方钢管膨胀混凝土短柱偏压极限承载力研究

方钢管膨胀混凝土是一种较为理想的钢管混凝土结构。在偏压试验的基础上,依据现有规程对方钢管膨胀混凝土偏压短柱构件承载力进行研究,并依据极限平衡理论,提出适合方钢管膨胀混凝土短柱偏压极限承载力的计算方法,供工程实践和相关理论研究参考。     

方钢管膨胀混凝土性能实验研究

实验研究了膨胀剂掺量和钢管厚度对不同强度等级方钢管膨胀混凝土力学性能的影响.研究结果表明:在一定膨胀剂掺量条件下,方钢管膨胀混凝土极限承载力比方钢管普通混凝土提高了15%;钢管厚度越大,方钢管膨胀混凝土极限承载力越大.     

钢管微膨胀混凝土界面粘结性能的试验研究

对4根钢管微膨胀混凝土短柱和3根普通钢管混凝土短柱先后进行了收缩/膨胀性能和推出试验的研究。试验结果表明,由于膨胀剂的掺入,核心混凝土在钢管的限制作用下产生了一定的预压应力,膨胀剂掺量和水灰比对钢管微膨胀混凝土的限制膨胀性能有重要影响,核心混凝土中的预压应力能有效提高钢管混凝土短柱的界面粘结强度。根据推出试验结果,分析了粘结破坏的发展过程;给出了试件的荷载—滑移曲线;最后建议了一种新的改善组合结构界面粘结性能的方法。     

钢管混凝土短柱补偿收缩试验研究

为探究钢管混凝土短柱的收缩变形并补偿收缩,进行了2个钢管混凝土短柱收缩试验和5个不同膨胀剂掺量收缩补偿试验研究。试验结果表明,普通钢管混凝土在密封状态下,早期发生膨胀,之后由于水化收缩、徐变收缩及温度收缩等使混凝土发生收缩现象;径向收缩的影响会使钢管对混凝土的紧箍力推迟产生,影响钢管混凝土的力学性能;膨胀剂掺量为12%时,能够完全补偿混凝土的收缩,使核心混凝土与钢管壁紧密结合,且承载力高、变形小,为最佳掺量。     

方钢管高强膨胀混凝土性能实验研究

方形钢管混凝土由于节点构造简便,截面惯性矩大而更适合承受压弯作用,因而具有更优越的综合性能。但与圆形钢管相比,方钢管对核心混凝土的约束效应低。将膨胀混凝土灌入方钢管形成的构件是一种更好的组合结构形式:一方面使混凝土的组织结构更为密实;另一方面使核心混凝土在受荷初期就处于侧向受压的状态,弥补钢管对混凝土紧箍力出现太迟的缺陷。本文通过试验研究了膨胀剂掺量和钢管厚度对方钢管高强膨胀混凝土力学性能的影响,研究结果表明:膨胀剂掺量在一定范围内,方钢管高强膨胀混凝土极限承载力比普通方钢管混凝土可提高15%,钢管壁越厚,其承载力越大。     

内置碳纤维复材圆管直径尺度对方钢管混凝土短柱力学性能的影响

为分析内置不同管径的碳纤维复材(CFRP)圆管对方钢管混凝土(CFSST)短柱轴压力学性能的影响,探索偏压短柱的失效原因,基于短柱轴压与双向偏压试验数据,剖解了双向偏压短柱,并使用ABAQUS软件对短柱进行了有限元计算。在验证有限元模型正确的基础上,计算和分析不同直径的CFRP管对轴压短柱极限承载力的影响,提出了内置CFRP管的方钢管混凝土轴压短柱极限承载力提高度计算式。结果表明:增加CFRP管径尺度可以提高内置CFRP管的方钢管混凝土轴压短柱极限承载力;CFRP管破裂是偏心距较小的内置CFRP管的方钢管混凝土偏压短柱最终失效的直接原因;内置CFRP管的方钢管混凝土短柱极限承载力提高度计算式综合反映了CFRP管径尺度、CFRP约束效应系数、钢管约束效应系数等的影响;增加双向偏压短柱的偏心距,会导致内置CFRP管的方钢管混凝土双向偏压短柱的极限承载力降低;偏心距较大的短柱临近失效时,内核混凝土受压区减小,CFRP管可能不会发生纤维方向的断裂损坏。     

圆钢管微膨胀陶粒混凝土短柱轴压极限承载力计算公式

以陶粒混凝土中的膨胀剂掺量(0、4%、8%、12%)和钢管壁厚(含钢率)为变量,制作了12组(24根)短柱,进行了轴压试验。结果表明:在本试验的膨胀剂掺量范围内,圆钢管微膨胀陶粒混凝土短柱试件的轴压承载力随膨胀剂掺量的增大而逐渐提高;根据试验结果建立了考虑膨胀剂掺量的受圆钢管约束微膨胀陶粒混凝土的强度准则计算公式,进而推导出了考虑膨胀剂掺量的圆钢管微膨胀陶粒混凝土短柱的极限承载力公式。     

