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.

A Quick and Practical Approach for Concept-design of Submerged Thin-walled Stiffened Cylinders

Goal based and limit state design is nowadays a well-established approach in many engineering fields.Ship construction rules started introducing such concepts since early 2000.However,classification societies’rules do not provide hints on how to verify limit states and to determine the structural layout of submerged thin-walled stiffened cylinders,whose most prominent examples are submarines.Rather,they generally offer guidance and prescriptive formulations to assess shell plating and stiffening members.Such marine structures are studied,designed and built up to carry payloads below the sea surface.In the concept-design stage,the maximum operating depth is the governing hull scantling parameter.Main dimensions are determined based on the analysis of operational requirements.This study proposes a practical conceptdesign approach for conceptual submarine design,aimed at obtaining hull structures that maximize the payload capacity in terms of available internal volume by suitably adjusting structural layout and stiffening members’scantling,duly accounting for robustness and construction constraints as well as practical fabrication issues.The proposed scantling process highlights that there is no need of complex algorithms if sound engineering judgment is applied in setting down rationally the hull scantling problem.A systematic approach based on a computer-coded procedure developed on purpose was effectively implemented and satisfactorily applied in design practice.

Microstructures and Properties of 550 MPa Grade High Strength Thin-walled H-beam Steel

The microstructures and mechanical properties of 550 MPa grade lightweight high strength thin-walled H-beam steel were experimentally studied. The experimental results show that the microstructure of the air-cooled H-beam steel sample is consisted of ferrite, pearlite and a small amount of granular bainites as well as fine and dispersive V（C,N） precipitates. The microstructure of the water-cooled steel sample is consisted of ferrite and bainite as well as a small amount of fine pearlites. The microstructure of the water-cooled sample is finer than that of the air-cooled sample with the average intercept size of the surface grains reaching to 3.5 gna. The finish rolling temperature of the thin-walled high strength H-beam steel is in the range of 750 ~C-850 ~C. The lower the finish rolling temperature and the faster the cooling rate, the finer the ferrite grains, the volume fraction of bainite is increased through water cooling process. Grain refinement strengthening and precipitation strengthening are used as major strengthening means to develop 550 MPa grade lightweight high strength thin- walled H-beam steel. Vanadium partially soluted in the matrix and contributes to the solution strengthening. The 550 MPa grade high-strength thin-walled H-beam steel could be developed by direct air cooling after hot rolling to fully meet the requirements of the target properties.

Drivability of Large Diameter Steel Cylinders During Hammer-Group Vibratory Installation for the Hong Kong–Zhuhai–Macao Bridge

The Hong Kong–Zhuhai–Macao Bridge(HZMB)involved the installation of 120 mega-cylinders with a diameter of 22 m,weights up to 513 t,and penetration depths up to 33 m using an eight-vibratory hammer group.Due to the lack of engineering experience on the drivability of large-diameter cylinders under multiple vibratory hammers,predicting the penetration rate and time of steel cylinders is an open challenge that has a considerable impact on the construction control of the HZMB.In this study,the vibratory penetration of large-diameter steel cylinders in the HZMB is investigated based on geological surveys,field monitoring,and drivability analysis.The vibratory penetration rate,installation accuracy,and dynamic responses of the steel cylinders at both the eastern and western artificial islands are analyzed.The dynamic soil resistance has a great influence on the cylinder drivability.However,the current design methods for estimating the vibratory driving soil resistance are proven inaccurate without considering the scale effects.Therefore,a modified method with a normalized effective area ratio A_(r,eff)is proposed in this study to calculate the vibratory soil resistance for open-ended thin-wall cylinders under unplugged conditions.Considering the scale effects on the vibratory driving soil resistance,the proposed method leads to closer results to the measured data,providing a reference for future engineering practice.

A nonlinear explicit dynamic GBT formulation for modeling impact response of thin-walled steel members

A nonlinear explicit dynamic finite element formulation based on the generalized beam theory(GBT)is proposed and developed to simulate the dynamic responses of prismatic thin-walled steel members under transverse impulsive loads.Considering the rate strengthening and thermal softening effects on member impact behavior,a modified Cowper-Symonds model for constructional steels is utilized.The element displacement field is built upon the superposition of GBT cross-section deformation modes,so arbitrary deformations such as cross-section distortions,local buckling and warping shear can all be involved by the proposed model.The amplitude function of each cross-section deformation mode is approximated by the cubic non-uniform B-spline basis functions.The Kirchhoff s thin-plate assumption is utilized in the construction of the bending related displacements.The Green-Lagrange strain tensor and the second Piola-Kirchhoff(PK2)stress tensor are employed to measure deformations and stresses at any material point,where stresses are assumed to be in plane-stress state.In order to verify the effectiveness of the proposed GBT model,three numerical cases involving impulsive loading of the thin-walled parts are given.The GBT results are compared with those of the Ls-Dyna shell finite element.It is shown that the proposed model and the shell finite element analysis has equivalent accuracy in displacement and stress.Moreover,the proposed model is much more computationally efficient and structurally clearer than the shell finite elements.

