Approach for analyzing the ultimate strength of concrete filled steel tubular arch bridges with stiffening girder

A convenient approach is proposed for analyzing the ultimate load carrying capacity of concrete filled steel tubular (CFST) arch bridge with stiffening girders. A fiber model beam element is specially used to simulate the stiffening girder and CFST arch rib. The geometric nonlinearity, material nonlinearity, influence of the construction process and the contribution of prestressing reinforcement are all taken into consideration. The accuracy of this method is validated by comparing its results with experimental results. Finally, the ultimate strength of an abnormal CFST arch bridge with stiffening girders is investigated and the effect of construction method is discussed. It is concluded that the construction process has little effect on the ultimate strength of the bridge.

Numerical analysis of ultimate strength of concrete filled steel tubular arch bridges

The calculation of ultimate bearing capacity is a significant issue in the design of Concrete Filled Steel Tubular (CFST) arch bridges. Based on the space beam theory, this paper provides a calculation method for determining the ultimate strength of CFST structures. The accuracy of this method and the applicability of the stress-strain relationships were validated by comparing different existing confined concrete uniaxial constitutive relationships and experimental results. Comparison of these results indicated that this method using the confined concrete uniaxial stress-strain relationships can be used to calculate the ultimate strength and CFST behavior with satisfactory accuracy. The calculation results are stable and seldom affected by concrete con-stitutive relationships. The method is therefore valuable in the practice of engineering design. Finally, the ultimate strength of an arch bridge with span of 330 m was investigated by the proposed method and the nonlinear behavior was discussed.

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.

Seismic Behavior of Diaphragm-Through Connections of Concrete-Filled Square Steel Tubular Columns and H-Shaped Steel Beams

Based on the introductions of a type of diaphragm-through connection between concrete-filled square steel tubular columns (CFSSTCs) and H-shaped steel beams,a finite element model of the connection is developed and used to investigate the seismic behavior of the connection.The results of the finite element model are validated by a set of cyclic loading tests.The cyclic loading tests and the finite element analyses indicate that the failure mode of the suggested connections is plastic hinge at the beam with inelastic rotation angle exceeding 0.04 rad.The suggested connections have sufficient strength,plastic deformation and energy dissipation capacity to be used in composite moment frames as beam-to-column rigid connections.

Influence of Axial Load Ratio on Shear Behavior of Through-Diaphragm Connections of Concrete-Filled Square Steel Tubular Columns

Nonlinear finite element analysis and parametric studies were carried out to study the influence of axial load ratio on the shear behavior of the through-diaphragm connections of concrete-filled square steel tubular columns. The analysis reveals that smaller axial load ratio can improve the shear bearing capacity and ductility while larger axial load ratio will decrease the shear behavior of the through-diaphragm connections. The parametric studies indicate that the axial load ratio should be limited to less than 0.4 and its influence should be considered in the analysis and design of such connections.

Research on stress concentration at tubular joints in concrete filled steel tubular truss arch bridge

In this paper stresses at joints forming by hollow steel tube and concrete filled steel tube （CFST） are calculated, analyzed and compared. It is founded that the stress concentration at joints of CFST is a quite different from that of hollow steel tube. A conclusion can be made that analysis of fatigue at the joints of CFST truss arch bridge can not apply the results developed from analyzing at joints of hollow steel tube in marine structure.

In-Plane Creep Buckling of Concrete-Filled Steel Tubular Arches

The creep-induced deformation of the arch rib of concrete-filled steel tubular （CFST） arches under a sustained load can increase the bending moment, which may lead to earlier stability failure called creep buckling. To investigate the influences of concrete creep on the buckling strength of arches, a theoretical analysis for the creep buckling of CFST circular arches under distributed radial load is performed. The simplified Arutyunyan-Maslov （AM） creep law is used to model the creep behavior of concrete core, and the creep integral operator is introduced. The analytical solutions of the time-dependent buckling strength under the sustained load are achieved and compared with the existing formula based on the age-adjusted effective modulus method （AEMM）. Then the solutions are used to determine the influences of the steel ratio and the first loading age on the creep buckling of CFST arches. The results show that the analytical solutions are of good accuracy and applicability. For CFST arches, the steel ratio and the first loading age have significant influences on creep buckling. An approximate log-linear relationship between the decreased degrees of the creep buckling strength and the first loading age is found. For the commonly used parameters, the maximum loss of the buckling strength induced bv concrete creen is close to 40%

