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.

Effect of contact thermal resistance on temperature distributions of concrete-filled steel tubes in fire

To predicate the temperature distribution of concrete-filled steel tubes(CFSTs) being exposure to fire,a finite element analysis model was developed using a finite element package,ANSYS.A suggested value of contact thermal resistance was therefore proposed with the supporting of massive numbers of collected test data.Parametric analysis was conducted subsequently towards the cross-sectional temperature distribution of CFST columns in four-side fire,in which the exposure time,width of the cross section,steel ratio were taken into account with considering contact thermal resistance.It was found that contact thermal resistance has little effect on the overall temperature regulation with the exposure time,the width of cross-section or the change of steel ratio.However,great temperature dropping at the concrete adjacent to the contact interface,and gentle temperature increase at steel tube,exist if considering contact thermal resistance.The results of the study are expected to provide theoretical basis for the fire resistance behavior and design of the CFST columns being exposure to fire.

Reliability analysis of circular concrete-filled steel tube with material and geometrical nonlinearity

Most of the previous research on concrete-filled steel tube is restricted to a deterministic approach. To gain clear insight into the random properties of circular concrete-filled steel tube, reliability analysis is carried out in the present study. To obtain the Structural nonlinear response and ultimate resistance capacity, material and geometrical nonlinear analysis of circular concrete-filled steel tube is performed with a three-dimensional degenerated beam ele- ment. Then we investigate the reliability of concrete-filled steel tube using the first-order reliability method combined with nonlinear finite element analysis. The influences of such parameters as material strength, slenderness, initial geo- metrical imperfection, etc. on the reliability of circular concrete-filled steel tube column are studied. It can be con- cluded that inevitable random fluctuation of those parameters has significant influence on structural reliability, and that stochastic or reliability methods can provide a more rational and subjective evaluation on the safety of CFT structures than a deterministic approach.

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.

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.

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.

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.

Expansive Performance of Self-stressing and Self-compacting Concrete Confined with Steel Tube

Combining with the technology of self-compacting concrete, self-stressing concrete and concrete-filled steel tube, we can get self-compacting and self-stressing concrete-filled steel tube. In order to study the expansive mechanism of self-stressing concrete, the continuous observation of 47 days on six specimens was carried on. The specimens have different steel area to concrete area ratio. The expansive process in hoop and axial direction were studied, and the expansive mechanism was discussed too. The experimental results identify that the creep and elastic deformation take a large proportion in effective free expansion. The calculating formulas of self-stress in hoop and axial directions were presented here.

两端简支GFRP管-钢骨混凝土构件抗侧向冲击性能有限元分析

目的 研究两端简支GFRP管-钢骨混凝土构件的抗侧向冲击性能,为该类构件的工程应用提供参考。方法 建立并验证侧向冲击荷载作用下两端简支GFRP管-钢骨混凝土构件有限元模型,分析了典型构件在侧向冲击荷载作用下的全过程、破坏形态、应力发展、相互作用力时程曲线和弯矩时程曲线等动态响应;研究了冲击能量、冲击冲量、钢材强度、GFRP管厚度以及截面含钢率对构件抗冲击性能的影响。结果 随着冲击能量及冲量的增大,冲击持时和构件弯曲变形增大;提高钢材强度、GFRP管厚度可以改善构件的抗冲击性能。结论 GFRP管对混凝土有较好的约束作用,构件在侧向冲击荷载作用下整体发生弯曲破坏,内部钢骨塑性变形发展充分,构件抗侧向冲击性能优越。

基坑装配式内支撑高脚螺栓-模袋混凝土固支端及其承载性能

基坑工程内支撑体系中,混凝土支撑因其承载能力高、布置不受限制、端部节点现浇、整体性良好等优势得以在基坑工程中广泛使用,但混凝土支撑在设计与施工中的弊病也十分显著,存在设计截面过大、施工周期长、污染性强、成本高、浪费严重等问题。因而,针对混凝土支撑在基坑工程中表现出的优势与劣势,并结合地铁明挖车站深基坑工程的特点,设计一种装配式组合钢管混凝土内支撑,从提高端部节点刚度和强度、实现端部固定连接等角度出发,提出一种适应于地铁基坑装配式组合钢管混凝土内支撑的高脚螺栓-模袋混凝土固支端。通过阐明固支端的设计方案、构造特点和工作原理,并将其与混凝土支撑现浇节点进行对比分析,论证了由预埋钢板、空心法兰盘、模袋混凝土和高脚螺栓等特殊构件组成的固支端,在支撑体系中发挥了固定支座的作用;为建立固支端设计与验算的理论依据,通过分析固支端的力学机理、破坏模式及其演变规律,得到固支端的抗压与抗弯承载力的解析方法;为验证固支端承载性能的理论解析方法的可行性,结合数值模拟验证分析了理论与数值结果,并对影响固支端承载性能的主要因素进行参数化分析。