再生混凝土收缩补偿及其钢管混凝土轴压短柱试验研究

通过掺入不同掺量的膨胀剂对再生混凝土的干缩变形进行补偿,制成补偿收缩钢管再生混凝土,试验分析不同掺量的膨胀剂对于钢管再生混凝土短柱轴压力学性能的影响。试验结果表明:掺入适量的膨胀剂能够提高再生混凝土的强度和短柱轴压极限荷载,膨胀剂掺量过大则会降低再生混凝土的强度和短柱轴压极限荷载;补偿收缩钢管再生混凝土短柱的钢管与再生混凝土之间相互作用的产生要早于未经收缩补偿钢管再生混凝土;补偿收缩钢管再生混凝土与未经收缩补偿钢管再生混凝土的变形性能较为相似。     

钢管初应力对内配型钢钢管混凝土偏压柱受力性能的影响

本文在以往内配型钢钢管混凝土偏压柱力学性能试验研究、钢管初应力对钢管混凝土偏压柱力学性能影响的试验研究基础上,利用ABAQUS有限元软件,首先建立了内配型钢钢管混凝土偏压柱、考虑钢管初应力的钢管混凝土柱有限元计算模型,数值模拟结果与试验结果吻合良好。进而建立考虑钢管初应力的内配十字形型钢圆钢管混凝土偏压柱受力性能影响模型,详细分析了钢管初应力对其力学性能的影响规律。最后,对影响承载力影响系数kp的参数进行了系统分析。     

钢管高强膨胀混凝土的力学性能研究

配制出了具有良好工作性能和膨胀性能的C50自密实膨胀混凝土,试验研究了该种素混凝土及钢管混凝土的力学性能和膨胀性能。在此基础上,采用有限元方法对钢管膨胀混凝土的自应力性能和极限承载力进行了模拟分析。结果表明,掺加适量膨胀剂的钢管膨胀混凝土具有较优的力学性能,其极限承载力比普通钢管混凝土可提高7%左右。有限元方法能够较好地评估试验结果,为今后分析类似试验提供了依据。     

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.     

方钢管混凝土中钢管和混凝土抗压强度研究

对于方钢管混凝土柱在轴压作用下的受力性能,国内外学者已经进行了大量的试验研究和理论分析,但常规轴压试验无法得到钢管和混凝土各自承担的轴压力。为此,提出了一种在方钢管混凝土柱试件上部设置轴力测量段的试验方法,用于直接测量轴压下方钢管混凝土柱中钢管和混凝土所承担的轴压力。通过对5个不同宽厚比的方钢管混凝土柱试件开展轴压试验,发现方钢管混凝土柱中混凝土的抗压强度与其对应的轴心抗压强度相近。将试验得到的钢管抗压强度与已有经验公式结果进行对比,发现已有经验公式可合理预测钢管的抗压强度,针对钢管的屈曲后行为和其他因素的影响需要展开更深入的研究。在试验结果的基础上,提出了方钢管混凝土柱的轴压承载力计算式,其计算结果与文献试验结果吻合良好。     

A study on the behavior of eccentrically compressed square concrete-filled steel tube columns

In this study the bending moment-axial force-curvature (M-N-Φ) relation for eccentrically compressed square CFT columns is obtained by basic analysis of mechanics which takes into account the effect of residual stress of steel and non-linearity of concrete and steel. This study presents a simplified analytical method for predicting the ultimate strength of eccentrically compressed square concrete filled steel tube (CFT) columns based on the collapse theory. The proposed method can also be used in the prediction of ultimate strength of axially compressed columns with initial imperfections as they are treated as equivalent slightly eccentrically compressed columns. The results obtained by the proposed method agree well with the experiments.     

Experimental investigation of eccentrically loaded fibre reinforced concrete-filled stainless steel tubular columns

This paper presents an experimental investigation of axially and eccentrically loaded plain and fibre reinforced (FR) concrete-filled stainless steel circular tubular columns. The composite columns were pin-ended subjected to axial and eccentric loads. The stainless steel tubes were relatively slender having a diameter-to-plate thickness ratio of 50. The composite columns had different lengths varied from 3D to 12D. The column ultimate loads, load–axial shortening relationships, load–strain relationships, load–mid-height lateral deflection relationships and failure modes of the concrete-filled stainless steel circular tubular columns were measured from the tests. The study has shown that FR concrete-filled stainless steel tubular columns offer a considerable increase in column ductility compared with plain concrete-filled tubular columns. The test ultimate loads were compared with the design ultimate loads calculated using the Eurocode 4 for composite columns. Generally, it has been shown that the EC4 accurately predicted the ultimate loads of axially loaded concrete-filled stainless steel circular tubular columns, but were quite conservative for predicting the ultimate loads of the eccentrically loaded columns. It has also been shown that the conservatism of the EC4 predictions is increased as the eccentricity is increased. The test results provide useful information regarding the behaviour of FR concrete-filled stainless steel columns.     