Quantifying Creep of Concrete Filled Steel Tubes

Using age adjusted effective modulus(AAEM)method,creep of concrete filled steel tube(CFST)member was formulated considering of creep coefficient and aging coefficient.Ten CFST specimens were tested including eight for creep and two for shrinkage.The experimental result was compared with the computed result using AAEM in which the creep coefficient was taken from calibration of ACI model based on experimental result on sealed concrete,and aging coefficient was supplied from relaxation test on sealed concrete specimen.Furthermore,the creep of CFST member was analyzed using author's own subroutine to input concrete properties through user programmable feature(UPF)in ANSYS software.Comparison was made on authors' own experimental database,some existing experimental results,and results from AAEM and numerical analysis.Finally,the conditions of applicability of AAEM method are put forward,and numerical approach to compute creep of CFST specimen is delineated.

Concrete-Filled Steel Tube Arch Bridges in China

In the past 20 years, great progress has been achieved in China in the construction of concrete-filled steel tube （CFST） arch bridges and concrete arch bridges with a CFST skeleton. The span of these bridges has been increasing rapidly, which is rare in the history of bridge development. The large-scale construction of expressways and high-speed railways demands the development of long-span arch bridges, and advances in design and construction techniques have made it possible to construct such bridges. In the present study, the current status, development, and major innovative technologies of CFST arch bridges and concrete arch bridges with a CFST skeleton in China are elaborated. This paper covers the key con- struction technologies of CFST arch bridges, such as the design, manufacture, and installation of steel tube arch trusses, the preparation and pouring of in-tube concrete, and the construction of the world＇s longest CFST arch bridge-the First Hejiang Yangtze River Bridge. The main construction technologies of rein- forced concrete arch bridges are also presented, which include cable-stayed fastening-hanging cantilever assembly, adjusting the load by means of stay cables, surrounding the concrete for arch rib pouring, and so forth. In addition, the construction of two CFST skeleton concrete arch bridges-the Guangxi Yongning Yong River Bridge and the Yunnan-Guangxi Railway Nanpan River Bridge--is discussed. CFST arch bridges in China have already gained a world-leading position; with the continuous innovation of key technologies, China will become the new leader in promoting the development of arch bridges.

Application of Large-diameter and Long-span Micro-expansive Pumping Concrete Filled Steel Tube Arch Bridge

In this article the high strength micro-expansive concrete that has been applied on big-diameter and long-span steel arch bridge is researched. The applications show that the concrete has some merits, such as good fluidity, low bleeding ratio and no segregation, low slump loss, high early strength and high later strength, micro-expansion etc.

基于互信息和MiniRocket网络的CFST脱空识别

为提高钢管混凝土(concrete filled steel tube,CFST)脱空检测的效率和精度,本文提出了一种基于快速傅里叶变换(fast fourier transform,FFT)、互信息(mutual information,MI)和MiniRocket神经网络的智能识别方法。首先,采用FFT将待测CFST敲击声波时域信号转换为频域信号;其次,采用MI建立频域信号与脱空状态的相关性,提取相关性最大的前30个特征建立数据集,避免了复杂的数学运算和冗余信息;建立MiniRocket深度学习网络,通过使用更少的参数量和更小的特征尺寸,提高分类的速度和精度。最后,考察了模型的噪音鲁棒性,并与其他算法、特征提取方法和识别方法进行对比。结果表明,在不同脱空深度和脱空宽度下,所提的方法在100次重复试验中获得了100%的平均预测精度。在高信噪比下,该方法受影响较小。此外,与其他算法、特征提取方法和识别方法相比,本方法具有更好的预测性能。因此,所提出的方法在未来实际CFST结构的智能脱空识别中具有较大的应用潜力。

