길이조절식 강관을 이용한 철근콘크리트 기둥의 비틀림을 고려한 내진보강효과

임지훈,김찬휘,이영학 대한건축학회 2022 대한건축학회논문집 Vol.38 No.3

The seismic retrofit method for reinforced concrete (RC) column using steel rod is proposed to resist combined load including torsion and to enhance constructability. The proposed method involves the installation of steel rods on the RC column externally to improve seismic capacity when subjected to seismic load. To investigate seismic performance, three RC columns with non-seismic detail were manufactured and a cyclic loading test was conducted. To evaluate the seismic performance of retrofitted column in practical, the eccentricity of both axial and lateral load was applied on control specimen and on one retrofitted column; to compare the effect of eccentricity of axial load, the other retrofitted column was subjected to no eccentricity on axial load. The experiment results indicated that the proposed steel rod retrofit method effectively resisted seismic load by enhancing the maximum load about 61% compared to the control specimen. Similar to the result of maximum load, retrofitted column showed improvement in twist response, effective stiffness, ductility, and energy dissipation capacity. Additionally, since torsion is applied by eccentric lateral load on RC column, the concentric axial load caused the reduction of seismic capacity compared to eccentric axial load. 본 연구에서는 철근콘크리트 기둥의 비틀림 하중을 포함한 복합하중에 효과적으로 저항하며 시공성 또한 향상시킬 수 있는 steel rod 공법을 제안하였다. 제안된 공법은 RC 기둥 외부에 steel rod를 시공하는 것으로 지진하중 가력 시 내진성능을 높일 수 있다. 제안된 공법이 시공된 기둥의 내진성능평가를 위해 비내진 상세를 갖는 세 개의 RC 기둥을 제작해 반복가력실험을 수행하였다. 보강법이 시공된 기둥의 실제에 가까운 내진성능평가를 위해 control 시험체와 보강법이 적용된 시험체에 축력과 횡력의 편심을 도입해 가력했으며, 추가로 축력 편심의 영향을 분석하기 위해 동일한 보강법으로 시공된 시험체에 횡력의 편심만을 도입해 가력하였다. 실험결과 보강법이 적용된 시험체의 최대하중이 control 시험체 대비 61% 증가하였다. 최대하중과 유사하게, 보강된 시험체는 유효강성, 연성, 에너지 소산능력, 비틀림 거동에 있어서도 내진성능의 향상을 나타냈다. 추가로 RC 기둥에 편심을 갖는 횡력 가력 시 축력 편심이 있는 시험체 대비 축력 편심이 없는 시험체에서 내진성능의 감소를 나타냈다.

Seismic behaviour of enlarged cross steel-reinforced concrete columns under various loadings

Peng Wang,Qingxuan Shi,Feng Wang,Qiuwei Wang 국제구조공학회 2021 Steel and Composite Structures, An International J Vol.40 No.1

Based on finite element software, a simulation programme is used to evaluate the seismic behaviour of new-type steel-reinforced concrete (SRC) columns, called enlarged cross steel-reinforced concrete (ECSRC) columns. With abundant simulations, the effects of the loading paths, number of loading cycles, incremental amplitude of displacement and variable axial load on the seismic response of the ECSRC columns were investigated. The results indicate that the seismic behaviour of the column is highly dependent on the loading paths, and it was observed that the loading paths produced a significant effect on the hysteretic response of the columns. Compared with those under uniaxial loading, the yield load, maximum load, ultimate displacement and ductility coefficient of the ECSRC columns under biaxial loading are reduced by 13.47%, 18.01%, 12.17% and 32.64%, respectively. The energy dissipation capacity of the columns is highly dependent on the loading paths. The skeleton curves are not significantly influenced by the number of loading cycles until the yield point of steel and longitudinal reinforcement is reached. With an increase in loading cycles, the yield load, yield displacement, ductility coefficient and maximum load, as well as the corresponding horizontal displacement of the column, are reduced, while the energy dissipation grows. In addition, the yield displacement, yield load, and ductility coefficient increase with an increase in the incremental amplitude of displacement; however, the energy dissipation decreases under these conditions. The seismic performance of the SRC column under variable axial loads clearly exhibits asymmetry that is worse than that observed under constant axial loads.

