钢管混凝土柱抗火性能浅析

介绍了钢管混凝土柱的特点及其抗火性能研究的必要性,分析其抗火性能机理及其主要的影响因素,包括截面尺寸、含钢率、长细比、保护层厚度、边界条件、受火情况等,提出了进行钢管混凝土结构构抗火性能研究的几个关键问题。     

Seismic performance of CFST column to steel beam joint with RC slab: Experiments

The objective of this research is to investigate the seismic behaviour of the composite joint consisting of circular concrete filled steel tubular (CFST) column and steel beam with reinforced concrete (RC) slab. Six specimens, including four interior and two exterior joints, were tested under constant axially compressive load on the top of the columns and cyclic loads at the ends of the beams. The main experimental parameters were the type of the joint, the axial load level on the CFST column and the section configuration of the beam. Several indexes that could reflect the seismic behaviour of the composite joint, such as the ductility, the strength degradation, and the energy dissipation capacity were analyzed. It was found that the composite joints exhibited favorable seismic performance.     

往复荷载作用下钢管混凝土叠合柱-钢梁连接节点力学性能研究

建立了钢管混凝土叠合柱-钢梁连接节点在往复荷载作用下力学性能分析的有限元计算模型。利用平面与空间连接节点试验结果,对建立的数值模型进行验证。采用有限元模型分析不同空间双向加载方式对钢管混凝土叠合柱-钢梁空间连接节点力学性能的影响规律,研究该类组合节点在往复荷载作用下荷载(P)-位移(Δ)关系全过程受力机理与核心区剪力分配机制,并从承载力及刚度等方面对比平面与空间连接节点的性能。研究结果表明,不同加载方式对节点的承载力有明显影响。相比平面节点,钢管混凝土叠合柱-钢梁空间连接节点在双向往复荷载作用下正、负向承载力分别降低约14%和18%。     

Seismic performance of CFST column to steel beam joints with RC slab: Analysis

This paper presents a finite element analysis (FEA) model for the concrete-filled steel tubular (CFST) column to steel beam joint with a reinforced concrete (RC) slab under cyclic loading. The feasibility of the FEA model is verified by a set of experimental results presented in the companion paper as well as available test data from other researchers. Stress analysis is conducted by using this FEA model to investigate the failure mode and mechanism of the composite joint. Parametric studies are then carried out to study the influence of the following parameters for the composite joint: material strength, the thickness of RC slab, the slenderness ratio and steel ratio of the column, the dimension of the diaphragm and the axial load level of the CFST column.     

方钢管混凝土柱-钢梁框架耐火性能分析

研究方钢管混凝土柱-钢梁框架结构的耐火性能。基于有限元方法,分析了GB/T 9978（同ISO-834）加热条件下,带有混凝土楼板的方钢管混凝土柱-钢梁单向螺栓连接框架结构的温度分布、耐火时间和破坏模式,并对有限元模拟结果进行了试验验证,在试验结果基础上采用有限元方法分析了方钢管混凝土柱构件与方钢管混凝土框架柱的耐火极限差异。研究结果表明：与方钢管混凝土框架柱的其他区域相比,方钢管混凝土框架柱节点区的温度相对较低;根据本文建议的框架结构判定准则,当单向螺栓节点连接可靠,随着作用在柱和梁上荷载水平的变化,柱破坏模式和梁破坏模式是方钢管混凝土柱-钢梁框架的主要破坏模式;当框架梁上不施加荷载,只对框架柱起到约束作用,其他条件相同时,方钢管混凝土框架柱的耐火极限大于两端铰接柱构件的耐火极限,但小于一端固接一端铰接支撑柱构件的耐火极限。     

Behaviour of fire-exposed concrete-filled steel tubular beam columns repaired with CFRP wraps

This paper presents the test results of fire-exposed concrete-filled steel tubular (CFST) beam columns repaired by unidirectional carbon fibre reinforced polymer (CFRP) composites. Both circular and square specimens were tested to investigate the repair effects of CFRP composites on them. The test results showed that the load-bearing capacity of the fire-exposed CFST beam columns was enhanced by the CFRP jackets to some extent, while the influence of CFRP repair on stiffness was not apparent. The strength enhancement from CFRP confinement decreased with the increasing of eccentricity or slenderness ratio. Ductility enhancement was also observed except those axially loaded shorter specimens with rupture of CFRP jackets at the mid-height, occurred near the peak loads. However, the strengths of all repaired specimens have not been fully restored due to the long exposure time of them in fire. From the test results, it is recommended that, in repairing severely fire-damaged CFST members, slender members or those members subjected to comparatively large bending moments, other appropriate repair measures should be taken.     

