Experimental research on ultimate bearing capacity of N-joints of grouted square steel tube trusses

Cave-in failure is apt to occur in joints of trusses made of square hollow sections. In order to turn the failure mode into a strength failure mode of joint members, the idea is proposed that the chord of the truss is grouted to increase the cave-in beating capacity of a hollow tube chord. An experiment of eight specimens of N- joints made of grout-filled square steel tubes is performed. Based on the experimental study, the geometrical parameters of specimens are analyzed, and the effects of the confinement index ε, the spacing between the two web members g and the ratio of side length of the vertical web member to that of the chord β on the behavior of specimens are investigated through simulation analysis by simulation analyses, the mechanical properties and the failure an ANSYS program. Based on the test results and modes of this kind of joints are analyzed and the formulae to predict the ultimate bearing capacities corresponding to different failure modes are developed. The ultimate bearing capacity of compressive N-joints is calculated in accordance with the cave-in failure mode of a chord member; the ultimate bearing capacity of tension N-joints is calculated in accordance with the punchingshear failure mode; the ultimate bearing capacity of a chord member is calculated in accordance with the shear failure mode in normal sections.

Seismic performance of recycled concrete-filled square steel tube columns

An experimental study on the seismic performance of recycled concrete-filled square steel tube （RCFST） columns is carried out. Six specimens were designed and tested under constant axial compression and cyclic lateral loading. Two parameters, replacement percentage of recycled coarse aggregate （RCA） and axial compression level, were considered in the test. Based on the experimental data, the hysteretic loops, skeleton curves, ductility, energy dissipation capacity and stiffness degradation of RCFST columns were analyzed. The test results indicate that the failure modes of RCFST columns are the local buckling of the steel tube at the bottom of the columns, and the hysteretic loops are full and their shapes are similar to normal CFST columns. Furthermore, the ductility coefficient of all specimens are close to 3.0, and the equivalent viscous damping coefficient corresponding to the ultimate lateral load ranges from 0.323 to 0.360, which demonstrates that RCFST columns exhibit remarkable seismic performance.

Axial Compression Behavior and Analytical Method of L-Shaped Column Composed of Concrete-Filled Square Steel Tubes

Based on the characteristics of an L-shaped column composed of concrete-filled square steel tubes, the axial compression experiment and nonlinear finite element analysis were carried out to study the mechanical property of the L-shaped column. The load-displacement curve for the L-shaped column, the deflection and load-strain curves for the mono columns were obtained by the axial compression experiment. The results show that the L-shaped column exhibits a flexural-torsional buckling failure mode. The numerical simulation by the finite element analysis shows that the bearing capacity and failure mode are in accordance with those of the axial compression experiment and the feasi- bility of the finite element analysis is proved. For the calculation of the bearing capacity of the L-shaped column com- posed of concrete-filled square steel tubes, an analytical method is proposed based on the theory of the elastic stability and spatial truss model. The results of the analytical method are in good agreement with those of the axial compression experiment and the finite element analysis.

Behavior of High Strength Concrete Filled Square Steel Tube Stub Columns with Inner CFRP Tube Under Biaxial Eccentric Compression

This paper studies the contribution of CFRP(carbon fiber-reinforced polymer)to the mechanical behavior of high strength concrete-filled square steel tube(HCFST)under biaxial eccentric compression.The new type of composite member is composed of an inner CFRP tube and an outer steel tube with concrete filled in the two tubes.The finite element analysis was made by ABAQUS on the behavior of high strength concrete filled square steel tubular columns with inner CFRP circular tube subjected to bi-axial eccentric loading.The results obtained from the finite element analysis were verified with the experimental results.In addition,the load-deflection curves in the whole process were calculated and analyzed,which can be divided into three segments:Elastic phase,plastic phase,descending phase.Based on the load-deflection curves,the stresses analysis on the core concrete,CFRP tube and steel tube were conducted.The confinement effect of the CFRP tube improves the ductility of HCFST-CFRP stub column.CFRP ratio and eccentricity affect the ultimate bearing capacity of HCFST stub column.Finally,a calculation formula of ultimate bearing capacity was proposed in the paper.