Effects of loading history on seismic performance of SRC T-shaped column, Part I: Loading along web

J. Wang,Z.Q. Liu,J.Y. Xue,C.M. Hu 국제구조공학회 2018 Structural Engineering and Mechanics, An Int'l Jou Vol.68 No.2

This paper describes an experimental study on the seismic performance of steel reinforced concrete (SRC) T-shaped columns. The lateral loads were applied along the web of the column with different loading histories, such as monotonic loading, mixed loading of variable amplitude cyclic loading and monotonic loading, constant amplitude cyclic loading and variable amplitude cyclic loading. The failure modes, load-displacement curves, characteristic loads and displacements, ductility, strength and stiffness degradations and energy dissipation capacity of the column were analyzed. The effects of loading history on the seismic performance were focused on. The test results show that the specimens behaved differently in the aspects of the failure mode subject to different loading history, although all the failure modes can be summarized as flexural failure. The hysteretic loops of specimens are plump, and minimum values of the failure drift angles and ductility coefficients are 1/24 and 4.64, respectively, which reflect good seismic performance of SRC T-shaped column. With the increasing numbers of loading cycles, the column reveals lower bearing capacity and ductility. The strength and stiffness of the column with variable amplitude cyclic loading degrades more rapidly than that with constant amplitude cyclic loading, and the total cumulative dissipated energy of the former is less.

Effects of loading history on seismic performance of SRC T-shaped column, Part I: Loading along web

Wang, J.,Liu, Z.Q.,Xue, J.Y.,Hu, C.M. 국제구조공학회 2018 Structural Engineering and Mechanics, An Int'l Jou Vol.68 No.2

This paper describes an experimental study on the seismic performance of steel reinforced concrete (SRC) T-shaped columns. The lateral loads were applied along the web of the column with different loading histories, such as monotonic loading, mixed loading of variable amplitude cyclic loading and monotonic loading, constant amplitude cyclic loading and variable amplitude cyclic loading. The failure modes, load-displacement curves, characteristic loads and displacements, ductility, strength and stiffness degradations and energy dissipation capacity of the column were analyzed. The effects of loading history on the seismic performance were focused on. The test results show that the specimens behaved differently in the aspects of the failure mode subject to different loading history, although all the failure modes can be summarized as flexural failure. The hysteretic loops of specimens are plump, and minimum values of the failure drift angles and ductility coefficients are 1/24 and 4.64, respectively, which reflect good seismic performance of SRC T-shaped column. With the increasing numbers of loading cycles, the column reveals lower bearing capacity and ductility. The strength and stiffness of the column with variable amplitude cyclic loading degrades more rapidly than that with constant amplitude cyclic loading, and the total cumulative dissipated energy of the former is less.

Simplified elastic-plastic analysis procedure for strain-based fatigue assessment of nuclear safety class 1 components under severe seismic loads

Kim, Jong-Sung,Kim, Jun-Young Korean Nuclear Society 2020 Nuclear Engineering and Technology Vol.52 No.12

This paper proposes a simplified elastic-plastic analysis procedure using the penalty factors presented in the Code Case N-779 for strain-based fatigue assessment of nuclear safety class 1 components under severe seismic loads such as safety shutdown earthquake and beyond design-basis earthquake. First, a simplified elastic-plastic analysis procedure for strain-based fatigue assessment of nuclear safety class 1 components under the severe seismic loads was proposed based on the analysis result for the simplified elastic-plastic analysis procedure in the Code Case N-779 and the stress categories corresponding to normal operation and seismic loads. Second, total strain amplitude was calculated directly by performing finite element cyclic elastic-plastic seismic analysis for a hot leg nozzle in pressurizer surge line subject to combined loading including deadweight, pressure, seismic inertia load, and seismic anchor motion, as well as was derived indirectly by applying the proposed analysis procedure to the finite element elastic stress analysis result for each load. Third, strain-based fatigue assessment was implemented by applying the strain-based fatigue acceptance criteria in the ASME B&PV Code, Sec. III, Subsec. NB, Article NB-3200 and by using the total strain amplitude values calculated. Last, the total strain amplitude and the fatigue assessment result corresponding to the simplified elastic-plastic analysis were compared with those using the finite element elastic-plastic seismic analysis results. As a result of the comparison, it was identified that the proposed analysis procedure can derive reasonable and conservative results.

