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Experimental behavior of eccentrically loaded R.C. short columns strengthened using GFRP wrapping

  • Elwan, S.K.;Rashed, A.S.
    • Structural Engineering and Mechanics
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    • v.39 no.2
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    • pp.207-221
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    • 2011
  • This paper aims to study the behavior of short reinforced concrete columns confined with external glass Fiber Reinforced Polymers (GFRP) sheets under eccentric loads. The experimental part of the study was achieved by testing 9 specimens under eccentric compression. Three eccentricity ratios corresponding to e/t = 0, 0.10, 0.50 in one direction of the column were used. Specimens were divided into three groups. The first group was the control one without confinement. The second group was fully wrapped with GFRP laminates before loading. The third group was wrapped under loading after reaching 75% of failure loads of the control specimens. The third group was investigated in order to represent the practical case of strengthening a loaded column with FRP laminates. All specimens were loaded until failure. The results show that GFRP laminates enhances both failure load and ductility response of eccentrically loaded column. Moreover, the study also illustrates the effect of confinement on the first crack load, lateral deformation, strain in reinforcement and failure pattern. Based on the analysis of the experimental results, a simple model has been proposed to predict the improvement of load carrying capacity under different eccentricity ratios. The predicted equation takes into consideration the eccentricity to cross section depth ratio, the ultimate strength of GFRP, the thickness of wrapping laminate, and the time of wrapping (before loading and under loading). A good correlation was obtained between experimental and analytical results.

Bidirectional Lateral Loading of RC Columns with Short Lap Splices (겹침이음 길이가 짧은 RC 기둥의 이방향 횡하중 가력 실험)

  • Lee, Chang Seok;Park, Yi Seul;Han, Sang Whan
    • Journal of the Earthquake Engineering Society of Korea
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    • v.24 no.1
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    • pp.19-27
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    • 2020
  • Reinforced concrete (RC) buildings built in the 1980s are vulnerable to seismic behavior because they were designed without any consideration of seismic loads. These buildings have widely spaced transverse reinforcements and a short lap splice length of longitudinal reinforcements, which makes them vulnerable to severe damage or even collapse during earthquakes. The purpose of this study is to investigate the impact of bidirectional lateral loads on RC columns with deficient reinforcement details. An experimental test was conducted for two full-scale RC column specimens. The test results of deficient RC columns revealed that bidirectional loading deteriorates the seismic capacity when compared with a column tested unidirectionally. Modeling parameters were extracted from the tested load-displacement response and compared with those proposed in performance-based design standards. The modeling parameters proposed in the standards underestimated the deformation capacity of tested specimens by nearly 50% and overestimated the strength capacity by 15 to 20%.

Axial compression behavior of circular recycled concrete-filled steel tubular short columns reinforced by silica fume and steel fiber

  • Chen, Juan;Liu, Xuan;Liu, Hongwei;Zeng, Lei
    • Steel and Composite Structures
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    • v.27 no.2
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    • pp.193-200
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    • 2018
  • This paper presents an experimental work for short circular steel tube columns filled with normal concrete (NAC), recycled aggregate concrete (RAC), and RAC with silica fume and steel fiber. Ten specimens were tested under axial compression to research the effect of silica fume and steel fiber volume percentage on the behavior of recycled aggregate concrete-filled steel tube columns (RACFST). The failure modes, ultimate loads and axial load- strain relationships are presented. The test results indicate that silica fume and steel fiber would not change the failure mode of the RACFST column, but can increase the mechanical performances of the RACFST column because of the filling effect and pozzolanic action of silica fume and the confinement effect of steel fiber. The ultimate load, ductility and energy dissipation capacity of RACFST columns can exceed that of corresponding natural aggregate concrete-filled steel tube (NACFST) column. Design formulas EC4 for the load capacity NACFST and RACFST columns are proposed, and the predictions agree well with the experimental results from this study.