Behaviour of flush end plate joints to concrete-filled steel tubular columns

This paper presents the results of an experimental program for bolted moment connection joints of circular or square concrete filled steel tubular (CFST) columns, and H-shaped steel beams using high-strength blind bolts. In order to investigate the static performance and failure modes of the blind bolted connection, an experimental program was conducted involving four sub-assemblages of cruciform beam-to-column joints subjected to monotonic loading. Moment-rotation relationships of the tested connections were obtained and their performance was evaluated in terms of their stiffness, moment capacities and ductility. The test parameters varied were the column section type and the thickness of the end plate. The results showed that the proposed blind bolted connection, which behaves in a semi-rigid and partial strength manner according to the EC3 specification, displays reasonable strength and stiffness. The rotation capacity of this type of connection to square or circular CFST columns exceeds 70 mrad and this satisfies the ductility requirements for earthquake-resistance in most aseismic regions. The blind bolted connection is shown to be a reliable and effective solution for moment-resisting composite frame structures.     

Seismic behaviour of concrete-filled steel tubular frame to RC shear wall high-rise mixed structures

Composite frames consisting of concrete-filled steel tubular (CFST) columns and steel beam are being used more and more popularly in building structures. In China, the composite frame structures are often mixed with reinforced concrete shear walls to form a high-rise building system. However, there was seldom information on the seismic performance of this kind of mixed construction. Shaking table tests on two building models with 30 storeys consisting of composite frames and RC shear walls were thus presented in this paper. CFST columns with circular and square sections were used in the composite frames respectively. Three kinds of real earthquake records, including Taft (EW), El Centro (NS) and Tianjin waves with peak accelerations of 0.2g, 0.4g, 0.6g, and 0.8g, were applied respectively to simulate different levels of earthquakes in the tests. It was found that the composite frames cooperated well with the core RC shear wall structure under earthquakes, and the two building models exhibited excellent seismic performance.     

Performance of CFST column to steel beam joints subjected to simulated fire including the cooling phase

This paper presents the experimental results of three concrete filled steel tube (CFST) column to steel beam joints with reinforced concrete (RC) slabs under combined loading and fire including the heating and cooling phases. The test parameters include heating time and thickness of the fire protection material. Temperatures and deformations of the joint specimens during the heating, cooling and post-fire phases were measured. A finite element analysis (FEA) model to simulate the action of a CFST column to steel beam joint under combined loading and fire is developed. The FEM model was verified by the experimental results. The FEA model is then used to analyse the temperature distribution in the heating and cooling phases. The moment versus relative rotation angle between the CFST column and the beam under combined loading and fire including the heating and cooling phases is also discussed.     

新型方钢管混凝土梁柱节点力学性能分析

钢管混凝土能够充分发挥混凝土和钢材两种材料的特性,混凝土受到钢管环箍作用,具有很高的抗压承载力.但由于梁柱连接节点部位构造较为复杂,施工难度大,还有待进一步改进改善.利用ANSYS对新型方钢管混凝土柱-钢筋混凝土梁内插钢板连接节点的受力特性进行了研究,通过与普通钢筋混凝土梁柱节点的对比分析,得到新型节点具有较高承载力、抗震性能优越、延性非常好、有很长的屈服平台、屈服后承载力下降不多等优点.破坏时节点域变形很小,塑性角外移,避免了节点域的脆性破坏.     

Experimental behaviour of concrete-filled stiffened thin-walled steel tubular columns

An experimental study on the structural behaviour of concrete-filled stiffened thin-walled steel tubular columns is presented in this paper. The stiffening was achieved by welding longitudinal stiffeners on the inner surfaces of the steel tubes. Companion tests were also undertaken on 12 unstiffened concrete-filled steel tubular (CFST) columns, with or without steel fibres in the infill concrete. The test results showed that the local buckling of the tubes was effectively delayed by the stiffeners. The plate buckling initially occurred when the maximum load had almost reached for stiffened specimens, thus they had higher serviceability benefits compared to those of unstiffened ones. Some of the existing design codes were used to predict the load-carrying capacities of the tested composite columns.     

中海广场钢管混凝土柱-钢梁节点性能研究

采用试验的方法对中海广场钢管混凝土柱-钢梁节点的性能进行了研究,得出该种节点的破坏形式、主要力学性能指标以及加强环上的应力分布。试验结果表明该种节点形式的承载力高、延性好,节点区加强环受力均匀,满足强柱弱梁的设计原则。对试验节点进行了有限元分析,数值分析结果与试验数据吻合较好,可为推广该节点形式的工程应用提供可靠依据。     

Analytical behavior of frames with steel beams to concrete-filled steel tubular column

This paper reports the mechanism of composite frames with steel beams connected to concrete-filled square hollow section (SHS) columns. Detailed analysis was carried out on longitudinal stress in steel beams, axial stress distribution in concrete, and concrete stress along the column height and at the connection panel. Parametric studies were conducted to investigate the influence of axial load level, beam-to-column linear stiffness ratio on the structural behavior of composite frames. Simplified hysteretic lateral load (P) versus lateral displacement (Δ) models are proposed for such composite frames.     