Chatter stability and precision during high-speed ultrasonic vibration cutting of a thin-walled titanium cylinder

Titanium alloys are widely used in the aviation and aerospace industries due to their unique mechanical and physical properties.Specifically,thin-walled titanium(Ti)cylinders have received increasing attention for their applications as rocket engine casings,aircraft landing gear,and aero-engine hollow shaft due to their observed improvement in the thrust-to-weight ratio.However,the conventional cutting(CC)process is not appropriate for thin-walled Ti cylinders due to its low thermal conductivity,high strength,and low stiffness.Instead,high-speed ultrasonic vibration cutting(HUVC)assisted processing has recently proved highly effective for Ti-alloy machining.In this study,HUVC technology is employed to perform external turning of a thinwalled Ti cylinder,which represents a new application of HUVC.First,the kinematics,tool path,and dynamic cutting thickness of HUVC are evaluated.Second,the phenomenon of mode-coupling chatter is analyzed to determine the effects and mechanism of HUVC by establishing a critical cutting thickness model.HUVC can increase the critical cutting thickness and effectively reduce the average cutting force,thus reducing the energy intake of the system.Finally,comparison experiments are conducted between HUVC and CC processes.The results indicate that the diameter error rate is 10%or less for HUVC and 51%for the CC method due to a 40%reduction in the cutting force.In addition,higher machining precision and better surface roughness are achieved during thin-walled Ti cylinder manufacturing using HUVC.

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.

Feasibility of developing composite action between concrete and cold-formed steel beam

Cold-formed steel structures are steel structure products constructed from sheets or coils using cold rolling, press brake or bending brake method. These structures are extensively employed in building construction industry due to their light mass, ductility by economic cold forming operations, favorable strength-to-mass ratio and other factors. The utilization of cold formed steel sections with concrete as composite can hugely reduce the construction cost. However, the use of cold formed steel members in composite concrete beams has been very limited. A comprehensive review of developments in composite beam with cold formed steel sections was introduced. It was revealed that employing cold-formed steel channel section to replace reinforcement bars in conventional reinforced concrete beam results in a significant cost reduction without reducing strength capacity. The use of composite beam consisting of cold-formed steel open or close box and filled concrete could also reduce construction cost. Lighter composite girder for bridges with cold-formed steel of U section was introduced. Moreover, types of shear connectors to provide composite action between cold-formed steel beam and concrete slab were presented. However, further studies to investigate the effects of metal decking on the behavior of composite beam with cold-formed steel section and introduction of ductile shear connectors were recommended.

The comprehensive utilization of Baosteel steel slag

Summarizes the processes and development of Baosteel slag processing techniques such as the instantaneous slag chill （ISC） process, the tank-type hot disintegrating process and the rotary drum process. A detailed introduction of the slag comprehensive utilization at Baosteel is given. The details of Baosteel＇ s comprehensive utilization in the fields of simering materials, returned slag for steelmaking, road construction, cement production, mixed concrete, new construction materials, ground-filling materials and reinforced material for soft earth are given. Emphasis is placed on source management and ensuring that from both organizational and managerial perspectives, Baosteel＇ s slag processing techniques are safe and energy-saving, thus constantly demonstrating the issue of sustainable development.

大直径钢筒圆度异常区快速检测方法

大直径钢筒在制作、运输、安装及运行时均可能因某些原因导致其出现一个或多个圆度异常区,以至于不满足设备验收和运行的相关要求。目前,针对大直径钢筒圆度异常的检测方法均较为复杂,并不适合快速检出。为此,本文基于三坐标测量原理,结合高精度全站仪的非接触自动测量模式,并采用Matlab编制了自动搜索程序,提出了大直径钢筒圆度异常区的快速检测方法。通过AutoCAD算例模拟和现场实测,结果表明,该检测方法不仅速度快,且可通过增加测点密度实现大幅提高检出精度,为后续修复和改进工作提供准确数据。

