Compressive resistance behavior of UHPFRC encased steel composite stub column

Zhenyu Huang,Xinxiong Huang,Weiwen Li,Jiasheng Zhang 국제구조공학회 2020 Steel and Composite Structures, An International J Vol.37 No.2

To explore the feasibility of eliminating the longitudinal rebars and stirrups by using ultra-high-performance fiber reinforcement concrete (UHPFRC) in concrete encased steel composite stub column, compressive behavior of UHPFRC encased steel stub column has been experimentally investigated. Effect of concrete types (normal strength concrete, high strength concrete and UHPFRC), fiber fractions, and transverse reinforcement ratio on failure mode, ductility behavior and axial compressive resistance of composite columns have been quantified through axial compression tests. The experimental results show that concrete encased composite columns with NSC and HSC exhibit concrete crushing and spalling failure, respectively, while composite columns using UHPFRC exhibit concrete spitting and no concrete spalling is observed after failure. The incorporation of steel fiber as micro reinforcement significantly improves the concrete toughness, restrains the crack propagation and thus avoids the concrete spalling. No evidence of local buckling of rebars or yielding of stirrups has been detected in composite columns using UHPFRC. Steel fibers improve the bond strength between the concrete and, rebars and core shaped steel which contribute to the improvement of confining pressure on concrete. Three prediction models in Eurocode 4, AISC 360 and JGJ 138 and a proposed toughness index (T.I.) are employed to evaluate the compressive resistance and post peak ductility of the composite columns. It is found that all these three models predict close the compressive resistance of UHPFRC encased composite columns with/without the transverse reinforcement. UHPFRC encased composite columns can achieve a comparable level of ductility with the reinforced concrete (RC) columns using normal strength concrete. In terms of compressive resistance behavior, the feasibility of UHPFRC encased steel composite stub columns with lesser longitudinal reinforcement and stirrups has been verified in this study.

Strengthening of reinforced concrete columns by High-Performance Fiber-Reinforced Cementitious Composite (HPFRC) sprayed mortar with strengthening bars

Cho, Chang-Geun,Han, Byung-Chan,Lim, Seung-Chan,Morii, Noharu,Kim, Jae-Whan Elsevier 2018 Composite structures Vol.202 No.-

<P><B>Abstract</B></P> <P>Under severe earthquake, lack of strength and ductility in the plastic hinge region of the reinforced concrete column raises serious concerns for overall structural safety. In the current study, experimental research was performed to improve the seismic strength and performance of reinforced concrete columns under cyclic load reversals. A new strengthening approach of reinforced concrete columns was introduced by applying High-Performance Fiber-Reinforced Cementitious Composites (HPFRC) sprayed mortar combined with additional reinforcing steel bars.</P> <P>For the practice of strengthening of old reinforced concrete columns, the surface of old concrete column section was treated and grooved in advance, later the longitudinal and/or transverse strengthening bars were placed in the groove of concrete surface, and finally the column section was increased by HPFRC sprayed mortar. As experimental variables such as the HPFRC sprayed mortar, use of additional transverse strengthening bars, and the use of additional longitudinal strengthening bars, the performance of the strengthened columns were compared with that of the conventional reinforced concrete column under reversed cyclic loads.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Seismic strengthening of concrete column was newly applied by HPFRC sprayed mortar. </LI> <LI> Damage of column plastic hinge was minimized by HPFRC and additional reinforcing bars. </LI> <LI> The crack width of concrete was controlled by multiple micro-cracks induced by HPFRC. </LI> <LI> The strengthened method could improve the hysteretic damping energy of the column. </LI> </UL> </P>

탄소섬유복합체 그리드 보강 콘크리트 기둥에 관한 연구 동향

윤현도(Yun, Hyun-Do),박완신(Park, Wan-Shin),김선우(Kim, Sun-Woo),김정은(Kim, Jeong-Eun) 대한건축학회 2022 대한건축학회논문집 Vol.38 No.11

Reinforced concrete is the most widely used construction material for building structures. However, the durability of this material is reduced due to various factors such as the cracking of concrete and corrosion of steel reinforcement. Fiber Reinforced Polymer (FRP) material, which is highly evaluated for its applicability as a concrete reinforcement, is known to be effective in enhancing the durability of structures. In this study, previous research on concrete column reinforced with carbon fiber reinforced polymer (CFRP) grid was reviewed. By analyzing these studies on replacing steel hoop, a concrete column reinforcement, with CFRP grid, it could provide reference data for future research on CFRP grid reinforced concrete columns and basic data necessary for designing CFRP grid reinforced concrete columns. The concrete column that replaced the steel hoop with the CFRP grid was divided into three categories: the column under concentric loading, the column subjected to bending and axial force, and the lateral confinement effect of the column. As a result, regarding behavior characteristics, there was no difference between ordinary steel hoop and CFRP grid; therefore, the possibility of substituting CFRP grid for ordinary steel reinforcement was confirmed. However, brittle fracture of the CFRP grid was observed during this experiment; further research on the improvement of joint strength of the CFRP grid edge joint is needed. Upon analyzing the proposed equation for the lateral confinement effect, it was found that the equations for estimating the ultimate strength of confinement concrete suggested by previous researchers could even be applied for the CFRP grid reinforced concrete column.

