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.

Ductility and Ultimate Capacity of Concrete-Filled Lattice Rectangular Steel Tube Columns

A kind of concrete-filled lattice rectangular steel tube(CFLRST)column was put forward.The numerical simulation was modeled to analyze the mechanical characteristic of CFLRST column.By comparing the load-deformation curves from the test results,the rationality and reliability of the finite element model has been confirmed,moreover,the change of the section stiffness and stress in the forcing process and the ultimate bearing capacity of the column were analyzed.Based on the model,the comparison of ultimate bearing capacity and ductility between CFLRST column and reinforced concrete(RC)column were also analyzed.The results of the finite element analysis show that the loading process of CFLRST column consists of elastic stage,yield stage and failure stage.The failure modes are mainly strength failure and failure of elastoplastic instability.CFLRST column has higher bearing capacities in comparison with reinforced concrete columns with the same steel ratio.In addition,the stiffness degeneration of CFLRST column is slower than RC column and CFLRST column has good ductility.

Axial Bearing Capacity of Short FRP Confined Concrete-filled Steel Tubular Columns

The bearing capacity of FRP confined concrete-filled steel tubular （FRP-CFST） columns under axial compression was investigated. This new type of composite column is a concrete-filled steel tube （CFST） confined with fiber-reinforced polymer （FRP） wraps. Totally 11 short column specimens were tested to failure under axial compression. The influences of the type and quantity of FRP, the thickness of steel tube and the concrete strength were studied. It was found that the bearing capacity of short FRP-CFST column was much higher than that of comparable CFST column. Furthermore, the formulas for calculating the bearing capacity of the FRP-CFST columns are proposed. The analytical calculated results agree well with the experimental results.

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.

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.

厚硬顶板结构下巷旁超前卸压与高强支护技术研究

白庄煤矿9701工作面采用沿空留巷开采技术,其工作面顶板厚度及硬度大,巷旁支承压力高,巷旁围岩支护控制及整体留巷难度系数大。为此,设计采用“水力压裂超前断顶+钢管混凝土墩柱巷旁高强支护”组合技术方案,对上覆厚硬顶板结构进行综合控制。通过水力压裂超前断顶技术对巷旁厚硬顶板进行充分采前断顶卸压,形成巷旁短悬臂梁结构,有效缓解巷旁支护体所承受的压力。通过钢管混凝土墩柱作为主要巷旁支护体对沿空留巷的围岩进行高强支撑。经工程效果分析,该技术方案取得了良好的控顶效果,最大顶板下沉量为55 mm,巷道整体成型效果良好。研究成果可以对同类矿井开采提供安全指导。

A simplified model to predict blast response of CFST columns

In order to study the dynamic response of concrete-filled steel tube(CFST) columns against blast loads,a simplified model is established utilizing the equivalent single-degree-of-freedom(SDOF) method,which considers the non-uniform distribution of blast loads on real column and the axial load-bending moment(P-M) interaction of CFST columns.Results of the SDOF analysis compare well with the experimental data reported in open literature and the values from finite element modeling(FEM) using the program LS-DYNA.Further comparisons between the results of SDOF and FEM analysis show that the proposed model is effective to predict the dynamic response of CFST columns with different blast conditions and column details.Also,it is found that the maximum responses of the columns are overestimated when ignoring the non-uniformity of blast loads,and that neglecting the effect of P-M interaction underestimates the maximum response of the columns with large axial load ratio against close range blast.The proposed SDOF model can be used in the design of the blast-loaded CFST columns.

钢管混凝土叠合柱高墩的概率抗震能力模型

为评估钢管混凝土叠合柱高墩的抗震性能,以曲率为性能指标,采用拉丁超立方抽样方法,对截面样本偏心受压进行了全过程数值模拟.根据破坏形态,将叠合柱截面损伤划分为轻微损伤、中等损伤、严重损伤和完全损伤4种极限状态并进行量化.将曲率指标的统计特征值与轴力进行三次多项式回归分析,建立了以轴力为变量的钢管混凝土叠合柱高墩的概率抗震能力模型.结果表明:以外围箍筋约束混凝土破坏为分界,叠合柱分别表现出钢筋混凝土和钢管混凝土的破坏特征;不同轴力作用下4种极限损伤状态的曲率指标均服从对数正态分布,其均值随轴力增大而减小.