곡선교의 합리적인 지진해석기법 및 지진응답특성에 관한 연구

김상효(Kim Sang Hyo),조광일(Cho Kwang Il),박병규(Park Byung Kyu) 대한토목학회 2006 대한토목학회논문집 A Vol.26 No.6A

곡선교의 기하학적 특징으로 인하여 곡선교의 지진응답은 직선교와는 다른 응답특성을 나타내게 될 것으로 예상된다. 본 논문에서는 곡선교의 모형화 방법 및 다양한 영향인자들의 적용에 따른 지진응답특성을 분석하고자한다. 곡선교의 지진응답 특성을 분석하기 위하여 일반적으로 사용되는 곡선교의 수치해석모형을 지점부가 보강된 모형으로 개선하였으며, 정밀모형과의 비교를 통하여 개선된 모형의 적합성을 검증하였다. 본 논문에서는 곡선교의 지진응답에 영향을 미칠 수 있는 독선반경이나 받침배치 조건에 따른 독선교의 지점부 및 교각에서의 변위와 수평력을 중심으로 분석하였다. 지진하중은 직교되는 2 방향으로 작용하는 것으로 가정하여, 지진하중의 작용방향을 변화시키면서 지진응답을 분석하였으며, 대상교량으로는 곡선교의 대표적인 형식인 단경간 곡선교와 3경간 연속 곡선교를 선택하였다. 분석결과, 단경간 곡선교는 고정하중 및 지진하중의 작용으로 인한 지점부의 정반력 및 부반력이 크게 발생할 수 있는 것으로 나타났으며, 연속 곡선교의 경우 대상교량의 곡선 반경에 따라 지진하중의 작용방향에 영향을 받는 것으로 나타났다. 또한, 곡선반경 변화에 따라 접선방향 받침배치와 현방향 받침배치의 지진응답 특성에 차이가 있는 것으로 나타났다. As the geometrical characteristic of the curved bridge, the seismic response of curved bridges are different from straight bridges. This study analyzed the seismic response of the curved bridges considering diverse factors such as radius of curvature, direction of seismic load and support condition. The improved simple modeling of the curved bridge for seismic analysis is proposed, and it is compared with the detail modeling in order to verify the simple modeling. Three simply supported curved bridges and six 3-span continuous bridges are selected for seismic analysis. The behavior of curved bridges are evaluated in terms of the displacement and the force at supports and piers under seismic load applied in various directions. The results of this study show that upward reaction force may appear in simply supported curved bridge under seismic load. And continuous curved bridges are affected by the direction of the seismic load.

Design Principles for Wind Turbine Earthquake and Wind Load Combinations

Elif Altunsu,Onur Gunes,Ali Sarı 한국강구조학회 2022 International Journal of Steel Structures Vol.22 No.3

With the ongoing changes in the modern world, the usage of renewable energy sources is increasing. The negative impact of fossil fuels on global warming has led to the search for clean energy sources. Wind energy, which is the most widely used of those sources, is discussed in this study. Numerous studies have been undertaken in this regard, but seismic eff ects are only newly being considered. In addition to having strong wind zones, Turkey is located in a geographical position through which active fault lines pass. The presence of high wind zones overlapping with these fault lines necessitates seismic analysis for turbines planned to be built in the country. Analysis of wind and seismic load simulation is diffi cult with traditional structural design programs. In this study, coeffi cients including wind loads are suggested for civil engineers who plan to analyze wind turbines with only seismic eff ects. For this purpose, a horizontal axis steel wind turbine with a 5 MW scale is analyzed in this work considering a series of wind and seismic loads in the area around Gelibolu. These environmental eff ects are evaluated under diff erent operating conditions of the turbine, including normal operation with no earthquake loads, park condition with earthquake loads, idling condition with wind loads, normal operation with earthquake loads, and idling condition with earthquake and wind loads. The full system model of the turbine is developed with the FAST fi nite element program employing a special code for wind turbines developed by the National Renewable Energy Laboratory. As a result of the analysis, it is concluded that seismic loads acting with the wind signifi cantly change the internal forces. Damping eff ects occur when seismic and wind loads act at the same time. For this reason, wind loads need to be reduced by a certain coeffi cient in some cases. Coeffi cients are proposed here for application in initial designs and load combinations for certain wind and earthquake conditions.

