恒定轴压力下材料特性对方钢管混凝土柱防火性能的影响

介绍了温度升高时钢管混凝土柱力学性能的材料模型的性能。因此,采用了热传递数值分析和非线性热应力分析,其中考虑到现有的材料特性如混凝土和钢筋的热学及力学特性。此外,对10个300~350mm矩形横截面的钢管混凝土柱构件,根据KSF2257(等同于ASTME119和JISA1304)加热2h,将数值分析与试验结果相对比可知,现有的材料模型如Eurocode,AIJ,Lie’s材料模型和Yin’s材料模型都可以有效用于此分析。     

Mechanical behavior of stirrup-confined circular concrete-filled steel tubular stub columns under axial loading

通过井字形拉筋、米字形拉筋和圆环箍筋等3组拉筋约束形式带拉筋圆钢管混凝土短柱轴压性能对比试验,研究不同拉筋约束形式、拉筋体积配箍率对圆钢管混凝土轴压短柱的承载力和延性等的影响;采用合理的混凝土三轴受力本构模型和钢材本构模型,应用ABAQUS非线性有限元分析软件对带拉筋圆钢管混凝土轴压短柱进行三维有限元分析,有限元计算结果与试验结果吻合较好;在此基础上,分析了带拉筋圆钢管混凝土轴压短柱中钢管、拉筋或箍筋、核心混凝土之间的组合作用。结果表明：井字形拉筋圆钢管混凝土轴压短柱的承载力最高,延性最好,钢管、拉筋和核心混凝土之间的组合作用最强;提高体积配箍率可以有效提高圆钢管混凝土短柱的轴压承载力和延性。     

Investigation of Proposed Concrete Filled Steel Tube Connections under Reversed Cyclic Loading

Concrete-filled steel tube (CFT) columns are used in the primary lateral resistance systems. The objective of this research is to analyse the behavior of the steel beam to CFT column connections. A three-dimensional numerical model for simulating the behavior of CFT connections was developed with the aid of the general purpose nonlinear finite element analysis package ABAQUS. In this paper, 90 CFT connection specimens include simple and moment connections that were tested under reversed cyclic loading. Shear capacity of joint, moment-drift response, energy absorption, and displacement ductility were studied in those models. The results have indicated that, the hysteresis curve of CFT columns was plump; no pinch phenomenon can be found; the damage and degradation degree of the strength and stiffness of specimens is lower; and high energy dissipation capacity can be achieved. Improvement in the behavior of CFT connection depends on the beam characteristics and column features.     

Realistic modelling of thermal and structural behaviour of unprotected concrete filled tubular columns in fire

This paper employs the commercial finite element analysis package ANSYS to model the thermal and structural behaviour of isolated CFT columns in fire. Although CFT columns have been numerically analysed by many researchers, this paper presents details of a number of features which have often been neglected by many researchers, including the influence of an air gap and slip at the steel/concrete interface on CFT column temperatures and structural behaviour, the sensitivity of CFT fire resistance to concrete tensile behaviour and CFT column initial imperfections. The finite element model is validated by comparing the simulation results against experimental results of standard fire resistance tests on 34 CFT columns with different structural boundary and loading conditions. A numerical parametric study is then performed to investigate the sensitivity of simulation results to different assumptions introduced in the finite element model. The results of these numerical studies show that whether or not including slip between the steel tube and concrete core in the numerical model has minor influence on the calculated column fire resistance time. The fire resistance of CFT columns with an air gap is generally slightly higher than that without an air gap. However, including slip gives a better prediction of column deflection behaviour. Using different tensile strength or tangent stiffness of concrete has a minor effect on the calculated column fire resistance. Different amounts of column initial deflection have some influence on column fire resistance times. Nevertheless, the influence is relatively small so that it is acceptable to use a maximum initial deflection of L/1000 as commonly assumed by other researchers.     

Analytical modeling of the standard fire behavior of loaded CFT columns

This paper presents a three-step sequentially coupled analytical approach for predicting the standard fire behavior of concrete filled steel tube (CFT) columns. Numerical models were developed for each step of the approach, namely, (1) fire dynamics analysis, (2) nonlinear heat transfer analysis, and (3) nonlinear stress analysis. 3D finite element models with identical meshes were used for steps 2 and 3. An analytical matrix consisting of fifteen CFT column specimens subjected to standard fire tests by different researchers was selected to verify the numerical models. Sensitivity analyses were conducted to finalize the values of the major model input parameters. This paper summarizes the development of the numerical models, the findings from the sensitivity analyses, and the comparisons of the numerical predictions with experimental results. The verified numerical models (and model input parameters) are recommended for predicting the behavior of CFT columns subjected to fire loading, and for conducting analytical parametric studies.     