Seismic Performance Assessment of Hollow Reinforced Concrete and Prestressed Concrete Bridge Columns

Kim, Tae-Hoon,Seong, Dai-Jeong,Shin, Hyun Mock Korea Concrete Institute 2012 International Journal of Concrete Structures and M Vol.6 No.3

The aim of this study is to assess the seismic performance of hollow reinforced concrete and prestressed concrete bridge columns, and to provide data for developing improved seismic design criteria. By using a sophisticated nonlinear finite element analysis program, the accuracy and objectivity of the assessment process can be enhanced. A computer program, RCAHEST (Reinforced Concrete Analysis in Higher Evaluation System Technology), is used to analyze reinforced concrete and prestressed concrete structures. Tensile, compressive and shear models of cracked concrete and models of reinforcing and prestressing steel were used to account for the material nonlinearity of reinforced concrete and prestressed concrete. The smeared crack approach was incorporated. The proposed numerical method for the seismic performance assessment of hollow reinforced concrete and prestressed concrete bridge columns is verified by comparing it with the reliable experimental results. Additionally, the studies and discussions presented in this investigation provide an insight into the key behavioral aspects of hollow reinforced concrete and prestressed concrete bridge columns.

Post-fire test of precast steel reinforced concrete stub columns under eccentric compression

Yong Yang,Yicong Xue,Yunlong Yu,Zhichao Gong 국제구조공학회 2019 Steel and Composite Structures, An International J Vol.33 No.1

This paper presents an experimental work on the post-fire behavior of two kinds of innovative composite stub columns under eccentric compression. The partially precast steel reinforced concrete (PPSRC) column is composed of a precast outer-part cast using steel fiber reinforced reactive powder concrete (RPC) and a cast-in-place inner-part cast using conventional concrete. Based on the PPSRC column, the hollow precast steel reinforced concrete (HPSRC) column has a hollow column core. With the aim to investigate the post-fire performance of these composite columns, six stub column specimens, including three HPSRC stub columns and three PPSRC stub columns, were exposed to the ISO834 standard fire. Then, the cooling specimens and a control specimen unexposed to fire were eccentrically loaded to explore the residual capacity. The test parameters include the section shape, concrete strength of inner-part, eccentricity ratio and heating time. The test results indicated that the precast RPC shell could effectively confine the steel shape and longitudinal reinforcements after fire, and the PPSRC stub columns experienced lower core temperature in fire and exhibited higher post-fire residual strength as compared with the HPSRC stub columns due to the insulating effect of core concrete. The residual capacity increased with the increasing of inner concrete strength and with the decreasing of heating time and load eccentricity. Based on the test results, a FEA model was established to simulate the temperature field of test specimens, and the predicted results agreed well with the test results.

Seismic Performance Assessment of Hollow Reinforced Concrete and Prestressed Concrete Bridge Columns

Tae-Hoon Kim,Dai-Jeong Seong,Hyun Mock Shin 한국콘크리트학회 2012 International Journal of Concrete Structures and M Vol.6 No.3

The aim of this study is to assess the seismic performance of hollow reinforced concrete and prestressed concrete bridge columns, and to provide data for developing improved seismic design criteria. By using a sophisticated nonlinear finite element analysis program, the accuracy and objectivity of the assessment process can be enhanced. A computer program, RCAHEST (Reinforced Concrete Analysis in Higher Evaluation System Technology), is used to analyze reinforced concrete and prestressed concrete structures. Tensile, compressive and shear models of cracked concrete and models of reinforcing and prestressing steel were used to account for the material nonlinearity of reinforced concrete and prestressed concrete. The smeared crack approach was incorporated. The proposed numerical method for the seismic performance assessment of hollow reinforced concrete and prestressed concrete bridge columns is verified by comparing it with the reliable experimental results. Additionally, the studies and discussions presented in this investigation provide an insight into the key behavioral aspects of hollow reinforced concrete and prestressed concrete bridge columns.

Partially encased composite columns using fiber reinforced concrete: experimental study

Margot F. Pereira,Silvana De Nardin,Ana L.H.C. El. Debs 국제구조공학회 2020 Steel and Composite Structures, An International J Vol.34 No.6

This paper addresses the results of an experimental study involving 10 partially encased composite columns under concentric and eccentric compressive loads. Parameters such as slenderness ratio, ordinary reinforced concrete and fiber reinforced concrete, load eccentricity and bending axis were investigated. The specimens were tested to investigate the effects of replacing the ordinary reinforced concrete by fiber reinforced concrete on the load capacity and behavior of short and slender composite columns. Various characteristics such as load capacity, axial strains behavior, stiffness, strains on steel and concrete and failure mode are discussed. The main conclusions that may be drawn from all the test results is that the behavior and ultimate load are rather sensitive to the slenderness of the columns and to the eccentricity of loading, specially the bending axis. Experimental results also indicate that replacing the ordinary reinforced concrete by steel fiber reinforced concrete has no considerable effects on the load capacity and behavior of the short and slender columns and the proposed replacement presented very good results.