Prediction of Axial Capacity of Concrete-Filled Square Steel Tubes Using Neural Networks

The application of artificial neural network to predict the ultimate bearing capacity of CFST （ concrete-filled square steel tubes） short columns under axial loading is explored. Input parameters consiste of concrete compressive strength, yield strength of steel tube, confinement index, sectional dimension and width-to-thickness ratio. The ultimate bearing capacity is the only output parameter. A multilayer feedforward neural network is used to describe the nonlinear relationships between the input and output variables. Fifty-five experimental data of CFST short columns under axial loading are used to train and test the neural network. A comparison between the neural network model and three parameter models shows that the neural network model possesses good accuracy and could be a practical method for predicting the ultimate strength of axially loaded CFST short columns.

Joint member angle limits of composite beams and CFT square columns

This work aims to understand the relationship between the member angle limit and the energy ratio for 24 test samples of composite beams and CFT square steel tube columns. This work also compares the formula applicability for member angle limit with the previous test result to provide the basic data for the design of composite beam-CFT column. The evaluation of the member angle limit was performed with concrete compressive strength (fC =22.16 MPa, 30.49 MPa), breadth-to-thickness ratio (B/t=25.0, 33.3, 43.5), and axial capacity ratio (N/N0=0, 0.3, 0.4, 0.5) as the main variables of the test samples. For the relationship between the member angle limit (Ru) and the energy ratio (ES/EC ), the test result shows that the energy ratio becomes lower as the axial capacity ratio and the breadth-to-thickness ratio increase. The energy ratio is lower for the Type B test sample compared with that of Types A and C. For the formula suggested by SATO, the test samples are distributed evenly for comparison between test values and the member angle limit; however, other formulas indicate a deviation. Specifically, for the comparison between R u,cal and R u (Test), Maeda's formula shows severe deviation.

新型波纹管连接方钢管混凝土拼接柱抗震性能试验研究

为研究一种新型波纹管连接方钢管混凝土拼接柱的抗震性能,以不同节点配筋率、不同节点锚固长度和轴压比为主要研究变量,对1个整浇柱和4个装配柱进行低周往复加载试验。研究分析了整浇柱与装配柱在破坏模式、滞回性能、位移延性等方面的抗震性能差异。结果表明:装配柱与整浇柱破坏模式类似,采用不同节点构造的装配柱与整浇柱在滞回曲线、骨架特性和刚度退化等方面差异不大,装配柱的耗能性能优于整浇柱。各装配柱极限位移角为1/16.7~1/25,满足规范设计要求。在较大轴压比下,装配柱的承载力提升,延性降低。在较大位移角下,装配柱节点抗震性能受焊缝质量的影响较大,建议实际工程中加强焊接质量管理,以保证构件具有足够的变形能力。

局部环向变厚度方钢管混凝土柱偏压力学性能研究

针对海洋环境中飞溅区造成的钢管混凝土柱局部环向腐蚀现象,采用机械削减方式模拟钢管壁厚局部环向腐蚀,进行了7个方钢管混凝土柱偏压试验,揭示了削弱率和偏心率对其偏压承载力的影响,并通过数值模拟对削弱率进行拓展分析.提出了基于削弱率的偏压承载力降低系数,代入中、美规范进行偏压承载力计算.结果表明:钢管的局部环向变厚度严重削弱了方钢管混凝土柱的偏压承载力和侧向挠曲能力;较大的加载偏心率也降低了其偏压承载力,但增大了其侧向挠曲能力.引入偏压承载力降低系数后,根据中、美规范计算得到的偏压承载力与试验值均吻合较好;相比于我国规范,美国规范在计算偏压承载力时相对更加保守.