Finite element simulation on mechanical and structural properties of cold-formed dimpled steel

The dimpling process is a novel cold-roll forming process that can enhance the steel material and structural performance by plastically deforming the material surface prior to the section forming operation [1]. Owing to the complex and interrelated nonlinear changes in contact, geometry and material properties that occur in the process and section forming, there have been no existing methods to simulate the process and resultant dimpled products and validate through physical measurements. This paper describes a numerical modelling approach and results into the mechanical properties and structural behaviour of cold-formed dimpled steel. A series of mechanical tests including tensile, plate bending and column compression tests on cold-formed plain and dimpled steel material were conducted for evaluation of numerical results. A finite element approach to practically simulate the dimpling process and experimental tests was presented. True stress–strain data obtained from tests were incorporated into nonlinear simulations of dimpled steel sheets and sections. The simulation of the dimpling process revealed that during the process, various levels of plastic strain are developed throughout the thickness of the steel sheet; this could correlate to the increase in the strength of the dimpled steel as observed in experimental tests and simulations. The simulation of the mechanical tests of dimpled specimens predicted similar results to the experiments, in terms of mechanical properties and structural behaviour. Since the finite element approach was able to successfully represent mechanical properties and structural behaviour of dimpled steel, it can be a powerful method in analysis and design of dimpled steel material and completed sections.     

Seismically induced cyclic buckling of steel columns including residual-stress and strain-rate effects

Compression buckling tests were performed on four full-scale W-shaped column specimens to investigate the buckling response of columns in multi-storey braced steel frame structures subjected to seismic strong ground motions. The test protocols included monotonically and cyclically applied concentric and eccentric axial loading. One test was conducted under dynamic cyclic loading. End moments were applied on one cyclic test. The columns were W310×129 compact (class 1) sections made with ASTM A992 steel. Weak axis buckling was studied and the column had an effective slenderness ratio of 48. The response of the test columns was also examined using numerical simulations based on fibre discretization of the member cross-section. Column residual stresses and strain rate effects on the material properties were both characterized and accounted for in the numerical models. The study showed that steel columns can sustain several cycles of inelastic buckling under seismic induced loading while maintaining sufficient compressive resistance to support the applied gravity loads. Residual stresses affected the column response only at the first buckling occurrence with a gradual reduction of the columns’ tangent stiffness prior to buckling as well as a reduction of the column’s compressive resistance. High strain rates anticipated during strong earthquakes increased the column buckling and post-buckling strengths. The cyclic buckling response of steel columns can be predicted adequately when using nonlinear beam-column elements and cross-section fibre discretization provided that residual stresses and strain rate effects are included in the modelling.     

Response of self-compacting concrete filled tubes under eccentric compression

Self-Compacting Concrete (SCC) use is spreading worldwide and it is becoming a regular solution in some special applications, including steel-concrete composite columns. In the particular case of Concrete Filled Tubes (CFT), the main advantage from a practical point of view in the use of SCC consists in employing the steel tube as a formwork to directly cast concrete inside it, without the need of vibration. The study of three different concretes for structural applications as composite elements is presented, each of them designed for a 28-day cylindrical compressive strength of 50 MPa: (i) a Normal Vibrated Concrete, (ii) a Self-Compacting Concrete, (iii) an expansive SCC (with the goal of an increase in bond strength as a consequence of the expansion).CFT with critical length ranging from 131 cm to 467 cm have been experimentally and analytically investigated in uniaxial compression. In each case the steel case presents a cross section of 139.6 mm of external diameter and 4.0 mm thickness and with a fixed eccentricity of the applied load equal to 25 mm. The bond strength at the steel-concrete interface is reported for each of the three mixes.The experimental and analytical results show that the behavior of eccentrically loaded columns is governed by the bending moment-axial load interaction. As a consequence, perfect bond at the interface can be assumed and the axial capacity of the column is only a function of its geometry and of the mechanical properties of the materials.A numerical procedure is proposed to evaluate the increase in the axial capacity of the composite columns consequent to the confinement of the internal concrete in case of zero-eccentricity of the applied axial load with respect to the column’s axis.Finally, the obtained numerical results are introduced into code provisions to evaluate modified axial force N-bending moment M interaction diagrams to predict the axial capacity of the column in the particular test configuration.     

