• Steel and Composite Structures
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• 제48권6호
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• pp.667-679
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• 2023

Concrete filled rectangular steel tubular (CFRST) composite truss girder is composed of the CFRST truss and concrete slab. The failure mechanism of the girder was different under bending and shear failure modes. The bending and shear strength of the girder were investigated experimentally. The influences of composite effect and shear to span ratio on failure modes of the girder was studied. Results indicated that the top chord and the joint of the truss were strengthened by the composited effect. The failure modes of the specimens were changed from the joint on top chord to the bottom chord. However, the composite effect had limited effect on the failure modes of the girder with small shear to span ratio. The concrete slab and top chord can be regarded as the composite top chord. In this case, the axial force distribution of the girder was close to the pin-jointed truss model. An approach of strength prediction was proposed which can take the composite effect and shear to span ratio into account. The approach gave accurate predictions on the strength of CFRST composite truss girder under different bending and shear failure modes.

• Steel and Composite Structures
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• 제7권3호
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• pp.185-200
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• 2007

Tubular construction is widely used in a range of civil and structural engineering applications. To date, the principal product range has comprised square, rectangular and circular hollow sections. However, hot-rolled structural steel elliptical hollow sections have been recently introduced and offer further choice to engineers and architects. Currently though, a lack of fundamental structural performance data and verified structural design guidance is inhibiting uptake. Of fundamental importance to structural metallic design is the concept of cross-section classification. This paper proposes slenderness parameters and a system of cross-section classification limits for elliptical hollow sections, developed on the basis of laboratory tests and numerical simulations. Four classes of cross-sections, namely Class 1 to 4 have been defined with limiting slenderness values. For the special case of elliptical hollow sections with an aspect ratio of unity, consistency with the slenderness limits for circular hollow sections in Eurocode 3 has been achieved. The proposed system of cross-section classification underpins the development of further design guidance for elliptical hollow sections.

• Journal of Mechanical Science and Technology
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• 제17권2호
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• pp.207-214
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• 2003

The fatigue behaviour of six different hollow section T-joints subjected to out-of-plane bending moment was investigated experimentally using scaled steel models. The joints had circular brace members and rectangular chord members. Hot spot stresses and the stress concentration factors. (SCFs) were determined experimentally. Fatigue testing was carried out under constant amplitude loading in air. The test results have been statistically evaluated, and show that the experimental SCF values for circular-to-rectangular (CHS-to-RHS) hollow section joints were found to be below those of circular-to-circular (CHS-to-CHS) hollow section joints. The fatigue strength, referred to experimental hot spot stress, was in reasonably good agreement with referred fatigue design codes for tubular joints.

• Steel and Composite Structures
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• 제31권3호
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• pp.291-301
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• 2019

Pure torsion loading conditions were not frequently occurred in practical engineering, but the torsional researches were important since it's the basis of mechanical property researches under complex loading. Then a 3D finite element model with precise material constitutive models was established, and the effectiveness was verified with test data. Parametric studies with varying factors as steel yield strength, concrete strength and sectional height-width ratio, were performed. Internal stress state and the interaction effect between encased steel tube and the core concrete were analyzed. Results indicated that due to the confinement effect between steel tube and core concrete, the torsional strength of CFT columns was greatly improved comparing to plain concrete columns. The steel ratio would greatly influence the torque share between the steel tube and the core concrete. Then the torsional strength calculation formulas for core concrete and the whole CFT column were proposed. The proposed formula could be simpler and easier to use with guaranteed accuracy. Related design codes were more conservative than the proposed formula, but the proposed formula presented more satisfactory agreement with experimental results.

