Axial compressive behavior of Moso Bamboo and its components with respect to fiber-reinforced composite structure

Bamboo is a unique fiber-reinforced bio-composite with fibers embedded into a parenchyma cell matrix.We conducted axial compression tests on bamboo blocks prepared from bottom to top,and from inner to outer portions of the culm.The apparent Young’s modulus and compressive strength of whole thickness bamboo blocks exhibited slight increases with increasing height along the culm,due to slight increases of fiber volume fraction(Vf)from 28.4 to 30.4%.Other blocks showed a significant increase in apparent Young’s modulus and strength from the inner to outer part of the culm wall,mainly owing to a sharp increase of Vf from 17.1 to 59.8%.With a decrease of fiber fraction volume there was a transition from relatively brittle behavior to very ductile behavior in bamboo blocks.Results indicated that stiffness and strength of bamboo was primarily due to fiber in compression,and ductility of bamboo was provided by the parenchyma cell matrix acting as a natural fiber-reinforced composite.

Experimental study on axial compressive behaviors of prefabricated composite thermal insulation walls after single-side fire exposure

The axial bearing capacity of prefabricated composite walls composed of inner and outer concrete wythes,expandable polystyrene(EPS)boards and steel sleeve connectors is investigated.An experimental study on the axial bearing capacity of four prefabricated composite walls after fire treatment is carried out.Two of the prefabricated composite walls are normal-temperature specimens,and the others are treated with fire.The damage modes and crack development are observed,and the axial bearing capacity,lateral deformation of the specimens,and the concrete and reinforcing bar strain are tested.The results show that the ultimate bearing capacity of specimens after a fire is less than that of normal-temperature specimens;when the insulation board thicknesses are 40 mm and 60 mm,the decrease amplitudes are 20.8%and 16.8%,respectively.The maximum lateral deformation of specimens after a fire is greater than that of normal-temperature specimens,and under the same level of load,the lateral deformation increases as the insulation board thickness increases.Moreover,the strain values of the concrete and reinforcing bars of specimens after a fire are greater than those of normal-temperature specimens,and the strain values increase as the thickness of insulation board increases.

In-plane Tensile Behaviors of Bi-axial Warp-Knitted Composites under Quasi-static and High Strain Rate Loading

The in-plane tensile behaviors of bi-axial warp-knitted(BWK) composites under quasi-static and high strain rates loading were experimentally analyzed in this article. The tensile tests were conducted along warp direction( 0°) and weft direction( 90°) at quasi-static rate of 0. 001 s^(-1) and high strain rates ranging from 1 450 to 2 540 s^(-1),respectively. It is found that the significant strain rate sensitivity can be observed in the stress-strain curves of BWK composites. The fracture morphologies of BWK composites demonstrate that the tensile failure modes are shear failure and fiber breakage under the quasi-static testing condition while interface failure and fibers pullout are at high strain rates.

Modeling size-dependent behaviors of axially functionally graded Bernoulli-Euler micro-beam

This work focus on the mechanical behaviors,which are related to the size effect,functionally graded(FG)effect and Poisson effect,of an axially functionally graded(AFG)micro-beam whose elastic modulus varies according to sinusoidal law along its axial direction.The displacement field of the AFG micro-beam is set according to the Bernoulli-Euler beam theory.Employing the modified couple stress theory(MCST),the components of strain,curvature,stress and couple stress are expressed by the second derivative of the deflection of the AFG micro-beam.A size-dependent model related to FG effect and Poisson effect,which includes the formulations of bending stiffness,deflection,normal stress and couple stress,is developed to predict the mechanical behaviors of the AFG microbeam by employing the principle of minimum potential energy.The mechanical behaviors of a simply supported AFG micro-beam are numerically investigated using the developed model for demonstrating the size effects,FG effects and Poisson effects of the AFG micro-beam.Results show that the mechanical behaviors of AFG micro-beams are distinctly size-dependent only when the ratio of micro-beam height to material length-scale parameter is small enough.The FG parameter is an important factor that determines and regulates the size-dependent behaviors of AFG micro-beams.The influences of Poisson’s ratio on the mechanical behaviors of AFG micro-beams are not negligible,and should be also considered in the design and analysis of an AFG micro-beam.This work supplies a theoretical basis and a technical reference for the design and analysis of AFG micro-beams in the related regions.