FRP-钢夹层复合管混凝土桥墩轴压承载力试验

为改善现有钢管混凝土不耐腐蚀以及FRP约束钢管混凝土施工复杂的缺点,提出一种新型组合构件:FRP-钢夹层复合管混凝土.为探究其受力性能,进行了FRP-钢夹层复合管混凝土柱式桥墩轴压试验研究,并与FRP约束钢管混凝土以及钢管混凝土进行对比,分析3种结构形式的受力性能和破坏模式.试验结果表明:钢管混凝土短柱因含钢率较低而发生剪切破坏,而FRP-钢夹层复合管混凝土短柱与FRP约束钢管混凝土短柱由于外部FRP的附加约束作用均产生腰鼓型破坏; FRP约束钢管混凝土短柱树脂基体被挤压破碎,而FRP-钢夹层复合管混凝土短柱由于夹层的存在未发生树脂基体的挤压破碎;与FRP约束钢管混凝土短柱相比,由于夹层灌浆料的作用,FRP-钢夹层复合管混凝土短柱承载力提高35.3%,极限变形提高22.5%.此外,在现有钢管混凝土和FRP约束混凝土承载力计算公式基础上得到了FRP-钢夹层复合管混凝土短柱的承载力计算公式,计算结果与试验值吻合良好.

钢管混凝土组合格构柱高墩大跨连续刚构桥非线性研究

腊八斤特大桥是雅泸路上一座高墩大跨连续刚构桥,该桥在国内首次提出并采用了钢管混凝土组合格构柱高墩。考虑钢管混凝土组合格构柱截面的组合性能,建立了三维非线性数值计算模型。按照桥梁施工过程,进行了施工状态和成桥状态的非线性研究。计算结果表明,钢管混凝土组合格构柱高墩具有较大的刚度,横向联系能明显减小桥梁的横向变形。

钢管混凝土叠合柱式桥墩受力性能分析

为减小桥墩阻水面积,跨南水北调中线工程主干渠的大油村北桥2号墩墩身采用圆形钢管混凝土叠合柱。采用有限元法进行计算分析,研究叠合柱钢管壁厚与轴向应力比率、弯曲应力比率、抗剪应力比率和组合应力比率、荷载下位移及自振周期等因素的影响规律。结果表明,叠合柱能以较小的直径满足既定承载能力的要求,比普通混凝土桩柱式结构具有更好的经济性和抗震性能。

钢管混凝土墩柱截面选型

为了获得一种易于操作的钢管混凝土墩柱单肢截面优选方法,对工程中常见的3种截面形式(圆形、矩形与矩形中空夹层截面)进行了截面优选研究。基于统一理论和等效截面思想,提出了表征截面压弯承载力的经济性指标界限偏心率,研究了套箍系数、矩形截面高宽比、矩形中空夹层截面挖空率对界限偏心率以及3种钢管混凝土截面经济性的作用规律。结果表明:套箍系数、矩形截面高宽比、矩形中空夹层截面挖空率越大,矩形和矩形中空夹层截面的经济性越好;当套箍系数大于0.8,矩形截面高宽比大于2.0,矩形中空夹层截面挖空率大于0.3时,这3个参数对界限偏心率的影响较小;界限偏心率能够很好地表征钢管混凝土单肢截面的经济性;在截面内力和材料给定的条件下,通过查界限偏心率表能够快速确定钢管混凝土墩柱最优截面形式,对工程实际具有一定的参考价值。

叠合柱高墩概率地震易损性分析

为了评估叠合柱高墩的抗震性能,根据结构可靠度理论,推导了概率地震易损性函数解析式。以一座叠合柱高墩连续刚构为研究对象,对叠合柱高墩的合理性能指标进行分析和量化,建立了以轴力为变量的截面概率抗震能力模型。考虑材料强度和地震动的不确定性,采用IDA方法对结构-地震动样本进行地震需求分析,建立了以PGA为变量的控制截面概率地震需求模型并进行概率地震易损性分析。结果表明曲率指标对数均值与对数轴力之间符合三次多项式回归关系,曲率抗震能力随轴力的增大而减小。在纵向地震作用下,曲率需求与PGA之间仍然满足对数线性关系,墩底区域最容易发生损伤,矮墩比高墩更容易发生损伤,在设计地震作用下,叠合柱高墩发生倒塌的概率极小。

