Experimental investigation of axially loaded steel fiber reinforced high strength concrete-filled steel tube columns

An experimental study on the compressive behavior of steel fiber reinforced concrete-filled steel tube columns is presented. Specimens were tested to investigate the effects of the concrete strength, the thickness of steel tube and the steel fiber volume fraction on the ultimate strength and the ductility. The experimental results indicate that the addition of steel fibers in concrete can significantly improve the ductility and the energy dissipation capacity of the concrete-filled steel tube columns and delay the local buckling of the steel tube, but has no obvious effect on the failure mode. It has also been found that the addition of steel fibers is a more effective method than using thicker steel tube in enhancing the ductility, and more advantageous in the case of higher strength concrete. An analytical model to estimate the load capacity is proposed for steel tube columns filled with both plain concrete and steel fiber reinforced concrete. The predicted results are in good agreement with the experimental ones obtained in this work and literatures.

Seismic ductility of very-high-strength-concrete short columns subject to combined axial loading and cyclic lateral loading

The seismic ductility of reinforced very-high-strength-concrete (VHSC) short columns was studied by combinatively applying axial load and low cyclic lateral load on specimens to simulate seismic impact. Twelve specimens with concrete compressive strength ranging from 95.6 MPa to 118.6 MPa and a shear-span ratio of 2.0 were tested for shear failure pattern and fear force-displacement hysteretic responses. Combinative application of axial load and low cyclic lateral load to VHSC short columns incurs shear failure. The displacement ductility is much smaller when the axial load ratio is larger;whereas a larger stirrup ratio is accompanied with a better displacement ductility. The relationship of displacement ductility factor, μ?, with stirrup characteristic value, λv, and test axial load ratio, nt, is μ?=(1+8λv)/(0.33+nt). By this relationship and relevant codes for aseismatic design, the axial load ratio limits for aseismatic design of reinforced VHSC (C95 to C100) short columns for frame construction are respectively 0.5, 0.6, and 0.7 for seismic classes I, II, and Ⅲ;corresponding minimum characteristic values of stirrups are calculated according to the required characteristic values of at least 1.273 times of experimental results. These data are very useful to aseismatic engineering.

Estimation of Axial Pile Bearing Capacity According to Shear Strength Parameters of Soil

At pesent, it is very popular to estimate pile bearing capacity by use of empirical formula and physical indexes of soil provided in the design codes for civil construction in China. This paper attempts to apply mechanical indexes of soil and semi-empirical formulas, which are based on soil mechanical theories and were summarized and presented by Meyerhof in 1976, to calculate the axial pile bearing capacity. Loading test results of 24 single piles in Tianjin area have been collected and compared with the proposed calulation approach.

航空液压管路轴向挤压式接头组件连接强度的数值分析

针对目前航空液压管接头无法满足高工作压力要求的问题,以Φ12 mm的钛合金轴向挤压式接头为研究对象,利用Abaqus平台建立了轴向挤压连接成形与拉脱试验过程的有限元模型,通过同参数条件下的拉脱试验验证了有限元模型的准确性。结果表明,有限元模型计算误差仅为3.4%,接头组件连接强度是由导管与管套凹槽的轴向对抗阻力和导管与管套径向接触力共同决定的。系统研究了管套材料力学性能、凹槽结构、摩擦因数对接头组件连接强度的影响规律,管套材料屈服强度越高,连接强度越强;管套凹槽宽度每增长0.2 mm,连接强度提高约2.4%;摩擦因数每增加0.01,接头连接强度平均提升18%左右。

再生粗骨料取代率及粒径对混凝土抗压性能影响试验研究

为研究单轴受压情况下再生粗骨料粒径范围、取代率对再生混凝土抗压性能的影响规律,分别以粒径范围5~10、10~20和20~31.5 mm,以及取代率分别为0%、10%、30%和50%为参量设计制作再生混凝土棱柱体试件,并对其开展单轴抗压性能试验研究。结果表明:在取代率相同时,粒径范围为5~10 mm时再生混凝土的抗压强度及峰值应变均比粒径范围为10~20、20~31.5 mm时的大;在粒径范围相同情况下,随取代率增大,再生混凝土抗压强度呈现出逐渐减小的变化趋势,而峰值应变则呈现出逐渐增大的变化趋势。根据试验数据,得出了再生混凝土抗压强度和峰值应变的函数关系式。