淬火温度对气瓶用Fe-Cr-Ni-Mo钢组织和力学性能的影响

为了优化一种气瓶用Fe-Cr-Ni-Mo钢的淬火工艺,采用SEM,TEM,EBSD和拉伸、冲击等观察和检测手段,研究了淬火温度对一种气瓶用Fe-Cr-Ni-Mo钢微观组织和力学性能的影响。结果表明,不同淬火温度处理后的合金钢,均呈现为板条马氏体组织,其碳化物析出和板条亚结构基本保持不变,而原始奥氏体晶粒则随淬火温度的提高而出现明显的粗化,由800℃的4.3µm长大到930,1200℃的29.6,371.1µm,同时有效晶粒尺寸(EGS)也逐渐增加,800,930,1200℃的EGS分别为0.60,1.20,3.22µm。淬火温度对合金钢的室温抗拉、屈服强度和断后伸长率影响较小,而随着淬火温度的提高,冲击吸收能量则出现了显著的下降,由800℃的119 J,下降到930,1200℃的68,38 J。EGS增大导致冲击断裂时出现解理断裂,是较高淬火温度合金钢冲击吸收能量下降的主要原因。淬火温度为800~860℃时,Fe-Cr-Ni-Mo钢具有良好的强韧性匹配,该研究结果对Fe-Cr-Ni-Mo钢制气瓶的工业化生产具有指导意义。

深水FPSO吸力锚建造工艺

以某深水浮式生产储卸油装置(FPSO)的吸力锚建造为例,对吸力锚的钢制筒体、顶盖结构、内部切泥板、铸造吊耳及锚链等主要结构预制安装流程与吸力锚整体装船工艺进行阐述。研究结果表明:深水FPSO吸力锚在建造过程中通过制定合理的施工顺序、严格控制组对尺寸公差和焊接参数等措施,对整个项目的质量管控和工效提升至关重要,也为后期同类大型管状结构物的建造提供了有益的参考。

关于钢质无缝气瓶热处理工艺评定规范性的思考

在钢质无缝气瓶的制造工序中,热处理工序对产品的安全性能起着至关重要的作用。TSG 23—2021《气瓶安全技术规程》和钢质无缝气瓶的制造标准均明确提出气瓶的热处理应按评定合格的热处理工艺进行。目前,国内还没有相应的规范或标准能够明确指导钢质无缝气瓶热处理工艺评定的制定过程,各制造厂在生产中的热处理工艺评定制定标准和水平也参差不齐。提出了钢质无缝气瓶的热处理工艺评定涵盖的内容及相应要求,并通过试验进行了举例。

钢支撑轴向力伺服油缸优化设计

针对钢支撑轴力伺服油缸在大腔压力波动时无法定性监测围护变形量的问题,采用内置压力传感器和MT磁致式位移传感器优化钢支撑伺服油缸结构,同时采集油缸大腔压力和位移信号,当大腔压力变化量ΔP、油缸活塞杆位移ΔS均超过预设量时,系统发出预警信号,实践证明,此方案能极大地降低原系统误预警的频率,并能保证施工围护的变形量,验证了设计模型的可行性,可为钢支承轴向力伺服油缸的结构设计提供参考。

黏土中大直径钢圆筒在桩靴贯入时的稳定性研究

某在建水下生产系统附近有自升式平台的频繁桩靴插拔作业,采用了大直径薄壁钢圆筒作为水下生产系统的保护结构,因此钢圆筒在自升式平台桩靴插拔过程中的受力与变形备受关注。开展了离心模型试验,揭示了桩靴贯入过程导致的钢圆筒受力与变形规律;进而应用经离心试验验证的耦合欧拉与拉格朗日数值模拟方法,开展了筒-靴不同相对位置工况下,桩靴贯入对钢圆筒稳定性的影响分析。结果表明:桩靴贯入导致的筒壁附加应力及位移随筒-靴间距的增加而衰减,其衰减程度随筒靴间距的增加而减小,且由于筒靴间距的不同,钢圆筒对应存在两种受力模式。筒靴间距为2倍桩靴直径时,筒身附加应力可达110 MPa,表明桩靴对钢圆筒的影响距离可达2倍桩靴直径以上。