空心钢管混凝土支撑试验及其在深基坑中的应用研究

为解决地铁车站深基坑开挖支护工程作业面小、施工困难等难题,提出采用空心钢管混凝土支撑进行支护。推导并简化空心钢管混凝土组合强度计算公式,利用电液伺服压力机对构件进行横向加载试验,分析空心率和长细比对构件承载力的影响。采用有限元软件MIDAS GTS对西安某地铁车站基坑地表沉降和桩体变形进行仿真验算。研究结果表明,空心钢管混凝土支撑承载力显著高于空心钢管支撑承载力,且空心钢管混凝土支撑承载力随着空心率的减小逐渐增大,随着长细比的增大逐渐减小;相比于空心钢管支撑,采用空心钢管混凝土支撑后地表沉降和桩体变形均减小,有利于控制地表沉降和围护桩变形。

碗扣式钢管支撑架不同构造形式节点的转动刚度试验研究

为研究碗扣式钢管支撑架不同构造形式节点的转动刚度特性,提出测定支撑架体的角节点、边节点与中间节点转动刚度的试验方案,对应分别插入2根、3根和4根水平杆的节点转动刚度试验。在利用相应扣件式节点试验来验证本方案合理性的基础上,对当地市场随机采购的碗扣式钢管的弹性模量进行测定。采用三折线模型对碗扣式节点的M-θ曲线进行拟合,分析了不同水平杆数量对其转动刚度的影响及其破坏特点。研究结果表明:(1)碗扣式钢管支撑架角节点、边节点的转动刚度分别为中间节点转动刚度的77.93%、92.14%,且均高于规范给出的建议值25 kN·m·rad-1;角节点与边节点的转动刚度相对较弱,对架体整体稳定性的影响不可忽略;(2)当地市场随机采购的碗扣式钢管的弹性模量较新构件有不同程度的下降,最大降幅约为30%;(3)碗扣式节点的破坏先后顺序为水平杆、上碗扣、立杆和下碗扣;节点的破坏发生在水平杆接头处,应对此处加强质量监管。相关结论可为同类半刚性节点的转动刚度确定提供参考。

巷道防冲吸能钢管混凝土拱架支护性能研究

针对目前巷道支护中钢管混凝土拱架缺乏可缩让压性能的问题,从吸能让位角度设计了一种防冲吸能钢管混凝土拱架结构。通过Abaqus建立新型钢管混凝土拱架与围岩组合模型,在静载与动载两种荷载状态下,对比分析新型拱架对巷道的支护效果与抗冲击能力。结论如下:①根据合理的让位阻力特性设计吸能构件壁厚与尺寸,在拱架上部连接处和底弧段中部设置吸能构件,可避免弯曲过大发生失稳。套管形状依据U型钢拱架卡揽结构设置为折纹型,与拱架摩擦实现缩动让压;②在竖向与侧向冲击下,优化后拱架支护巷道各点位移量呈减少趋势,降低了拱架顶弧段下沉与底弧段上拱,支护效果更强;③静载作用下,优化后拱架与吸能构件接触后,拱架各点处塑性应变不再增加,吸能构件代替拱架发生形变。在受到动载后,吸能构件能快速响应,同时拱架两帮拐角发生弯曲变形,其余部分仍未发生明显变形。吸能构件压溃后,拱架整体塑性应变开始增加,最终优化后拱架各点等效塑性应变竖向与侧向冲击下分别降低了10%~50%和13%~78%。

大跨度钢管混凝土系杆肋拱桥拱圈整体拼装施工关键技术

针对北澄子河大桥钢管混凝土主拱圈整体拼装施工及高精度拱圈线形控制难题,采用基于位移传感器的智能调控钢管支架法进行整体拼装施工。为了实现拱桥安装合理成桥状态,对影响拱桥轴线线形控制的两个重要因素进行分析,结果表明:通过对拱圈节段拼装进行水平竖向双向精度控制,并使用智能同步顶升系统对节段安装高程进行调节,对拱圈节段焊接进行轴心对称合理施工,保证了拱轴线平顺,误差控制在±5 mm,成桥状态符合设计要求。

An Experimental Study on the Behavior of Square Concrete-Filled High Strength Steel Tube Columns

The paper presents an experimental study on the behavior of square concrete-filled high strength steel tube columns until failure.Four specimens were tested to investigate the effect of high strength steel and plain strength concrete on the load carrying capacity of the square concrete-filled steel tube columns.The effect of the concrete which filled in the steel tube was also investigated.Also,the effect of high strength steel and the presence of concrete were also investigated.The main parameters in the tests were:(1) the ultimate strength of steel (800 Mpa),(2) the presence of concrete in steel tube (hollow steel tube and concrete-filled steel tube),and (3) slender ratio.The main objectives of these tests were three-step:(1) to describe a series of tests on composite columns,(2) to analyze the influence of several parameters,and (3) to compare the accuracy of the predictions by using the specifications in the code (AISC-LRFD,EC4 and AIJ etc.) for the design of high-strength composite columns.Experimental results indicate that the ultimate strength of steel and presence of concrete had significant influence on both the axial compressive load capacity and the ductile of the square steel tube.

