• Title, Summary, Keyword: plastic hinge length

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Behavior of Concrete-Filled Tube Column to H-Beam Connections with External Stiffeners and Reinforcing Bar (외부스티프너와 철근으로 보강한 CFT 기둥-H형강 보 접합부의 거동)

  • Kang, Chang-Hoon;Shin, Kyung-Jae;Oh, Young-Suk;Moon, Tae-Sup
    • Journal of Korean Society of Steel Construction
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    • v.12 no.1
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    • pp.55-63
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    • 2000
  • This paper is a study on the behavior of Concrete-Filled Square Tubular(CFST) column to H-beam connections reinforced with external stiffeners and reinforcing bar. The cyclic loading tests of 5 test specimens were carried out. The main Parameters are as follows; 1)the length of the stiffener: 200mm, 250mm, 2)the diameter of reinforcing bar: HD16, 19. The results of the researches demonstrate that the increase of the stiffener length was more effective than the increase of the area of reinforcing bar in the point of both strength and stiffness. By reinforcing external stiffeners, stable hysteretic behavior was shown and plastic hinge was formed on the beam flange. Cold-formed tube sections should be used carefully to avoid the welding fracture at the round corners of section, and the proposed welding methods are suitable for this connections.

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Degradation Characteristics of Symmetric Unbraced Steel Frames According to Variations of Member Stiffness and Axial ratio (축력비 및 부재강성에 따른 강구조 대칭형 비가새 골조의 열화특성)

  • Lee, Myung-Jae;Kim, Hee-Dong;Lim, Yoo-Ha
    • Journal of Korean Society of Steel Construction
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    • v.23 no.3
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    • pp.327-335
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    • 2011
  • This study has two objectives: (1) to evaluate the degradation characteristics of symmetric unbraced steel frames by using analytical approach, and (2) to suggest equation which can approximately estimate the effect of degradation during the schematic design stage. For the analytical approach, the refined plastic hinge method with an arc length algorithm was adopted. The subject of analysis was one story one-bay, multistory one-bay, and multistory three-bay unbraced steel frames. The main parameters of the analytical approach include the stiffness ratio of column to beam and the axial force ratio. The study led to the following conclusions. The normalized stiffness of degradations is affected by both stiffness ratio of column to beam and the axial load ratio; however, the major influence on degradations is the axial force ratio. The equation, which can approximately estimate the effect of degradation, was suggested together with the research results.

Behavior of Solid and Hollow Rectangular RC Piers with 50% of Lap-Spliced Longitudinal Bars (50%주철근 겹침이음을 갖는 중실 및 중공 사각단면 교각의 거동특성)

  • 김익현;이종석;이윤복;김원섭;선창호
    • Journal of the Earthquake Engineering Society of Korea
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    • v.7 no.5
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    • pp.25-35
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    • 2003
  • Scale model tests were performed to investigate the seismic behavior of the solid and hollow rectangular RC piers with 50% of lap-spliced longitudinal bars in plastic hinge regions. Continuous bars and lap-spliced ones with a lap length of 39 times the bar diameter were arranged alternately in the sections. In order to clarify the influence of lap splice on a ductility the effect of axial force and lateral confinement were excluded in the test. The typical flexural failure conducting a ductile behavior were observed in both models. It is confirmed that the 50% of lap-spliced bars can be considered as an alternative of seismic detailing for longitudinal bars.

Seismic Performance of Square RC Column Confined with Spirals (나선철근으로 횡구속된 정사각형 RC 기둥의 내진성능)

  • Ko, Seong Hyun
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.16 no.5
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    • pp.88-97
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    • 2012
  • The objective of this research is to investigate the seismic performance and flexure-shear behavior of square reinforced concrete bridge piers with solid and hollow cross section. Test specimens were nonseismically designed with the aspect ratio 4.5 Two reinforced concrete columns were tested under constant axial load while subjected to lateral load reversals with increasing drift levels. Longitudinal steel ratio was 2.217 percent. The transverse reinforcement ratio As/($s{\cdot}h$), corresponding to 58 percent of the minimum lateral reinforcement required by Korean Bridge Design Specifications for seismic detailing, which represent existing columns not designed by the current seismic design specifications or designed by limited ductility concept. This study are to provide quantitative reference data for the limited ductility design concept and tendency for performance or damage assessment based on the performance levels such as cracking, yielding, collapse, etc. Failure behavior, ultimate displacement/drift ratio, displacement ductility, response modification factor, equivalent viscous damping ratio, residual deformation, effective stiffness, plastic hinge length, strain of reinforcements and nonlinear analysis are investigated and discussed in this paper.