재활용 FRP로 보강된 섬유 보강 콘크리트 부재의 구조적 특성

박종원(Park Jong-Won),백주현(Paek Joo-Hyun) 대한건축학회 2010 大韓建築學會論文集 : 構造系 Vol.26 No.7

Increase of waste FRP(fiber reinforced plastics) has caused environmental problems. Recently, the technology of making concrete-reinforcing fibers from waste FRP was developed and experimental tests were performed to study the mechanical properties of concrete reinforced with fibres recycled from waste FRP. The purpose of this study is to investigate the effect of recycled glass-fibers from waste FRP on the structural performance of reinforced concrete beams and columns. Experimental tests were performed for two reinforced concrete beams with the same reinforcements and two reinforced concrete column with the same reinforcements. One reinforced concrete beam and one reinforced concrete column were strengthened with recycled fibers at a fibre volumn fraction of 1.0% . Shear strength tests were performed on beam specimens and axial load tests were performed on column specimens. Test results showed that use of recycled fibers increased the shear strength of reinforced concrete beam and the axial strength of reinforced concrete column by 9.0% and 6.4% respectively.

연속 횡방향철근 개발을 통한 사각기둥의 연성화

조경훈,이태희,이정빈,김성보,김장호 대한토목학회 2023 대한토목학회논문집 Vol.43 No.2

Recently, concerns about natural disasters such as earthquakes, tsunamis and typhoons have increased. As the magnitude and frequency of earthquakes increase, research is needed to prevent structures from collapsing due to earthquake loads. Research is needed to increase the ductility of columns to prevent the collapse of structures. In this study, the ductility improvement of square columns achieved by applying spiral stirrups to square columns. Square columns reinforced with spiral stirrups are more resistant to repetitive loads such as seismic loads than columns reinforced with tie stirrups. Also, the spiral stirrups can apply better confinement to the concrete. In this study, an uniaxial compression test was conducted to evaluate the performance of columns reinforced with spiral stirrups. The results showed that the columns reinforced with spiral stirrups in both the circular and square columns showed higher compressive strength than the columns reinforced with the tie stirrups. In addition, the columns reinforced with spiral stirrups for both the square and circle columns, showed a tendency to endure the load even after the initial cracking and rebar yielding. 최근 지진, 쓰나미, 태풍 등의 자연재해에 관한 우려가 점점 커지고 있다. 지진의 규모와 빈도가 커짐에 따라 구조물이 지진하중에 의하여 붕괴되는 것을 막기 위한 연구가 필요한 실정이다. 구조물의 붕괴를 막기 위하여 기둥의 연성화를 높이는 연구가 필요하다. 본 연구에서는 사각기둥에 연속 횡방향철근을 적용하여 사각기둥의 연성화 향상을 연구하려고 한다. 연속 횡방향철근으로 보강한 사각기둥은 띠철근으로 보강한 기둥보다 지진하중과 같은 반복하중에 강하다. 또한 연속 횡방향철근은 콘크리트에 더 나은 구속력을 적용할 수 있다. 본 연구에서 연속 횡방향철근으로 보강된 기둥의 성능 평가를 위해 1축 압축 실험을 진행하였다. 그 결과 원형기둥과 사각기둥 모두에서 연속 횡방향철근으로 보강한 기둥이 띠철근으로 보강한 기둥보다 더 높은 압축강도가 나타났다. 또한, 사각기둥과 원형기둥 모두 나선철근으로 보강된 기둥에서는 초기 균열 및 항복 후에도 하중을 버티는 경향을 보였다.

Simplified Design Procedure for Reinforced Concrete Columns Based on Equivalent Column Concept

Afefy, Hamdy M.,El-Tony, El-Tony M. Korea Concrete Institute 2016 International Journal of Concrete Structures and M Vol.10 No.3

Axially loaded reinforced concrete columns are hardly exist in practice due to the development of some bending moments. These moments could be produced by gravity loads or the lateral loads. First, the current paper presents a detailed analysis on the overall structural behavior of 15 eccentrically loaded columns as well as one concentrically loaded control one. Columns bent in either single curvature or double curvature modes are tested experimentally up to failure under the effect of different end eccentricities combinations. Three end eccentricities ratio were studied, namely, 0.1b, 0.3b and 0.5b, where b is the column width. Second, an expression correlated the decay in the normalized axial capacity of the column and the acting end eccentricities was developed based on the experimental results and then verified against the available formula. Third, based on the equivalent column concept, the equivalent pin-ended columns were obtained for columns bent in either single or double curvature modes. And then, the effect of end eccentricity ratio was correlated to the equivalent column length. Finally, a simplified design procedure was proposed for eccentrically loaded braced column by transferring it to an equivalent axially loaded pin-ended slender column. The results of the proposed design procedure showed comparable results against the results of the ACI 318-14 code.