• 대한금속재료학회지
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• 제48권5호
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• pp.377-386
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• 2010

An investigation was conducted into the effects of $\kappa$-carbides on the cracking phenomenon, which often occurred in cold-rolled light-weight steel plates. Three kinds of steels were fabricated by varying the C content, and their microstructures and tensile properties were investigated. In the two steels that contained a high carbon content, the band structures of ferrites and $\kappa$-carbides that were severely elongated along the rolling direction were well developed, whereas continuous arrays of $\kappa$-carbides were formed in the steel that contained a low carbon content. Detailed microstructural analyses of the deformed region beneath the tensile fracture surface showed that the cracks initiated at arrays of $\kappa$-carbides or $\kappa$-carbides formed interfaces between the band structures, which initiated cleavage fractures in the ferrite bands, while the bands populated with a number of $\kappa$-carbides did not play an important role in propagating the cracks. Thus, the minimization of interfacial $\kappa$-carbides or $\kappa$-carbide arrays by increasing the carbon content was essential for preventing cracking from occurring during cold rolling.

• 한국강구조학회 논문집
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• 제27권2호
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• pp.207-217
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• 2015

철골 중심 가새골조는 최소의 물량으로 건물의 횡력에 대한 저항력을 확보할 수 있는 매우 효과적인 시스템이다. 그러나 중심가새 골조는 탄성거동을 전제로 풍하중에 대한 구조시스템으로 비탄성거동을 수반하는 지진하중에 대해서는 가새 좌굴 이후의 에너지 소산능력저하와 반복하중 하에 가새 및 접합부의 취성파단 가능성이 제기된다. 그로 인해 가새의 좌굴이 최초로 발생한 층에 소성변형이 집중되어 연약층 발생에 의한 건물의 붕괴로 이어질 가능성이 높다. 따라서 본 논문에서는 기 설치된 H형 가새를 무용접 냉간성형보강재로 보강하여 휨-좌굴을 억제하고 인장력과 압축력에 동일한 강도를 확보하는 보강안에 대한 연구를 진행하였다.

• 대한건축학회논문집:구조계
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• 제35권4호
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• pp.157-165
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• 2019

Recently, lean duplex stainless steel, STS329FLD with less nickel (reduced to 0.5~1.5%) has been developed as a substitute of austenitic stainless steel (8%~10.5% nickel in STS304) and included in Korean standards (KS). This paper investigates the block shear behavior of cold-formed duplex stainless steel (STS329FLD, nominal plate thickness of 1.5mm) fillet-welded connection with base metal fracture. Main variables are weld lengths in the longitudinal and the transverse directions of applied force ranged from 20mm to 50mm. As a result, specimens failed by typical block shear facture (the combination of gross section tensile fracture and shear fracture or shear yielding) and ultimate strength of the specimens got higher with the increase of weld length. Block shear fracture strengths predicted by current design specifications (KBC2016/AISC2016 and EC3) and existing proposed equations for welded connections by Topkaya, Oosterhof & Driver and Lee et al. were compared with test strengths. KBC2016/AISC2016 and EC3 design specifications underestimated block shear strength of STS329FLD welded connections by on average 24%, 29%, respectively and Oosterhof & Driver, Topkaya and Lee et al's equations overestimated the ultimate strength of the welded connection by the range of 3% to 44%.

• Steel and Composite Structures
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• 제29권4호
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• pp.509-526
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• 2018

The direct strength method adopted by the AISI Standard and AS/NZS 4600 is an advanced design method meant to substitute the effective width method for the design of cold-formed steel structural members accounting for local instability of thin plate elements. It was proven that the design strength formula for the direct strength method could predict the ultimate strength of medium strength steel welded section compressive and flexural members with local buckling reasonably. This paper focuses on the modification of the direct strength formula for the application to high strength and high performance steel welded section columns which have the nominal yield stress higher than 460 MPa and undergo local buckling, overall buckling or their interaction. The resistance of high strength steel welded H and Box section columns calculated by the proposed direct strength formulae were validated by comparison with various compression test results, FE results, and predictions by existing specifications.

