FRP强约束混凝土配筋中长柱稳定系数的研究

本文通过长细比L/ b为4.5～17.5截面经圆弧化处理、外包FRP后的矩形截面的钢筋混凝土柱的轴心受压试验,研究了长细比对稳定承载力的影响.结果表明长细比对FRP约束混凝土柱的稳定承载力影响远比螺旋配筋柱和普通钢筋混凝土柱严重,但当长细比不大于17.5时,其稳定承载力仍比未包裹柱高20%(约束比ξ=0.198)以上.文章还通过FRP强约束混凝土的本构关系、破坏准则的选择及初始缺陷的设置等,成功地利用ANSYS有限元软件对该类柱进行了非线性分析.获得了试件截面形状和约束比ξ等因素对该类柱稳定系数ψ的影响规律,归纳了可供工程设计人员参考的稳定系数的计算公式.     

高强混凝土L形截面柱抗剪承载力的试验研究

为研究高强混凝土L形截面柱的抗剪性能 ,对 9根试件 (其中 7根正向加载 ,2根变角度加载 )进行了试验研究。研究分析了轴压比、剪跨比、加载角度、配箍率等因素对试件抗剪性能的影响 ,提出了考虑剪跨比、配箍率和轴压比等影响和便于工程设计使用的高强混凝土L形截面柱抗剪承载力设计建议公式     

废弃玻璃细骨料钢筋混凝土柱的受压性能

为研究废弃玻璃细骨料对混凝土柱受力性能的影响,对6个普通骨料钢筋混凝土柱和12个废弃玻璃细骨料钢筋混凝土柱进行了静力受压试验。考虑废弃玻璃细骨料取代率、长细比和偏心距3个因素,分析了不同废弃玻璃细骨料掺量对钢筋混凝土柱的破坏形态、极限承载力、轴向位移、跨中挠度、混凝土应变和钢筋应变的影响。不论是轴心受压还是偏心受压,废弃玻璃细骨料钢筋混凝土柱破坏机理均与普通钢筋混凝土柱相似。掺量100%的废弃玻璃细骨料钢筋混凝土柱的正截面承载力较高。废弃玻璃细骨料钢筋混凝土柱的正截面应变符合平截面假定,采用中国相关规范计算试件的极限承载力,并将理论值与试验值进行对比,证明可以采用现行的国家规范对废弃玻璃细骨料钢筋混凝土柱进行正截面承载力计算。研究表明,废弃玻璃细骨料可以100%替代混凝土柱中普通砂,且抗压性能可以满足使用要求。     

7A04高强铝合金L形截面柱轴压整体稳定性能试验研究

为研究高强铝合金轴心受压构件整体稳定性能,对42根7A04高强铝合金L形截面柱进行轴压整体稳定性能试验,其中包含2种截面和7种长细比。对L形截面柱的破坏形态、稳定承载力和荷载-位移曲线进行研究,并将试验结果与GB50429—2007《铝合金结构设计规范》计算结果进行对比。试验中,长细比为80~100的L形截面柱发生弯曲失稳破坏,长细比为30~60的L形截面柱发生弯扭失稳破坏,长细比在30以下的L形截面柱发生局部失稳破坏。研究结果表明:对于宽厚比较大的长柱,GB 50429—2007中过多地考虑了局部稳定的影响,进而低估其承载能力。     

偏心荷载作用下细长型高强钢管混凝土柱的防火性能

对受偏心轴向荷载作用、分别填充普通混凝土和高强混凝土的细长型圆钢管柱进行24组防火试验。此试验是对Romero等人在2011年所做的中心荷载柱的试验结果的进一步探讨。此防火试验中的试验参数涵盖了混凝土标准强度(30MPa和90MPa)、填充类型(普通混凝土、钢筋混凝土和钢纤钢筋混凝土)、轴向荷载水平(20%和40%)和荷载偏心(20mm和50mm)。在固定的边界条件下对室内温度下相对长细比高于其他样本0.5的柱进行试验。研究这种内填混凝土组合件偏心荷载的影响。试验结果显示,与填充普通混凝土的柱相比,添加钢纤维并不能提高细长型柱在偏心荷载下的防火性能。然而,在混凝土柱中添加钢筋则可以提高防火性能。在中空圆钢管中填充混凝土可以提高其防火性能,钢管高强混凝土柱在承载力方面有更明显的提升。与欧洲规范4-1-2中的简易计算模型相比较,尽管此方法可用于偏心荷载作用下的柱,但在预测内填普通混凝土柱和钢纤维钢筋混凝土柱时仍会产生较大的误差。     