A Comparison of Design Strength Equations between Steel and Fiber Reinforced Polymer Composites Columns (철골 및 섬유보강 폴리머(FRP) 복합 기둥의 설계강도식에 관한 비교 연구)

  • Choi, Yeol;Pyeon, Hae-Wan
    • Journal of the Korean Association for Spatial Structures
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    • v.3 no.3
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    • pp.85-93
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    • 2003
  • Steel, concrete and their combination materials are the most 6commonly used materials for civil engineering structural systems such as buildings, bridge structures and other structures. Recently, however, fiber reinforced polymer (FRP) composites, a relatively new composite material made of fibers and polymer resins, have been gradually used in structural systems as an alternative structural material. This paper describes a comparison of design strength equations for steel column and FRP composite column based on design philosophies. The safety factors used in allowable stress design (ASD) are relatively higher in FRP structural design than steel structural design. Column critical stress equations of FRP composites column from an experimental study can be represented by Euler elastic buckling equation at the long-range of slenderness, and an exponential form at the short-range of slenderness as defined in Load and Resistance Factor Design (LRFD) of steel column. The column strength of steel and FRP composite columns in large slenderness is independent of material strength, this result verified the elastic buckling equation as derived by Eq. (15) and Eq. (5).

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Evaluation of R/C Short Columns Strength by Concrete Compressive Strength and Transverse Reinforcement Ratios (콘크리트 압축강도와 띠철근의 체적비에 따른 R/C 단주의 내력평가)

  • 김경회;김재환;한범석;반병열;이광수;신성우
    • Proceedings of the Korea Concrete Institute Conference
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    • pp.505-508
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    • 1999
  • To evaluate the strength of square reinforced concrete shot columns, thirty specimens were manufactured and tested under monotonically increasing concentric compression. The test parameters included the volumetric ratio of transverse reinforcement($\rho$h = 0.49~2.65), and concrete compressive strength (234, 437, 704 kgf/$\textrm{cm}^2$). Test results are shown that : (1) Behavior of high -strength concrete column is improved by providing increased volumetric ratio; and (2) ACI, Eq. is not proper to evaluate HSC short column strength.

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Transformation of Bicyclic Ketal Compound to 1,2-Cyclopentanediol via 1,5-Diketone

  • Jun Jong-Gab;Shin Dong Gyun;Shin Hyun Shun;Kim Sung Hoon
    • Bulletin of the Korean Chemical Society
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    • v.13 no.2
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    • pp.176-179
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    • 1992
  • New method for preparing cyclopentanediol from bicyclic ketal is described. Bicyclic ketal is cleaved to give 1,5-diketone, which is then reductively coupled intramolecularly to yield 1,2-cyclopentanediol. A solution of bicyclic ketal (1a) in methylene chloride was treated with aluminum chloride(2 eq.)-sodium iodide(l.5 eq.) at ambient temperature for 3 h to give the 1,5-diketone (2a) in 71% yield after basic work-up followed by short path column chromatography. A solution of the 1,5-diketone (2a) in THF was reacted with titanium tetrachloride(6 eq.)-Mg(Hg)(0.3 eq.) at $0^{\circ}C$ for 4 h to give the 1,2-cyclopentanediol (3a) in 75% yield after basic work-up followed by short path column chromatography.

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Seismic response of substandard RC frame buildings in consideration of staircases

  • Karaaslan, Ayberk;Avsar, Ozgur
    • Earthquakes and Structures
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    • v.17 no.3
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    • pp.283-295
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    • 2019
  • During the seismic performance assessment of existing buildings, staircases are generally not taken into account as structural members but as dead load. Staircases, as secondary structural members, not only serve for connecting successive floors but also provide considerable amount of strength and stiffness to the building which can modify its seismic behaviour considerably. In this parametric study, the influence of staircases on the seismic response of substandard RC frame buildings which differ in number of storey and span, presence of staircase and its position has been examined. Modal Analyses and bi-directional Non-Linear Time History Analyses (NLTHA) were conducted to compare several engineering demand parameters (EDPs) such as inter-storey drift ratio (ISDR), floor accelerations, modal properties, member shear forces and plastic hinge distribution. Additionally, short column effect, variation in shear forces of columns that are attached to the staircase slab, failure and deformation in staircase models have also been investigated. As the staircase was considered in the analytical model, a different damage pattern can be developed especially in the structural components close to staircase.