配筋空心方钢管高强混凝土纯弯构件受力性能有限元分析

目的 研究配筋空心钢管高强混凝土构件的抗弯性能,推动其在建筑结构中的应用。方法 采用有限元分析软件ABAQUS建立配筋空心钢管混凝土构件有限元模型,在验证模型准确的基础上,分析构件的受力全过程及钢材屈服强度、混凝土抗压强度、钢管壁厚、钢筋直径、普通钢筋数量对构件受弯性能的影响。结果 纯弯试件在荷载作用下受力过程可分为3个阶段:弹性阶段、弹塑性阶段和强化阶段;试件破坏形态均为受弯破坏,表现出较好地延性。结论 组合构件在弯矩作用下可以很好地协同工作;钢材屈服强度和钢管壁厚的增加对构件承载力的提高影响最显著,建议配置普通钢筋数量在6~8根为最优。

方钢管砖混再生骨料混凝土短柱轴压性能有限元研究

目的 研究方钢管砖混再生骨料混凝土短柱的力学性能,推动建筑固废资源化利用。方法 利用ABAQUS软件建立方钢管砖混再生骨料混凝土短柱模型,将模拟结果与试验结果进行对比,验证了模型的正确性。然后分析砖混骨料取代率、倒角率、钢管屈服强度及厚度对短柱轴压力学性能的影响。结果 砖混骨料取代率小于50%时,极限承载力降低幅度在10%以内;当倒角率提高至0.16时,极限承载力有小幅度提升;试件的极限承载力随着钢管的厚度及屈服强度的增大而提高。结论 砖混骨料取代率较小时对试件承载能力影响较小,外包钢管的强度与厚度对试件承载能力有较大影响。对于方柱,适当提高倒角率可以使钢管更好约束混凝土,提高试件承载能力,但倒角率过大时截面面积有较大削弱,承载能力降低。

轴压比对波纹侧板-方钢管混凝土柱抗震性能的影响研究

为研究轴压比对波纹侧板-方钢管混凝土柱抗震性能的影响,使用ABAQUS软件建立了组合结构柱的有限元模型,通过破坏形态和滞回曲线等对模型的准确性进行了验证,运用参数模型讨论了不同轴压比对试件的破坏形态、滞回曲线、骨架曲线、压弯承载力和延性系数的影响。结果表明,随着轴压比增大,方钢管的高应力高度逐渐升高,波纹板的应力由水平分布变化为斜向分布;提高轴压比会使试件的压弯承载力和延性系数呈先升高后降低的趋势,建议轴压比不应超过0.30,满足规范中对延性系数的要求并在一定程度上提高结构的压弯承载力。通过合理控制轴压比,可以提升波纹侧板-方钢管混凝土柱抗震性,确保其在实际应用中的安全性和稳定性。

MS1180方管连续辊弯成形角部开裂机理

方矩形管在辊弯成形中会产生角部开裂现象,这已成为严重制约方矩形管质量的关键问题,为解决其角部开裂缺陷展开深入研究,寻找控制开裂缺陷的方法。首先通过对MS1180进行单轴拉伸、缺口拉伸和平面应变实验得到了材料的力学特性,并分别利用3种拉伸试验将Ayada、Rice-Tracey和标准化Cockroft-Latham准则进行校准,得到了预测误差最小的一种断裂准则,并以此构建了方矩管辊弯开裂模型。其次利用辊弯成形COPRA RF设计软件和有限元MARC仿真专业软件,结合生产实际条件建立了方矩形管连续辊弯成形三维有限元模型,并进行辊弯实验验证模型的准确性。最后采用扫描电镜和金相显微镜对方矩形管开裂件以及断口进行微观观察,针对性的利用有限元模型探究了方矩形管连续辊弯成形时应力-应变分布规律,并分析了道次数量、角部成形半径和机架间距对方矩管角部应力-应变分布的影响。结果表明:发现材料起裂点位于角部近外层,对开裂断口进行分析,得到其开裂方式为准解理开裂,角部剪切面上所受的主应力过大导致其开裂;增加辊弯道次数量、方矩形管角部成形半径以及机架之间的间距能有效减少开裂问题的出现,为以后解决方矩形管角部开裂问题提供了理论基础。