L形截面部分包覆钢-混凝土组合柱弱轴压弯整体稳定

为了研究L形截面部分包覆钢-混凝土组合(PEC)柱的压弯稳定性能，对L形截面PEC柱进行了弱轴压弯试验和有限元分析。试验研究中设计并制作了3个L形PEC柱试件，变化参数为长细比和偏心距。试验结果表明：截面形状和主钢件分布的几何非对称性，以及混凝土材料拉压强度的非对等性，造成L形PEC柱在受力后截面中和轴的偏转，导致构件发生弯扭变形。有限元分析表明，L形截面的肢背或肢端受压对构件承载力有一定影响；长细比较小(即长细比为10～30)时，肢背受压的构件轴力-弯矩相关曲线具有大小偏心分界的特征，但长细比较大(即长细比大于60)时，整体失稳成为控制破坏模式，相关曲线向原点内凹。建议了L形PEC柱绕弱轴压弯时的整体稳定承载力计算公式，与试验和有限元参数分析结果对比表明：当长细比小于60时，建议公式可以适用，当长细比大于80时，建议公式偏不安全，需进一步改进后才能用于工程设计。     

钢异形柱轴心受压承载力实用计算研究

继文献[1]对L形截面钢柱的弯扭相关屈曲一般性方程研究后,又研究了L形截面钢柱轴心受压承载力实用计算方法,推导出了L形截面柱换算长细比计算公式,考虑了柱缺陷影响,给出了轴心受压稳定系数φ,从而得出L形截面柱轴心受压实用设计计算公式,并做了几组L形截面柱轴心受压承载力试验,验证了计算公式。     

T形截面钢骨混凝土柱延性性能分析

利用大型有限元分析软件ABAQUS分析了T形截面钢骨混凝土柱在低周反复荷载作用下的受力性能,综合钢骨混凝土柱现有的试验研究成果,研究了T形截面钢骨混凝土柱在不同轴压比系数、配钢率、混凝土强度等级和长细比等参数对其延性的影响,得出了T形截面钢骨混凝土柱具有很好的延性性能,并提出了不同参数影响下T形截面钢骨混凝土柱满足一定延性要求的轴压比限值。     

钢异形柱轴心受压承载力实用计算研究

继文献[1]对L形截面钢柱的弯扭相关屈曲一般性方程研究后,又研究了L形截面钢柱轴心受压承载力实用计算方法,推导出了L形截面柱换算长细比计算公式,考虑了柱缺陷影响,给出了轴心受压稳定系数φ,从而得出L形截面柱轴心受压实用设计计算公式,并做了几组L形截面柱轴心受压承载力试验,验证了计算公式.     

FRP强约束混凝土配筋柱稳定承载力的试验研究

通过长细比Lb为4.5～17.5的6根截面经圆弧化处理、外包FRP后的矩形截面的钢筋混凝土柱的轴心受压试验,研究了长细比对稳定承载力的影响。结果表明:长细比对FRP约束混凝土柱的稳定承载力影响远比螺旋配筋柱和普通钢筋混凝土严重,但当长细比不大于17.5时,其稳定承载力仍比未包裹柱高20%(约束比ξ=0.188)以上。讨论了影响稳定系数φ的因素,给出了稳定系数的参考值,可供工程设计人员参考。     

Experimental behaviour of eccentrically loaded slender circular hollow steel columns in-filled with fibre reinforced concrete

This paper is based on the experimental study of twelve slender steel tubular columns of circular sections filled with both plain and fibre reinforced concrete. The specimens were tested under eccentric compression to investigate the effects of fibre reinforced concrete on the strength and behaviour of slender composite columns. The slenderness ratio was considered to be the main test parameter. Hollow steel sections of similar specimens were also tested as reference columns. The test results were illustrated by load-deflection and load-strain curves. Various characteristics such as strength, stiffness, ductility, energy absorption capacity and failure mode are discussed. Interpretation of the experimental results indicates that the use of fibre reinforced concrete as infill material has a considerable effect on the strength and behaviour of slender composite columns.     

Behaviour of reinforced and concrete-encased composite columns subjected to biaxial bending and axial load

An experimental investigation of the behaviour of reinforced concrete columns and a theoretical procedure for analysis of both short and slender reinforced and composite columns of arbitrarily shaped cross section subjected to biaxial bending and axial load are presented. In the proposed procedure, nonlinear stress–strain relations are assumed for concrete, reinforcing steel and structural steel materials. The compression zone of the concrete section and the entire section of the structural steel are divided into adequate number of segments in order to use various stress–strain models for the analysis. The slenderness effect of the member is taken into account by using the Moment Magnification Method. The proposed procedure was compared with test results of 12 square and three L-shaped reinforced concrete columns subjected to short-term axial load and biaxial bending, and also some experimental results available in the literature for composite columns compared with the theoretical results obtained by the proposed procedure and a good degree of accuracy was obtained.     