考虑上部质量的双柱CFST桥墩抗车辆撞击力学性能研究

钢管混凝土(CFST)构件可充分发挥钢管与核心混凝土优点,在桥梁墩柱中已得到应用,抗撞设计是其在墩柱中推广应用的关键问题。因此,该文基于LS-DYNA有限元软件建立了56个车辆撞击双柱CFST桥墩分析模型并进行抗撞机理与参数分析。基于前期落锤撞击结果与实车撞击试验验证了模型可靠性;对典型工况下撞击力和桥墩塑性应变发展、内力分布和能量转换进行研究并重点分析了含钢率、轴压比、货物刚度、车辆质量和速度对CFST桥墩撞击力和侧向位移分布的影响规律;采用等效静力法计算得到25 ms等效车辆撞击力(ESF25)并对AASHTO规程建议值进行评估,提出车撞CFST桥墩撞击力预测公式。结果表明:车辆撞击下CFST桥墩钢管与核心混凝土协同工作,钢管是主要耗能部件;由于上部结构和桥墩惯性作用,不同撞击时刻桥墩内力分布具有显著差异;车辆质量与速度对撞击力发展影响显著,含钢率与轴压比影响较小,货物弹性模量在2000 MPa内变化时影响较大;建议的撞击力公式可较好预测考虑上部质量影响的CFST桥墩撞击力。

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.

大跨CFST拱桥拱轴线形的综合评分法

为探究500m级钢管混凝土拱桥拱轴线形的合理程度,从钢管混凝土拱桥成桥状态的强度、刚度、稳定性和拱轴线形优化方法的操作复杂性角度,对各最优拱轴线形进行拱轴线形评判指标计算对比,提出一种可用于定量评判钢管混凝土拱桥拱轴线形的优化程度的方法——钢管混凝土拱桥拱轴线形优化综合评分法(CFST-ARO综合评分法)。文中以波司登大桥为工程实例,对经优化后的抛物线、悬链线及三次样条曲线拱轴线形采用综合评分法进行定量评定。结果表明选用3次样条插值函数优化的拱轴线形内力状态优化效果显著,沿跨径方向应力幅度比其他曲线小且均匀,刚度和稳定性都有所提高;以期为同类型拱桥拱轴线形优化评价提供科学参考。

RPC外包方钢管混凝土柱轴压受力性能研究

为了研究活性粉末混凝土(Reactive powder concrete,RPC)外包方钢管混凝土柱的轴压受力性能,以RPC厚度和长细比为参数,对6根构件开展轴压试验研究,探讨该类组合柱的破坏模式、受力机理、套箍效应和承载力。试验结果表明:外层RPC可为内部方钢管混凝土柱提供较强的约束力,在受力后期套箍效应凸显。随着RPC厚度的增加,组合柱的承载力逐渐提高;随着组合柱长细比的增大,虽然其弹性刚度和承载力逐渐降低,但延性改善。采用ABAQUS软件建立RPC外包方钢管混凝土柱的有限元模型,分析RPC强度、RPC厚度、钢管强度等级、含钢率、内部混凝土强度和长细比等参数对组合柱承载力的影响规律,可得方钢管混凝土柱发挥系数的变化幅值为0.78~1.01。在试验研究、有限元参数分析和理论探讨的基础上,借鉴钢管混凝土结构技术规范,提出了RPC外包方钢管混凝土轴压短柱和长柱的承载力简化计算方法,公式计算值与已有数据样本吻合良好。

新型钢管混凝土梁柱节点力学性能试验研究

为研究内加强环式圆钢管混凝土柱与矩形钢管混凝土梁这种新型连接节点的力学性能,设计了缩尺钢管混凝土梁柱节点试件,开展了相同梁柱节点试件的静力加载试验和低周往复加载试验。通过研究该节点试件的破坏模式、荷载-位移曲线以及拟静力加载试验的骨架曲线、核心区剪切变形等,分析了节点试件的承载能力、延性和耗能能力,全面考察了同一梁柱节点在静力加载和低周往复加载两种工况下的受力性能和破坏模式。结果表明:钢管混凝土梁柱节点试件核心区强度较强,破坏模式主要为梁端破坏,低周往复加载试验时试件梁柱连接处附近的梁端钢板发生拉裂破坏和钢板鼓曲,静力加载试验时试件梁端焊缝发生拉裂破坏;试件延性较好,加载过程中经历了弹性、弹塑性和塑性发展阶段。最后提出了该类钢管混凝土梁柱节点核心区的抗剪强度计算公式。

