Seismic performance of recycled concrete-filled square steel tube columns

An experimental study on the seismic performance of recycled concrete-filled square steel tube （RCFST） columns is carried out. Six specimens were designed and tested under constant axial compression and cyclic lateral loading. Two parameters, replacement percentage of recycled coarse aggregate （RCA） and axial compression level, were considered in the test. Based on the experimental data, the hysteretic loops, skeleton curves, ductility, energy dissipation capacity and stiffness degradation of RCFST columns were analyzed. The test results indicate that the failure modes of RCFST columns are the local buckling of the steel tube at the bottom of the columns, and the hysteretic loops are full and their shapes are similar to normal CFST columns. Furthermore, the ductility coefficient of all specimens are close to 3.0, and the equivalent viscous damping coefficient corresponding to the ultimate lateral load ranges from 0.323 to 0.360, which demonstrates that RCFST columns exhibit remarkable seismic performance.

Effect of contact thermal resistance on temperature distributions of concrete-filled steel tubes in fire

To predicate the temperature distribution of concrete-filled steel tubes(CFSTs) being exposure to fire,a finite element analysis model was developed using a finite element package,ANSYS.A suggested value of contact thermal resistance was therefore proposed with the supporting of massive numbers of collected test data.Parametric analysis was conducted subsequently towards the cross-sectional temperature distribution of CFST columns in four-side fire,in which the exposure time,width of the cross section,steel ratio were taken into account with considering contact thermal resistance.It was found that contact thermal resistance has little effect on the overall temperature regulation with the exposure time,the width of cross-section or the change of steel ratio.However,great temperature dropping at the concrete adjacent to the contact interface,and gentle temperature increase at steel tube,exist if considering contact thermal resistance.The results of the study are expected to provide theoretical basis for the fire resistance behavior and design of the CFST columns being exposure to fire.

Reliability analysis of circular concrete-filled steel tube with material and geometrical nonlinearity

Most of the previous research on concrete-filled steel tube is restricted to a deterministic approach. To gain clear insight into the random properties of circular concrete-filled steel tube, reliability analysis is carried out in the present study. To obtain the Structural nonlinear response and ultimate resistance capacity, material and geometrical nonlinear analysis of circular concrete-filled steel tube is performed with a three-dimensional degenerated beam ele- ment. Then we investigate the reliability of concrete-filled steel tube using the first-order reliability method combined with nonlinear finite element analysis. The influences of such parameters as material strength, slenderness, initial geo- metrical imperfection, etc. on the reliability of circular concrete-filled steel tube column are studied. It can be con- cluded that inevitable random fluctuation of those parameters has significant influence on structural reliability, and that stochastic or reliability methods can provide a more rational and subjective evaluation on the safety of CFT structures than a deterministic approach.

Performance Investigation of Square Concrete-filled Steel Tube Columns

The behaviour of square concrete-filled steel tube columns under concentrical loading was studied. More than one hundred specimens were tested to investigate the effects of thickness of steel tube on the load carrying capacity of the concrete-filled tubular columns （CFTs）. The effect of the grade of concrete and content of expansive agent were also investigated. The effect of these parameters on the confinement of the concrete core was studied as well. From the experimental study it was found that for both CFTs with different strength grade concrete core, the ultimate load carrying capacity increases with the increase in percentage of expansive agent up to 20% but it again decreases at 25% of expansive agent content. It was also shown that the failure mode of CFTs depends on the strength grade of concrete core.

Ductility and Ultimate Capacity of Concrete-Filled Lattice Rectangular Steel Tube Columns

A kind of concrete-filled lattice rectangular steel tube(CFLRST)column was put forward.The numerical simulation was modeled to analyze the mechanical characteristic of CFLRST column.By comparing the load-deformation curves from the test results,the rationality and reliability of the finite element model has been confirmed,moreover,the change of the section stiffness and stress in the forcing process and the ultimate bearing capacity of the column were analyzed.Based on the model,the comparison of ultimate bearing capacity and ductility between CFLRST column and reinforced concrete(RC)column were also analyzed.The results of the finite element analysis show that the loading process of CFLRST column consists of elastic stage,yield stage and failure stage.The failure modes are mainly strength failure and failure of elastoplastic instability.CFLRST column has higher bearing capacities in comparison with reinforced concrete columns with the same steel ratio.In addition,the stiffness degeneration of CFLRST column is slower than RC column and CFLRST column has good ductility.

Prediction of Axial Capacity of Concrete-Filled Square Steel Tubes Using Neural Networks

The application of artificial neural network to predict the ultimate bearing capacity of CFST （ concrete-filled square steel tubes） short columns under axial loading is explored. Input parameters consiste of concrete compressive strength, yield strength of steel tube, confinement index, sectional dimension and width-to-thickness ratio. The ultimate bearing capacity is the only output parameter. A multilayer feedforward neural network is used to describe the nonlinear relationships between the input and output variables. Fifty-five experimental data of CFST short columns under axial loading are used to train and test the neural network. A comparison between the neural network model and three parameter models shows that the neural network model possesses good accuracy and could be a practical method for predicting the ultimate strength of axially loaded CFST short columns.