• Steel and Composite Structures
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• 제50권5호
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• pp.515-529
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• 2024

Cold-formed steel (CFS) is a popular choice for construction due to its low cost, durability, sustainability, resistance to high environmental and seismic pressures, and ease of installation. The beam-column connections in residential and medium-rise structures are formed using self-drilling screws that connect two CFS channel sections and a gusset plate. In order to increase the moment capacity of these CFS screwed beam-column connections, stiffeners are often placed on the web area of each single channel. However, there is limited literature on studying the effects of stiffeners on the moment capacity of CFS screwed beam-column connections. Hence, this paper proposes a new test approach for determining the moment capacity of CFS screwed beam-column couplings. This study describes an experimental test programme consisting of eight novel experimental tests. The effect of stiffeners, beam thickness, and gusset plate thickness on the structural behaviour of CFS screwed beam-column connections is investigated. Besides, nonlinear elasto-plastic finite element (FE) models were developed and validated against experimental test data. It found that there was reasonable agreement in terms of moment capacity and failure mode prediction. From the experimental and numerical investigation, it found that the increase in gusset plate or beam thickness and the use of stiffeners have no significant effect on the structural behaviour, moment capacity, or rotational capacity of joints exhibiting the same collapse behaviour; however, the capacity or energy absorption capacities have increased in joints whose failure behaviour varies with increasing thickness or using stiffeners. Besides, the thickness change has little impact on the initial stiffness.

• Advances in Computational Design
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• 제3권1호
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• pp.71-86
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• 2018

Thin-walled cross-sections can be optimized to enhance their resistance and progress their behaviour, leading to more competent and inexpensive structural system. The aim of this study is to afford a methodology that would facilitate progress of optimized cold formed steel (CFS) column section with maximum ultimate strength for practical applications. The proposed sections are designed to comply with the geometrical standards of pre-qualified column standards for CFS structures as well as with the number of industrialized and practical constraints. The stiffening evaluation process of CFS lipped channel columns, a five different cross section are considered. The experimental strength and behaviour of the proposed sections are verified by using the finite element analysis (FEA). A series comprehensive parametric study is carried out covering a wide range of section slenderness and overall slenderness ratio of the CFS column with and without intermediate web stiffeners. The ultimate strength of the sections is determined based on the Direct Strength Specification and other design equation available from the literature for CFS structures. A modified design method is proposed for the DSM specification. The results indicate that the CFS column with complex edge and intermediate web stiffeners provides an ultimate strength which is up to 78% higher than standard optimized shapes with the same amount of cross sectional area.

• Structural Engineering and Mechanics
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• 제90권2호
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• pp.117-125
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• 2024

This article presents the behaviour and design of cold-formed steel (CFS) web-stiffened lipped channel beams that primarily fail owing to the buckling interaction of distortional and global buckling modes. The incorporation of an intermediate stiffener in the web of the lipped channel improved the buckling performance leads to distortional buckling at intermediate length beams. The prediction of the strength of members that fail in individual buckling modes can be easily determined using the current DSM equations. However, it is difficult to estimate the strength of members undergoing buckling interactions. Special attention is required to predict the strength of the members undergoing strong buckling interactions. In the present study, the geometric dimensions of the web stiffened lipped channel beam sections were chosen such that they have almost equal distortional and global buckling stresses to have strong interactions. A validated numerical model was used to perform a parametric study and obtain design strength data for CFS web-stiffened lipped channel beams. Based on the obtained numerical data, an assessment of the current DSM equations and the equations proposed in the literature (for lipped channel CFS sections) is performed. Suitable modifications were also proposed in this work, which resulted in a higher level of design accuracy to predict the flexural strength of CFS web stiffened lipped channel beams undergoing distortional and global mode interaction. Furthermore, reliability analysis was performed to confirm the reliability of the proposed modification.

• Steel and Composite Structures
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• 제30권6호
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• pp.551-565
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• 2019

A total of 36 carbon steel and stainless steel bolted connections subjected to shear loading at different strain rates was experimentally investigated. The connection specimens were fabricated from carbon steel grades 1.20 mm G500 and 1.90 mm G450, as well as cold-formed stainless steel types EN 1.4301 and EN 1.4162 with nominal thickness 1.50 mm. The connection tests were conducted by displacement control test method. The strain rates of 10 mm/min and 20 mm/min were used. Structural behaviour of the connection specimens tested at different strain rates was investigated in terms of ultimate load, elongation corresponding to ultimate load and failure mode. Generally, it is shown that the higher strain rate on the bolted connection specimens, the higher ultimate load was obtained. The ultimate loads were averagely 2-6% higher, while the corresponding elongations were averagely 8-9% higher for the test results obtained from the strain rate of 20 mm/min compared with those obtained from the lower strain rates (1.0 mm/min for carbon steel and 1.5 mm/min for stainless steel). The connection specimens were generally failed in plate bearing of the carbon steel and stainless steel. It is shown that increasing the strain rate up to 20 mm/min generally has no effect on the bearing failure mode of the carbon steel and stainless steel bolted connections. The test strengths and failure modes were compared with the results predicted by the bolted connection design rules in international design specifications, including the Australian/New Zealand Standard (AS/NZS4600 2018), Eurocode 3 - Part 1.3 (EC3-1.3 2006) and North American Specification (AISI S100 2016) for cold-formed carbon steel structures as well as the American Specification (ASCE 2002), AS/NZS4673 (2001) and Eurocode 3 - Part 1.4 (EC3-1.4 2015) for stainless steel structures. It is shown that the AS/NZS4600 (2018), EC3-1.3 (2006) and AISI S100 (2016) generally provide conservative predictions for the carbon steel bolted connections. Both the ASCE (2002) and the EC3-1.4 (2015) provide conservative predictions for the stainless steel bolted connections. The EC3-1.3 (2006) generally provided more accurate predictions of failure mode for carbon steel bolted connections than the AS/NZS4600 (2018) and the AISI S100 (2016). The failure modes of stainless steel bolted connections predicted by the EC3-1.4 (2015) are more consistent with the test results compared with those predicted by the ASCE (2002).

