EXPERIMENTAL RESEARCH AND NONLINEAR FINITE ELEMENT ANALYSIS ON NEW TYPE JOINT BETWEEN COLUMN AND STEEL BEAM OF CONCRETE-FILLED RECTANGULAR STEEL TUBULAR

Experimental results of new type joints between the column and the. steel beam of concrete-filled rectangular steel tubular （CFRT） under reversed cyclic loads are presented. The earthquake resistant capacity of the joint is influenced by infilled concrete, stiffener length and relative dimensions of column and beam. It is found that the hysteresis curves obtained in the experiment are full and the joints have a good energy dissipation capacity. The nonlinear finite element models are also used to analyze the hysteresis behavior of the joints under reversed cyclic loads using ANSYS 8.0. The influences of the stiffener length and the infilled concrete are analyzed. Analytical results show that the stiffener length and the infilled concrete are critical for the joints. Furthermore, the skeleton curves of the finite element models are in good agreement with those of experiments.

Seismic Behavior of Diaphragm-Through Connections of Concrete-Filled Square Steel Tubular Columns and H-Shaped Steel Beams

Based on the introductions of a type of diaphragm-through connection between concrete-filled square steel tubular columns (CFSSTCs) and H-shaped steel beams,a finite element model of the connection is developed and used to investigate the seismic behavior of the connection.The results of the finite element model are validated by a set of cyclic loading tests.The cyclic loading tests and the finite element analyses indicate that the failure mode of the suggested connections is plastic hinge at the beam with inelastic rotation angle exceeding 0.04 rad.The suggested connections have sufficient strength,plastic deformation and energy dissipation capacity to be used in composite moment frames as beam-to-column rigid connections.

Behavior of concrete and concrete-filled circular steel tubular stub columns at constant high temperatures

Based on reanalyzing test results of uniaxial compressive behavior of concrete at constant high temperatures in China, with the compressive cube strength of concrete from 20 to 80 MPa, unified formulas for uniaxial compressive strength, elastic modulus, strain at peak uniaxial compression and mathematical expression for unaxial compressive stress-strain relations for the concrete at constant high temperatures were studied. Furthermore, the axial stress-axial strain relations between laterally confined concrete under axial compression and multiaxial stress-strain relations for steel at constant high temperatures were studied. Finally, based on continuum mechanics, the mechanics model for concentric cylinders of circular steel tube with concrete core of entire section loaded at constant high temperatures was established. Applying elasto-plastic analysis method, a FORTRAN program was developed, and the concrete-filled circular steel tubular （CFST） stub colunms at constant high temperatures were analyzed. The analysis results are in agreement with the experiment ones from references.

Influence of Axial Load Ratio on Shear Behavior of Through-Diaphragm Connections of Concrete-Filled Square Steel Tubular Columns

Nonlinear finite element analysis and parametric studies were carried out to study the influence of axial load ratio on the shear behavior of the through-diaphragm connections of concrete-filled square steel tubular columns. The analysis reveals that smaller axial load ratio can improve the shear bearing capacity and ductility while larger axial load ratio will decrease the shear behavior of the through-diaphragm connections. The parametric studies indicate that the axial load ratio should be limited to less than 0.4 and its influence should be considered in the analysis and design of such connections.

In-Plane Creep Buckling of Concrete-Filled Steel Tubular Arches

The creep-induced deformation of the arch rib of concrete-filled steel tubular （CFST） arches under a sustained load can increase the bending moment, which may lead to earlier stability failure called creep buckling. To investigate the influences of concrete creep on the buckling strength of arches, a theoretical analysis for the creep buckling of CFST circular arches under distributed radial load is performed. The simplified Arutyunyan-Maslov （AM） creep law is used to model the creep behavior of concrete core, and the creep integral operator is introduced. The analytical solutions of the time-dependent buckling strength under the sustained load are achieved and compared with the existing formula based on the age-adjusted effective modulus method （AEMM）. Then the solutions are used to determine the influences of the steel ratio and the first loading age on the creep buckling of CFST arches. The results show that the analytical solutions are of good accuracy and applicability. For CFST arches, the steel ratio and the first loading age have significant influences on creep buckling. An approximate log-linear relationship between the decreased degrees of the creep buckling strength and the first loading age is found. For the commonly used parameters, the maximum loss of the buckling strength induced bv concrete creen is close to 40%

