation and the architectural aspect. When there is an increase in loading due to changes in usage or revision in the design codes these columns need to be strengthened for enhanced performance during their service life. Strengthening materials such as carbon fiber and glass fiber polymer has been successfully used however, due to high cost application other alternative materials need to be explore. Galvanized steel wire mesh (GSWM) is one of the suitable materials locally available. High tensile strength, low weight, corrosion resistance, easy installation, minimum change in dimensions of the sections and cost effectives are the advantages of GSWM. Therefore, in this paper, four different shapes of column such as circular, square, rectangular and L were wrapped with different layers GSWM and jacketed with mortar. All the specimens were tested under axial compression. The objective of the study is to investigate the effectiveness of GSWM as a confining material for strengthening of column having varying shape. Test results shows that the axial strength enhanced with wrapping of GSWM jacket and a circular column presented the highest load carrying capacity and ductility as compared to the others. From the study of 22 column specimens, it is found that axial load is increased upto 20% and 19% when circular and square column are strengthened with one wrap of GSWM respectively, while a rectangular and L column required a wraps of two and three layers respectively in order to achieved the same load capacity as that of a circular column. Based on the present study, it is concluded that GSWM can be effectively used for strengthening of different shapes of concrete columns economically.

• Structural Engineering and Mechanics
• /
• 제76권1호
• /
• pp.83-99
• /
• 2020

Shear walls are structural members in buildings that are used extensively in reinforced concrete frame buildings, and almost exclusively in the UK, regardless of whether or not they are actually required. In recent years, the UK construction industry, led by the Concrete Centre, has questioned the need for such structural elements in low to mid-rise reinforced concrete frame buildings. In this context, a typical modern, 5-storey residential building is studied, and its existing shear walls are replaced with columns as used elsewhere in the building. The aim is to investigate the impact of several design variables, including concrete grade, column size, column shape and slab thickness, on the building's structural performance, considering two punching shear limits (V_Ed/V_Rd,c), lateral drift and accelerations, to evaluate its maximum possible height under wind actions without the inclusion of shear walls. To facilitate this study, a numerical model has been developed using the ETABS software. The results demonstrate that the building examined does not require shear walls in the design and has no lateral displacement or acceleration issues. In fact, with further analysis, it is shown that a similar building could be constructed up to 13 and 16 storeys high for 2 and 2.5 punching shear ratios (V_Ed/V_Rd,c), respectively, with adequate serviceability and strength, without the need for shear walls, albeit with thicker columns.

• Steel and Composite Structures
• /
• 제26권6호
• /
• pp.745-757
• /
• 2018

The inclusion of a ductile steel bracing as means of repairing an earthquake-damaged bridge bent is evaluated and experimentally assessed for the purposes of restoring the damaged bent's strength and stiffness and further improving the energy dissipation capacity. The study is focused on substandard reinforced concrete multi-column bridge bents constructed in the 1950 to mid-1970 in the United States. These types of bents have numerous deficiencies making them susceptible to seismic damage. Large-scale experiments were used on a two-column reinforced concrete bent to impose considerable damage of the bent through increasing amplitude cyclic deformations. The damaged bent was then repaired by installing a ductile fuse steel brace in the form of a buckling-restrained brace in a diagonal configuration between the columns and using post-tensioned rods to strengthen the cap beam. The brace was secured to the bent using steel gusset plate brackets and post-installed adhesive anchors. The repaired bent was then subjected to increasing amplitude cyclic deformations to reassess the bent performance. A subassemblage test of a nominally identical steel brace was also conducted in an effort to quantify and isolate the ductile fuse behavior. The experimental data from these large-scale experiments were analyzed in terms of the hysteretic response, observed damage, internal member loads, as well as the overall stiffness and energy dissipation characteristics. The results of this study demonstrated the effectiveness of utilizing ductile steel bracing for restoring the bent and preventing further damage to the columns and cap beams while also improving the stiffness and energy dissipation characteristics.