热-湿-力耦合作用对高温后方钢管混凝土短柱轴压力学性能影响试验研究

火灾发生时钢管混凝土内部会产生水蒸气,为探讨热-湿-力耦合作用对高温后方钢管混凝土轴压力学性能的影响,进行了10根高温后方形钢管混凝土短柱轴压力学性能试验,研究排气孔数量、布置位置、轴压比和升温时间等参数对其破坏形态、轴压刚度与剩余承载力等力学性能的影响。试验结果表明,试件破坏形态表现为压溃破坏;在其他参数相同的情况下,与升温前相比,随着排气孔数量从2个增加至4个和6个,轴压刚度分别降低了69.1%、73.3%、76.4%,剩余承载力分别降低了15.8%、16.2%、21.7%。轴压刚度随轴压比的增大而降低;随着升温时间的延长,剩余承载力先随轴压比的增大而增大,后随轴压比的增大而减小。研究结果可为钢管混凝土柱的抗火设计和该类结构火灾后的损伤评估与加固提供参考。

方钢管螺旋筋约束自密实高强混凝土柱抗震性能试验研究

为研究方钢管螺旋筋约束自密实高强混凝土柱的抗震性能,以轴压比、剪跨比、有无配制螺旋筋以及螺旋筋间距作为设计参数,进行了7个试件的低周反复加载试验,获取了各试件的滞回曲线以及应变分布。试验结果表明:试件破坏特征主要为方钢管柱脚区域出现明显鼓曲形成塑性铰区域;随轴压比的提高,试件抗剪承载力、环线刚度和耗能能力均有提升,剪跨比对试件抗震性能的影响规律不明显。配制螺旋筋对峰值承载力和刚度的影响较小,而对试件延性及耗能的提升明显,与无配筋试件相比试件延性平均提升了15.4%,耗能平均提升了114.9%。螺旋筋间距越密对试件抗震性能提升效果更优;适当增大轴压比,控制剪跨比在5以内以及增设螺旋筋对提升其承载能力和变形能力有积极作用。

不同约束方式的方钢管混凝土柱力学性能研究综述

通过分析国内外对方钢管混凝土柱力学性能的研究,总结了不同约束方式的方钢管混凝土柱的轴压性能、压弯性能、抗震性能、局部屈曲和轴向承载力计算公式。结果表明:各种不同的加劲约束措施能提升钢管对混凝土的约束作用,改善了柱的延性与抗震性能。计算方钢管混凝土柱的轴向承载力时,应考虑约束措施对核心混凝土的影响,以提高计算精度。最后对不同约束方式的方钢管混凝土柱的研究进行了总结与展望。

侧向冲击下不锈钢方形钢管动力响应分析

文中为研究侧向冲击下不锈钢方形钢管动力响应,建立两端简支的不锈钢方形钢管数值模型,与已有的冲击试验结果进行对比,验证了有限元模型的准确性。重点分析了冲击过程中钢管的能量吸收和应力变化状况,研究不同钢管壁厚、截面尺寸、冲击动量和冲击动能对不锈钢方形钢管动力响应的影响。结果表明冲击动能主要通过钢管的变形来耗散,随着钢管壁厚和截面尺寸的增加,跨中位移显著减小,钢管壁厚增加,冲击持续时间大幅增加,不锈钢方形钢管的抗冲击力学性能增强。冲击动量的改变对跨中位移的影响较小,冲击动量增加2916.54kg·m/s,跨中位移略微减小,冲击力持续时间增加0.076s。冲击动能增加2187.42J,跨中位移增加41.9%。研究为工程结构的设计和抗冲击性能的提高提供了重要的参考。