Prediction of hysteretic behavior of high-strength square concrete-filled steel tubular columns subjected to eccentric loading

This study aimed at predicting the structural behavior of high-strength square CFT (concrete-filled steel tube) columns. First, the material models of the existing steel tube and concrete were compared, and a nonlinear fiber element analysis method was proposed. To verify the proposed fiber element analysis method, the behavior of CFT columns made from high-strength materials was investigated experimentally. CFT members consisted of high-strength steel tubes (yield strength; f_y=913MPa) and high-strength concrete (f_ck=91.3 MPa). The moment-rotation relationships for hollow and concrete-filled steel tubes were compared. In addition, the P-M interaction diagrams for the experiment result and AISC-LRFD code provisions were compared. Finally, the result of the fiber element analyses was compared with the test results.     

Research on mechanical behavior of prefabricated steelframe columns using high-strength bolted flangeconnection with tapping steel plate

为了研究多高层装配式钢框架结构体系方钢管柱采用钢板攻丝高强螺栓法兰连接节点的受力性能,进行了钢柱法兰连接节点的足尺模型静力和拟静力试验,分析了这类节点的承载力、失效模式以及在单向水平地震作用下的滞回性能。试验研究表明：试件在静力试验中表现出较强的承载能力,失效模式为短柱受压侧屈服;试件在拟静力试验中得到的滞回曲线比较饱满,试件延性较好,耗能性能优良,失效模式为短柱受压屈服。对这类钢柱法兰节点的受力性能进行了有限元数值模拟分析,数值模拟结果与试验结果吻合较好。通过比较节点刚接模型及栓接模型的有限元分析结果,从设计角度考虑,认为该类节点在实际工程应用中可视为等效刚性连接。     

Axial strength of circular concrete-filled steel tube columns — DOE approach

This paper presents the effect of changes in diameter of the steel tube (D), wall thickness of the steel tube (t), strength of in-fill concrete (f_cu), and length of the tube (L) on ultimate axial load (P_ue) and axial shortening at the ultimate point (δ_ue) of circular Concrete Filled steel Tubes (CFT). Taguchi’s approach with an L9 orthogonal array is used to reduce the number of experiments. With the help of initial experiments, linear regression models are developed to predict the axial load and the axial shortening at the ultimate point. A total of 243 circular CFT samples are tested to verify the accuracy of these models at three factors with three levels. The experimental results are analyzed using Analysis Of Variance to investigate the most influencing factor on strength and axial shortening of CFT samples. Comparisons are made with predicted column strengths using the existing design codes, AISC-LRFD-2005 and EC4-1994.     

型钢混凝土桥墩的延性系数分析

采用ANSYS对单柱式矩形截面桥墩的受力性能进行有限元数值分析,对型钢混凝土结构数值模拟中材料本构的定义、有限元建模和边界条件设置等关键技术进行研究,计算构件延性系数并分析位移延性系数的影响因素。结果表明：在其它条件不变的情况下,位移延性系数随含钢率、体积配箍率和剪跨比的增加而增大,随轴压比的增加而减小。     

A simplified numerical model for post-tensioned steel connections with bolted angles

Post-tensioned (PT) self-centering beam–column connections has been developed for its good seismic performance. Many researchers have investigated its mechanical behavior by numerical or experimental method. Prior researches have indicated that the analysis by elaborate FE models is very time consuming. To overcome this disadvantage, a simplified numerical model was established in this paper. The accuracy of results derived by this model was validated against prior investigations on interior PT connections with top-and-seat angles. Influence of initial PT force on mechanical behavior of PT connection was investigated. The Geometric and material nonlinearities, and strands can be considered in the modeling. A planar steel frame structure was established and hysteretic analysis was conducted. Results indicated that the computational cost can be greatly reduced by this model.     

Behaviour of column web component of steel beam-to-column joints at elevated temperatures

This paper presents an experimental investigation on stocky column web panels of semi-rigid beam-to-column joints exposed to fire conditions in order to verify an analytical prediction model. Recent experimental studies show that the degradation of material properties and high axial forces, due to restrained thermal expansion of beams at elevated temperatures, significantly affect the moment–rotation response of the joints. The component method originally established for the evaluation of the joint behaviour at ambient conditions can be adopted for elevated-temperature cases. Recently developed mechanical models for joints may not be accurate as the column web component is simultaneously subjected to bending moments and axial forces. This paper focuses on the component column web in shear in order to identify the key parameters which affect joint behaviour in shear at elevated temperatures. This experimental work was conducted on three extended end-plate connections subjected to both ambient and elevated temperature conditions. After validations by test results, detailed finite element simulations were performed for a series of parametric studies at other elevated temperatures. Both experimental and numerical results are finally compared with analytical predictions.     