Load Ratio Effect on Fracture Resistance Curve of SA312 TP304 under Reverse Cyclic Loading Condition

김상영(Sang-Young Kim) Korean Society for Precision Engineering 2017 한국정밀공학회지 Vol.34 No.6

Seismic load induces a reverse cyclic load that alternately applies a tensile and a compressive load to a structure. For nuclear piping material, safety is assessed in terms of fracture toughness. However, test results using a quasi-static load can’t guarantee safety if there is a seismic load. In this paper, the fracture toughness of SA312 TP304 stainless steel, which is used as the safety injection pipe of a nuclear power plant, was estimated by using reverse cyclic loads with different ratios of tensile load to compressive load. The test results using a load ratio of -1 (compressive load / tensile load) show that fracture toughness decreases to approximately 10% against a load ratio of zero. These test results show that the reverse cyclic load must be considered in planning for the safety of nuclear power plants under seismic loads.

Seismic response of geosynthetic reinforced retaining walls

Jesmani, Mehrab,Kamalzare, Mehrad,Sarbandi, Babak Bahrami Techno-Press 2016 Geomechanics & engineering Vol.10 No.5

The effects of reinforcement on the horizontal and vertical deformations of geosynthetic reinforced retaining walls are investigated under a well-known seismic load (San Jose earthquake, 1955). Retaining walls are designed with internal and external stability (with appropriate factor of safety) and deformation is chosen as the main parameter for describing the wall behavior under seismic load. Retaining walls with various heights (6, 8, 10, 12 and 14 meter) are optimized for geosynthetics arrangement, and modeled with a finite element method. The stress-strain behavior of the walls under a well-known loading type, which has been used by many previous researchers, is investigated. A comparison is made between the reinforced and non-reinforced systems to evaluate the effect of reinforcement on decreasing the deformation of the retaining walls. The results show that the reinforcement system significantly controls the deformation of the top and middle of the retaining walls, which are the critical points under dynamic loading. It is shown that the optimized reinforcement system in retaining walls under the studied seismic loading could decrease horizontal and vertical deformation up to 90% and 40% respectively.

Seismic behavior of composite walls with encased steel truss

Yun-tian Wu,Dao-yang Kang,Yi-ting Su,Yeong-Bin Yang 국제구조공학회 2016 Steel and Composite Structures, An International J Vol.22 No.2

This paper studies the seismic behavior of reinforced concrete (RC) walls with encased cold-formed and thin-walled (CFTW) steel truss, which can be used as an alternative to the conventional RC walls or steel reinforced concrete (SRC) composite walls for high-rise buildings in high seismic regions. Seven one-fourth scaled RC wall specimens with encased CFTW steel truss were designed, manufactured and tested to failure under reversed cyclic lateral load and constant axial load. The test parameters were the axial load ratio, configuration and volumetric steel ratio of encased web brace. The behaviors of the test specimens, including damage formation, failure mode, hysteretic curves, stiffness degradation, ductility and energy dissipation, were examined. Test results indicate that the encased web braces can effectively improve the ductility and energy dissipation capacity of RC walls. The steel angles are more suitable to be used as the web brace than the latticed batten plates in enhancing the ductility and energy dissipation. Higher axial load ratio is beneficial to lateral load capacity, but can result in reduced ductility and energy dissipation capacity. A volumetric ratio about 0.25% of encased web brace is believed cost-effective in ensuring satisfactory seismic performance of RC walls. The axial load ratio should not exceed the maximum level, about 0.20 for the nominal value or about 0.50 for the design value. Numerical analyses were performed to predict the backbone curves of the specimens and calculation formula from the Chinese Code for Design of Composite Structures was used to predict the maximum lateral load capacity. The comparison shows good agreement between the test and predicted results.