Nonlinear Study on the Mechanical Performance of Built-Up Cold-Formed Steel Concrete-Filled Columns under Compression

Given their numerous functional and architectural benefits,such as improved bearing capacity and increased resistance to elastic instability modes,cold-formed steel(CFS)built-up sections have become increasingly developed and used in recent years,particularly in the construction industry.This paper presents an analytical and numerical study of assembled CFS two single channel-shaped columns with different slenderness and configurations(backto-back,face-to-face,and box).These columns were joined by double-row rivets for the back-to-back and box configurations,whereas they were welded together for the face-to-face design.The built-up columns were filled with ordinary concrete of good strength.Finite element models were applied,using ABAQUS software,to assess mechanical performance and study the influence of assembly techniques on the behavior of cold-formed columns under axial compression.Analytical approaches based on Eurocode 3 and Eurocode 4 recommendations for un-filled and concrete-filled columns respectively were followed for the numerical analysis,and concrete confinement effects were also considered per American Concrete Institute(ACI)standards for face-to-face and box configurations.The obtained results indicated a good correlation between the numerical results and the proposed analytical methodology which did not exceed 8%.The failure modes showed that the columns failed due to instabilities such as local and global buckling.

Numerical Analysis of Cold-Formed Thin-Walled Steel Short Columns with Pitting Corrosion during Bridge Construction

Pitting corrosion is harmful during bridge construction,which will lead to uneven roughness of steel surfaces and reduce the thickness of steel.Hence,the effect of pitting corrosion on the mechanical properties of cold-formed thin-walled steel stub columns is studied,and the empirical formulas are established through regression fitting to predict the ultimate load of web and flange under pitting corrosion.In detail,the failure modes and load-displacement curves of specimens with different locations,area ratios,and depths are obtained through a large number of non-linear finite element analysis.As for the specimens with pitting corrosion on the web,all the specimens are subject to local buckling failure,and the failure mode will not change with pitting corrosion,but the failure location will change with pitting corrosion location;the size,location,and area ratio of pitting corrosion have little influence on the ultimate load of cold-formed thin-walled steel short columns,but the loss rate of pitting corrosion section area has a greater impact on the ultimate bearing capacity.As for the specimen with flange pitting corrosion,the location and area ratio of pitting corrosion have less influence on the ultimate load of cold-formed thin-walled steel short columns,and the section area loss rate has greater influence on the ultimate bearing capacity;the impact of web pitting corrosion on the ultimate load is greater than that of flange pitting corrosion under the same condition of pitting corrosion section area.The prediction formulas of limit load which are suitable for pitting corrosion of web and flange are established,which can provide a reference for performance evaluation of corroded cold-formed thin-walled steel.

Some Advances in the Application of Weathering and Cold-Formed Steel in Transmission Tower

Application of weathering and cold-formed steel in transmission lines can reduce steel consumption and environmental pollution. Some advances in the studies on the weathering and cold-formed steel in transmission tower are introduced. Firstly, corrosion-resistant tests of weathering steel samples under different simulating technical atmospheres were carried out separately for 240 hours. It shows that the corrosion degree of joint samples is higher than that of single chip samples, and the corrosion-resistant performance of weathering steel is superior to common carbon steel. The corrosion-resistance of weathering steel meets with the requirement of transmission tower. Secondly, experiments and finite element analysis for cold-formed angles and a 220kV prototype tower were completed, and the stability coeffi-cient fitting curves as well as the modification formulas of slenderness ratio for cold-formed members were determined. According to the structural characteristics of transmission towers, four sections of cold-formed angles with different sections and slenderness ratios were selected in this study. The finite element model well predicted the buckling behav-iour of the cold-formed members. Ultimate loads calculating by the fitting curve were well agreed to the experimental values, especially for the members with small slenderness ratios. Weight of the cold-formed steel tower can be reduced by more than 5 percent after considering the strength enhancement. Cost of the weathering and cold-formed steel transmission tower is nearly equivalent to that of hot-rolled steel tower with hot galvanizing.