Axial capacity of rectangular concrete-filled steel tube columns – DOE approach

This paper presents the effect of change in wall thickness of the steel tube (t), strength of in-filled concrete (f_cu), cross-sectional area of the steel tube (A) and length of the tube (L) on ultimate axial load and axial shortening at ultimate point of rectangular concrete-filled steel tubes (CFT). Taguchi’s approach with an L9 orthogonal array is used to reduce the number of experiments. With the help of initial experiments, linear regression models are developed to predict the ultimate axial load and the axial shortening at ultimate point. A total of 243 rectangular CFT samples are tested to verify the accuracy of these models at three factors with three levels. The experimental results are analyzed using Analysis Of Variance to investigate the most influencing factor on strength and axial shortening of CFT samples. Comparisons are made with predicted column strengths using the existing design codes, AISC–LRFD-1994 and EC4-1994.     

Experimental and numerical studies of lean duplex stainless steel beams

Stainless steel is well suited to a range of engineering applications owing to its durability and favourable mechanical properties. The most widely used grades of stainless steel are from the austenitic family and typically contain around 18% chromium and 8%-11% nickel — these grades have a relatively high initial material cost, due, in part, to their high nickel content, and a nominal yield strength (in the annealed condition) of around 220 N/mm². A new, low nickel grade of stainless steel (UNS 32101/EN 1.4162), commonly referred to as ‘lean duplex’, has been developed, that offers over two times the strength of the familiar austenitic grades and at approximately half the initial cost — this lean duplex stainless steel appears well suited to load-bearing applications in construction. This paper reports material and 3-point bending tests on lean duplex stainless steel hollow sections. The 3-point bending tests were replicated by finite element (FE) analysis and, upon validation of the numerical models, parametric studies were conducted to assess the effect of key parameters such as cross-section aspect ratio, cross-section slenderness and moment gradient on the strength and deformation capacity of lean duplex stainless steel beams. Based on both the experimental and numerical results, appropriate slenderness limits and design rules, suitable for incorporation into structural stainless steel design standards, have been proposed.     

Finite element analysis of CFT columns subjected to an axial compressive force and bending moment in combination

Proper material constitutive models for concrete-filled tube (CFT) columns subjected to an axial compressive force and bending moment in combination are proposed and verified in this paper by using the nonlinear finite element program ABAQUS compared against experimental data. In the numerical analysis, the cross sections of the CFT columns are categorized into three groups, i.e., ones with circular sections, ones with square sections, and ones with square sections stiffened with reinforcing ties.It is shown that the steel tubes can provide a good confining effect on the concrete core when the axial compressive force is large. The confining effect of a square CFT stiffened by reinforcing ties is stronger than that of the same square CFT without stiffening ties but weaker than that of a circular CFT. Nevertheless, when the spacing of reinforcing ties is small, a CFT with a square section might possibly achieve the same confining effect as one with a circular section.     

方钢管混凝土柱钢管的非线性分析

为研究轴心受压方钢管混凝土短柱钢管的力学性能,利用通用有限元分析软件ANSYS建立了方钢管混凝土柱的有限元模型,考虑了混凝土强度、截面宽厚比以及钢材强度对方钢管混凝土柱钢管纵向应力-应变关系的影响,为纤维模型数值分析提供了钢管的等效单轴应力-应变关系曲线的简化计算方法。     

约束钢管混凝土柱的开发研究(英文)

本文提出了一种更适合抗震设计的新型钢管混凝土体系———约束钢管混凝土柱体系。它建立在清楚的力学概念基础上,其设计着眼于在可能出现塑性铰的部位附加横向约束以控制钢管的局部屈曲和更有效地约束混凝土。这一新型钢管混凝土柱体系兼具了钢管混凝土及套管混凝土柱两者的优点,克服了传统钢管混凝土柱的抗震缺陷,为抗震地区的高层结构和桥梁设计提供了理想的选择。在本研究的第一阶段,作者们对FRP约束的圆钢管柱和钢板约束的方钢管柱进行了模拟地震力的加载试验。其结果验证了约束钢管混凝土柱的良好抗震性能。     

ABAQUS钢与混凝土复合材料模型的二次开发

为了找出结构的薄弱位置,往往需要对各种复杂的建筑结构进行整体结构层次上的弹塑性数值模拟。为提高建模以及数值计算效率,需要采用梁单元计算模型模拟钢筋、钢骨以及钢管混凝土梁柱等复杂的构件。在混凝土弹塑性损伤模型的基础上,基于ABAQUS平台开发了能够描述以上复杂梁柱构件力学行为的梁单元复合材料模型。模型的提出使整体结构的弹塑性数值计算可以采用较为简单的梁单元和板壳单元模拟,提高了超高层建筑结构整体弹塑性分析的效率。