Estimation of the load-deformation responses of flanged reinforced concrete shear walls

  • Wang, Bin;Shi, Qing-Xuan;Cai, Wen-Zhe;Peng, YI-Gong
    • Structural Engineering and Mechanics
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    • v.73 no.5
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    • pp.529-542
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    • 2020
  • As limited well-documented experimental data are available for assessing the attributes of different deformation components of flanged walls, few appropriate models have been established for predicting the inelastic responses of flanged walls, especially those of asymmetrical flanged walls. This study presents the experimental results for three large-scale T-shaped reinforced concrete walls and examines the variations in the flexural, shear, and sliding components of deformation with the total deformation over the entire loading process. Based on the observed deformation behavior, a simple model based on moment-curvature analysis is established to estimate flexural deformations, in which the changes in plastic hinge length are considered and the deformations due to strain penetration are modeled individually. Based on the similar gross shapes of the curvature and shear strain distributions over the wall height, a proportional relationship is established between shear displacement and flexural rotation. By integrating the deformations due to flexure, shear, and strain penetration, a new load-deformation analytical model is proposed for flexure-dominant flanged walls. The proposed model provides engineers with a simple, accurate modeling tool appropriate for routine design work that can be applied to flexural walls with arbitrary sections and is capable of determining displacements at any position over the wall height. By further simplifying the analytical model, a simple procedure for estimating the ultimate displacement capacity of flanged walls is proposed, which will be valuable for performance-based seismic designs and seismic capacity evaluations.

Implications of yield penetration on confinement requirements of r.c. wall elements

  • Tastani, Souzana P.;Pantazopoulou, Stavroula J.
    • Earthquakes and Structures
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    • v.9 no.4
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    • pp.831-849
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    • 2015
  • Seismic-design procedures for walls require that the confinement in the critical (plastic hinge) regions should extend over a length in the compression zone of the cross section at the wall base where concrete strains in the Ultimate Limit State (ULS) exceed the limit of 0.0035. In a performance-based framework, confinement is linked to required curvature ductility so that the drift demand at the performance point of the structure for the design earthquake may be met. However, performance of flexural walls in the recent earthquakes in Chile (2010) and Christchurch (2011) indicates that the actual compression strains in the critical regions of many structural walls were higher than estimated, being responsible for several of the reported failures by toe crushing. In this study, the method of estimating the confined region and magnitude of compression strain demands in slender walls are revisited. The objective is to account for a newly identified kinematic interaction between the normal strains that arise in the compression zone, and the lumped rotations that occur at the other end of the wall base due to penetration of bar tension yielding into the supporting anchorage. Design charts estimating the amount of yield penetration in terms of the resulting lumped rotation at the wall base are used to quantify the increased demands for compression strain in the critical section. The estimated strain increase may exceed by more than 30% the base value estimated from the existing design expressions, which explains the frequently reported occurrence of toe crushing even in well confined slender walls under high drift demands. Example cases are included in the presentation to illustrate the behavioral parametric trends and implications in seismic design of walls.

Numerical Approach for a Partial CFST Column using an Improved Bond-Slip Model (개선된 부착슬립 모델을 적용한 부분 CFST 기둥의 수치해석)

  • Hwang, Ju-young;Kwak, Hyo-Gyoung
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.33 no.3
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    • pp.153-158
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    • 2020
  • In this study, a numerical approach for evaluating the resisting capacity of a partial concrete-filled steel tube (CFST) column is introduced. By strengthening the plastic hinge part of a traditional reinforced concrete column with a steel tube, a partial CFST shows a similar bending moment capacity as that of a full CFST column but with reduced material cost. To conduct an elaborate numerical analysis of a partial CFST column, an improved bond-slip model is applied to a finite element (FE) model at the interface between the steel tube and in-filled concrete. This numerical model is verified through the results of a double curvature bending-compression test. A parametric study with the proposed numerical model is used to obtain the load moment interaction diagrams for evaluating the resisting capacity based on various dimensions. Finally, the required strengthening length is estimated for each degree of thickness of the steel tube, and the failure mechanism of the partial CFST column based on the dimensions of the steel tube are identified.