方钢管约束超高强混凝土短柱轴压承载力试验研究

为探究方钢管约束超高强混凝土(UHSC)短柱的轴压受力机理与极限承载力计算方法的准确性,以混凝土抗压强度、钢材屈服强度、含钢率为参数,开展了试验研究和有限元分析;依据约束机理提出了短柱轴压极限承载力计算方法。结果表明:套箍系数是影响方钢管约束UHSC短柱轴压破坏模式的主要因素,小于0.83时表现为剪切破坏,大于等于0.83时表现为压溃破坏;通过荷载-位移曲线与荷载-应变曲线发现,在极限荷载前钢管的环向约束能力未被充分发挥,约束作用主要表现在极限荷载后,增加含钢率可有效提高试件破坏后的受压延性,含钢率最小的试件均出现荷载突降的现象,在设计方钢管约束UHSC短柱时,需要根据混凝土抗压强度匹配合适的约束力;由于普通混凝土与UHSC压拉比不同,在核心混凝土临近极限荷载前,UHSC塑性发展程度更低,降低了与钢管之间的相互作用,所以方钢管约束UHSC短柱极限荷载提高幅度小于内填普通混凝土的试件;基于Mander模型与中国标准的计算方法无法对套箍系数大于0.3的内填UHSC试件做出准确的评估,中国标准的计算误差更小,依据试验与有限元分析结果,引入约束折减系数后,可将计算偏差控制在10%以内。

装配式方钢管约束混凝土桥墩恢复力模型研究

采用ABAQUS通用有限元软件对装配式方钢管约束混凝土桥墩进行建模,计算了桥墩试件荷载-位移滞回曲线与骨架曲线特征值;以轴压比、长细比、约束系数、方钢管屈服强度、混凝土强度、钢管嵌入深度与桥墩边长比、嵌套钢管直径与桥墩边长比、嵌套钢管厚度与桥墩边长比为拓展参数,研究各参数对装配式方钢管约束混凝土桥墩荷载-位移骨架曲线的影响规律;借鉴钢管约束钢筋混凝土柱的计算框架,拟合得出装配式方钢管约束混凝土桥墩各特征值(弹性刚度、水平荷载峰值、峰值荷载位移与下降段刚度)的计算公式;该计算公式与有限元分析结果吻合良好,有限元分析值与公式计算值之比的平均值为1.004~1.035,均方差为0.133~0.162;选取实际工程对算法进行实例验证,计算结果与有限元数值吻合良好。

方钢管煤矸石混凝土短柱轴压承载力有限元分析

目的 研究各设计参数在不同煤矸石粗骨料取代率下对方钢管煤矸石混凝土短柱轴压承载力的影响规律,提出轴压承载力计算式。方法 利用ABAQUS有限元分析软件建立方钢管煤矸石混凝土短柱轴压有限元模型,并与试验结果对比,验证模型的准确性;分析试件应力分布与荷载分配,并采用控制变量法分析试件在5种煤矸石粗骨料取代率下主要参数对其轴压承载力的影响。结果 相同设计参数下,试件轴压承载力随煤矸石粗骨料取代率的提高而降低,且最大降幅未超过14%;当试件截面边长一定时,含钢率对试件轴压承载力的影响最显著,其中,含钢率由7.4%增加至20.3%使试件轴压承载力在不同取代率下平均提升68.85%。结论 掺入煤矸石粗骨料不会使构件轴压承载力显著劣化,依据《钢管混凝土结构技术规范》(GB 50936—2014),引入煤矸石粗骨料取代率影响系数后的计算误差小于5%,可为相关研究提供参考。

广州白云国际会议中心国际会堂结构设计和施工重难点

采用YJK和ETABS对广州白云国际会议中心国际会堂结构进行弹性分析,采用Perform-3D进行罕遇地震作用下的整体结构弹塑性动力分析,并通过采取针对性的加强措施,改善了结构受力,提高了结构抗震性能,达到了预设的抗震性能目标。对大跨度钢结构构件进行方案选型,提出了大跨度钢结构桁架局部构件后装施工控制法和大悬挑钢结构桁架构件局部弯矩释放法,可以有效地减小结构构件局部受力,更加经济合理。对主会场大跨度楼盖进行竖向舒适度分析,结果表明竖向振动加速度满足规范要求,人群激励模式起控制性作用。通过采用合理的结构方案,以及与建筑专业的密切配合,很好地实现了建筑功能及建筑造型,以及项目快速建造的要求。