• 한국구조물진단유지관리공학회 논문집
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• 제19권2호
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• pp.10-21
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• 2015

합성구조의 안전성의 보장을 위해 대부분의 설계기준은 경험적 사실을 기반으로 강재의 설계기준항복강도의 상한선을 제시하고 있다. 그러나 세장비가 큰 콘크리트충전강관기둥과 같이 탄성 좌굴하중에 영향을 받는 부재의 경우 설계강도를 크게 낮게 평가함에 따라 비경제적 설계가 수행될 경우가 발생한다. 따라서 세장한 기둥의 경제적 설계를 위해 현행 설계기준에서 제시하고 있는 강재의 설계기준항복강도 이상의 항복강도를 보유한 강재가 사용될 경우 설계기준의 안전성에 대한 평가를 수행하였다. 다양한 경우에서의 높은 설계기준항복강도의 적용성 평가를 위하여 유한요소해석을 사용한 변수분석을 계획하였으며, 680MPa 급의 항복강도를 보유한 강재가 적용된 세장한 직사각형 콘크리트 충전 강관기둥의 실험을 수행하여 유한요소해석 모델의 적합성 평가와 고강도 강재의 적용성 평가를 수행하였다. 변수분석에 적용된 변수는 강재의 항복강도, 콘크리트의 설계기준압축강도, 강재의 두께와 세장비로 구성되었다. 각 변수들은 KBC 2009에 의한 강도와 비교되었다. 54개의 모델에 대한 변수분석 결과와 기 수행 연구결과들을 통해 세장한 직사각형 콘크리트 충전 강관기둥은 KBC에서 제안하고 있는 강재항복강도의 제한을 초과할 경우에도 안전하게 설계될 수 있는 것으로 나타났다.

• Steel and Composite Structures
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• 제19권1호
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• pp.21-41
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• 2015

Push-out tests have been conducted on 18 rectangular concrete-filled steel tubular (CFST) columns with the aim of studying the bond behaviour between the steel tube and the concrete infill. The obtained load-slip response and the distribution of the interface bond stress along the member length and around the cross-section for various load levels, as derived from measured axial strain gradients in the steel tube, are reported. Concrete compressive strength, interface length, cross-sectional dimensions and different interface conditions were varied to assess their effect on the ultimate bond stress. The test results indicate that lubricating the steel-concrete interface always had a significant adverse effect on the interface bond strength. Among the other variables considered, concrete compressive strength and cross-section size were found to have a pronounced effect on the bond strength of non-lubricated specimens for the range of cross-section geometries considered, which is not reflected in the European structural design code for composite structures, EN 1994-1-1 (2004). Finally, based on nonlinear regression of the test data generated in the present study, supplemented by additional data obtained from the literature, an empirical equation has been proposed for predicting the average ultimate bond strength for SHS and RHS filled with normal strength concrete.

• 한국강구조학회 논문집
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• 제24권4호
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• pp.451-458
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• 2012

구조적 우수성이 입증된 콘크리트 충전 강관 (CFT) 시스템은 폭두께비가 큰 강관을 사용할 때 더욱 경제적인 설계가 될 수 있다. 하지만, 현재 국내외의 규준에서는 CFT에 사용할 수 있는 강관의 폭두께비를 제한하고 있어 건설 재료를 보다 더 효율적으로 활용할 수 있는 가능성을 미리 차단하고 있다. 본 연구에서는 폭두께비 60, 70, 80, 90, 100를 갖는 각형 단주 CFT에 대해 압축실험을 실시하여 CFT에서의 좌굴 후 내력을 확인하였고 기존의 규준에서 제시한 폭두께비 제한치를 완화한 식을 제시하였다.

• 한국강구조학회 논문집
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• 제25권4호
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• pp.389-398
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• 2013