Corner strength enhancement of high strength cold-formed steel at normal room and elevated temperatures

In this study, the suitability of current design methods for the 0.2% proof yield strength of the comer regions for high strength cold-formed steel at normal room temperature was investigated. The current standard predictions are generally accurate for outer comer specimen but conservative for inner comer specimen. Based on the experimental results, an analytical model to predict the comer strength of high strength cold-formed steel at normal room temperature was also proposed. The comparison indicated that the proposed model predicted well the comer strength of high strength cold-formed steel not only at normal room temperature but also at elevated temperatures. It is shown that the predictions obtained from the proposed model agree well with the test results. Generally the comer strength enhancement of high strength cold-formed steel decreases when the temperature increases.

Relationship between the specific surface area of rust and the electrochemical behavior of rusted steel in a wet–dry acid corrosion environment

The relationship between the specific surface area（SSA） of rust and the electrochemical behavior of rusted steel under wet-dry acid corrosion conditions was investigated. The results showed that the corrosion current density first increased and then decreased with increasing SSA of the rust during the corrosion process. The structure of the rust changed from single-layer to double-layer, and the γ-FeOOH content decreased in the inner layer of the rust with increasing corrosion time; by contrast, the γ-FeOOH content in the outer layer was constant. When the SSA of the rust was lower than the critical SSA corresponding to the relative humidity during the drying period, condensed water in the micropores of the rust could evaporate, which prompted the diffusion of O_2 into the rust and the following formation process of γ-FeOOH, leading to an increase of corrosion current density with increasing corrosion time. However, when the SSA of the rust reached or exceeded the critical SSA, condensate water in the micro-pores of the inner layer of the rust could not evaporate which inhibited the diffusion of O_2 and decreased the γ-FeOOH content in the inner rust, leading to a decrease of corrosion current density with increasing corrosion time.

Mechanical Properties of Two Kinds of New Cold-Formed Flange-Closed Welding Section Members

The hollow flange beam(HFB) is a unique cold-formed steel section developed in Australia for use as a flexural member.It′s a particular cross section with two torsion rigid closed triangular flanges and a comparatively flexible web,and it is a type of high efficient cross section.This paper presents two kinds of new cold-formed flange-closed welding sections named HF1 and HF2 according to different section component and parameters of HFB.Nonlinear finite element method has been adopted to investigate the mechanical properties such as buckling mode,deformation process,rigidity,ductility and correlation curve of two kinds of new section members which being subjected to axial compression,flexure,combined compression and bending.Systematical comparisons of the consumed steel quantities of per unit load carrying capacity between new section members and the same section dimensions of cold-formed C-section members have been carried out.Some conclusions can be drawn from above work that the new sections have some superior properties including higher load carrying capacity and section modulus,sufficient section stiffness,and difficult occurrence for the sub element local buckling.The new sections are suitable for bearing flexure,compression,combined compression and bending.The new sections′ consumed steel quantities of per unit load carrying capacity are almost half as those of the same dimension C-section members′.The experimental investigation is carried out further on the new cold-formed flange-closed welding section members and can be used in the practical engineering.

铸造低合金钢回火焊道与焊后热处理焊接接头性能对比研究

为评估回火焊道工艺在铸造低合金钢焊接中的应用效果,研究回火焊道工艺能否替代传统的焊后热处理工艺。采用焊条电弧焊(SMAW),选用R307、R407焊条分别对A217 WC6和A217 WC9进行焊接。控制预热温度、电流、电压、搭接率和层厚,以实现回火焊道工艺。焊后对接头进行金相、硬度、拉伸、冲击和侧弯试验。试验结果表明,A217 WC6焊接接头在焊态和热处理态下的性能均满足标准要求,而A217 WC9焊接接头在焊态下的冲击功小于母材,侧弯试样在熔合线附近出现表面裂纹,且硬度明显高于热处理态。分析表明,回火焊道工艺能有效改善A217 WC6钢焊接接头的组织和性能,可替代焊后热处理。但在A217 WC9钢的焊接中,回火焊道工艺未能达到改善组织和性能的目的,焊接接头性能不满足标准要求,不能替代传统的焊后热处理工艺。

山地大跨结构关键设计技术研究

恒力应急指挥中心三侧靠山,形成两个高低接地面、具有特色的掉层高层建筑。结构通过设置钢桁架连接构件,将主体结构与山体形成有效连接,将掉层部分简化了嵌固端,简化了结构的边界条件。采用弹塑性分析对结构在罕遇地震下的承载力及刚度进行验证。同时采用山体与主体结构一体化的分析技术,找寻在真实地震工况下,主体与山体连接构件的内力,验证其可靠性。对于大跨结构,采用了新型的预应力型钢混凝土梁,有效降低结构自重,减小梁高,大幅提高结构效率。本工程属于具有特色的山地建筑,结构设计采用创新处理方法,能够为类似工程项目提供参考。

