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.

内置碳钢不锈钢管海洋混凝土柱轴压试验及承载力计算

为研究不锈钢管海洋混凝土柱及内配碳钢后的轴压力学性能,以型钢类型、螺旋筋间距、纵筋直径为变化参数,完成了10个试件的轴心受压静力加载试验。观察了试件的受力破坏全过程及形态,获取了轴向荷载-位移曲线及各钢材应变曲线,基于试验实测数据,就各变化参数对试件的轴压承载力、延性、耗能能力和损伤发展的影响规律进行了分析。结果表明:不同试件的破坏形态相似,均表现为不锈钢管局部屈曲压皱,混凝土斜向剪切破坏;内置碳钢可以提高试件的极限承载力、轴压延性和耗能能力,抑制试件的损伤发展;在增加相同用钢量的条件下,增加圆钢管含钢量对试件轴压性能提升幅度最大;基于“复合约束叠加法”推导计算公式所得承载力计算值与试验值吻合良好。

不锈钢复合钢材焊接方管T形管节点试验研究

不锈钢复合钢材是一种成本低、强度高、耐腐蚀性能优异的高性能钢材,其在对耐腐蚀要求高的工程结构应用中尤其具有竞争力。该文旨在通过试验,研究不锈钢复合钢材焊接方管T形节点在静力和低周往复荷载作用下的力学性能,设计、制作了4个管节点试件并完成了加载,基于试验结果重点研究了各管节点试件的试验过程、破坏模式、荷载-位移响应和应变发展等;按中国规范GB 50017和欧洲规范EN 1993-1-8进行了节点承载力计算,并与试验值进行了对比。研究结果表明,对于支管承受轴向压力的管节点试件,以主管上表面塑性破坏为主;对于支管承受水平低周往复荷载的管节点试件,以主管上表面塑性变形和主管与支管之间连接焊缝断裂破坏为主;当管节点破坏模式符合现行规范GB 50017和EN 1993-1-8中规定时,相关承载力计算公式仍适用于此类不锈钢复合钢材焊接方管T形管节点的设计计算。

采用铁素体不锈钢的圆形不锈钢管混凝土柱的设计方法研究

为研究采用铁素体不锈钢的圆形不锈钢管混凝土短柱的轴压性能,首先建立并验证其有限元模型,然后利用该模型创建典型算例数据库。基于算例数据库分析径厚比、名义屈服强度、混凝土强度等参数对其轴压性能的影响规律,并基于该有限元算例数据库验证现有圆钢管混凝土短柱设计方法的有效性。最后建议了采用铁素体不锈钢的圆形不锈钢管混凝土短柱的轴压承载力、轴压刚度和峰值应变的简化模型。简化计算结果和有限元计算结果吻合良好。

内置型钢方形不锈钢管超高性能混凝土柱偏压性能

为研究内置型钢的方形不锈钢管超高性能混凝土柱的偏压性能,考虑长径比、宽厚比、偏心率、型钢含钢率和加载方向(强弱轴加载)等因素的影响,设计了18根试件进行偏心受压试验研究。观察试件在偏心受压状态下的破坏过程及破坏形态,并通过荷载-跨中侧向挠度关系曲线及侧向挠度曲线,分析各因素对试件偏压性能的影响。结果表明:试件的破坏形态表现为短柱的强度破坏和中长柱的非弹性失稳破坏,且伴有局部鼓曲现象产生;试件的极限承载力随着长径比、宽厚比、偏心率的增加而减小,随着型钢含钢率的增加而增大;与绕弱轴方向加载的试件相比,绕强轴方向加载的试件具有更高的极限承载力。利用ABAQUS软件建立了偏压试件的有限元模型,基于试验结果对有限元模型的可靠性进行了验证,有限元计算结果与试验结果吻合良好,有利于进一步分析组合柱的工作性能。基于已有的相关研究成果提出了内置型钢方形不锈钢管超高性能混凝土柱的偏压极限承载力简化计算公式,为工程设计及相关规范的制定提供了一定的参考。

奥氏体不锈钢管坯镦挤法兰工艺

针对应用广泛的奥氏体不锈钢中间带大孔的高颈法兰类零件传统锻造工艺的不足,提出了一种利用管坯直接镦挤法兰的新工艺;用DEFORM-3D软件模拟了奥氏体不锈钢(0Cr18Ni9)法兰锻件的管坯镦挤成形过程。结果表明:该工艺是可行的,与传统工艺相比,该工艺工序少,材料利用率高,成形载荷小,提高了生产效率,降低了生产成本。对类似零件的成形具有一定的参考价值。

超声冲击法提高T型焊接管接头疲劳性能

为了提高T型管接头疲劳性能,提出采用超声冲击方法对具有相同级别的低碳钢和奥氏体不锈钢 1Cr18Ni9Ti钢管接头进行疲劳性能对比试验．结果表明:超声冲击处理低碳钢后疲劳强度提高67％左右,疲劳寿命延长了22-45倍;超声冲击处理奥氏体不锈钢1Cr18Ni9Ti疲劳强度提高69％左右,疲劳寿命延长了21-30倍．在低应力比R(R≤0)条件下使用超声冲击处理技术能够大幅度改善管接头的疲劳性能．将超声冲击处理方法用于提高具有相同强度级别的不锈钢和普通碳素结构钢管接头疲劳性能的效果相差不大．超声冲击法对提高疲劳强度效果显著．

