钢管混凝土圆拱的面内承载力分析

迄今为止,全世界已有400多座钢管混凝土拱桥。然而,有关钢管混凝土拱面内承载力的设计规范仍没有。目前,钢管混凝土拱的设计广泛采用钢筋混凝土及预应力混凝土拱的面内承载力设计方法。这样钢管混凝土拱可认为受轴压或偏压作用,相当于钢管混凝土柱。将钢管混凝土柱的经典屈曲荷载作为钢管混凝土拱的参考弹性屈曲荷载。然而,在横向荷载作用下,钢管混凝土拱的面内弹性屈曲性能与轴压下的钢管混凝土柱完全不同,尤其是对于薄壁钢管混凝土拱。另外,与轴压或偏压下钢管混凝土柱不同,钢管混凝土拱在屈曲之前就发生非线性弯曲和横向变形,这严重影响钢管混凝土拱的承载力。因此,钢管混凝土面内承载力的设计方法是否正确值得商榷。提出与现有钢结构设计规范基本一致的钢管混凝土圆拱承载力设计方法,并同时考虑了几何非线性和材料非线性的影响。提出均匀轴压下钢管混凝土拱的面内承载力设计方程,及弯矩和轴压共同作用下钢管混凝土拱面内承载力验算的下限设计方程。     

In-plane strength of concrete-filled steel tubular circular arches

More than 400 concrete-filled steel tubular (CFST) arch bridges have been constructed worldwide so far. However, design codes or guidance for the in-plane strength design of CFST arches are yet to be developed. In current design practice, the philosophy for the in-plane strength design of reinforced and prestressed concrete arches is widely adopted for CFST arches. For this, the CFST arches are considered under central or eccentric axial compression and are treated similarly to CFST columns, and the classical buckling load of CFST columns is used as the reference elastic buckling load of CFST arches. However, under transverse loading, the in-plane elastic buckling behaviour of CFST arches, particularly shallow CFST arches, is very different from that of CFST columns under axial compression. In addition, different from CFST columns under central or eccentric axial compression, CFST arches are subjected to significant nonlinear bending actions and transverse deformations prior to buckling and these will influence the strength of CFST arches greatly. Therefore, it is doubtful if the current method for in-plane strength design of CFST arches can provide correct strength predictions. In this paper, a method for the in-plane strength design of CFST circular arches, which is consistent with the current major design codes for steel structures, is developed by considering both geometric and material nonlinearities. A design equation for the in-plane strength capacity of CFST arches under uniform compression, and a lower-bound design equation for the in-plane strength check of CFST arches under combined actions of bending and compression are proposed.     

Concrete filled steel tube stub columns under combined temperature and loading

A finite element analysis (FEA) model was developed to predict the load versus deformation relationships of concrete filled steel tube (CFST) stub columns subjected to a combination of temperature and axial compression. This model was used to simulate a set of CFST stub column experiments under various thermal and mechanical loading conditions, including tests at high temperature, tests on the residual strength of specimens subjected to uniform heating, and tests on specimens exposed to the ISO-834 standard fire without initial loads. Comparisons between the predicted results and the test results show that this model can predict the load versus deformation relationships with reasonable accuracy. The FEA model was then used to investigate the behaviour of CFST stub columns in a complete loading history including initial loading, heating and cooling by examing the cross-sectional stress distribution and confinement stress development at different loading phases. All specimens were loaded to ultimate strength after cooling and the residual stress index was studied with respect to a group of parameters. It can be found that the ultimate strength when considering the mutual actions of temperature and loading was slightly lower than that after exposure to fire without initial load, but the peak strain corresponding to the ultimate strength was increased significantly.     