一级能效电工钢片比总损耗的精确测量与仿真分析

针对国标爱泼斯坦方圈法测量新一级能效硅钢片比总损耗结果的不确定性问题,本文提出了一种工频下基于双爱泼斯坦方圈的新一级能效硅钢片比总损耗测量方法。通过双爱泼斯坦方圈法测量硅钢片的比总损耗,分析并修正了测量方法中的误差,实现了对爱泼斯坦方圈测量时接缝区和均匀区的损耗分离,并分析了接缝区比总损耗对爱泼斯坦方圈测量结果的影响机理。建立了爱泼斯坦方圈有限元模型,对其接缝区和均匀区的损耗进行研究,仿真结果与双方圈法测量结果吻合,验证了本文提出的新一级能效超低损耗薄硅钢片的比总损耗时测量方法的有效性和准确性。测量和仿真结果表明,基于双方圈法测量薄硅钢片比总损耗的结果比单方圈法测量的结果更精确。本文提出的测量和修正方法可用于一级能效薄硅钢片损耗特性的精确测量。

薄规格无取向硅钢的卷取错层原因与控制

薄规格无取向硅钢的卷取错层严重影响产品的出厂质量,如何将错层控制在±1 mm以内是生产现场的重要研究课题。于是从薄规格无取向硅钢现有生产设备和工艺技术入手,从剪切不齐和卷取不齐两个方面探索错层产生的原因,总结控制措施并在生产现场实施验证。

RO相选取对钢渣粉改性试验探究

我公司钢渣全年经破碎磁选后的尾渣在60万t左右,但钢渣因其性能不够稳定、RO相易磨性差且其中的氧化物没有水化活性,严重影响钢渣粉的最终活性指标。通过磁选可以有效降低钢渣中的RO相,改善其在水泥中使用性能。试验结果表明:钢渣在粉磨至合适的比表面积时进行RO相选取能够较大幅度的选取出钢渣中的非活性物质,实现RO相与活性矿物质的分解并降低MgO;当钢渣粉的比表面积控制在450~500 m^(2)/kg时,可以很好的发挥其活性;当钢渣粉在复合粉中的比例为5%时,水泥的性能和各项指标较好,能够替代部分优质混合材,具有较好的经济效益。

刍议路面工业固废钢渣集料粒径规格质量提升

采用工业废弃钢渣代替天然玄武岩应用于新建公路沥青路面面层,是目前常见工业固体废渣利用的措施之一,在施工过程中发现钢渣集料的粒径规格合格率偏低,严重影响了该固废材料在道路施工中的有效利用,针对此问题,进行原因分析并提出解决措施,研究表明:影响钢渣集料粒径规格质量的主要因素钢渣与筛网间的缺陷累计频率为91.7%,根据ABC分析方法,累计百分数在0~80%的因素为主要因素,80%~90%的因素为次要因素,90%~100%的因素为一般因素。通过采取措施,钢渣与筛网间的缺陷已经由主要因素变为一般因素,不再是影响钢渣集料粒径合格率主要因素。

浅析中美钢结构规范设计

在全球化的背景下,工程公司积极拓展海外业务,对国际钢结构设计规范的研究日益重要。特别是美国规范,因其广泛认可性,成为提升企业国际竞争力的关键。通过对设计方法、受弯构件的计算以及实际案例的详细分析和对比,可以更好地理解两国规范的异同,从而为工程实践提供指导。在进行中美规范的比较分析时,发现在相同的荷载条件和材料强度下,根据美国规范计算出的受弯构件尺寸往往稍小于中国规范的结果。此研究不仅可以提升企业在海外市场的竞争力,还有助于推动我国钢结构设计水平提升,促进建筑行业的持续发展。