方钢管混凝土柱与钢梁框架节点的抗震性能试验研究

为验证方钢管混凝土柱与工形钢梁框架节点的破坏特征和抗震性能,本文进行了A、B两组共6个足尺节点试件的低周反复循环加载试验,其中A组三个试件梁端采用栓-焊连接;B组三个试件梁端为全对接焊接。试验结果表明:6个试件的层间位移延性系数μ≈2.28～3.86,弹性极限层间位移角y≈0.001～0.014,弹塑性极限层间位移角u≈0.0297～0.0424,节点梁柱的相对极限塑性转角θu≈0.0163～0.0343rad,能量耗散系数E≈2.029～2.494;A、B两类节点均有良好的抗震性能,在相同轴压比下A类节点的延性较B类略好一些,而耗能能力B类节点却略大一些,但二者相差不大,均满足结构抗震设计的要求。文章还分析了节点域的剪切变形,给出了改造节点设计的几点建议。     

Post-fire bond between the steel tube and concrete in concrete-filled steel tubular columns

Push-out tests were carried out on 64 concrete-filled steel tubular columns, which had been exposed to ISO 834 standard fire for 90 min or 180 min, respectively. At the same time, 12 unheated specimens were also prepared and tested for comparison. The variables investigated in the bond tests were selected as (a) fire exposure time; (b) cross-section type; (c) cross-sectional dimension; (d) interface length to diameter (or width) ratio; (e) concrete type; (f) fly ash type; and (g) concrete curing condition. The effects of the above different parameters on the bond behaviour are discussed. The test results indicate that fire exposure had a significant effect on the bond between a steel tube and its concrete core. A decrease in bond strength was generally observed for specimens after a fire exposure of 90 min; however, bond strength recovery was found when the fire exposure time was extended to 180 min. Other factors also had influence to some extent.     

火灾作用后钢管混凝土柱-钢梁节点滞回性能试验研究

进行了外加强环板型钢管混凝土柱-钢梁节点在恒定轴压力和水平往复荷载作用下的滞回性能试验研究,考察了试验参数,如柱截面形式(圆形和方形截面)、受火时间、梁柱线刚度比和轴压比等对该类节点的延性和耗能指标的影响规律,并对该类节点火灾后的节点刚性和节点域剪切变形性能进行了分析。试验结果表明,本次试验的节点层间位移延性系数μ=2.723~7.856,弹性极限层间位移角θy=1.64[θe]~4.39[θe],弹塑性极限层间位移角θu=1.15[θp]~3.06[θp],等效粘滞阻尼系数ξeq=0.2266~0.3358,故可认为,本文试验参数范围内的该类节点试件都具有良好的抗震性能;此外,火灾后该类节点仍可视为刚性节点,且可不计节点域剪切变形对结构变形的影响。     

Behaviour of concrete-filled steel tubular members subjected to shear and constant axial compression

Concrete-filled steel tubes (CFST) are used extensively in modern civil engineering. In many cases, they are often subjected to shear and constant axial compression, particularly when being used in high-rise buildings. ABAQUS Programming is used in this paper for the analysis of CFST subjected to shear and constant axial compression. A comparison of results calculated using this model shows good agreement with test results in general. The theoretical model was used to investigate the influence of important parameters that determine the ultimate shearing strength of the composite members. The parametric studies provide information for the development of formulae to calculate the ultimate strength of CFST members subjected to shear and constant axial compression.     

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.     

钢管混凝土异形柱与U形钢-混凝土组合梁穿心式连接抗震性能试验研究

为研究异形钢管混凝土柱与U形钢-混凝土组合梁穿心式连接的破坏特征和抗震性能,进行了3个足尺边节点试件低周反复循环加载试验,试验参数为节点域构造和轴压比,考察了试件的受力过程及破坏特征,分析了节点的荷载-位移滞回曲线、承载力、刚度和强度退化性能、耗能能力以及延性等力学指标。研究表明：该类型连接的典型破坏形态为节点域钢管柱壁鼓屈、节点域连接槽钢拉裂和组合楼板压溃;试件的滞回曲线较饱满;3个试件的层间位移延性系数μ为1.43~2.02,弹性层间位移角θy为1/62~1/48,弹塑性层间位移角θu为1/39~1/30,等效黏滞阻尼系数ξeq为0.140~0.170,节点的变形能力较好,也具有一定耗能能力;梁底布置贯穿节点域的钢筋能提高节点正向的承载力和刚度;提高轴压比可以提高该类型节点的耗能能力。     

A numerical investigation on the behaviour of concrete-filled steel tubular columns under initial stresses

In the practical construction of concrete-filled steel tubular (CFST) structures, the steel tubes usually have already had some initial stresses before they work together with the core-concrete. The initial stress should affect the behaviour of the whole member. In this paper, a comprehensive numerical investigation is presented on the behaviour of CFST columns under initial stresses by the non-linear finite element method. The investigation includes several parametrical studies such as initial stress ratio, slenderness ratio, eccentricity ratio, etc. Numerical analysis results are verified with published experimental ones. Recommendations on how to consider the effect in design formulae are also suggested.