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.

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.

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.

嵌套加强的LQ550高强冷弯薄壁C型钢连续檩条受力性能研究

为提高LQ550级高强冷弯薄壁C型钢连续檩条的承载能力,采用在支座处嵌套的方法来加强连续檩条。对未加强和采用两种嵌套方式加强的檩条共7组试件进行三点受弯试验,得到了试件的承载性能和破坏形态,试验结果表明加强后的试件出现跨中局部屈曲和嵌套端部局部屈曲两种破坏形态。采用ABAQUS软件建立了非线性有限元模型对嵌套加强的檩条进行数值模拟,有限元分析得到的承载力和破坏形态与试验结果吻合良好,验证了有限元模型的准确性。基于验证的有限元模型,分析了两种嵌套方式和不同嵌套长度对檩条承载力的提升,且表明嵌套檩条的长度宜取为连续檩条跨度的1/5~1/4。

装配式双拼钢围檩的拼接节点承载性能研究

结合某下穿通道基坑开挖的装配式钢结构支护体系,对双拼钢围檩拼接节点及相关组合桩和支撑进行现场测试,获取围檩承担的荷载数据,进而建立有限元分析模型。对比有限元计算值与实测值,分析拼接节点的承载性能。结果表明,依据等值梁法所得的组合桩内力可以用于围檩的荷载计算;拼接节点的有限元计算结果与现场监测数据较吻合,可为装配式双拼钢围檩的应用提供参考。

早强水泥基砂浆增强H型钢节点承压能力试验研究

装配式钢结构支护体系在基坑支护中被逐步推广。针对H型钢围檩的局部承压能力低的难题,使用早强水泥基砂浆填充承压节点区。试验研究表明,填充早强水泥基砂浆可以有效约束H型钢翼缘和腹板的屈曲及变形,增强H型钢承压节点的局部承载能力。

光伏支架高强冷弯C型钢檩条的受弯性能研究

为研究光伏支架中高强冷弯C型钢檩条的受弯性能,对5种布置方式下的LQ550高强冷弯C型钢檩条(下文简称为“C型钢檩条”)开展了跨间6个加载点集中加载试验。建立C型钢檩条有限元模型,并通过试验得到的C型钢檩条受弯性能验证模型的准确性,并依此模型探究檩条相对长细比对其受弯稳定承载力的影响规律。参照GB 50018—2002《冷弯薄壁型钢结构技术规范》的规定,分析了撑杆约束对檩条受弯稳定承载力的有利作用。结合实际项目,对采用C型钢撑杆的光伏支架开展现场加载试验。研究结果表明:1)檩条的抗弯刚度和受弯稳定承载力通过在跨间设置撑杆约束后明显提高,且设置C型钢撑杆约束的提高效果强于圆管撑杆。2)C型钢撑杆可视为理想侧向支承,檩条平面外计算长度系数可以根据C型钢撑杆的设置情况取值。3)现场加载试验证明C型钢撑杆对檩条扭转具有良好的约束效果,充分验证了采用C型钢撑杆体系的新型光伏支架结构的适用性。

大型透水式防撞墩施工技术

为满足海洋环境保护的相关要求大连湾海底隧道防撞墩工程作为沉管主体的保护结构,采用透水式结构。施工过程中为解决该结构没顶沉箱水上作业难度高、潮差段底模支立难度大等难题,采用一种大型钢结构提前安放至沉箱顶部,作为沉箱接高段,辅助沉箱安装。同时该钢结构作为海上施工平台,用以辅助灌注桩及箱内施工,实现“一物多用”。上部结构采用一种可调托架作为底模支撑,解决了潮差段焊接牛腿困难的难题,缩短了工期且保证安全质量要求。

基于BIM技术的装配式钢围檩施工工艺

基坑支护工程中传统钢围檩多使用长尺寸出厂成品H型钢,需频繁切割、焊接,材料一次性损耗较大。装配式钢围檩增加了H型钢的周转使用次数,同时拥有运输便捷、安拆方便、低碳环保等优点。从装配式钢围檩施工工艺入手,对以“BIM技术指导、现场拼装”为核心理论的装配式钢围檩施工工艺进行了研究分析,研究结果可为同类型装配式钢围檩的应用提供借鉴。

大型圆竹拱-钢拱组合结构建筑施工技术

合理利用竹材作为建筑材料,在创造经济效益的同时,对推动绿色低碳建造方式具有重要意义。但因圆竹特性与节点构造的复杂特性,限制了其在大型公共建筑中的发展。将竹拱与钢拱进行组合,利用钢拱为竹拱提供中间支撑,从而满足圆竹在大空间建筑上的使用需求。结合实际工程,详细介绍了大型圆竹拱–钢拱组合穹顶式建筑施工技术,以期为同类工程提供参考。