Experimental Study on Seismic Behavior ofSeismic-damaged Lateral Joints in CompositeFrame Consisting of CFSST Columns and SteelBeams Strengthened with Enclosed ReinforcedConcrete

A new composite strengthening method of seismic-damaged lateral joints in composite frame consisting of Concrete-Filled SquareSteel Tubes （CFSST） columns and steel beams strengthened with enclosed Reinforced Concrete （RC） at the ends of columns andwelding steel plates at the ends of beams was presented. Based on the current design specifications, one half scaled models of 4lateral joints in composite frame consisting of CFSST columns and steel beams were designed and manufactured. One model wasoriginal control specimen, one was strengthened by enclosed RC, and the others were strengthened after pre-damage. The destructiontests under lateral cyclic load on the models were carried. The effectiveness of seismic-damaged joints strengthened with enclosedRC and the reinforcement effect on different levels of seismic damage were studied. The test results show that seismic- damagedjoints in composite frame consisting of CFSST columns and steel beams strengthened with enclosed RC meets the strongcolumn-weak beam joints requirement of seismic design, and the failure modes are of all joints are the bending failure of steel beam.The reinforcement with enclosed RC has a significant on increasing the ultimate capacity and the seismic behaviors of joints. Thestudy indicated the rehabilitated joints recover the level of their original seismic performances before seismic damage in a certainextent damage level. Based on the test data, namely the ultimate capacity, limit displacement, ductility, the energy consumptioncoefficient, limit displacementthe strengthening method of seismic-damaged joints by strengthened with enclosed RC is an effectivemethod for seismic strengthening.

青浦题学平和学校综合馆结构设计

青浦题学平和学校综合馆由游泳馆和篮球馆组成,下部两层采用钢框架结构,上部屋盖采用格构柱-空间管桁架屋盖体系。对屋盖抗侧力体系及截面选取、格构柱与下部结构连接方式等关键技术进行研究。采用SAP2000软件分别建立屋盖单体模型和结构整体模型,并对两种模型在水平和竖向荷载作用下屋盖的内力和变形进行分析比较;同时针对本项目的受力特点,对屋盖整体稳定及关键节点应力等进行多方面的分析。分析结果表明:关键构件应力比不应大于0.85,屋盖其他构件应力比不大于0.90,屋盖在竖向荷载下挠度及风荷载、地震作用下的位移均满足规范要求,屋盖结构体系安全可行,节点连接可靠,现行的设计能够满足设计目标。

构造因素对超限梁扣件式钢管支撑架稳定承载力的影响

在目前超限模架搭设施工中,诸多项目常忽略超限梁扣件式钢管支撑架的构造措施,为了探究架体构造因素对稳定承载力的影响,应用有限元分析软件SAP2000,理论分析了节点刚性、梁底构造措施、剪刀撑布置等构造因素的影响机理。结果表明:梁底承重小横杆与相邻2根板下立杆可靠连接、梁侧设置斜撑的构造形式可有效改善架体受力性能,提高稳定承载力;节点刚度及剪刀撑布置对超限梁稳定承载力影响显著,且水平剪刀撑应与双向垂直剪刀撑同时布置,以保证架体的整体稳定性。

深部巷道钢管混凝土支架与锚杆-索耦合支护技术的理论分析与数值模拟研究

在深部巷道中使用的钢管混凝土支架与锚杆-索的耦合支护技术经常失效,导致巷道失稳。其中,增加锚杆-索的长度是一种现场常用的返修方式,但比较浪费支护材料。本文提出通过改变锚杆-索的预紧力来改善钢管混凝土支架的受力状态。首先,总结了钢管混凝土支架常见的破坏模式,并利用弹性中心法获得了钢管混凝土支架与锚索耦合支护情况下的钢管混凝土支架的内力;结果表明,施加锚索可以减小钢管混凝土支架的内力,保证其高承载力。然后,建立了钢管混凝土支架与锚杆-索在不同侧压力系数和不同耦合支护条件下的数值计算模型;进一步研究了不同侧压、不同支护方案以及在不同角度范围内增加锚杆-索预紧力下巷道围岩与支护体的应力和位移演化规律。结果表明,当锚杆和锚索预紧力分别为60和100 kN时,钢管混凝土支架与锚杆-索的耦合支护效果可以达到最佳,且最佳锚杆-索预紧力增加角度范围为15°~45°。最终将钢管混凝土支架与锚杆-索的耦合支护技术进行了现场应用,有效控制了深部巷道大变形,对深部巷道的支护方案设计具有一定的指导意义。