带肋方钢管混凝土轴压短柱试验研究及有限元分析

以方钢管宽厚比和加劲肋高厚比为主要变化参数,进行了14个带肋方钢管混凝土轴压短柱试验研究;同时采用有限元软件ABAQUS对带肋方钢管混凝土轴压短柱的荷载-变形关系进行了计算,计算结果与试验结果吻合良好。同时从应力-应变关系、核心混凝土和钢管的纵向应力分布及其相互作用等方面对比分析了无肋、单肋和双肋方钢管混凝土轴压短柱的受力性能。分析结果表明：设置加劲肋不仅提高了核心混凝土的纵向应力,而且明显减小了钢管管壁的拉应力区范围,改善了管壁的稳定性;带肋试件的约束作用主要集中在钢管角部和加劲肋处,随着每边加劲肋数量的增加,角部约束力明显增大。图13表1参11     

Nonlinear behavior of concrete-filled stainless steel stiffened slender tube columns

This paper investigates the nonlinear behavior of concrete-filled high strength stainless steel stiffened slender square and rectangular hollow section columns. The stiffened slender tubes had overall depth-to-plate thickness (D/t) ratios ranging 60–160. The concrete strengths covered normal and high-strength concrete. The investigation focused on short axially loaded columns. A nonlinear finite element (FE) model has been developed to study the behavior of the concrete-filled stiffened tube columns. A parametric study was conducted to investigate the effects of cross-section geometry and concrete strength on the behavior and strength of the columns. The results of the concrete-filled stiffened tube columns were compared with the results of the companion concrete-filled unstiffened tube columns. It is shown that the concrete-filled stiffened slender tube columns offer a considerable increase in the column strength and ductility than the concrete-filled unstiffened slender tube columns. The column strengths obtained from the FE analysis were compared with the design strengths calculated using the American specifications and Australian/New Zealand standards. A design equation was proposed for concrete-filled stainless steel stiffened slender tube columns. It is shown that the proposed modified equation provides more accurate design strengths compared to the American and Australian/New Zealand predictions.     

Experimental investigation on concrete-filled stainless steel stiffened tubular stub columns

This paper presents an experimental investigation on concrete-filled normal-strength stainless steel stiffened tubular stub columns using the austenitic stainless steel grade EN 1.4301 (304). The stiffened stainless steel tubes were fabricated by welding four lipped angles or two lipped channels at the lips. Therefore, the stiffeners were formed at the mid-depth of the sections. In total, five hollow columns and ten concrete-filled columns were tested. The longitudinal stiffener of the column plate was formed to avoid shrinkage of the concrete and to behave as a continuous connector between the concrete core and the stainless steel tube. The behavior of the columns was investigated using two different nominal concrete cubic strengths of 30 and 60 MPa. A series of tests was performed to investigate the effects of cross-section shape and concrete strength on the behavior and strength of concrete-filled stainless steel stiffened tubular stub columns. The measured average overall depth-to-width ratios (aspect ratio) varied from 1.0 to 1.8. The depth-to-plate thickness ratio of the tube sections varied from 60 to 90. Different lengths of columns were selected to fix the length-to-depth ratio to a constant value of 3. The concrete-filled stiffened stainless steel tubular columns were subjected to uniform axial compression over the concrete core and the stainless steel tube to force the entire section to undergo the same deformations by blocking action. The column strengths, load–axial strain relationships and failure modes of the columns are presented. Several comparisons were made to evaluate the test results. The results of the experimental study showed that the design rules, as specified in the European specifications and the ASCE, are highly conservative for square and rectangular cold-formed concrete-filled normal-strength stainless steel stiffened stub columns.     

Seismic behavior and modeling of high-strength composite concrete-filled steel tube (CFT) beam–columns

The behavior of square concrete-filled steel tube (CFT) beam–columns made from high-strength materials was investigated experimentally. The effects of the width-to-thickness ratio, yield stress of the steel tube and the axial load level on the stiffness, strength and ductility of high-strength CFT beam–columns were studied. Sixteen three-quarter scale CFT specimens, which included eight monotonic beam–column specimens and eight cyclic beam–column specimens, were tested. The experimental results indicate that cyclic loading does not have a significant influence on the stiffness or strength of CFT beam–columns. However, it causes a more rapid decrease of the post-peak moment resistance. The moment capacity of high-strength CFT beam–columns can be predicted with reasonable accuracy using the American Concrete Institute (ACI) code provisions for composite columns.Fiber-based models were developed for the CFT beam–column specimens. The uniaxial stress–strain curves for the fibers were derived from three-dimensional nonlinear finite element analyses of the CFTs. The results from the fiber analyses of the monotonic and cyclic beam–column specimens compare favorably with the experimental results.     

Column tests of dodecagonal section double skin concrete-filled steel tubes

A series of tests on dodecagonal section double skin concrete-filled steel columns (DCS) were carried out in this study. Column specimens having different lengths ranged from 1000 mm to 3500 mm were tested. The behavior and strengths of dodecagonal section double skin concrete-filled steel columns were investigated. In addition, local bucking of inner and outer steel tubes were also investigated. Material properties of the concrete and steel used in the test specimens were measured. The test strengths are compared with the design strengths calculated using the proposed methods based on current AISC Specification and Eurocode for the design of composite structural members. The suitability of design method proposed by other researcher for circular section double skin concrete-filled steel columns for dodecagonal section specimens was also evaluated.