钢管混凝土柱轴压力-弯矩-扭矩空间复合受力拟静力试验研究

采用自行设计的压力-弯矩-扭矩复合受力加载装置,基于力-位移混合控制加载方法,完成了8个钢管混凝土柱试件在压-弯-扭等复合荷载作用下的拟静力试验,变化了截面形式、加载方式和弯扭比等参数。试验结果表明：圆钢管混凝土柱和矩形钢管混凝土柱在压-弯-扭等复合受力往复荷载作用下的滞回曲线较为饱满,没有“捏拢”现象产生,具有较好的耗能能力;弯扭比较大的矩形钢管混凝土试件在扭转角较大时由于钢管底部局部屈曲较为明显,存在承载力退化现象;钢管混凝土截面轴向应变基本满足平截面假定;弯矩的存在将削弱钢管混凝土柱的受扭能力;在压-弯-扭等复合受力往复荷载作用下,钢管剪应变与扭转角之间存在较好的线性关系。对试验实测结果和已有文献分析表明：在弯扭比较大时由主压应力导致钢管表面发生局部鼓曲而破坏,弯扭比较小时,主拉应变将导致钢管混凝土柱表面在低周往复荷载作用下开裂。研究成果可为进一步开发考虑扭转作用的钢管混凝土纤维梁单元提供基础性依据。     

带环向脱空缺陷的钢管混凝土构件在压弯扭复合#br# 受力作用下的滞回性能研究

为研究环向脱空缺陷对钢管混凝土试件在压弯扭复合受力作用下抗震性能的影响,进行了12个钢管混凝土试件（包括8个带缺陷试件、2个无脱空试件以及2个空钢管对比试件）在恒定轴压力和反复弯扭耦合荷载作用下的滞回性能试验。试验主要参数为：脱空率、弯扭比和轴压比。基于试验结果考察了带脱空缺陷的钢管混凝土试件在压弯扭复合受力作用下的破坏模态,并分析了脱空对试件滞回曲线、骨架曲线、刚度和耗能等力学指标的影响规律,结果表明：环向脱空缺陷的存在会改变钢管混凝土构件的破坏模态,并使试件的承载力、刚度和耗能能力有不同程度的降低。同时,建立钢管混凝土压弯扭构件的有限元模型,分析环向脱空对构件承载力系数,以及钢管与核心混凝土接触时刻的影响规律,在此基础上提出相关工程建议。     

各种截面钢管混凝土轴压短柱基本性能连续性的理论研究

根据“统一”理论推断 ,对不同截面形式的钢管混凝土轴压短柱采用有限元方法进行分析 ,得到了圆形、方形、矩形和八边形截面轴压短柱的平均应力 -应变全过程关系曲线。最后导得各种截面钢管混凝土轴压短柱的组合性能指标及承载力设计公式。研究结果表明 ,各种截面形式的钢管混凝土的性能变化是连续的。     

钢筋混凝土偏心受压和偏心受拉构件的抗剪强度

本文讨论了钢筋混凝土构件在轴向力、弯矩和剪力共同作用下的抗剪强度。对171根构件试验结果的分析表明,用我国《钢筋混凝土结构设计规范》(TJ 10-74)中受弯构件的抗剪强度计算公式来计算偏压和偏拉构件的抗剪强度是不合适的,对于偏压构件偏于保守,而对于偏拉构件则偏于不安全。在分析试验资料的基础上,本文提出了一个考虑轴向压力和拉力影响的抗剪强度实用计算方法。计算结果与试验结果符合较好。     

钢管煤矸石混凝土轴压短柱极限承载力计算方法研究

为促进煤矸石在钢管混凝土结构中的应用,选取辽宁地区的煤矸石作为粗骨料,开展6根钢管混凝土和12根钢管煤矸石混凝土短柱轴压试验。根据构件破坏形式与荷载-应变曲线讨论材料强度、钢管约束和取代率对构件轴压承载力的影响规律,进行了设计参数与承载力的相关性分析,在此基础上,讨论规范GB 50936—2014和规程T/CECS 625—2019中的轴压短柱极限承载力计算方法对钢管煤矸石混凝土的适用性,给出圆钢管煤矸石混凝土短柱极限承载力计算公式的建议修正系数。结果表明:轴向压缩试验下构件呈现出局部鼓曲与剪切破坏形态; 与钢管普通混凝土短柱相比,钢管对核心煤矸石混凝土具有更好的横向约束效应; 相同取代率下提高套箍系数与含钢率将显著提升构件承载力,构件的轴压承载力随煤矸石取代率提升而降低,但最大降低幅度未超过11%:煤矸石粗骨料对承载力的相关系数为-0.33且不具有显著性; 现有的规范GB50936—2014和规程T/CECS 625—2019中相关计算方法适用于钢管煤矸石混凝土短柱,引入修正系数后承载力计算的平均相对误差在3%以内。     

