Experimental and Numerical Studies on Sea Sand Concrete Filled Stainless Steel Tube with Inner FRP Tube Subjected to Axial Compression

Since fibre-reinforced polymer(FRP) and stainless steel(SS) offer advantages of corrosion resistance and hybrid confinement, this study proposed a new type of composite column: sea sand concrete(SSC)-filled SS tubular columns with an inner FRP tube(CFSTFs) to help exploit abundant ocean resources in marine engineering. To study compressive behaviours of these novel members, eight CFSTFs and two SSC-filled SS tubular columns(CFSTs)were tested under axial compression. Their axial load-displacement curves, axial load-strain curves in SS or FRP tubes were obtained, and influences of key test parameters(the existence of glass FRP(GFRP) tubes, steel tube shapes, and GFRP tube thicknesses and diameters) were discussed. Further, specimen failure mechanism was analyzed employing the finite element method using ABAQUS software. Test results confirmed the excellent ductility and load-bearing capacity of CFSTFs. The existence of GFRP tubes inside can postpone SS tube buckling, and the content of inner FRP tubes, particularly increasing diameters, was found to improve compressive behaviours. GFRP contents helped develop the second elastic-plastic stage of the load-displacement curves. Furthermore, the bearing capacity of CFSTFs with a circular cross-section was approximately 26% higher than that with a square cross-section, and this difference narrowed with the increase in GFRP ratios.

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.

Damage assessment for seismic response of recycled concrete filled steel tube columns

A model for evaluating structural damage of recycled aggregate concrete filled steel tube （RCFST） columns under seismic effects is proposed in this paper. The proposed model takes the lateral deformation and the effect of repeated cyclic loading into account. Available test results were collected and utilized to calibrate the parameters of the proposed model. A seismic test for six RCFST columns was also performed to validate the proposed damage assessment model. The main test parameters were the recycled coarse aggregate （RCA） replacement percentage and the bond-slip property. The test results indicated that the seismic performance of the RCFST member depends on the RCA contents and their damage index increases as the RCA replacement percentage increases. It is also indicated that the damage degree of RCFST changes with the variation of the RCA replacement percentage. Finally, comparisons between the RCA contents, lateral deformation ratio and damage degree were implemented. It is suggested that an improvement procedure should be implemented in order to compensate for the performance difference between the RCFST and normal concrete filled steel tubes （CFST）.

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.

Bearing capacity of composite columns reinforced by concrete filled steel tube

In this study, nine simplified short composite columns consisting of core CFST (concrete filled steel tube) of different diameters and outer reinforced concrete were constructed to study their compressive performance under axial or eccentric compression. The failure mode is characterized by the crush of the outer concrete. The bearing capacity increases at first and then decreases with further increase of the position coefficient. It can be concluded that position coefficient is an important structural parameter that has considerable influences on the ultimate bearing capacity of the composite columns. The outer concrete, steel tubes and longitudinal reinforcement are found to work in a cooperative manner under axial or eccentric compression when the position coefficient is about 0.5. An improved bearing capacity algorithm that takes the position coefficient into account has been proposed based on the experimental and simulation results and current technical specification in China. It has been proven to be precise and safe.

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.

Three-dimensional nonlinear analysis of creep in concrete filled steel tube columns

This paper proposes a based on 3D-VLE （three-dimensional nonlinear viscoelastic theory） three-parameters viscoelastic model for studying the time-dependent behaviour of concrete filled steel tube （CFT） columns. The method of 3D-VLE was developed to analyze the effects of concrete creep behavior on CFT structures. After the evaluation of the parameters in the proposed creep model, experimental measurements of two prestressed reinforced concrete beams were used to investigate the creep phenomenon of three CFT columns under long-term axial and eccentric load was investigated. The experimentally obtained time-dependent creep behaviour accorded well with the cu~＇es obtained from the proposed method. Many factors （such as ratio of long-term load to strength, slenderness ratio, steel ratio, and eccentricity ratio） were considered to obtain the regularity of influence of concrete creep on CFT structures. The analytical results can be consulted in the engineering practice and design.

Performance Investigation of Square Concrete-filled Steel Tube Columns

The behaviour of square concrete-filled steel tube columns under concentrical loading was studied. More than one hundred specimens were tested to investigate the effects of thickness of steel tube on the load carrying capacity of the concrete-filled tubular columns （CFTs）. The effect of the grade of concrete and content of expansive agent were also investigated. The effect of these parameters on the confinement of the concrete core was studied as well. From the experimental study it was found that for both CFTs with different strength grade concrete core, the ultimate load carrying capacity increases with the increase in percentage of expansive agent up to 20% but it again decreases at 25% of expansive agent content. It was also shown that the failure mode of CFTs depends on the strength grade of concrete core.