Flexural and compression behavior for steel structures strengthened with Carbon Fiber Reinforced Polymers (CFRPs) sheet

  • Park, Jai-woo;Yoo, Jung-han
    • Steel and Composite Structures
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    • v.19 no.2
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    • pp.441-465
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    • 2015
  • This paper presents the experimental results of flexural and compression steel members strengthened with carbon fiber reinforced polymers (CFRP) sheets. In the flexural test, the five specimens were fabricated and the test parameters were the number of CFRP ply and the ratio of partial-length bonded CFRP sheets of specimen. The CFRP sheet strengthened steel beam had failure mode: CFRP sheet rupture at the mid span of steel beams. A maximum increase of 11.3% was achieved depending on the number of CFRP sheet ply and the length of CFRP sheet. In the compression test, the nine specimens were fabricated and the main parameters were: width-thickness ratio (b/t), the number of CFRP ply, and the length of the specimen. From the tests, for short columns it was observed that two sides would typically buckle outward and the other two sides would buckle inward. Also, for long columns, overall buckling was observed. A maximum increase of 57% was achieved in axial-load capacity when 3 layers of CFRP were used to wrap HSS columns of b/t = 60 transversely.

Experiments on Second -Order Behavior of High Strength Concrete Columns (고강도 콘크리트 기둥의 2계 거동에 관한 실험적 연구)

  • 김진근;양주경
    • Proceedings of the Korea Concrete Institute Conference
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    • pp.167-172
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    • 1992
  • To analyze the effects compressive strength of concrete and longitudinal steel ratio on second-order moment of columns, 30tied rein reinforced concrete columns with hinged ends were tested. The 80mm square cross section was used and the amount of eccentricity was 24mm. The compressive strengths of column specimens with slenderness ratios of 10, 60, and 100were 250, 648 and 880kg/$\textrm{cm}^2$, and the longitudinal steel ratios were 1.98%(4-D6) and 3.95%(8-D6). The ratio of ultimate load capacity to that of short column with the same eccentricity (Pu/Pn) was much decreased at high slenderness ratio with increasing the compressive strength of concrete. And the lateral displacement of slender column at the ultimate load was decreased as the strength was increased. These are due to that at high slenderness ratio the load capacity and behavior of column are affected by flexural rigidity. And, it was also found that with increasing steel ratio, the value of Pu/Pn and the lateral displacement at the ultimate load were larger for the same slenderness ratio.

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Optimal Design of Reinforced Concrete Frame Structure by Limit State Design Method (LSD에 의한 철근콘크리트 뼈대 구조의 최적설계)

  • 김동희;유홍렬;박문호
    • Magazine of the Korean Society of Agricultural Engineers
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    • v.27 no.4
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    • pp.61-67
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    • 1985
  • This study is concerned with the optimum design of reinforced concrete frame structure with multi-stories and multi-bays by Limit State Design Method aimed to establish a synthetical optimal method that can simultaneously acomplish structural analysis and sectional desig. For optimum solution, the Successive Linear Programming known as effective to nonlinear optimization problem: including both multi-design variables and mulit-constrained condition was applied. The developed algorithm was applied to an actual structure and reached following results. 1)The developed algorithm was rvey effective converging to an optimal solution with 3 to 5 iteration. 2)An optimal solution was showed when bending moment redistribution factor a was 0.80. 3)The column was, regardless of story, controlled by the long column when unbraced, while in case of braced column, it is designed with 3 short column controlled by thrust and bending moment, and the supporting condition had little effect on the optimization results.

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