Behaviors of concrete-filled steel tubular members subjected to combined loading

The present study is an investigation on the behaviors of concrete-filled thin-walled steel tubular members subjected to combined loading, such as compression and torsion, bending and torsion, compression, bending and torsion. ABAQUS software is used in this paper for the finite element analysis (FEA). A comparison of results calculated using this modeling shows generally good agreement with test results. The FEA modeling is then used to investigate the influence of important parameters that determine the ultimate strength of the composite members under combined loading, such as compression and torsion, bending and torsion, compression, bending and torsion. The parametric studies provide information for the development of formulae for calculating the ultimate strength of the composite members subjected to combined loading.     

Performance of concrete-filled thin-walled steel tubes under pure torsion

In practice, concrete-filled steel tubes (CFST) are often subjected to torsion. To date, such a problem however has not been addressed satisfactorily by design codes. The present study is thus an attempt to study the torsional behaviours of concrete-filled thin-walled steel tubes. ABAQUS software is used in this paper for the finite element analysis (FEA) of CFST subjected to pure torsion. A comparison of results calculated using this modelling shows good agreement with test results. The FEA modelling was used to investigate the influence of important parameters that determine the ultimate torsional strength of the composite sections. The parametric studies provide information for the development of formulae to calculate the ultimate torsional strength, as well as the torsional moment versus torsional strain curves of the composite sections.     

拉压变轴力下小剪跨比预应力混凝土墙往复受剪试验研究

为了研究预应力混凝土（PC）剪力墙的抗震性能,提出剪力墙在拉压变轴力作用下的水平往复加载试验加载制度,完成3片剪跨比为1.0的预应力混凝土墙在恒定轴拉力、恒定轴压力和拉压变轴力作用下的水平往复加载试验,研究其破坏模式、滞回性能、承载力、变形能力、刚度和残余裂缝宽度,并与型钢混凝土（SRC）墙和普通RC墙的抗震性能进行了对比。试验结果表明：恒定轴拉力试验中,预应力混凝土墙发生了腹板剪切破坏;恒定轴力试验中墙体发生了斜压破坏;拉压变轴力试验中,墙体在压剪方向加载时发生剪压破坏。拉压变轴力加载导致预应力混凝土墙拉剪和压剪承载力分别降低了18.7%和10.5%。预应力混凝土墙在恒定轴拉力和拉压变轴力作用下的极限位移角为1.2%~1.6%,变形能力大于JGJ 3—2010《高层建筑混凝土结构技术规程》规定的弹塑性位移角限值(1/100);恒定轴压力试验中水平峰值荷载超过了墙体截面受剪承载力限值,出现斜压破坏,极限位移角仅为0.6%。预应力混凝土墙试件与SRC墙试件的刚度、承载力和变形能力接近,前者的残余裂缝宽度小于后者的,表现出更好的震后可修复性。由于预应力有效抑制了墙体水平贯通裂缝的形成、防止出现沿水平裂面的滑移破坏,因此在较大轴拉力水平时预应力混凝土墙比普通RC墙的抗侧刚度和承载能力均显著提高。总体来看,预应力混凝土墙抗震性能优良,是一种改善高层建筑中受拉剪力墙抗震性能的有效手段。     

High strength circular concrete-filled steel tubular slender beam-columns, Part II: Fundamental behavior

There is relatively little experimental and numerical research on the fundamental behavior of high strength circular concrete-filled steel tubular (CFST) slender beam-columns. In a companion paper, a new numerical model for predicting the nonlinear inelastic behavior of high strength circular CFST slender beam-columns under axial load and bending was presented. The numerical model developed accounts for confinement effects on the strength and ductility of the concrete core and on circular steel tubes as well as initial geometric imperfections of beam-columns. This paper presents the verification of the numerical model and extensive parametric studies on the fundamental behavior of high strength circular CFST slender beam-columns. The ultimate strengths and axial load-deflection responses of circular CFST slender beam-columns under eccentric loading predicted by the numerical model are verified by corresponding experimental results. The computer program implementing the numerical model is used to investigate the fundamental behavior of high strength circular CFST slender beam-columns in terms of load-deflection responses, ultimate strengths, axial load-moment interaction diagrams, and strength increase due to concrete confinement. Parameters examined include column slenderness ratio, eccentricity ratio, concrete compressive strengths, steel yield strengths, steel ratio and concrete confinement. It is demonstrated that the numerical model developed is an efficient computer simulation and design tool for high strength circular CFST slender beam-columns. Benchmark numerical results presented in this paper are valuable in the development of composite design codes for high strength circular CFST slender beam-columns.     