水压和波浪荷载作用下钢圆筒护岸结构变形研究

针对水压和波浪荷载作用下大直径钢圆筒护岸结构的受力和变形特性,开展了离心模型试验研究,分析了耦合荷载作用下的筒体位移和转角,采用PIV技术分析了土体的流动机制。试验结果表明:在开挖施工期,土体孔压迅速上升,开挖完成后孔压逐渐趋于平缓,但是孔压的变化具有迟滞性,开挖完成一段时间后土体孔压才能保持平稳;随着开挖施工的进行,筒体发生向陆侧的旋转,在开挖进行旋转速度最快,开挖完成后转角变化逐渐趋缓,筒体最大转角为0.32°,最大水平位移为358 mm,方向指向陆侧;在筒体旋转的影响下,地基土发生显著的水平位移,但当距筒的距离超过30 m后,土体的位移较小可忽略不计。总的来说,筒体在施工期位移和变形较小,未发生倾覆和滑移破坏,表明采用该结构能够满足工程要求。

水下防护设施插桩响应的离心模型试验研究

某拟建水下油气生产系统采用大直径薄壁钢圆筒作为防护设施。自升式钻井船进行钻修井作业时,桩靴插拔会产生较大范围的挤土作用,当钻井船插拔桩位置靠近水下生产系统的防护设施时,会导致钢圆筒产生附加的应力和变形,从而对水下生产系统产生影响。为此开展离心模型试验,研究黏土中不同桩靴插桩深度,不同间距对水下生产系统防护设施钢圆筒的影响。研究表明,钢圆筒的筒壁应变、筒顶变形及筒壁土压力均随筒靴间距的增加而减小,随桩靴贯入深度的增加而增加,与桩靴下压阻力同步发展。插桩引起的筒身应变主要集中在正对桩靴一侧,当筒靴间距小于0.9倍桩靴直径时,钢圆筒筒壁发生屈服;筒顶位移主要为向筒内发展的水平向位移;筒壁土压力增量约为静止土压力的0.6倍。桩靴插桩对钢圆筒的影响范围超过了1.3倍的桩靴直径。

高速激光熔覆马氏体不锈钢涂层与电镀层性能对比与研究

为对比研究不同液压缸服役工况下高速激光熔覆涂层替代电镀硬铬层的可行性,分别制备了马氏体不锈钢熔覆层XG-1、XG-2和电镀硬铬涂层,开展了三种涂层组织、硬度、腐蚀性能及模拟不同工况(划伤磨损、干砂摩擦磨损、滑动摩擦磨损)下磨损性能测试,探讨了涂层失效行为及其应用工况。结果表明:XG-1、XG-2涂层微观组织致密且均匀,平均显微硬度为720.5 HV、653 HV;电镀硬铬涂层分布孔隙和裂纹等缺陷,自腐蚀电流密度为10.45μA/cm^(2),耐腐蚀性能最差;三种磨损形式下电镀硬铬涂层均发生了开裂及剥落,高速激光熔覆涂层表现出更优异的耐磨性能,适用于活塞杆易拉伤、外界富集硬质颗粒污染物、大侧向载荷等液压缸服役工况。

大容积全海深环境模拟装置结构及低温控制分析

深海环境模拟装置是开展深海技术与装备研发中必不可少的试验系统。本文基于预应力钢丝缠绕技术,将传统的单层筒体拆分成双层结构,并在内套筒和外套筒间设有冷却通道。以筒体内径1 000 mm、筒深2 500 mm、最高设计压力200 MPa的深海环境模拟装置为例,进行筒体结构和低温控制过程的初步计算分析。通过计算结果可知:在筒体结构设计上,缠绕预紧系数η=1.13时,筒体外半径r0=795 mm,芯筒总厚度为177 mm,所需缠绕钢丝层厚度为118 mm;在低温控制过程,增压器等熵效率为0.6时,需要通过制冷系统将初始状态的工质水冷却至0℃,并保持筒内不少于4.6%的含冰量,且制冷系统总制冷量不低于24.62 kW,则可以实现筒内200 MPa下4℃及以下低温控制。研究结果可以为大型全海深环境模拟装置的低温控制策略研究提供参考。

钢筋混凝土梁锈胀开裂计算研究

【目的】钢筋锈蚀引起的钢筋混凝土构件锈胀开裂是混凝土结构退化的重要原因,有必要对锈胀裂缝机理进行探究。【方法】基于人工通电锈蚀试验对钢筋混凝土梁进行锈胀开裂计算,通过计算锈蚀钢筋混凝土梁锈胀开裂锈蚀深度,从而得到锈胀裂缝宽度值。【结果】研究结果表明,考虑电流腐蚀密度与电解液浓度的锈胀裂缝计算公式能有效预测钢筋混凝土梁的锈胀开裂宽度。【结论】钢筋混凝土梁的锈胀开裂机理十分复杂,裂缝宽度受到的影响较多,结合电流腐蚀密度与电解液浓度所修正的裂缝计算公式为裂缝研究提供了一种有效的思路。