Experimental study on the seismic behavior of high strength concrete fi lled double-tube columns

To study the seismic behavior of high strength concrete fi lled double-tube(CFDT) columns,each consisting of an external square steel tube and an internal circular steel tube,quasi-static tests on eight CFDT column specimens were conducted.The test variables included the width-to-thickness ratio(β1) and the area ratio(β2) of the square steel tube,the wall thickness of the circular steel tube,and the axial force(or the axial force ratio) applied to the CFDT columns.The test results indicate that for CFDT columns with a square steel tube with β1 of 50.1 and 24.5,local buckling of the specimen was found at a drift ratio of 1/150 and 1/50,respectively.The lateral force-displacement hysteretic loops of all specimens were plump and stable.Reducing the width-to-thickness ratio of the square steel tube,increasing its area ratio,or increasing the wall thickness of the internal circular steel tube,led to an increased fl exural strength and deformation capacity of the specimens.Increasing the design value of the axial force ratio from 0.8 to 1.0 may increase the fl exural strength of the specimens,while it may also decrease the ultimate deformation capacity of the specimen with β1 of 50.1.

Unified bearing capacity model of confined concrete column subjected to axial compression

To better study the behavior of confined concrete, this paper presents the basic hypothesis of uhimate equilibrium of confined concrete and the unified yield criteria of confining material. Based on the static equilibrium condition and yield criteria of components, a unified bearing capacity model of confined concrete column is proposed, and a simplified calculating equation of the model is also given. The model captures the character of confined concrete column. Effects of the confinement effect ratio, the lateral confinement ratio, unconfined concrete strength and the properties of confining material on the bearing capacity of confined concrete column are carefully considered. The model may be applicable to the calculation of bearing capacity of steel-confined concrete, concrete filled steel tube and FRP-confined concrete. The predictions of the model agree well with test data.

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.

Analysis and seismic tests of composite shear walls with CFST columns and steel plate deep beams

A composite shear wall concept based on concrete filled steel tube （CFST） columns and steel plate （SP） deep beams is proposed and examined in this study. The new wall is composed of three different energy dissipation elements： CFST columns; SP deep beams; and reinforced concrete （RC） strips. The RC strips are intended to allow the core structural elements - the CFST columns and SP deep beams - to work as a single structure to consume energy. Six specimens of different configurations were tested under cyclic loading. The resulting data are analyzed herein. In addition, numerical simulations of the stress and damage processes for each specimen were carried out, and simulations were completed for a range of location and span-height ratio variations for the SP beams. The simulations show good agreement with the test results. The core structure exhibits a ductile yielding mechanism characteristic of strong column-weak beam structures, hysteretic curves are plump and the composite shear wall exhibits several seismic defense lines. The deformation of the shear wall specimens with encased CFST column and SP deep beam design appears to be closer to that of entire shear walls. Establishing optimal design parameters for the configuration of SP deep beams is pivotal to the best seismic behavior of the wall. The new composite shear wall is therefore suitable for use in the seismic design of building structures.

A Review of Fibre Reinforced Polymer (FRP) Reinforced Concrete Composite Column Members Modelling and Analysis Techniques

The use of fibre-reinforced polymer(FRP)to confine concrete columns improves the strength and ductility of the columns by reducing passive lateral confinement pressure.Many numerical and analytical formulations have been proposed in the literature to describe the compressive behaviour of FRP confined concrete under both monotonic and cyclic loads.However,the efect of a stress/strain level in the columns has not been well defined because of the lack of well-defined strategies of modeing and oversimplification of the model.This paper reviews the existing FRP combinations and the available numerical and analytical methods to determine the effectiveness of the adopted method.An effort has been made to examine the usage of FRP materials in column applications in exist-ing building regimes and highlights the possible future scopes to improve the use of FRP confined concrete in civil applications.

反复荷载下圆钢管型钢再生混凝土组合柱恢复力模型研究

为建立圆钢管型钢再生混凝土组合柱的恢复力模型,对11根圆钢管型钢再生混凝土组合柱试件进行了低周反复荷载试验研究,考虑了再生骨料取代率、配钢率及钢管径厚比等不同设计参数的影响,分析了组合柱的地震破坏形态及滞回性能。基于组合柱的力学特征及曲线形状,提出了圆钢管型钢再生混凝土组合柱骨架曲线的三折线参数模型,采用理论推导与数据拟合的方法确定了组合柱骨架曲线的模型参数。在此基础上,给出了组合柱的滞回规则和卸载规律,构建了组合柱的恢复力模型,计算滞回曲线与试验滞回曲线吻合良好,表明该恢复力模型较好地反映了反复荷载下组合柱的受力特征点及滞回性能,可为此类组合柱的推广提供技术参考。