• Earthquakes and Structures
• /
• 제8권3호
• /
• pp.555-572
• /
• 2015

This paper presents an experimental study of three two-dimensional (2D/planar) steel reinforced concrete (SRC) T-shaped column-RC beam hybrid joints and six 3D SRC T-shaped column-steel beam hybrid joints under low cyclic reversed loads. Considering different categories of steel configuration types in column cross section and horizontal loading angles for the specimens were selected, and a reliable structural testing system for the spatial loading was employed in the tests. The load-displacement curves, carrying capacity, energy dissipation capacity, ductility and deformation characteristics of the test subassemblies were analyzed. Especially, the seismic performance discrepancies between planar hybrid joints and 3D hybrid joints were intensively compared. The failure modes for planar loading and spatial loading observed in the tests showed that the shear-diagonal compressive failure was the dominating failure mode for all the specimens. In addition, the 3D hybrid joints illustrated plumper hysteretic loops for the columns configured with solid-web steel, but a little more pinched hysteretic loops for the columns configured with T-shaped steel or channel-shaped steel, better energy dissipation capacity & ductility, and larger interlayer deformation capacity than those of the planar hybrid joints. Furthermore, it was revealed that the hysteretic loops for the specimens under $45^{\circ}$ loading angle are generally plumper than those for the specimens under $30^{\circ}$ loading angle. Finally, the effects of steel configuration type and loading angle on the seismic damage for the specimens were analyzed by means of the Park-Ang model.

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

• Computers and Concrete
• /
• 제29권 6호
• /
• pp.375-391
• /
• 2022

This paper examined the impact of the cross-sectional structure on the structural results under different loading conditions of reinforced concrete (RC) members' management limited in Carbon Fiber Reinforced Polymers (CFRP). The mechanical properties of CFRC was investigated, then, totally 32 samples were examined. Test parameters included the cross-sectional shape as square, rectangular and circular with two various aspect rates and loading statues. The loading involved concentrated loading, eccentric loading with a ratio of 0.46 to 0.6 and pure bending. The results of the test revealed that the CFRP increased ductility and load during concentrated processing. A cross sectional shape from 23 to 44 percent was increased in load capacity and from 250 to 350 percent increase in axial deformation in rectangular and circular sections respectively, affecting greatly the accomplishment of load capacity and ductility of the concentrated members. Two Artificial Intelligence Models as Extreme Learning Machine (ELM) and Particle Swarm Optimization (PSO) were used to estimating the tensile and flexural strength of specimen. On the basis of the performance from RMSE and RSQR, C-Shape CFRC was greater tensile and flexural strength than any other FRP composite design. Because of the mechanical anchorage into the matrix, C-shaped CFRCC was noted to have greater fiber-matrix interfacial adhesive strength. However, with the increase of the aspect ratio and fiber volume fraction, the compressive strength of CFRCC was reduced. This possibly was due to the fact that during the blending of each fiber, the volume of air input was increased. In addition, by adding silica fumed to composites, the tensile and flexural strength of CFRCC is greatly improved.

• 한국구조물진단유지관리공학회 논문집
• /
• 제26권1호
• /
• pp.73-80
• /
• 2022

본 연구에서는 공장에서 L형강을 이용하여 선조립한 NRC 보와 NRC 기둥을 현장에서 볼트 조립하는 NRC 보-기둥접합부 상세를 개발하였다. 개발된 접합부 상세는 NRC-J형과 NRC-JD형이다. NRC-J형은 NRC 기둥 측면의 강재 플레이트와 NRC 보의 엔드플레이트의 측면과 하부면에 TS볼트로 인장접합하는 방식이다. NRC-JD형은 전단에 대해서 NRC 보와 NRC 기둥의 측면을 고력볼트접합하고, 휨에 대해서 접합부를 관통하는 철근연결재와 보의 보강재를 겹침이음하도록하는 강접합 방식이다. 접합부 내진성능평가를 위하여, 두 가지 NRC 보-기둥 접합부 상세를 가지는 NRC-J 실험체, NRC-JD 실험체와 RC 보-기둥 접합부 상세를 가지는 RC-J 실험체 등 3개의 실험체를 제작하였다. 반복횡하중가력 실험결과, 모든 실험체의 최종 파괴형상은 보-기둥 접합면에서 보의 휨파괴로 나타났다. 정가력에 의한 실험체 최대내력은 RC-J 실험체에 비하여 NRC-J 실험체와 NRC-JD 실험체가 각각 10.1%, 29.6% 크게 나타났다. 두가지 NRC 접합부 상세 모두 KDS 기준(KDS 41 3100)의 합성중간모멘트골조 모멘트접합부에서 요구되는 최소 총층간변위각 0.03 rad 이상의 연성능력을 확보는 것으로 평가되었다. 부재각 5.7%에서 NRC-J실험체, NRC-JD 실험체가 RC실험체에 비해 약 34.8%, 61.1% 큰 누적 에너지 소산능력을 보유하고 있었다. NRC 보-기둥 접합부의 실험내력이 KDS 기준식에 의한 이론내력에 비하여 30%~53% 큰 것으로 평가되어, 기준식이 보유성능을 안전측으로 평가하였다.