内置工字型CFRP型材高强圆钢管高强混凝土轴压短柱组合效应分析

目的 研究内置工字型CFRP型材的高强圆钢管高强混凝土短柱在轴心压力作用下三种材料的组合效应。方法 采用有限元分析软件ABAQUS对其进行数值模拟,通过相关试验验证模型的准确性,并对典型构件的破坏形态、受力全过程曲线进行分析,揭示构件各组成部分之间的相互作用和工作机理,评估CFRP配置率、钢材屈服强度、混凝土抗压强度、约束效应系数对组合效应的影响。结果 在高强圆钢管高强混凝土柱中内置CFRP型材,对构件的延性及安全裕度有显著提高,并改善了高强圆钢管对高强混凝土的约束,提高了构件的组合效应。结论 CFRP配置率控制在5.9%~8.4%,约束效应系数在1.2~1.4,钢材屈服强度不大于770 MPa时,构件中三种材料组合效应最佳。

仿木材料抗拉强度与应力-应变曲线试验研究

仿木材料是以氯氧镁水泥为基体,植物纤维为增强体,并添加柠檬酸、酒石酸、六偏磷酸钠搅拌均匀后经高压静置固化成型的无机胶凝材料,为研究其抗拉强度和抗拉本构关系,制作了30个试件进行轴心受拉试验,共采集到22个试件的有效数据。结果表明:仿木材料的轴心抗拉强度为7.98 MPa,变异系数为0.121,抗拉弹性模量为3600 MPa,变异系数为0.089,轴心拉力作用下,材料达到峰值应力后应力迅速下降,试件脆性破坏;根据应力、应变测试结果,拟合得到了材料的轴心抗拉本构关系,可供材料非弹性应用时参考。

足尺拼接式方形高强钢管混凝土柱轴压承载力数值分析

对两种不同的新型拼接式方形高强钢管混凝土足尺柱的轴压承载性能进行了数值模拟,分析了混凝土强度、钢材强度、缀材间距和宽厚比对该类组合柱轴压承载力及荷载–位移曲线的影响规律,研究表明:同种参数影响下两种形式的组合柱荷载–位移曲线及承载力变化规律相似;材料强度和宽厚比对承载力影较为显著,如钢材屈服强度从345 MPa提升至460 MPa时,两种组合柱承载力分别提高了9.13%和9.42%,宽厚比从83.3增大至100时,两类柱子承载力分别降低了5.08%和5.00%;可初步采用GB 50936—2014《钢管混凝土结构技术规范》计算该类新型柱的轴压承载力。

饱和珊瑚砂液化特性动三轴试验研究

为调查饱和珊瑚砂液化相关特性与发展规律,针对饱和Chibishi珊瑚砂,开展一系列不排水循环三轴试验,研究相对密度D r和循环应力比CSR对饱和Chibishi珊瑚砂的超孔隙水压力Δu、轴向应变εa及动强度特性的影响,并分析不同地区珊瑚砂抗液化强度的差异性。结果表明,饱和Chibishi珊瑚砂的Δu发展模式根据不同的CSR水平可以分为前期均匀增长型、前期突增型和后期突增型;此外,采用一种新的孔压模型对前期均匀增长型、前期突增型的孔压比r u进行表征,Chibishi珊瑚砂在相同的D r条件下,双幅应变εDA达到5%的循环次数N随着CSR水平的增加而逐渐减小;各珊瑚砂在同一里氏震级对应的等效循环振动次数下,抗液化强度CRR的增长模式存在显著差异。研究结果可丰富对珊瑚砂液化特征的认知,同时对近岸和沿海工程的抗震设计提供参考依据。