薄壁钢板局部屈曲关键问题研究进展

钢结构以及钢-混凝土组合结构由于其强度高、耗能能力好、施工方便等优异性能,被广泛应用于工程结构中。然而,随着高强度钢材的应用,薄壁钢板呈现薄壁化、宽厚比随着构件截面尺寸的增大而不断增大的趋势,由于工程结构及荷载的复杂性等因素,钢板过早发生局部屈曲的风险不断加大,薄壁钢板的局部屈曲问题凸显,亟待开展系统性深入研究。对薄壁钢板局部屈曲研究的进展进行了概述,分析总结了现有试验研究和理论研究方面存在的局限性,详细介绍了笔者团队近年来聚焦于薄壁钢板局部屈曲关键问题开展的一系列研究工作及成果。

大高宽比矩形钢管混凝土柱压弯性能研究

为了研究大高宽比矩形钢管混凝土柱的压弯性能,对大高宽比钢管混凝土短柱进行偏压试验并结合有限元模拟补充了4组试件进行对比,包括不同偏心率、高宽比、钢管壁厚度、截面尺寸情况下柱性能的对比分析。最后参考常用的4本国内外规范进行柱承载力计算,对比并判断现有规范是否适用。结果表明:试件破坏模式均为长边鼓曲,当荷载小于极限承载力的80%时,横截面高度上的应变分布服从平截面假定;随着偏心率增大,柱延性提升,在偏心率超过0.205后,柱延性开始下降;随着壁厚增加,柱延性提升,在壁厚达到8 mm后,柱延性开始下降;随着高宽比提升,柱延性降低;随着截面尺寸增大,在壁厚不变的情况下,柱延性降低,在壁厚等比例增大时,柱延性变化不大;随着高宽比、截面尺寸、钢管壁厚度的增大,柱承载力提升;随着偏心率升高,柱承载力降低;参考规范JGJ 138—2016对大高宽比钢管混凝土柱偏压承载力的计算更为准确。

钢管混凝土键连接框架梁和剪力墙的受剪性能

目的 研究钢管混凝土键连接框架梁和剪力墙的受剪性能,为工程应用提供设计依据。方法 应用有限元分析软件ABAQUS对比钢管混凝土键连接与现浇连接梁墙的结构受剪性能,分析前者受剪机理及不同因素对受剪性能的影响。结果 钢管混凝土键连接梁墙的结构承载力和延性系数较现浇结构分别提高约10%和34%;钢材强度从Q235到Q390,初始刚度增加8.44%;截面高度从100 mm到120 mm,延性系数提高17.73%;截面厚度每增加2 mm,承载力提高约15%;截面长度和混凝土强度等级对承载力、初始刚度和延性系数的影响均小于15%,纵向距离对其受剪性能几乎无影响。结论 采用钢管混凝土键连接梁墙的结构总体受剪性能优于现浇结构;钢材强度和截面厚度分别是影响初始刚度和承载力的主要因素。

圆钢管超高性能混凝土短柱偏压力学性能研究

为研究钢管超高性能混凝土短柱的偏压性能,以荷载偏心率和钢管径厚比为变化参数,设计了12个圆钢管UHPC短柱试件并对其进行偏心受压加载试验,分析了该类构件的破坏模式、荷载-挠度曲线、钢管应变和变形系数等,考察了主要因素对短柱偏压性能的影响规律。结果表明:试件的破坏特征为钢管屈服和核心混凝土压坏;荷载-挠度曲线有较明显的峰值点,偏心率越大和径厚比越小,曲线的下降段越平缓;达到60%峰值荷载时,钢管开始产生明显的约束作用,达到90%峰值荷载时,截面变形不再符合平截面假定;偏心率增大使试件的承载力和刚度下降,而径厚比减小可降低这种不利影响。在试验基础上,结合数值模拟对短柱的N-M曲线进行分析,建立了临界偏心率和套箍系数的关系表达式,并基于此提出短柱偏压承载力实用计算方法,理论与试验结果吻合较好。