Evaluation for Deformability of RC Members Failing in Bond after Flexural Yielding (휨항복 후 부착파괴하는 철근콘크리트 부재의 부착 연성 평가)

  • Choi, Han-Byeol;Lee, Jung-Yoon
    • Journal of the Korea Concrete Institute
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    • v.24 no.3
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    • pp.259-266
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    • 2012
  • A general earthquake resistant design philosophy of ductile frame buildings allows beams to form plastic hinges adjacent to beam-column connections. In order to carry out this design philosophy, the ultimate bond or shear strength of the beam should be greater than the flexural yielding force and should not degrade before reaching its required ductility. The behavior of RC members dominated by bond or shear action reveals a dramatic reduction of energy dissipation in the hysteretic response due to the severe pinching effects. In this study, a method was proposed to predict the deformability of reinforced concrete members with short-span-to-depth-ratios, which would result in bond failure after flexural yielding. Repeated or cyclic loading produces a progressive deterioration of bond that may lead to failure at lower cyclic bond stress levels. Accumulation of bond damage is caused by the propagation of micro-cracks and progressive crushing of concrete in front of the lugs. The proposed method takes into account bond deterioration due to the degradation of concrete in the post yield range. In order to verify bond deformability of the proposed method, the predicted results were compared with the experimental results of RC members reported in the technical literature. Comparisons between the observed and calculated bond deformability of the tested RC members showed reasonably good agreement.

The Strain of Transverse Steel and Concrete Shear Resistance Degradation after Yielding of Reinforced Concrete Circular Pier (철근콘크리트 원형 교각의 횡방향철근 변형률과 항복이후 콘크리트 전단저항 저감)

  • Ko, Seong Hyun
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.22 no.1
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    • pp.147-157
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    • 2018
  • The basis of capacity design has been explicitly or implicitly regulated in most bridge design specifications. It is to guarantee ductile failure of entire bridge system by preventing brittle failure of pier members and any other structural members until the columns provides fully enough plastic rotation capacity. Brittle shear is regarded as a mode of failure that should be avoided in reinforced concrete bridge pier design. To provide ductility behavior of column, the one of important factors is that flexural hinge of column must be detailed to ensure adequate and dependable shear strength and deformation capacity. Eight small scale circular reinforced concrete columns were tested under cyclic lateral load with 4.5 aspect ratio. The test variables are longitudinal steel ratio, transverse steel ratio, and axial load ratio. Eight flexurally dominated columns were tested. In all specimens, initial flexural-shear cracks occurred at 1.5% drift ratio. The multiple flexural-shear crack width and length gradually increased until the final stage. The angles of the major inclined cracks measured from the vertical column axis ranged between 42 and 48 degrees. In particular, this study focused on assessing transverse reinforcement contribution to the column shear strength. Transverse reinforcement contribution measured during test. Each three components of transverse reinforcement contribution, axial force contribution and concrete contribution were investigated and compared. It was assessed that the concrete stresses of all specimen were larger than stress limit of Korea Bridge Design Specifications.

Analytical Study of Ultimate Behavior of Steel Cable-stayed Bridges (완성계 강사장교의 극한 거동의 해석적 연구)

  • Kim, Seungjun;Im, Seok-Been;Lee, Kee-Sei;Kang, Young-Jong
    • Journal of The Korean Society of Civil Engineers
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    • v.32 no.2A
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    • pp.85-95
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    • 2012
  • This paper presents an investigation on the ultimate behavior of steel cable-stayed bridges using nonlinear finite element analysis method. Cable-stayed bridges exhibit various geometric nonlinearities as well as material nonlinearities, so rational nonlinear finite element analysis should be performed for investigation of the ultimate behavior. In this study, ultimate behavior of steel cable-stayed bridges was studied using rational ultimate analysis method. Nonlinear equivalent truss element and nonlinear frame element were used for modeling the cable, girder and mast. Moreover, refined plastic hinge method was adopted for considering the material nonlinearity of steel members. In this study, the 2-step analysis method was used. Before live load analysis, initial shape analysis was performed in order to consider the dead load condition. For investigation of the ultimate behavior of steel cable-stayed bridges, analysis models which span length is 920.0 m were used. Radiating type and fan type were considered as the cable-arrangement types. With various quantitative evidences such as load-displacement curves, deformed shapes, locations of the yield point or region, bending moment distribution and so on, the ultimate behavior of steel cable-stayed bridges was investigated and described in this paper.