圆中空夹层不锈钢管水泥砂浆短柱轴压性能研究

海洋工程平台塔架结构中,圆形截面中空双钢管是主要受力构件,工程界十分关注其受压性能和耐腐蚀性能。为研究圆中空夹层不锈钢管水泥砂浆短柱的轴压力学性能,以外不锈钢管壁厚、内碳素钢管直径和是否含夹层水泥砂浆为试验变量,共设计了12个短柱试件。分析各试件的破坏情况、荷载-位移曲线、承载力、变形能力及应变特征,研究不同变量对极限承载力的影响规律。结果表明:试件破坏形态为外钢管端部或中部局部屈曲破坏;随着不锈钢管壁厚的增大,试件的轴压承载力近似呈线性增长;夹层水泥砂浆对试件力学性能影响较大,可有效提高试件承载力,抑制外不锈钢管的变形,提高试件延性;对于含夹层水泥砂浆的试件,承载力随空心率增大而减小,不含夹层水泥砂浆的试件,承载力随空心率增大而增大。根据国内外规范以及相关学者提出的理论公式,计算了试件的极限承载力,并与试验承载力进行了对比分析,给出了设计建议。

矩形中空夹层钢管混凝土叠合长柱轴压性能研究

目的 研究矩形中空夹层钢管混凝土叠合长柱的轴压性能,提出轴压稳定承载力实用计算方法。方法 基于ABAQUS有限元分析软件,建立矩形中空夹层钢管混凝土叠合长柱有限元模型,分析其在不同参数下的工作机理;采用叠加原理并结合现行相关规范,给出适用于矩形中空夹层钢管混凝土叠合长柱的轴压稳定承载力计算公式。结果 矩形中空夹层钢管混凝土叠合长柱的破坏形态表现为在构件的中间位置产生侧向挠曲,最终因丧失稳定而破坏;长细比λ和外围混凝土强度fcu, out是影响叠合长柱轴压峰值荷载的关键参数;当λ由29增加到42和55时,峰值荷载分别降低7.3%和15.3%;当fcu, out由40 MPa提高到60 MPa和80 MPa时,峰值荷载分别提高21.4%和44.8%;轴压承载力简化计算公式与有限元模拟所得结果之比的均值和变异系数分别为0.927和0.017。结论 矩形中空夹层钢管混凝土叠合长柱具有良好的抗压性能和初始刚度,所提出的简化计算公式可为实际工程应用提供计算依据。

SRPE管-混凝土-钢双壁空心短柱轴压性能试验研究

针对西部盐渍土地区钢筋混凝土桥柱的腐蚀问题,提出“SRPE管-混凝土-钢双壁空心柱”。为研究其轴心受压力学性能,设计制作了6根SRPE管-混凝土-钢双壁空心短柱并进行轴压试验,获得了试件的破坏形态和荷载-位移曲线,进而分析了SRPE管压力等级、空心率和钢管径厚比对试件轴心受压力学性能的影响规律。研究结果表明:试件的破坏形态为中下部剪切破坏;试件极限承载力随SRPE管压力等级提高而增大,随空心率和钢管径厚比增大而减小,且空心率影响大于钢管径厚比。最后给出了SRPE管-混凝土-钢双壁空心短柱的轴心受压承载力计算式,计算结果与试验值吻合良好。