设有叠合柱的局部错层RC框架结构地震易损性分析

为研究某一设有叠合柱的局部错层钢筋混凝土(reinforced concrete,RC)框架结构在近断层和远场地震作用下的破坏概率,自定义钢管混凝土叠合柱塑性铰参数,并与试验对比验证塑性铰参数的有效性。采用SAP2000建立非线性分析模型,选取近断层和远场地震波共22条,分别以地震峰值加速度(peak ground acceleration,PGA)和最大层间位移角作为地震动强度指标和结构性能指标,基于增量动力分析(incremental dynamic analysis,IDA)结果和点估计函数对错层框架结构进行易损性分析。结果表明:对于远场地震动,结构满足“三水准”抗震设防要求,在罕遇地震下超越防止倒塌极限状态的概率仅为0.24%;结构在近断层多遇地震下仍能满足“小震不坏”的设计要求,设防地震下结构超越修复后使用极限状态的概率为53.63%,发生中等破坏的概率较大,罕遇地震下结构达到倒塌极限状态的概率为5.37%,较远场地震作用破坏更为严重。研究结果可为错层框架结构的设计和地震风险评估提供参考。

内置工字型CFRP型材高强圆钢管高强混凝土轴压短柱组合效应分析

目的 研究内置工字型CFRP型材的高强圆钢管高强混凝土短柱在轴心压力作用下三种材料的组合效应。方法 采用有限元分析软件ABAQUS对其进行数值模拟,通过相关试验验证模型的准确性,并对典型构件的破坏形态、受力全过程曲线进行分析,揭示构件各组成部分之间的相互作用和工作机理,评估CFRP配置率、钢材屈服强度、混凝土抗压强度、约束效应系数对组合效应的影响。结果 在高强圆钢管高强混凝土柱中内置CFRP型材,对构件的延性及安全裕度有显著提高,并改善了高强圆钢管对高强混凝土的约束,提高了构件的组合效应。结论 CFRP配置率控制在5.9%~8.4%,约束效应系数在1.2~1.4,钢材屈服强度不大于770 MPa时,构件中三种材料组合效应最佳。

内置型钢增强钢管约束钢筋混凝土柱节点抗震性能研究

采用钢管对传统RC柱进行约束,形成的钢管约束钢筋混凝土(STRC)柱具有优越的承载能力和耗能性能。但在应用于框架节点设计时,节点区域仍采用普通RC柱节点构造,可能导致节点处没有钢管约束而成为薄弱点,节点处易发生破坏。针对钢管约束钢筋混凝土(STRC)柱节点抗震性能薄弱的现状,提出采用内置型钢短柱进行增强。基于ABAQUS工作平台对具有相同构造形式的节点试件建立有限元模型,将数值计算所得破坏形态、滞回曲线和型钢应力与试验结果进行对比,两者吻合较好,在此基础上探讨内置型钢长度和轴压比对节点抗震性能的影响。结果表明:随着内置型钢长度增加,试件的承载力、极限位移和延性均有不同程度的提升,轴压比对试件受力性能影响较小。通过进一步分析试件的破坏机制、型钢抗弯性能和耗能能力,提出满足节点抗震性能需求的内置型钢长度建议取值。

圆钢管型钢再生混凝土组合柱水平承载力计算方法研究

通过对11个圆钢管型钢再生混凝土组合柱进行低周反复荷载试验,分析再生粗骨料取代率、型钢截面形式、轴压比、型钢配钢率及圆钢管壁厚参数对组合柱水平承载力的影响规律;观察了组合柱的破坏形态及特征,研究了圆钢管、型钢翼缘及腹板应变的发展规律,分析了组合柱的地震破坏特征。研究表明,在水平地震作用下组合柱发生典型的压弯塑性铰破坏。在此基础上,结合现有规范提出了基于叠加原理的圆钢管型钢再生混凝土组合柱水平承载力计算方法。计算结果表明,其水平承载力计算值与试验值吻合度较好,能较为准确地预测组合柱的水平承载力。

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。

开槽侧板加强型连接梁柱节点子结构抗连续倒塌性能研究

为了优化侧板加强型节点的抗连续倒塌性能,提出了一种开槽侧板加强型梁柱连接节点形式。通过静力加载试验,得到了新型节点子结构的破坏模式、竖向抗力发展机制、应变分布、延性水平和动力承载力等。试验结果表明:钢梁翼缘在盖板附近首先开裂并向腹板外排螺栓中部延伸贯穿,导致竖向承载力快速下降为峰值荷载的20%左右。相比传统侧板加强型和圆弧扩盖板型梁柱节点,新型节点的峰值承载力分别提高了62.1%和19.6%,塑性弦转角分别提高了203.6%和25.8%。通过有限元分析得到了试件的断裂路径发展过程,进一步地通过参数化分析发现:扩大过焊孔构造对改善峰值后塑性弦转角及残余强度提升无明显作用;随着螺栓群远离钢梁翼缘起始断裂位置,最小残余强度比不断增大,但峰值后塑性弦转角呈先增大后减小的趋势;当螺栓群内移45mm时,峰值后塑性弦转角及最小残余强度比分别达到0.149rad和0.88,提高了38.2%和200.8%。