• Architectural research
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• 제7권1호
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• pp.39-48
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• 2005

Main objective of this research is to evaluate performance of high-strength concrete (HSC) columns for ductility and strength. Eight one-third scale columns with compressive strength of 69 MPa were subjected to a constant axial load corresponding to 30 % of the column axial load capacity and a cyclic horizontal load-inducing reversed bending moment. The variables studied in this research are the volumetric ratio of transverse reinforcement (${\rho}_s=1.58$, 2.25 %), tie configuration (Type H, Type C and Type D) and tie yield strength ($f_{yh}=549$ and 779 MPa). Test results show that the flexural strength of every column exceeds the calculated flexural capacity based on the equivalent concrete stress block used in the current design code. Columns with 42 % higher amounts of transverse reinforcement than that required by seismic provisions of ACI 318-02 showed ductile behaviour, showing a displacement ductility factor (${\mu}_{{\Delta}u}$) of 3.69 to 4.85, and a curvature ductility factor (${\mu}_{{\varphi}u}$) of over 10.0. With an axial load of 30 % of the axial load capacity, it is recommended that the yield strength of transverse reinforcement be held equal to or below 549 MPa.

• Steel and Composite Structures
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• 제33권4호
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• pp.595-614
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• 2019

In cold-formed steel (CFS) structures, such as trusses, transmission towers and portal frames, the use of back-to-back built-up CFS unequal angle sections are becoming increasingly popular. In such an arrangement, intermediate welds or screw fasteners are required at discrete points along the length, preventing the angle sections from buckling independently. Limited research is available in the literature on axial strength of back-to-back built-up CFS unequal angle sections. The issue is addressed herein. This paper presents an experimental investigation on both the welded and screw fastened back-to-back built-up CFS unequal angle sections under axial compression. The load-axial shortening and the load verses lateral displacement behaviour along with the deformed shapes at failure are reported. A nonlinear finite element (FE) model was then developed, which includes material non-linearity, geometric imperfections and modelling of intermediate fasteners. The FE model was validated against the experimental test results, which showed good agreement, both in terms of failure loads and deformed shapes at failure. The validated FE model was then used for the purpose of a parametric study to investigate the effect of different thicknesses, lengths and, yield stresses of steel on axial strength of back-to-back built-up CFS unequal angle sections. Five different thicknesses and seven different lengths (stub to slender columns) with two different yield stresses were investigated in the parametric study. Axial strengths obtained from the experimental tests and FE analyses were used to assess the performance of the current design guidelines as per the Direct Strength Method (DSM); obtained comparisons show that the current DSM is conservative by only 7% on average, while predicting the axial strengths of back-to-back built-up CFS unequal angle sections.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 추계 학술발표회 제20권2호
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• pp.145-148
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• 2008

현행 AISC-LRFD, ACI 318과 국내의 설계지침에서는 CFT 기둥의 탄성계수와 항복강도 산정 시구속효과에 의한 축 강성의 증가를 반영하고 있지 않고 있다. 또한 AISC-LRFD와 ACI 318의 제시된 탄성계수와 항복강도의 산정방법으로 계산된 값이 차이가 큰 문제점이 있다. 본 연구에서는 CFT(Rectangular) 기둥을 강관의 두께 및 충진 콘크리트의 강도에 따른 시험체를 9개 제작하여, 실험을 통하여 AISC-LRFD, ACI 318과 국내의 설계지침과 비교하였다. 본 연구에서의 실험결과 현행 AISC-LRFD, ACI 318과 국내의 설계지침의 CFT 기둥의 항복강도는 실제 CFT 기둥의 항복강도와는 큰 차이가 있는 것으로 나타났다.

• 한국강구조학회 논문집
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• 제10권4호통권37호
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• pp.677-689
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• 1998

본 연구에서는 중심압축력을 받는 스털스터드의 설계강도에 대하여 다루었으며 비교 평가하였다. 미국규준인 냉간성형 LRFD 설계규준 (AISI). 유럽의 냉간박벽부재설계규준 (EC3 part 1.3) 및 독일의 관련규정 (DASt-Richtlinie 016)의 유사성과 차이점을 소개하고 분석하며 체계적으로 평가하였다. 특히 유효폭과 전체 안정성문제 (휨좌굴과 비틀림좌굴)가 이 논문에서 내포되어 있다. 또한 예제를 통하여 두 규준인 AISI와 EC3에 의한 설계압축강도를 산정하고 비교 분석하였다.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2001년도 추계 학술발표회 논문집 Proceedings of EESK Conference-Fall 2001
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• pp.423-430
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• 2001

This research was conducted to investigate the seismic behavior and ductility of circular spiral reinforcement concrete bridge columns used in high strength concrete. The experimental variables consisted of transverse steel amount and spacing, different axial load levels. From the test results, sufficient displacement ductility(at least 5.5) was observed for the columus which was satisfied wi th the requirement confinement steel amount of the Korean Bridge Design Specification. In case of the columns with 50 MPa of concrete compressive strength, the columns wi th 80 % of the confinement steel amount requirement showed adequate displacement ductility(at least 6.5) under 0.2 of axial load level. And in case of the columns with 60.2 77a of concrete compressive strength, the columns with 44 \ulcorner of the confinement steel requirement provided adequate displacement ductilit under less than 0.1 of axial load level and the columns with 0.22 % provided showed comparatively high the ducti1iffy under 0.21 of axial load level.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 봄 학술발표회 논문집
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• pp.151-156
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• 2003

On the basis of the philosophy that "the compressive axial load capacity after spalling of shell concrete should be maintained as that before spalling" by applying the confinement model of high strength concrete proposed in the previous proceeding paper and equivalent lateral confining pressure considering configurations of transverse reinforcement, the amounts of transverse reinforcement from the compressive capacity design method about high strength reinforced concrete tied columns can be calculated through the formula proposed in this paper. The proposed design equation of transverse steel amounts for high strength reinforced concrete tied columns was quite agreeable with the test results of HSC tied columns conducted by other researchers as well as author.as author.