火灾后高强钢管混凝土柱轴压的参数化分析

为研究不同参数对火灾后高强钢管混凝土柱受轴压时的性能影响,利用ABAQUS有限元软件模拟火灾后高强钢管混凝土柱轴压模型,对该构件以钢管屈服强度、受火时间、混凝土强度为主要参数进行承载力-位移曲线分析,并剖析火灾后高强钢管混凝土柱典型曲线。结果表明:随着钢管屈服强度和混凝土强度增大,构件极限承载力增大;随着受火时间增加构件极限承载力出现下降趋势;从整体上看,受火时间分别为60、90、120 min时,构件中的混凝土承担主要载荷。

基于超声多尺度衰减的螺栓轴向应力评价

针对超声波传统衰减法测量高强度短螺栓应-力时,难以达到预期精度,提出了一种基于超声散射衰减理论和小波多尺度分解的测量螺栓应力的方法。基于立方晶系材料的瑞利散射,推导了超声衰减系数与应力关系的理论模型。利用小波变换得到各个尺度的衰减系数并定义加权超声多尺度衰减系数,结合粒子群优化算法和灰色关联分析确定衰减系数最优尺度组合及其归一化权重系数,建立轴向应力的超声多尺度衰减测量模型。利用搭建的螺栓轴向应力超声波测量系统,对普通螺栓进行轴向应力测量,证明了该方法的可行性。对比了多尺度衰减法与渡越时间和传统衰减法对高强度短螺栓轴向应力的测量结果,验证了多尺度超声衰减法更适合高强度短螺栓的轴向应力测量。

玄武岩纤维混凝土的力学性能研究

玄武岩纤维作为一种高质量、经济、环保的最新科技纤维,被视为碳纤维、玻璃纤维和聚丙烯纤维等技术纤维的理想替代产品。尽管针对玄武岩纤维混凝土(BFRC)的力学属性的研究在全球范围内数量众多,但研究结果并未达成统一的共识。文章在审视BFRC现行的研究情况后,系统性地实验分析了BFRC的力学属性,并尝试通过调整玄武岩纤维的添加量来研究纤维对混凝土立方抗压强度和轴向抗压强度的影响规律。

考虑附加弯矩后的大直径螺栓承载能力研究

为获得大直径螺栓典型连接结构的承载特性,在有限元分析的基础上开展地面试验研究,获得大直径螺栓的轴力与附加弯矩,揭示其破坏机理。分析及试验结果表明,附加弯矩是影响大直径螺栓承载能力的重要因素,考虑附加弯矩后,等效轴力是原始轴力的数倍。提出了考虑附加弯矩影响后的大直径螺栓强度计算公式,提高了预示精度。此外,开展了降低大直径螺栓附加弯矩的方法研究,指出了结构优化方向。

高强螺旋筋约束普通混凝土柱轴压性能试验

为研究高强螺旋筋约束普通混凝土柱的轴压性能,以螺旋筋强度和螺旋筋配箍率为变化参数,制作了5个试件并进行了轴心受压试验。通过试验观测试件破坏全过程和最终失效模式,获取荷载-位移曲线和荷载-应变曲线,并对变化参数对约束混凝土力学性能指标的影响规律进行分析。试验结果表明:螺旋筋能提供较强约束作用,使得混凝土由脆性破坏转变为延性破坏;提高螺旋筋的配箍率能小幅提高螺旋筋的约束作用,当螺旋筋配箍率从1.89%提高到3.02%时,轴压承载力提高幅度为18%~38%,核心约束混凝土强度与非约束混凝土强度之比为1.8~3.8;提高螺旋筋强度能显著提高螺旋筋的约束作用,当螺旋筋强度从432 MPa提高到1 774 MPa时,核心约束混凝土强度与非约束混凝土强度之比从1.9提高到3.3,峰值位移增大约2.7倍。

高强度螺栓轴力与扭矩关系线性回归分析及不确定度评定

高强度螺栓广泛应用于各类高压罐体中,为了量化装配过程中的检验标准,建立高强度螺栓扭矩与轴力的对应关系模型。基于高强度螺栓轴力-扭矩实验,采用一元线性回归分析方法,建立高强度螺栓拧紧扭矩与轴力的理论关系模型;并采用剩余标准差对线性回归模型的斜率和截距进行不确定度评定。结果表明,模型计算的回归结果与实验结果的误差在±7%以内,螺栓轴力的剩余标准偏差与平均值的相对百分比小于3%,线性回归方程可以准确预测高强度螺栓扭矩与轴力的之间关系,不确定度分析可准确获取各参数的置信区间。研究对提升高强度螺栓的装配质量和连接性能,有一定的理论意义和应用价值。