Progressive Collapse Analysis of Concrete-Filled Steel Tubular Frames with Semi-rigid Connections

A 9-story concrete-filled steel tubular frame model is used to analyze the response of joints due to sudden column loss. Three different models are developed and compared to study the efficiency and feasibility of simulation, which include substructure model, beam element model and solid element model. The comparison results show that the substructure model has a satisfying capability, calculation efficiency and accuracy to predict the concerned joints as well as the overall framework. Based on the substructure model and a kind of semi-rigid connection for concretefilled square hollow section steel column proposed in this paper, the nonlinear dynamic analyses are conducted by the alternate path method. It is found that the removal of the ground inner column brings high-level joint moments and comparatively low-level axial tension forces. The initial stiffness and transmitted ultimate moment of the semi-rigid connection are the main factors that influence the frame behavior, and their lower limit should be guaranteed to resist collapse. Reduced ultimate moment results in drastic displacement and axial force development, which may bring progressive collapse. The higher initial stiffness ensures that the structure has a stronger capacity to resist progressive collapse.

Low cyclic fatigue performance of concrete-filled steel tube columns

Eight concrete-filled steel tubular(CFT) columns were tested subjected to cyclic loading under constant axial load. Experimental parameters included axial compression ratio, loading sequences, and strength of concrete and steel. The seismic performance of CFT columns and failure modes were analyzed. The test results show that different axial load ratios and loading sequences have effects on the load carrying capacity, ductility and energy dissipation capacity of CFT columns, as well as the failure modes of the CFT columns. The failure pattern can be categorized into two types: local buckling failure of steel tube in compression zone, and low cycle fatigue tearing rupture failure of steel tube. The seismic behavior was evaluated through the energy index obtained from each cycle.

Design equations for maximum stress concentration factors for concrete-filled steel tubular K-joints

Stress concentration factors(SCFs)for welded tubular joints can be decreased by filling the chord with concrete leading to a longer fatigue life.However,there are currently no design formula available in guidelines to predict the SCF of concrete-filled circular hollow section(CFCHS)K-joints,thus limiting their applicability in bridge design.To address this gap,finite element models for CFCHS K-joints were developed and compared against test results to ensure their accuracy.Then,a comprehensive parametric study was conducted to establish relationships between maximum SCFs and four variables:brace-to-chord diameter ratio(b),chord diameter-to-thickness ratio(2g),brace-to-chord thickness ratio(t),and the angle between braces and chord(q).A total of 480 FE models were examined under three loading conditions including brace and chord loading:balanced axial force,chord axial force,and chord bending.Design equations to predict the maximum SCF for CFCHS Kjoints were established by multiple regression analyses of the numerical results.A comparison of maximum SCFs between circular hollow section(CHS)and CFCHS K-joints was made,and it was concluded that average reductions of 42%and 33%in maximum SCFs in CFCHS K-joints at the locations of the chord and brace were found compared to CHS joints for balanced axial force,respectively.Finally,a case study illustrating how to use the proposed equations for fatigue safety verification was presented.

拱肋高度基于余弦曲线变化的钢管混凝土拱桥设计方法

大跨度钢管混凝土拱桥大多采用等宽变高的截面形式。分析了李特公式中影响变截面高度的设计参数,在此基础上提出了钢管拱变截面高度设计的一种新方法:将拱肋截面高度定义为拱顶高度与拱轴水平倾角余弦值的幂次方之比,幂次方由拱顶高度、拱脚高度和拱轴线方程唯一确定。结合钢管混凝土拱桥常用的矢跨比和拱轴系数,给出了幂次方的取值范围。为验证该方法在大跨度钢管拱设计中的可行性,开展了两座钢管混凝土拱桥的动力特性与弹性稳定分析。结果表明,采用该方法设计的钢管混凝土变截面拱,与设计文件和李特公式的计算结果相比,钢管拱弦杆轴力差异在1.7%~7.0%,动力特性、弹性稳定以及腹杆应力差异在5%内。文中提出的设计方法可以为今后钢管混凝土拱桥设计提供参考。