90 mm厚工程机械用Q460钢板热轧后的水冷工艺优化

采用低碳和添加铌、钒、钛、铬等微合金元素的成分设计,利用洁净钢冶炼、奥氏体再结晶区粗轧、奥氏体未再结晶区精轧等工艺生产90 mm厚Q460钢板,热轧后采用大流量低辊速控制策略的1次水冷工艺和小流量间断开水控制策略的3次往复式水冷工艺进行水冷,研究不同水冷工艺对钢板组织和力学性能的影响,以获得合适的水冷工艺。结果表明:1次水冷工艺生产的试验钢板的显微组织主要为针状铁素体+少量珠光体,3次往复式水冷工艺生产的试验钢板的显微组织主要为多边形铁素体+珠光体+少量粒状贝氏体;与3次往复式水冷工艺相比,1次水冷工艺生产的试验钢板厚度方向的组织更加均匀、细小,且形成了针状铁素体。2种水冷工艺生产的试验钢板的拉伸性能和冲击韧性均满足标准要求,但是1次水冷工艺生产的试验钢板的−40℃冲击韧性明显优于3次往复式水冷工艺生产的试验钢板,且厚度方向的冲击韧性更均匀。90 mm厚Q460钢板热轧后的合适水冷工艺为1次水冷工艺,所得钢板的屈服强度为495~512 MPa,抗拉强度为604~616 MPa,断后伸长率23%~24%,−40℃冲击吸收功为200 J以上。

钢桥规范受压板件局部稳定计算问题探讨

受压板件局部稳定计算方法是《公路钢结构桥梁设计规范》(JTG D64—2015)中的核心计算方法之一。通过实际设计工程中的应用,并结合一定的理论分析,发现该规范局部稳定计算方法存在以下问题:(1)板元局部稳定折减系数计算公式与宽厚比限制值不协调,宽厚比取上限时折减系数显著小于1;(2)横肋刚柔性判别公式精度不够高,导致在横肋刚柔分界线处加劲板局部稳定折减系数不连续,突变幅度可能较大,且横肋由柔性加强为刚性时折减系数可能反而减小。

500 kA铝电解槽阴极方钢电渣焊工艺的研究及应用

分析了影响电渣焊焊缝质量的因素:焊接电压、电流密度、渣池深度、焊丝送进速度、熔嘴与阴极钢棒两侧之间的距离等,优化了相应的工艺参数,焊接实践表明:启动6个月炉底压降平均值降低15.4 mV、平均工作电压降低0.09 mV,外观质量有较大改观。

我国钢铁行业债券市场融资分析与建议

通过分析2014~2023年钢铁行业债券发行情况,发现存在钢铁行业债券净融资额波动较大、净融资规模下降、特定品种债券快速扩容的现状,提出了积极发行创新品种、灵活运用可转债及可交债等融资方式的建议,希望能为钢铁企业债券融资提供一定的启示与帮助。

1.6 mm极薄热轧不锈钢带生产工艺研究与应用

结合900 mm热连轧产线的工艺、装备特点,研究了1.6 mm极薄热轧不锈钢带生产的难点、关键控制点、加热工艺、轧制工艺和二级模型,确定了详细的生产方案,保证了1.6 mm极薄规格热轧不锈钢的轧制稳定性,成功批量生产出了1.6 mm极薄规格的热轧不锈钢带,其尺寸精度、板形指标、力学性能等均符合产品要求。

ISO 4345《钢丝绳纤维芯规范》国际标准修订解读

现行的ISO 4345《钢丝绳纤维芯规范》国际标准制定于1988年,至今已有三十多年,许多技术指标已不能适应目前的产品需求。南通市产品质量监督检验所牵头了该标准的修订工作。本文回顾总结了该标准的修订背景、编制过程以及新老标准的变化情况。

Bond Performance of Adhesively Bonding Interface of Steel-Bamboo Composite Structure

The steel-bamboo composite structure is a newly developed structure,combining phyllostachys pubescens(also called Moso bamboo)plywood and cold-formed thin-walled steel with structural adhesive.The reliability of steelbamboo interface is the premise of composite effect.13 specimens were prepared to investigate the failure modes and mechanism of the steel-bamboo interface on the basis of push-out test,and the strain difference analysis method was proposed to study the distribution of shear stress.The results show that the main failure modes of steel-bamboo interface are adhesion failure and splitting of bamboo plywood.The shear stress is not evenly distributed along the longitudinal direction of the interface,showing a shape of“larger at two ends and smaller in the middle”.The lower end of the interface is the initial location of the interface failure and the shear stress concentration degree is positively correlated with the thickness of the externally bonded bamboo plate.The shear resistance of steel-bamboo interface can be enhanced by improving the adhesion between steel and structural adhesive and ameliorating the quality of bamboo products.