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.

Expansive Performance of Self-stressing and Self-compacting Concrete Confined with Steel Tube

Combining with the technology of self-compacting concrete, self-stressing concrete and concrete-filled steel tube, we can get self-compacting and self-stressing concrete-filled steel tube. In order to study the expansive mechanism of self-stressing concrete, the continuous observation of 47 days on six specimens was carried on. The specimens have different steel area to concrete area ratio. The expansive process in hoop and axial direction were studied, and the expansive mechanism was discussed too. The experimental results identify that the creep and elastic deformation take a large proportion in effective free expansion. The calculating formulas of self-stress in hoop and axial directions were presented here.

THE SHRINKAGE OF EXPANSIVE CONCRETE FILLED STEEL TUBE AND ITS IMPROVEMENT METHOD

The shrinkage characteristics tics of expansive concrete filled steel tube (CFST) are analyzed, Cold shrinkage, creep and autogenous shrinkage are considered as the main reasons of causing CFST contraction. In accordance with the shrinkage characteristics of expansive CFST, a kind of energy-stored delayed expansive agent is exploited, which can not only compensate the shrinkage of the core concrete in every stages, but also make CFST expand according to the delayed expansion mechanism. As the result, the prestress loss weill be reduced and expansive energy will be utilized effectively.

Behavior of High Strength Concrete Filled Square Steel Tube Stub Columns with Inner CFRP Tube Under Biaxial Eccentric Compression

This paper studies the contribution of CFRP(carbon fiber-reinforced polymer)to the mechanical behavior of high strength concrete-filled square steel tube(HCFST)under biaxial eccentric compression.The new type of composite member is composed of an inner CFRP tube and an outer steel tube with concrete filled in the two tubes.The finite element analysis was made by ABAQUS on the behavior of high strength concrete filled square steel tubular columns with inner CFRP circular tube subjected to bi-axial eccentric loading.The results obtained from the finite element analysis were verified with the experimental results.In addition,the load-deflection curves in the whole process were calculated and analyzed,which can be divided into three segments:Elastic phase,plastic phase,descending phase.Based on the load-deflection curves,the stresses analysis on the core concrete,CFRP tube and steel tube were conducted.The confinement effect of the CFRP tube improves the ductility of HCFST-CFRP stub column.CFRP ratio and eccentricity affect the ultimate bearing capacity of HCFST stub column.Finally,a calculation formula of ultimate bearing capacity was proposed in the paper.

膨胀剂和高吸水性树脂对钢壳沉管自密实混凝土体积变形性能的影响

通过对深中通道钢壳沉管自密实混凝土配合比进行优化设计,探讨了膨胀剂、高吸水性树脂对自密实混凝土工作性能和抗压强度的影响,并重点研究膨胀剂、高吸水性树脂对自密实混凝土的早期收缩和长期收缩变形的影响。研究结果表明:掺加适量的膨胀剂、高吸水性树脂均可提升自密实混凝土的工作性能,掺量过大时对混凝土工作性能不利,且抗压强度也随之降低;与掺加膨胀剂相比,掺加高吸水性树脂可更有效改善自密实混凝土的体积稳定性。

外约束作用对钢管内混凝土力学性能的影响

试验研究了掺入不同组成的钙镁复合膨胀剂对管内混凝土工作与力学性能的影响。结果表明,复合膨胀剂中氧化镁比例的增加会降低管内自密实混凝土流动性,而对间隙通过性和抗离析性影响不大。对于掺有复合膨胀剂的管内混凝土而言,相较于不受外约束作用的自由试件,其二维、三维外约束试件不同龄期抗压强度与弹性模量均显著增加。复合膨胀材料中氧化钙比例较高时,这一提升作用更加明显,可作为管内混凝土配合比设计时的安全储备。

An Experimental Study on the Behavior of Square Concrete-Filled High Strength Steel Tube Columns

The paper presents an experimental study on the behavior of square concrete-filled high strength steel tube columns until failure.Four specimens were tested to investigate the effect of high strength steel and plain strength concrete on the load carrying capacity of the square concrete-filled steel tube columns.The effect of the concrete which filled in the steel tube was also investigated.Also,the effect of high strength steel and the presence of concrete were also investigated.The main parameters in the tests were:(1) the ultimate strength of steel (800 Mpa),(2) the presence of concrete in steel tube (hollow steel tube and concrete-filled steel tube),and (3) slender ratio.The main objectives of these tests were three-step:(1) to describe a series of tests on composite columns,(2) to analyze the influence of several parameters,and (3) to compare the accuracy of the predictions by using the specifications in the code (AISC-LRFD,EC4 and AIJ etc.) for the design of high-strength composite columns.Experimental results indicate that the ultimate strength of steel and presence of concrete had significant influence on both the axial compressive load capacity and the ductile of the square steel tube.