Experimental research on CFST member with different sections under combined compression and bending

以轴压比为变化参数,进行了4根圆形和4根哑铃形钢管混凝土柱的压弯试验,对两种截面钢管混凝土柱在压弯荷载作用下的变形模式、荷载-变形曲线和压弯相关曲线进行了对比分析。结果表明：两种截面钢管混凝土构件随着轴压比的增大,构件的延性呈降低的趋势,由于哑铃形截面面内刚度较大,相同轴压比下哑铃形钢管混凝土抵抗弯矩和变形的能力要强于圆形钢管混凝土。通过对圆钢管混凝土和哑铃形钢管混凝土压弯曲线的分析,发现直接采用圆钢管混凝土的压弯相关曲线方程计算哑铃形钢管混凝土,结果偏于保守,还需进一步的有限元分析才能提出适用于哑铃形钢管混凝土的压弯相关曲线。     

Experimental study on seismic behavior of concrete filled steel tube columns under pure torsion and compression–torsion cyclic load

Based on the quasi-static test on eight CFST columns subjected to pure torsion and compression–torsion cyclic load, the torsion behavior of CFST columns with various section types, steel ratios and axial load levels was studied. The test results showed that the hysteretic curves of CFST columns under pure torsion and low compression–torsion cyclic load are very plump, which indicate that CFST columns have good seismic capacity. The unloading stiffness of CFST columns was equal to the initial elastic stiffness. The torsion capacity of CFST columns could be improved by the low compressive load, and the ductility was also good. But the torsion capacity of CFST columns would be reduced by the high compressive load. When CFST columns subjected to pure torsion, spiral diagonal compressive struts will be created in the in-filled concrete, and the axial components of the diagonal compressive force of the in-filled concrete was equal to the axial tensile force of the steel tube in order to satisfy the axial load equilibrium condition on the section, so the axial strain will be produced in the steel tube. The shear strain has good linear relationship with the rotation angle of the section when CFST columns subjected to pure torsion and compression–torsion combined action. Based on the test results and literatures available, the torsion mechanism of CFST columns was preliminarily analyzed.     

Concrete-filled circular steel tubes subjected to local bearing force: Experiments

Concrete filled steel tubular (CFST) members are subjected to local bearing forces in a large number of truss and lattice structures. Previous research has focused on rectangular CFST members under such loading condition. There is a lack of understanding on circular CFST members subjected to local bearing force. This paper intends to fill the knowledge gap in this area. A series of tests were conducted on circular CFST, unfilled circular hollow section (CHS) steel tube and plain concrete specimens loaded with local bearing force. The load was applied either perpendicularly to the member or at an angle of 45°. A deformation limit was adopted to define the ultimate strength of the specimen since the load verse deformation curve exhibits a ductile behavior. The effects of important parameters were investigated based on the test results. Finally, design formulae were developed to predict the ultimate strength of circular CFST members under local bearing forces.     

局部承压的圆形钢管混凝土构件试验

在很多桁架和网格结构中,钢管混凝土(CFST)构件都承受局部压力作用。以往的研究主要集中在这种荷载条件下的矩形CFST构件的性能,但是缺少对受局部承压力的圆形钢管混凝土构件的认识。文章意图填补这个领域的空白。对圆形钢管混凝土构件进行一系列试验,对无填充的圆钢管和素混凝土样本施加局部承压力。垂直加裁或呈45℃加载于构件上。由于荷载-变形曲线显示了其延性,采用一种变形极限来确定样本的极限强度。根据试验结果研究几种重要参数的影响。最后,提出可以预测局部承压的圆形钢管混凝土构件极限强度的设计公式。     