钢管混凝土组合格构柱高墩大跨连续刚构桥动力特性分析

结合某山区高墩大跨连续刚构桥的动力特性分析,研究了钢—混凝土组合格构柱高墩连续刚构桥的动力特性分析方法,探讨了该类桥梁的动力特性结构行为及规律;在一定参数的基础上,研究了墩高、边界约束条件、曲线形式、曲线半径和横向连接系等参数的影响。计算结果为该类桥梁的抗风、抗震设计研究提供了分析基础。

钢管混凝土格构式高墩连续弯梁桥地震响应及参数分析

钢管混凝土格构式高墩连续弯梁桥是强震区高速公路的新兴桥型之一。本文依托四川干海子特大桥实际工程,以梁墩刚度比、曲率半径、缀管布置形式以及有无减隔震装置为设计参数,应用Midas Civil有限元软件构造了26座三跨对称曲线连续梁桥计算模型,对E1地震作用下钢管混凝土组合桁梁和格构墩主要控制截面处的弯矩、扭矩、墩顶位移、位移率等地震响应值进行对比分析,探讨了各设计参数对钢管混凝土格构式高墩连续弯梁桥的影响规律和抗震适用性,给出了建议的参数适用取值范围,并对干海子大桥第一联结构进行了优化验证。该研究结论可为同类桥梁抗震优化设计提供理论支撑,提高结构安全度,同时也为钢管混凝土组合结构桥梁的抗震设计规程修编提供参考和借鉴。

钢骨钢管混凝土在单柱式桥墩中的应用研究

受压状态下的钢骨钢管混凝土柱,外围混凝土对内部钢管有一定的紧箍力,钢管又对内部混凝土有环向压力,使得核心混凝土处于三相受压状态,从而提高构件的整体刚度和极限承载力。根据结构的这种工作机理,从正截面承载能力研究出发,提出了把这种结构应用到桥梁的柱式桥墩上的构想,从而解决单柱式桥墩墩身截面粗大的问题,增加桥下使用空间。在施工工艺上简化柱内钢筋笼的制作,节省人力资源。

罕遇地震下钢管混凝土格构式高墩连续梁桥抗震简化分析方法研究

以干海子特大桥为工程背景,运用Midas Civil有限元软件建立钢管混凝土格构式高墩连续梁桥计算模型。分别采用弹性及弹塑性法对该类梁桥进行罕遇地震下地震响应时程分析对比,发现两种不同的计算方法下其桥墩控制截面处的位移、弯矩振型曲线图较为一致;在此基础上提出了罕遇地震下该类梁桥的"等效弹性法"简化计算法,并分别从不同的地震波、设防烈度和加速度峰值对算法验证。结果表明,等效弹性法与弹塑性纤维法计算结果数值吻合良好。该研究成果可有效提高工程抗震设计计算效率,同时也为该类结构体系的抗震设计规范提供了参考依据。

钢管混凝土叠合柱式桥墩考虑桩土作用的地震效应分析

为减小桥墩阻水面积,南水北调中线工程跨主干渠大油村北桥中墩墩身采用圆形钢管混凝土叠合柱,以避开阻水超限的普通钢筋混凝土桩柱式结构。探讨考虑桩土相互作用的三种模型并对计算结果进行了对比分析。发现等效三弹簧模型能较好地模拟桩土相互作用下桩基的地震反应,同时说明叠合柱能以较小的直径满足既定承载能力的要求,比普通钢筋混凝土桩柱式结构具有更好的经济性和抗震性能。

钢管混凝土叠合柱屈曲分析及施工技术研究

腊八斤特大桥主桥为连续刚构,采用钢管混凝土叠合柱桥墩(由4根外侧包裹钢筋混凝土的钢管混凝土柱组成,柱之间采用钢筋混凝土腹板连接,桥墩为内部空心结构),最高桥墩高182.64m。为给高墩的施工及质量控制提供理论依据,采用ABAQUS和MIDAS软件对高墩进行屈曲和受力分析,研究墩顶施工偏差和支撑对高墩极限承载力的影响。结果表明:桥墩极限承载力随墩顶施工偏差的增大而不断减小;横撑和斜撑对高墩的整体稳定极限承载力影响较小。为减少施工过程对桥墩极限承载力的影响,保证墩身线形和施工质量满足要求,研究了高墩施工技术,即采用全站仪和激光垂准仪开展高墩中心、垂直度及高程监测,采用高抛免振捣、对角线对称浇筑混凝土和钢结构高空吊装等施工技术。实桥应用表明,实际累计施工偏差约为0.072m,满足施工过程中高墩线形及其它质量控制要求。