广义李特公式在700 m钢管混凝土拱桥试设计中的应用

大跨度钢管混凝土拱桥常采用变截面拱肋,以满足受力需要。围绕钢管拱肋变截面高度设计,在李特公式基础上推导了广义李特公式,将其应用于一座700 m跨钢管混凝土拱桥试设计中,开展了不同抛物线次数下钢管拱内力、弹性稳定、动力特性及主拱刚度的计算。分析结果表明:主要参数均能满足规范要求;相比于李特公式,采用广义李特公式设计的变截面钢管拱,由于减小了拱脚截面负弯矩,使截面上、下弦管的轴向力分布更趋均匀。

南京某国家级重点实验室结构方案设计

文章以南京无线谷紫金山实验室为背景介绍其结构方案设计。紫金山实验室是国家级重点实验室,由于其特殊的建筑功能需求,存在着各种大空间暗室,在结构上表现为多层通高、高位转换等。经过各种结构方案设计研究比较,最终采用受力合理的屋顶吊挂桁架的方案,通过矩形钢管混凝土柱和屋面钢梁刚接的方案来减少计算长细比,从而解决柱子长细比超限问题,同时通过合理布置斜撑来调整整体方案的平面不规则情况。最后采用了钢结构框架-部分支撑-屋顶吊挂桁架的结构体系。

管拱型钢波纹管涵洞有限元计算分析

为拓展钢波纹管的应用型式,运用大型有限元分析软件建立合理的力学有限元模型,对管拱型钢波纹管涵洞的受力变形进行了计算分析。运用有限元法分析得出管拱型钢波纹管涵洞土体受力变形规律。在建立的有限元模型中,通过施加公路-Ⅰ级荷载分析得出,填土高度对不同的拱顶角度的管拱型钢波纹管的周向等效应力、最大等效应力、横向位移、竖向位移的变化规律,确定了最优管型。对管拱型钢波纹管涵洞在公路工程中的发展、运用具有重要现实指导意义。

扣件式钢管脚手架临界力下限计算方法

扣件式钢管脚手架临界力下限计算法是指扣件拧紧程度不足或不能保证时 ,其工作性能可能更接近于排架 ;整架按排架进行计算其临界力值既能确保安全 。

基于延性性能圆形钢桥墩內填混凝土补强填充高度的简易计算方法

目的探明圆形钢桥墩内填混凝土补强填充高度的计算方法及长细比和钢管径厚比参数对圆形截面钢桥墩承载力、延性等抗震性能的影响.方法在确定有限元分析与试验结果吻合的基础上,采用ABAQUS有限元软件对9组60个不同填充混凝土桥墩模型进行非线性数值模拟分析.结果与空钢管桥墩柱相比,部分填充混凝土圆形钢桥墩具有良好的抗震性能.随着混凝土填充率的增加,该类桥墩的延性和承载力均有所提高,超过最适填充率后,持续增加混凝土填充率,模型的承载力提高但延性下降.结论拟合出的混凝土填充率、承载力及延性与长细比和径厚比的关系公式为圆形钢桥墩内填混凝土补强填充高度的设计提供了依据.

镇江大港体育馆钢结构设计

镇江大港体育馆钢屋盖采用变高度管桁架结构体系,其屋盖和墙面组成一个整体,在充分考虑建筑空间要求与结构传力特点的基础上,优化布置次桁架和支撑体系,加强了管桁架结构体系的空间受力性能。通过灵活布置铰支座、X向弹簧支座、Y向弹簧支座和双向弹簧支座四种形式的支座,保证钢结构整体刚度和受力性能处于最优状态。

反复荷载作用下矩形钢管混凝土柱的滞回性能研究

文中首先建立了钢管与核心混凝土界面的粘结-滑移滞回模型、考虑包辛格效应的钢材单轴滞回模型和考虑矩形钢管约束效应后内填混凝土的单轴应力-应变滞回模型。在截面纤维模型的基础上,建立了考虑界面粘结-滑移的矩形钢管混凝土柱分析模型,用Fortran语言编制了相应的全过程分析程序。考虑轴压比和截面高宽比两个因素,对19个矩形钢管混凝土试件进行了数值模拟计算,并对荷载-位移滞回关系进行了初步的理论分析。