HRB500钢筋轻骨料混凝土柱轴压承载力试验研究及可靠度分析

为了研究高强钢筋页岩陶粒混凝土轴压柱的承载力,制作了8根试件,研究了配筋率、配箍率、混凝土强度等对其承载力和破坏形态的影响。此外,得到了相关文献的有关统计参数,采用JC法,并利用Matlab软件编程迭代求解高强钢筋页岩陶粒混凝土轴压柱的可靠度指标。结果表明:在其他设计参数相同前提下,轴压柱的可靠度指标随着配筋率、配箍率、稳定系数以及截面面积的增大而增大,随着荷载效应比的增大而降低;JGJ/T 12—2019《轻骨料混凝土应用技术标准》中的轴心受压承载力计算公式可以满足GB 50068—2018《建筑结构可靠性设计统一标准》中的可靠指标要求。

多轮次蒸汽吞吐水平井套管射孔参数优选方法研究

针对多轮次蒸汽吞吐水平井在确保套管安全寿命前提下,有利实现储层产能最大化释放的套管射孔参数优选问题,开展了射孔参数对产能影响和对套管安全性影响研究,建立了水平套管井表皮因子计算模型及产能预测模型。在此基础上提出了在满足储层产能最大化释放的射孔参数范围内,结合套管安全性校核结果优选射孔参数的方法。通过该方法设计的渤海某稠油油田的射孔参数可知,该井目前已完成超3轮次蒸汽吞吐过程,产能达到配产的同时,套管处于安全服役的状态。该方法可为多轮次蒸汽吞吐水平井套管射孔参数优选提供依据。

Behavior and design method of square-tubed reinforced concrete short columns under axial compression

The behavior of square-tubed reinforced concrete (STRC) short columns subjected to axial compression was studied in detail with an accurate nonlinear finite element model (FEM) . Different width to thickness ratios (D/t = 50 150) of the steel tube and the compressive strength of concrete (C80 and C50) were adopted in this research. The axial load strength,steel tube strain and load-shortening response were determined from FEM and the analysis results from FEM were compared with those from experiment. The analysis and test results indicate that the concrete strength little affectes the confinement of the steel tube on the concrete. The transverse stress of the tube at the axial load point increases with the increment in the width to thickness ratio. Based on the results from FEM and experiment,a formula for the prediction of the axial load strength was proposed in this paper.

Effect of Process Parameters on Tensile Strength of Friction Stir Welded Cast LM6 Aluminium Alloy Joints

This paper reports the effect of friction stir welding （FSW） process parameters on tensile strength of cast LM6 aluminium alloy. Joints were made by using different combinations of tool rotation speed, welding speed and axial force each at four levels. The quality of weld zone was investigated using macrostructure and microstructure analysis. Tensile strength of the joints were evaluated and correlated with the weld zone hardness and microstructure. The joint fabricated using a rotational speed of 900 r/min, a welding speed of 75 mm/min and an axial force of 3 kN showed superior tensile strength compared with other joints. The tensile strength and microhardness of the welded joints for the optimum conditions were 166 MPa and 64.8 Hv respectively.

Axial Tensile Testing of Single Fibres

The mechanical and damage properties of single fibres used in fibrous composite have gained tremendous importance in recent years. These properties are used in determination of effective properties of composites by micromechanics. These are also used in the micromechanical damage modeling. Further, these properties are used as an indicator of the excellence of product by manufacturers. In the present study the axial tensile modulus, ultimate strength and failure strain of single fibres are determined for carbon and glass fibres. ASTM D3379-75 standard is followed and a number of fibers are tested for statistical analysis. The axial tensile moduli measured are 246.7 GPa and 93.3 GPa, respectively and strength are 3031.6 MPa and 2035.9 MPa, respectively for carbon and glass fibres. Further, the respective axial tensile failure strains are 0.0137 and 0.0224. The error in the measurement of axial modulus is below 8% while for axial tensile strength is below 1%.