火灾下加设光伏板的下撑式檩条结构受力性能研究

轻钢厂房在加设光伏板后,增加的屋面恒荷载将导致简支檩条变形增大,往往会超出规范允许的限值,可采用下撑式檩条对结构进行加固,提高檩条的刚度和承载力。鉴于轻钢厂房的屋面檩条一般不进行被动防火保护,故有必要对火灾下加设光伏板的下撑式檩条结构的受力性能进行研究。研究结果表明:常温下,简支檩条的变形才是影响檩条安全的关键因素,通过采用下撑式檩条结构可有效提高檩条的刚度和承载力;火灾下,采用下撑式檩条仍然可以有效提高檩条的刚度,但对于檩条承载力的提高较为有限。因此,对于采用下撑式檩条加固的屋面,应该对下撑式檩条进行被动防火保护,比如刷防火涂料,确保下撑式檩条可以有效发挥作用。

轻钢屋面檩间支撑布置和分析

现阶段,建筑行业绿色转型发展进程加快,各种具备节能环保效果的建筑材料与建筑施工工艺得到实际应用,其中钢结构因具备强度高、自重轻、韧性塑性优越和抗震性能好等特点,在建筑工程中的应用尤为广泛,因此与钢结构建筑工程相关的研究成为工程技术人员的重要课题。鉴于檩间支撑是轻钢屋面重要组成部分,本文主要分析轻钢屋面及其檩间支撑布置原则及布置形式,并开展轻钢屋面檩间支撑体系研究,为轻钢屋面檩间支撑设计选型提供参考。

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.

简支C形钢檩条内嵌式连续化加固技术研究

简支变连续加固方式是解决现有檩条加固方式用钢量大、施工效率低等问题的有效方法。采用有限元软件ABAQUS对不同跨度L的简支C形钢檩条内嵌式连续化加固,搭接长度系数α取值0.02~0.20,根据连续性指标β得出简支C形钢檩条合理的嵌套搭接长度,并对比分析简支C形钢檩条支座处采用螺栓连接和结构胶粘结两种连接方式的连接性能。结果表明:简支C形钢檩条内嵌式连续化加固的搭接长度宜≥10%L且当α取0.10时,内嵌式C形钢檩条的β能够达到90%且能够满足檩条加固要求;综合考虑简支C形钢檩条支座处两种连接方式的施工操作性和加固成本,简支C形钢檩条内嵌式连续化加固可优先选择螺栓连接。

探讨钢板桩支护施工方法与工艺要求

该文主要以拉森钢板桩的施工方法为研究对象,结合东北亚国际贸易中心基础建设项目实例,对钢板桩的施工方法展开研究,并对其施工方法、施工工序、施工工艺等方面进行了详细的描述。结果表明,拉森钢板桩的连接方式为钢围檩,且其与每根钢板桩之间需要采用木楔抵紧。基于上述分析提出了相应的施工技术方案和流程,希望能够为其他类似工程提供参考。

拉森钢板桩支护在综合管廊施工中的应用

深基坑开挖支护工程的支护方案选择能有效减少施工安全隐患,提高施工效率,节约施工工期。通过支护方案的选择可减少施工单位和建设单位的成本。结合工程案例,重点分析深基坑开挖支护施工中拉森钢板桩支护和围檩支撑系统的结构,总结出深基坑开挖施工过程中基坑支护的围护和钢围檩支撑施工的质量安全控制要点和施工工艺。

钢板桩在深基坑支护中的模拟分析

钢板桩围堰由于具有成本低、整体刚度较强、施工周期短、易打入坚硬土层,兼有较好防水性能等优点,在砂类土、黏性土、以及深水基坑被广泛应用。施工过程中由于工况复杂,不可控因素多,需要提前对施工工况进行模拟分析。本文结合新建江苏南沿江城际铁路跨京沪高铁特大桥518#墩深基坑施工的工程实例,重点介绍钢板桩围堰设计、施工工艺,并利用理正深基坑软件和Midas Civil软件对基坑支护体系进行模拟验算,对关键工序、关键部位提前预控。可以在类似的深基坑工程中予以借鉴。

风吸力作用下仅考虑扭转约束的Z形和C形檩条弹性弯扭屈曲

采用开口薄壁构件理论,在忽略屋面板对檩条侧向约束的条件下,根据上翼缘受扭转约束简支檩条的线性总势能方程,应用变分法推导无支撑Z形和C形檩条在风吸力作用下的扭转角及位移表达式。考虑屈曲前应力在檩条弯扭屈曲变形过程中产生的非线性应变能,根据其弯扭总势能方程,采用势能驻值原理推导无支撑Z形和C形檩条的临界弯矩表达式。扭转角、位移和临界弯矩表达式与采用ANSYS板壳单元建模的计算结果对比,吻合较好,表明理论公式精度较高,可用于工程设计。

轻型钢结构中梁及檩条稳定性的研究进展

本文根据国内外研究现状 ,综述了新近轻型钢结构中梁及檩条稳定性方面研究的若干内容。首先简要介绍了目前轻钢结构的发展特点 ,然后着重就薄壁型钢梁及檩条的截面特性、屈曲行为及其研究方法以及稳定性方面研究的几个热点问题作了概述 。