CFRP-方钢管高强混凝土中长柱的轴压性能

目的研究内置CFRP圆管的方钢管高强混凝土轴压中长柱的受力全过程,得出内置CFRP圆管的方钢管高强混凝土轴压中长柱的工作机理和静力性能,为更进一步的研究奠定基础.方法在6根内置CFRP圆管的方钢管高强混凝土轴压中长柱试验的基础上,比较分析了6种构件不同的破坏形态、荷载—纵向应变曲线、荷载—横向应变曲线以及各种因素对承载力的影响.结果在加载过程中,对比于同等尺寸的普通方钢管高强混凝土构件,构件的弹性段明显增加,构件的破坏形态均为失稳破坏,达到极限承载力后,构件的承载力有反弹.结论CFRP的存在有效地延缓和抑制了高强混凝土中剪切斜裂缝的产生,使方钢管的约束作用得到充分发挥,内置CFRP圆管轴压中长柱的极限承载能力相比于普通方钢管高强混凝土轴压中长柱有了显著的提高.

空间倒三角形管桁架的整体稳定研究

空间倒三角形管桁架的稳定性直接影响其承载力。针对不同跨度的空间倒三角形管桁架,按静力分析结果确定截面参数,然后以管桁架结构的高跨比和宽高比作为变量建立了96个结构模型,利用有限元软件进行特征值屈曲分析和非线性屈曲分析。结果表明:高跨比的增大可以提高管桁架的稳定承载力,但结构会出现静力承载力小于稳定承载力的现象;宽高比对管桁架的稳定承载力影响较小,当高跨比不小于1/15时,一定范围内其宽高比的减小可以增大管桁架的稳定承载力,当高跨比小于1/15时,宽高比的减小可以降低管桁架的稳定承载力;同时,对75 m跨度的管桁架设置了中部空间侧向支撑,结果表明侧向支撑能大幅提高结构的稳定性。

方钢管混凝土柱-不等高钢梁组合框架结构受力性能有限元分析

基于一榀两跨三层方钢管混凝土柱-不等高钢梁组合框架结构的低周往复荷载试验,应用ABAQUS软件建立相应的有限元模型并对模型正确性进行了验证,利用该模型研究了轴压比、核心混凝土强度等级、钢管屈服强度、左右侧梁高比以及柱截面宽厚比对方钢管混凝土柱-不等高钢梁组合框架结构受力性能的影响。结果表明,方钢管混凝土柱-不等高钢梁组合框架结构的设计符合“强柱弱梁,强节点弱构件”的抗震设计原则;当轴压比大于0.6时,框架结构延性明显变差;当核心混凝土强度等级提高至C50后,框架结构的承载力主要取决于钢管强度;随着钢管屈服强度的提高,框架结构的峰值荷载和破坏荷载均不断增大;左右侧梁高比的变化对框架结构的侧向承载力和弹性阶段的受力情况均有影响;框架结构的刚度和承载力均随柱截面宽厚比的增大而逐渐减小。

方钢管混凝土柱-不等高钢梁框架节点抗剪承载力分析

为研究方钢管混凝土柱-H型不等高钢梁框架节点的抗剪承载力,分析其破坏机理,建立适用于不等高钢梁节点的抗剪计算模型,提出了节点的抗剪承载力计算公式,比较了基于不同抗剪模型建立的抗剪承载力计算值与试验值的差异性。结果表明:节点域的破坏模式主要为上核心区的剪切斜压破坏;节点域抗剪承载力主要由钢管腹板、核心区混凝土主斜压杆及约束斜压杆共同承担。对比分析表明:提出的节点屈服抗剪承载力和极限抗剪承载力理论公式计算值更为接近试验值,验证了方钢管混凝土柱-不等高钢梁框架节点传力机理和承载力计算公式的正确性。