본 연구에서는 향후 기준집필 및 연구방향 제시를 위한 선행연구로써, 2005/2010 AISC, ACI 318-08과 EC4 내 각형 CFT 기둥 설계조항 간의 부재강도 산정포맷, 단면구조성능, 구속효과. 재료강도 상한 및 강재비, 판-폭 두께비 제한 등을 간략히 요약하고 비교분석하였다. 전반적으로 2010 AISC는 ACI 기준과의 충돌 완화를 위해 변형률적합법을 도입하는 등 최신 실험 및 연구 결과들을 반영하여 개정하였으며 CFT 기둥에서 세장비를 더욱 세분화하거나 내진 판-폭 두께비를 고연성과 중간연성 부재로 구분하는 등, 타 기준에 비해 발전된 형태의 방안을 제시하고 있다. 하지만 AISC와 EC4에서의 재료강도 상한치는 너무나 제한적이기때문에 현재 사용 가능한 고강도 재료실험 데이터베이스를 고려하여 완화할 필요가 있다. 본 연구를 통해 AISC, ACI, EC4에서 제시하는 각형 CFT 기둥의 P-M 조합강도 산정식은 다양한 설계조건에 대해 만족스러운 강도예측을 하지 못함을 확인하였다. 따라서 각형 CFT 기둥의 신뢰도 높은 P-M 조합강도 산정을 위하여 구속된 콘크리트의 응력-변형률 관계를 합리적으로 반영할 수 있는 실용적인 구성 방정식이 개발되어야 한다.

• Advances in nano research
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• 제8권4호
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• pp.323-333
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• 2020

In recent years, there has been an upsurge for the usage of buckling restrained braces (BRB) rather than ordinary braces, as they have evidently performed better. If the overall brace buckling is ignored, BRBs are proven to have higher energy absorption capacity and flexibility. This article aims to deliberate an economically efficient yet adequate type of all-steel BRB, comprised of the main components as in traditional ones, such as : (1) a steel core that holds all axial forces and (2) a steel restrainer tube that hinders buckling to occurr in the core; there is a more practical detailing in the BRB system due to the elimination of a filling mortar. An investigation has been conducted for the proposed rectangular-tube core BRB and it is hysteric behavioral results have been compared to previous researches conducted on a structure containing a similar plate core profile that has the same cross-sectional area in its core. A loss of strength is known to occur in the BRB when the limiting condition of local buckling is not satisfied, thus causing instability. This typically occurs when the thickness of the restrainer tube's wall is smaller than the cross-sectional area of the core plate or its width. In this study, a parametric investigation for BRBs with different formations has been performed to verify the effect of the design parameters such as different core section profiles, restraining member width to thickness ratio and relative cross-sectional area of the core to restrainer, on buckling load evaluation. The proposed BRB investigation results have also been presented and compared to past BRB researches with a plate profile as the core section, and the advantages and disadvantages of this configuration have been discussed, and it is concluded that BRBs with tubular core section exhibit a better seismic performance than the ones with a plate core profile.

• Steel and Composite Structures
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• 제6권1호
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• pp.71-85
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• 2006

This paper presents the results of a series of tests carried out on cold-formed steel rectangular hollow and concrete infilled beam to column connections and frames. A stub column was chosen such that overall buckling does not influence the connection behaviour. The beam chosen was a short-span cantilever with a concentrated load applied at the free end. The beam was connected to the columns along the strong and weak axes of columns and these connections were tested to failure. Twelve experiments were conducted on cold-formed steel direct welded tubular beam to column connections and twelve experiments on connections with concrete infilled column subjected to monotonic loading. In all the experiments conducted, the stiffness of the connection, the ductility characteristics and the moment rotation behaviour were studied. The dominant mode of failure in hollow section connections was chord face yielding and not weld failure. Provision of concrete infill increases the stiffness and the ultimate moment carrying capacity substantially, irrespective of the axis of loading of the column. Weld failure and bearing failure due to transverse compression occurred in connections with concrete infilled columns. Six single-bay two storied frames both with and without concrete infill, and columns loaded along the major and minor axes were tested to failure. Concentrated load was applied at the midspan of first floor beam. The change in behaviour of the frame due to provision of infill in the column and in the entire frame was compared with hollow frames. Failure of the weld at the junction of the beam occurred for frames with infilled columns. Design expressions are suggested for the yielding of the column face in hollow sections and bearing failure in infilled columns which closely predicted the experimental failure loads.