• 한국강구조학회 논문집
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• 제27권2호
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• pp.169-180
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• 2015

최근 구조물의 내진설계 기준이 2009년도 개정되면서 내진설계기준이 점차 구체화 되고 있다. 이에 따라 내진설계기준이 반영되지 않았거나 현재의 기준을 만족시키지 못하는 국내 구조물에 대해 재 검토 될 필요가 있다. 특히 중 저층 구조물의 경우 횡력 저항 요소는 대부분 가새에 의해 설계되어 있다. 즉 현재 사용 중인 가새가 반복적인 지진하중에도 전체 구조물의 안정성을 확보할 수 있도록 합리적인 보강방안이 구체화 될 필요가 있다. 본 연구에서는 무용접 냉간성형 강재로 조립된 압축가새의 구조적 성능과 거동을 분석하고자 한다. 실험변수는 보강길이 그리고 보강단면 비를 중점으로 구조실험을 수행하였다. 따라서 본 연구에서는 세장한 H형강 가새의 휨좌 굴을 억제하여 압축내력을 발휘토록 보강방안을 제안하였고, 보강안의 압축거동을 검증하기 위해 세장비와 보강량을 변수로 구조 성능 실험을 수행하여 강도, 강성, 변형성능과 파괴거동의 분석을 수행하였다.

• Steel and Composite Structures
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• 제29권2호
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• pp.273-286
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• 2018

In recent years, significant progress has been made in developing design rules for stainless steel members, while the investigation on bolted connections is relatively limited, in particular at elevated temperatures. In this paper, experimental and numerical investigations on stainless steel bolted connections at ambient and elevated temperatures from the literature were reviewed. Firstly, the research program that focused on structural behavior of cold-formed stainless steel (CFSS) bolted connections at elevated temperatures carried out by the authors were summarized. Over 400 CFSS single shear and double shear bolted connection specimens were tested. The tests were conducted in the temperature ranged from 22 to $950^{\circ}C$ using both steady state and transient state test methods. It is shown that the connection strengths decrease as the temperature increases in the similar manner for the steady state test results and the transient state test results. Generally, the deterioration of the connection strengths showed a similar tendency of reduction to those of the material properties for the same type of stainless steel regardless of different connection types and different configurations. It is also found that the austenitic stainless steel EN 1.4571 generally has better resistance than the stainless steel EN 1.4301 and EN 1.4162 for bolted connections at elevated temperatures. Secondly, extensive parametric studies that included 450 specimens were performed using the verified finite element models. Based on both the experimental and numerical results, bearing factors are proposed for bearing resistances of CFSS single shear and double shear bolted connections that subjected to bearing failure in the temperature ranged from 22 to $950^{\circ}C$. The bearing resistances of bolted connections obtained from the tests and numerical analyses were compared with the nominal strengths calculated from the current international stainless steel specifications, and also compared with the predicted strengths calculated using the proposed design equations. It is shown that the proposed design equations are generally more accurate and reliable than the current design rules in predicting the bearing resistances of CFSS (EN 1.4301, EN 1.4571 and EN 1.4162) bolted connections at elevated temperatures. Lastly, the proposed design rules were further assessed by the available 58 results of stainless steel bolted connections subjected to bearing failure in the literature. It is found that the proposed design rules are also applicable to the bearing resistance design of other stainless steel grades, including austenitic stainless steel (EN 1.4306), ferritic stainless steel (EN 1.4016) and duplex stainless steel (EN 1.4462).