Numerical analysis of slender elliptical concrete filled columns under axial compression

This paper presents a non-linear finite element model (FEM) used to predict the behaviour of slender concrete filled steel tubular (CFST) columns with elliptical hollow sections subjected to axial compression. The accuracy of the FEM was validated by comparing the numerical prediction against experimental observation of eighteen elliptical CFST columns which carefully chosen to represent typical sectional sizes and member slenderness. The adaptability to apply the current design rules provided in Eurocode 4 for circular and rectangular CFST columns to elliptical CFST columns were discussed. A parametric study is carried out with various section sizes, lengths and concrete strength in order to cover a wider range of member cross-sections and slenderness which is currently used in practices to examine the important structural behaviour and design parameters, such as column imperfection, non-dimension slenderness and buckling reduction factor, etc. It is concluded that the design rules given in Eurocode 4 for circular and rectangular CFST columns may be adopted to calculate the axial buckling load of elliptical CFST columns although using the imperfection of length/300 specified in the Eurocode 4 might be over-conservative for elliptical CFST columns with lower non-dimensional slenderness.     

初始荷载下中空钢管混凝土柱轴向强度

与传统的钢管混凝土柱相比,中空钢管混凝土(CFDST)柱具有很多优点,诸如自重轻和良好的循环性能。CFDST柱可能被用于桥梁,高层建筑,高架桥和输电塔结构中。内外钢管将承担来自上部结构和浇筑的湿混凝土的初始荷载。由这些初始荷载造成的钢管初应力和变形会影响CFDST构件的性能。因此,对外钢管单独承担初始荷载和内外钢管同时承担初始荷载时,CFDST柱的轴力性能进行讨论。建立通用的有限元模型预测钢管负荷时CFDST柱的性能。通过承担初始荷载和不承担初始荷载的CFDST柱的试验结果对该有限元模型进行验证。讨论初始荷载水平、长细比、空心率和材料强度对轴向强度的影响。最后,给出初始荷载下的CFDST柱的极限强度计算公式。     

钢管混凝土T形相贯节点应力集中系数研究

通过对钢管混凝土T形相贯节点的试验和有限元分析,研究了在轴向荷载和平面内弯矩作用下节点的应力集中系数。结果表明：轴向荷载作用下钢管相贯节点的应力集中系数分布不均匀,而钢管混凝土相贯节点分布较均匀,主管内填混凝土有效降低了相贯节点的应力集中系数,同时也将热点的位置由鞍点变为冠点;平面内弯矩作用下钢管相贯节点主管的应力集中系数分布不均匀,而钢管混凝土相贯节点主管分布较均匀,主管内填混凝土有效降低了主管的应力集中系数,两者支管相差不大;主管轴力对节点的应力集中系数影响较大,进行轴向压力和平面内弯矩作用下节点的应力集中系数计算时,应考虑到主管轴压比的影响;现行规范对于钢管相贯节点应力集中系数的计算公式并不适用于钢管混凝土相贯节点。基于强度等效的原则,提出了改进的应力集中系数计算公式,计算结果和试验结果吻合较好。     

Compressive and flexural behaviour of concrete filled steel tubes after exposure to standard fire

This paper describes a series of new compression and bending tests carried out on concrete filled steel tubes (CFST) after exposure to the ISO-834 standard fire. A theoretical model that has been previously developed is used to predict the post-fire load versus deformation relationships of CFST stub columns and beams. The predicted curves of load versus deformation are in good agreement with the new test results.The previously developed theoretical model had been used to investigate the influence of a number of important parameters on the residual ultimate strength and flexural stiffness of the composite sections and the results of the parametric studies were used to develop formulas for calculating the composite section residual ultimate strength under axial compression or flexural bending and the composite section residual flexural bending stiffness. In these formulas, the ambient temperature compression resistance, bending moment capacity and initial flexural bending stiffness of the composite section should be calculated using an existing design code. In this paper, these formulas are applied to the new test data to assess the suitability of using several different design codes: AIJ-1997, AISC-LRFD-1999, BS5400-1979, DBJ13-51-2003 and EC4-1994.