钢骨-钢管高强混凝土轴压组合柱受力性能的试验研究

本文提出了一种重载柱设计的新模式,即钢骨-钢管混凝土组合柱。这种组合柱是在钢管混凝土的基础上内部埋设钢骨。通过13根组合柱的轴心受压试验,研究了这种新型组合柱的受力性能。试验研究结果表明,在钢管混凝土中加入钢骨后,可有效地提高柱子的承载力,并能在一定程度上延缓或抑制混凝土中剪切斜裂缝的产生,从而提高柱子的延性,而组合柱的承载力和延性则随长细比的增大而下降。基于试验研究结果,本文给出了适用于这种新型组合柱的承载力计算公式。     

Experimental behaviour of steel fiber high strength reinforced concrete and composite columns

This paper presents experimental behaviour of eccentrically loaded plain and steel fiber high strength reinforced concrete and concrete-encased composite columns. In the experimental study, a total of 32 square section both reinforced concrete and composite column specimens were fabricated at 0, 0.5, 0.75 and 1.0% volume fractions of steel fiber contents to examine the effects of steel fibers on column behaviour. Besides this, the composite columns were constructed and tested using almost the same conditions with reinforced concrete columns to investigate the column experimental behaviour. The complete load−deflection behaviour and strength of column specimens were obtained and the results were discussed in the study. In addition, the column specimens were analysed based on a theoretical method considering the nonlinear behaviour of the materials. The presented experimental study indicates that the inclusion of steel fibers in the range 0.75 to 1.0% volume fraction improves confinement and ductility features of high strength reinforced concrete and composite columns significantly.     

Nonlinear behaviour of eccentrically loaded FR concrete-filled stainless steel tubular columns

This paper investigates the nonlinear behaviour of eccentrically loaded fibre reinforced (FR) concrete-filled stainless steel tubular composite columns. A nonlinear 3-D finite element model for the axially loaded composite columns, recently reported by the author, was extended to study the structural performance of the eccentrically loaded composite columns. The columns were pin-ended subjected to an eccentric load acting along one axis. The model accounted for the inelastic behaviour of the composite column components, effect of FR concrete confinement and interface between the stainless steel section and concrete. The measured initial local and overall geometric imperfections were carefully incorporated in the model. The finite element model has been validated against tests previously reported by the author. Furthermore, the variables that influence the eccentrically loaded composite column behaviour and strength comprising different eccentricities, different column slenderness and different concrete strengths were investigated in an extensive parametric study comprising 72 columns. The composite column strengths and moment resistances predicted from the finite element analysis were compared with the design composite column strengths and moment resistances calculated using the Eurocode 4. The study has shown that finite element modelling could effectively assess the accuracy of the design rules in current codes of practice.     

HRB600钢筋混凝土短柱轴压性能试验研究

通过对6根HRB600钢筋、1根HRB500钢筋混凝土短柱和2根素混凝土短柱进行轴心受压试验,分析不同配筋率、混凝土强度、钢筋强度、长细比对钢筋混凝土柱轴压性能的影响,提出HRB600钢筋的抗压强度设计值,分析GB 50010-2010《混凝土结构设计规范》中关于轴心受压承载力计算公式的适用性。研究结果表明:随着纵筋配筋率、钢筋强度和混凝土强度的提高,轴压短柱的峰值荷载增大;轴压短柱峰值应变随混凝土强度提高而减小,随钢筋强度提高而略有增大,纵筋配筋率和长细比对峰值应变影响较小;HRB600钢筋抗压强度设计值取为500 MPa,HRB600钢筋混凝土短柱与普通钢筋混凝土短柱的受力性能相似,轴心受压承载力可以按照GB 50010-2010《混凝土结构设计规范》中规定的受压承载力公式进行计算,具有足够的安全储备。     

超高强混凝土型钢组合长柱静力性能试验研究

为解决目前规范中缺乏超高强混凝土型钢组合柱设计方法和静力受压试验研究不够深入的问题,开展了5个轴心受压和4个偏心受压的立方体抗压强度为120 MPa超高强混凝土型钢长柱的静力试验,通过考察其破坏形态、轴力-挠度曲线、轴力-竖向位移曲线和轴力-应变曲线,研究了长细比、相对偏心距和箍筋间距对其静力性能的影响.试验结果表明:...     