• 한국강구조학회 논문집
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• 제9권1호통권30호
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• pp.107-120
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• 1997

The purpose of this study is to develop composite structural system which is to have versatility in plan design and to improve economical efficieney, to maximise structural capacity than existing structural system. In this viewpoint, it was investigated to the properties of structural behaviors for i oint consisting of concrete filled steel square tube column and P.C reinforced concrete beam through a series of hysteretic behavior experiment. In the previous report, researched to the properties of joints with key parameters. such as Axial Force ratio and section types. From the based on previous results, this study investigated the properties of this joints with key parameters, such as strength of concrete, size of panel zone and Axial Force ratio. The obtained results are summarised as follows. (1) Investigating for the failure mode of the beam-to-column joint, the specimens of S,LL and LH series(except for L5H) presented flexural failure mode. (2) The initial stiffness of joint was increasd as the decrease of axial force ratio and increase of the concrete strength. (3) The rotation resisting capacity was effective as the increment of the concrete strength and decrement of the axial force ratio. (4) The emprical formula to predict the ultimate capacity of joint model to introduce decrease coefficient according to the axial force ratio to superimpose shearing strength of steel web(H section) and bending strength of reinforced concrete beam was expected.

• Steel and Composite Structures
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• 제31권6호
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• pp.601-615
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• 2019

In cold-formed steel (CFS) structures, such as trusses, wall frames and columns, the use of back-to-back built-up CFS angle sections are becoming increasingly popular. In such an arrangement, intermediate fasteners are required at discrete points along the length, preventing the angle-sections from buckling independently. Limited research is available in the literature on the axial strength of back-to-back built-up CFS angle sections. The issue is addressed herein. This paper presents the results of 16 experimental tests, conducted on back-to-back built-up CFS screw fastened angle sections under axial compression. A nonlinear finite element model is then described, which includes material non-linearity, geometric imperfections and explicit modelling of the intermediate fasteners. The finite element model was validated against the experimental test results. The validated finite element model was then used for the purpose of a parametric study comprising 66 models. The effect of fastener spacing on axial strength was investigated. Four different cross-sections and two different thicknesses were analyzed in the parametric study, varying the slenderness ratio of the built-up columns from 20 to 120. Axial strengths obtained from the experimental tests and finite element analysis were used to assess the performance of the current design guidelines as per the Direct Strength Method (DSM); obtained comparison showed that the DSM is over-conservative by 13% on average. This paper has therefore proposed improved design rules for the DSM and verified their accuracy against the finite element and test results of back-to-back built-up CFS angle sections under axial compression.

• Earthquakes and Structures
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• 제18권6호
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• pp.677-689
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• 2020

A building structural system of moment resisting frame (MRF) with concrete filled steel tubular (CFST) columns and wide flange H beams, is one of the most conveniently constructed structural systems. However, there were few studies on evaluating seismic performance of full-scale CFST columns under high axial compression. In addition, some existing famous design codes propose various limits of width-to-thickness ratio (B/t) for steel tubes of the ductile CFST composite members. This study was intended to investigate the seismic behavior of CFST columns under high axial load compression. Four full-scale square CFST column specimens with a B/t of 42 were carried out that were subjected to horizontal cyclic-reversal loads combined with constantly light, medium and high axial loads and with a linearly varied axial load, respectively. Test results revealed that shear strength and deformation capacity of the columns significantly decreased when the axial compression exceeded 0.35 times the nominal compression strength of a CFST column, P₀. It was obvious that the higher the axial compression, the lower both the shear strength and deformation capacities were, and the earlier and faster the shear strength degradation occurred. It was found as well that higher axial compressions resulted in larger initial lateral stiffness and faster degradation of post-yield lateral stiffness. Meanwhile, the lower axial compressions led to better energy dissipation capacities with larger cumulative energy. Moreover, the study implied that under axial compressions greater than 0.35P₀, the CFST column specimens with B/t limits recommended by AISC 360 (2016), ACI 318 (2014), AIJ (2008) and EC4 (2004) codes do not provide ultimate interstory drift ratio of more than 3% radian, and only the limit in ACI 318 (2014) code satisfies this requirement when axial compression does not exceed 0.35P₀.

• 한국구조물진단유지관리공학회 논문집
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• 제26권3호
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• pp.1-10
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• 2022

지중구조물에 많이 사용되는 파형강판 콘크리트 합성단면은 단면의 어려움으로 인하여 아직까지 보수적인 설계방법을 적용하고 있다. 본 연구에서는 LRFD와 LSD의 두가지 한계상태 설계방법을 사용하여 합성단면의 휨과 압축에 대한 소성해석을 실시하고자 하였다. 실험결과에 대한 분석결과 압축강도는 LRFD 해석값이 보다 안전측으로 해석되었으며, 강판의 강재비 보다는 콘크리트 압축강도의 영향이 큰 것으로 분석되었다. 휨강도는 LSD에 의한 해석치가 실험결과와 잘 일치하는 것으로 분석되었으며, 강판 인장강도의 영향을 받는 Hogging moment는 연결부 등의 영향에 의해 강도증가율이 감소하였으나, Sagging moment는 강재비에 따라 선형적으로 증가하는 것으로 분석되었다.