基于临界空穴扩张比理论的不锈钢管高温韧性损伤研究

针对不锈钢管在高温塑性加工过程中出现的裂纹缺陷,在Gleeble-3800热模拟试验机上对TP321奥氏体不锈钢光滑棒材进行高温拉断试验,得到了TP321在温度850~1180℃、应变速率0.01~10 s^(-1)下的真应力-真应变曲线和试样拉伸断裂瞬间的等效塑性应变。结合有限元仿真,对试验结果进行了数值模拟,得到了应力三轴度的数值,从而计算出了临界空穴扩张比参数V GC。在此基础上,验证了临界空穴扩张比参数韧性断裂准则在高温下的适用性。发现在特定温度范围内TP321断裂瞬间的V GC与应变速率相关性较小,与温度呈线性关系,并建立了奥氏体不锈钢断裂瞬间的V GC与温度的数学表达式。将得到的V GC准则应用于TP321管坯的不同辊形斜轧穿孔过程中的韧性损伤,对比分析了不同辊形斜轧穿孔仿真结果,发现V GC准则可准确预测缺陷情况。

Experimental Study on Seismic Behavior ofSeismic-damaged Lateral Joints in CompositeFrame Consisting of CFSST Columns and SteelBeams Strengthened with Enclosed ReinforcedConcrete

A new composite strengthening method of seismic-damaged lateral joints in composite frame consisting of Concrete-Filled SquareSteel Tubes （CFSST） columns and steel beams strengthened with enclosed Reinforced Concrete （RC） at the ends of columns andwelding steel plates at the ends of beams was presented. Based on the current design specifications, one half scaled models of 4lateral joints in composite frame consisting of CFSST columns and steel beams were designed and manufactured. One model wasoriginal control specimen, one was strengthened by enclosed RC, and the others were strengthened after pre-damage. The destructiontests under lateral cyclic load on the models were carried. The effectiveness of seismic-damaged joints strengthened with enclosedRC and the reinforcement effect on different levels of seismic damage were studied. The test results show that seismic- damagedjoints in composite frame consisting of CFSST columns and steel beams strengthened with enclosed RC meets the strongcolumn-weak beam joints requirement of seismic design, and the failure modes are of all joints are the bending failure of steel beam.The reinforcement with enclosed RC has a significant on increasing the ultimate capacity and the seismic behaviors of joints. Thestudy indicated the rehabilitated joints recover the level of their original seismic performances before seismic damage in a certainextent damage level. Based on the test data, namely the ultimate capacity, limit displacement, ductility, the energy consumptioncoefficient, limit displacementthe strengthening method of seismic-damaged joints by strengthened with enclosed RC is an effectivemethod for seismic strengthening.

我国特大直径热轧无缝钢管品种和装备的发展历程

简要介绍了我国特大直径热轧无缝钢管品种和装备的发展历程,分析了特大直径热轧无缝钢管的生产工艺特点。认为,挤压管机组可以生产包括碳钢管、合金钢管、不锈钢管、高温合金管和耐蚀合金管等品种,但生产成本高;二辊斜轧管机组可生产碳钢管、合金钢管,且生产效率高,壁厚精度高,但对于高合金钢、不锈钢、高温合金和耐蚀合金钢管的生产存在困难;周期轧管机组比斜轧管机组适应的钢管品种范围更宽,轧制时的变形量更大,但尺寸精度低。提出了各类特大直径热轧无缝钢管生产机组的供坯方案。

高锰钢无缝管膨胀前后组织与性能的对比研究

对热挤压成型的10Mn25Si3Al3高锰钢无缝管进行了15%和25%膨胀试验,对比了管体膨胀前后的拉伸和冲击性能以及微观组织等。结果表明,热挤压成型高锰钢无缝管的组织为均匀细小的奥氏体,屈服强度为340 MPa,屈强比为0.47,伸长率为64%,硬化指数为0.46,半尺寸冲击功为78 J,且壁厚偏差小于5%,表明管材具有较好的均匀变形能力,且低的屈服强度有利于膨胀;经15%和25%膨胀变形,管材屈服强度分别提高了67%和85%,抗拉强度分别提高了19%和27%,但伸长率分别降低至34%和29%,冲击功分别降低至47 J和38 J,膨胀后的力学性能满足API Spec 5CT对N80钢级的要求。

无缝钢管定径机组末架孔型的设计

介绍了一种钢管定径机组末架孔型的设计方法。从实际孔型设计中的数据出发,利用电子表格中的公式计算及函数关系,建立定径孔型设计方程,确定定径末架孔型设计值与钢管实际尺寸的关系,推导出影响定径出口温度的不同因素与定径精轧末架孔型设计值之间的关系,建立出适用的定径末架孔型设计回归方程。用该方法计算出的终轧温度与热膨胀系数与实测值几乎一致,说明该方法适用于现场生产。

铁镍基合金UNS N08810无缝管材的冷扩变形工艺研究

针对UNS N08810铁镍基合金无缝管材,设计了不同的扩模形状和4种不同的冷扩变形工艺。采用有限元分析方法分析了UNS N08810铁镍基合金大直径无缝管材在不同扩模形状、不同扩径量以及不同壁厚参数时的扩孔变形行为,总结出扩孔载荷曲线和扩孔后管材外径与壁厚的变化规律,归纳金属流动的特点。结合模拟试验结果,开展了UNS N08810无缝管材的实际冷扩工艺试验,对模拟结果进行了可靠性验证。