Experimental study on steel tubular columns in-filled with plain and steel fiber reinforced concrete

An experimental investigation on the structural behaviour of steel tubular columns in-filled with plain and steel fiber reinforced concrete is presented in this study. A total of 16 concrete-filled steel tubular columns were constructed and tested subjected to biaxial bending and short-term axial load. The main variables considered in the test study were the cross section, slenderness, concrete compressive strength and the load eccentricity. In the presented study, a theoretical method for the prediction of ultimate strength capacity and load-deflection curves of concrete filled steel tube columns is proposed. In the analysis procedure, the nonlinear behaviour of the materials is considered and the slenderness effect has been taken into account. The experimental ultimate strength capacities and load-deflection curves of both plain and steel fiber concrete-filled tube columns have been compared with the analysis results and discussed in the paper. The results indicate that the addition of steel fibers in core concrete has considerable effect on the behaviour of concrete-filled steel tube columns.     

Effect of preload on the axial capacity of concrete-filled composite columns

Concrete-filled tubes are often preferred for the construction of high-rise buildings because of their high strength and stiffness compared to conventional reinforced concrete or steel columns. However, prior to infilling of concrete, the steel tubes are subjected to preloads from upper floors arising from construction loads and permanent loads of the building. These preloads cause initial stresses and deformations in the steel tubes which would affect the load carrying capacity of the composite columns. In this paper, a design method based on a modified Eurocode 4 approach, incorporating the effect of preload, is proposed to evaluate the axial capacity of concrete filled composite columns. Eight full-scale composite column specimens were tested. Parameters studied included the strength of the concrete infill, slenderness of the columns and the amount of preload applied on the steel tubes. Results obtained from the proposed method are compared against test results and other published data. Comparison studies show that the test results are on average 3% higher than predicted results with a standard deviation of 0.089. Finite element analyses are also performed for systematic verification, and the results are 8% higher than predicted results. It is conclude that the proposed design method is accurate and mostly conservative and can be readily used in the context of Eurocode 4: Part 1.1 for designing composite columns.     

Untersuchungen und theoretische Modelle von druckbeanspruchten Stahlstützen in Verbundbauweise

Experimental and analytical modelling of steel columns reinforced by concrete encasement. Experimental investigations of steel‐concrete axially compressed columns that were tested in the Laboratory of the Institute of Building Structures of the Warsaw University of Technology are presented. The results of conducted experimental work created a basis for the detailed investigations into the appraisal of the influence of different factors associated with the behaviour of tested elements. Analytical modelling was done with use of the finite element method and the ABAQUS software. In the analysis, the emphasis was put on the influence of those factors that have the most important effect on strength and deformability of composite columns. As to the authors' knowledge, the investigated factors have not been accounted for accurately enough in current design codes. The factors such as the load application to the composite column end and the restraining conditions at the supports are among those most important from the design point of view. The investigations have a great practical aspect at this particular moment when in Poland there is an ongoing discussion associated with the proposed new national code on design of composite steel‐concrete structures. The said codification proposal is an attempt to harmonize the national design rules with those applied in the Eurocode 4. The experimental part was concerned with testing of 16 composite columns that were made as completely encased steel I‐type elements (HEA160 section used). The main sectional dimensions were 260 mm × 260 mm, and the column length – 2500 mm. In addition, the reference steel column of HEA160 section was tested. The parameters that were being changed during experiments consisted of the following ones: the way of the load application to the column end face, compressive strength of the concrete encasement and the restraining effect at the supports that reproduced that of assumed in the numerical studies. The behaviour of composite columns with fibre‐reinforced concrete heads was also investigated. The comparison of load deflection curves from the experiments and those from the computer modelling was carried out. In addition, failure loads from the laboratory tests were compared with those calculated according to some chosen design codes. The analysis carried out proven that both the way at which the load is applied to the element end face and the type of end restraints had a great influence on the strength of composite columns. It is clear from the experiments that in case of load application directly through the steel section, the attainment of the limit state of cracking was much earlier than the strength ultimate limit state, so that it controlled the design of composite columns. In this case, an increase in strain of steel sections was observed. In addition, the rigid restraining conditions at the column ends resulted in a decrease of the load bearing capacity because of the stress concentration in the concrete encasement within the support zones. The failure of composite columns was controlled by the combined stress state in the concrete encasement. The study carried out has shown that the load bearing capacity of composite columns can be substantially increased by the applications of fibre‐reinforced column heads at their end supports. The strength of such columns increased by 30–48% if compared with the same composite columns but made without fibre‐reinforced ends.