复式不锈钢管高强再生块体混凝土短柱轴压试验研究

在方不锈钢管混凝土中配置圆碳素钢管,可以改善方不锈钢管对核心混凝土约束效应低、变形能力差的特点,使复式不锈钢管混凝土(concrete-filled steel tube,CFST)截面具有较高的承载力、变形能力和抗火性能,减少普通钢结构的防腐和防火施工工序;钢管的约束效应也有利于弥补添加再生混凝土块体所带来的不利影响。开展16根复式不锈钢管高强再生块体混凝土短柱的轴压试验,考察了再生块体取代率、约束效应系数和新旧混凝土强度等参数对试件轴压力学性能的影响。研究结果表明:复式不锈钢管再生块体混凝土短柱试件的轴压承载力随再生块体取代率的增加而降低,替代率20%时承载力最大降低幅度为6.8%;试件破坏过程及破坏形态与普通复式不锈钢管混凝土短柱相似;内部圆钢管混凝土呈腰鼓型和剪切型破坏两种类型;复式不锈钢管再生块体混凝土短柱具有良好的变形能力和剩余承载力,超过峰值荷载后,荷载–位移曲线经过短暂下降,基本维持水平或略上升,所有试件的剩余承载力达到峰值荷载的63%以上。最后,提出了复式不锈钢管混凝土截面中钢管截面对核心混凝土的约束效应的简化方法,采用4种承载力计算方法进行轴压承载力的计算并对比,结果表明,考虑圆形截面部分的承载力乘以折减系数的假定具有较好的适用性,所得承载力的计算结果与试验结果吻合较好。

不锈钢管中管钢管混凝土抗剪性能试验研究

冰荷载是严寒地区海洋平台的主控荷载,对海洋平台导管腿抗剪承载力要求较高。为研究影响不锈钢管中管钢管混凝土海洋平台导管腿抗剪承载力的因素,共制作了18根管中管钢管混凝土抗剪构件,研究外钢管材料、混凝土强度、空心率和剪跨比对管中管钢管混凝土抗剪承载力的影响。通过研究不同情况下构件破坏形态、承载能力、局部应变关系来分析试件内部变化情况发现:随着空心率的减小、混凝土强度的增加,构件抗剪强度均有所增大;剪跨比越大,其抗剪强度越小。结合试验情况,提出了管中管钢管混凝土抗剪承载力经验公式,并通过ABAQUS有限元建模软件进行分析验证,结果表明模拟与试验结果吻合良好。

复式不锈钢管混凝土轴压试验研究

钢管混凝土在实际工程中已得到广泛应用,但普通碳素钢在极端环境中的应用存在局限性。不锈钢管混凝土既有类似于普通钢管混凝土的力学性能,又能在特定环境下起到耐腐蚀作用,在特殊工程中应用前景广阔。对一系列不同内钢管厚度和强度的复式不锈钢管混凝土轴压试验,结果表明应变达到0.07时,仍能够保持80%以上的峰值承载力,具有很好的延性;内钢管厚度的增加对极限轴向承载力的下降起到了明显减缓作用,但对其影响有限;提高内钢管厚度和强度均能显著提高试件的压缩刚度;现行规范能对复式不锈钢管混凝土轴压承载力进行较为准确的估计。

不锈钢管/普通钢管高强混凝土组合柱轴压力学性能研究

对7个不锈钢管/普通钢管高强混凝土组合柱的试件进行轴压试验,研究分析了混凝土的强度、内钢管的直径和壁厚对试件的极限承载力的影响。

无氟不锈钢管材草化剂的研制及应用

介绍一种新型无氟CL-3538型不锈钢管材草化剂,分析其草化腐蚀基本原理,论述其成膜反应过程,并阐述CL-3538型草化剂的配制管理与维护方法。分析认为:CL-3538型草化剂的配方组成能满足对草化膜性能的要求,使用后可获得理想的润滑载体——结晶草化膜;与CL-3518型草化剂相比,CL-3538型草化剂不仅更适宜作为冷拔(轧)不锈钢管材的润滑载体,而且草化剂因不含氟离子而更环保,废液更易处理。

外包不锈钢圆中空夹层钢管混凝土柱抗撞计算方法研究

目前钢筋混凝土和实心钢管混凝土构件已广泛应用于实际工程,在抗冲击性能方面已形成相关设计方法,而针对外包不锈钢圆中空夹层钢管混凝土(CFDST)柱的耐撞性能研究较少。为此,该文在前期试验研究的基础上,采用ABAQUS建立了该类构件在轴力与侧向撞击耦合作用下的有限元模型。分析了轴力-撞击共同作用下该类构件的抗撞机理;重点研究了轴压比、名义含钢率等对构件抗撞性能的影响;给出了该类构件在轴力-撞击耦合作用下撞击力平台值动力放大系数(DIF)的计算公式。结果表明:外钢管的塑性变形是构件耐撞的主要耗能机制;轴压比对构件抗撞性能起削弱作用,且当轴压比大于0.5时,削弱程度更加明显;名义含钢率、外钢管与混凝土强度、撞击速度和截面外径对构件抗撞性能影响较大;建议的计算公式能够较好预测该类构件侧向撞击下的撞击力平台值。