金属薄锥壳冲击响应行为及载荷特征研究进展综述

目的系统总结薄锥壳冲击试验方法和数值模拟方法,并分析其响应行为和载荷特征,以发展基于薄锥壳塑性变形的冲击载荷等效加载技术。方法全面调研国内外关于薄锥壳结构冲击响应的工作,总结其冲击试验加载技术和数值模拟方法,主要利用冲击块加速度变化以及载荷-位移曲线对薄锥壳力学响应及能量吸收特性进行表征,并结合弹塑性应力波进行理论分析。结论金属薄锥壳冲击试验加载方法主要有落锤冲击、化爆脉冲加载和气压推动质量块进行撞击等,数值模拟中通常采用刚性板挤压金属壳单元的方法进行验证。除对薄锥壳轴向加载外,还有斜向加载、引入刻槽、泡沫材料填充和复合材料夹层等试验设计。该领域研究仍处于初期发展阶段,今后有必要结合试验测试与数值模拟分析,全面而深入地研究薄锥壳参数变化对其冲击响应行为和载荷特征的影响规律及其物理机制。

双不锈钢管约束海水海砂混凝土柱轴压试验及承载力计算模型

目的 研究双不锈钢管约束海水海砂混凝土柱(DSTSCC)试件的轴压性能、破坏形态和轴压承载力计算模型,为该类构件的轴压承载力计算提供试验和理论研究参考。方法 对24个DSTSCC试件进行轴压试验,分析外管壁厚、芯管壁厚和芯管直径等参数对其破坏形态、应力-应变曲线和承载力的影响规律。结果 双不锈钢管约束试件的破坏形态以腰鼓型破坏为主;由于不锈钢受拉本构无明显的屈服台阶,可以持续地约束核心混凝土,试件应力-应变曲线无明显的下降段,表现出较好的延性特征;随外管壁厚增大,轴压承载力可提高6%~25%;随芯管壁厚增大,轴压承载力可提高3%~20%;随芯管直径增大,轴压承载力呈现为先提高后降低的趋势。结论 基于试验破坏机理分析和理论分析,所建立DSTSCC试件的轴压承载力计算模型相较于既有承载力计算模型,具有更好的适用性。

CFRP-铝合金复合管高强混凝土短柱轴压性能研究

为研究CFRP-铝合金复合管混凝土构件的轴压性能,进行了12根短柱试件的轴向压缩试验,主要研究参数为CFRP层数。试验结果表明:复合管混凝土试件出现了多处外凸鼓曲以及对应位置混凝土被压溃的破坏形态,而空复合管试件发生了局部内凹屈曲破坏;试件轴压承载力随CFRP层数的增加而增大,且复合管混凝土试件的承载力提高幅度高于相应的空复合管试件的提高幅度。对各部分的承载力贡献比例进行分析,发现复合管混凝土试件中混凝土的承载力贡献比例超过70%,且承载力贡献度随CFRP层数的增加而提高。提出了CFRP-铝合金复合管混凝土构件的轴压承载力计算公式。

热-湿-力耦合作用对高温后方钢管混凝土短柱轴压力学性能影响试验研究

火灾发生时钢管混凝土内部会产生水蒸气,为探讨热-湿-力耦合作用对高温后方钢管混凝土轴压力学性能的影响,进行了10根高温后方形钢管混凝土短柱轴压力学性能试验,研究排气孔数量、布置位置、轴压比和升温时间等参数对其破坏形态、轴压刚度与剩余承载力等力学性能的影响。试验结果表明,试件破坏形态表现为压溃破坏;在其他参数相同的情况下,与升温前相比,随着排气孔数量从2个增加至4个和6个,轴压刚度分别降低了69.1%、73.3%、76.4%,剩余承载力分别降低了15.8%、16.2%、21.7%。轴压刚度随轴压比的增大而降低;随着升温时间的延长,剩余承载力先随轴压比的增大而增大,后随轴压比的增大而减小。研究结果可为钢管混凝土柱的抗火设计和该类结构火灾后的损伤评估与加固提供参考。

稀疏波对不同装药圆柱壳体响应行为的影响

为了研究稀疏波对不同装药圆柱壳体响应行为的影响,采用AUTODYN软件研究了不同装药类型、复合装药排布方式及复合装药长度下轴向稀疏波的作用范围、稀疏波对壳体的破碎情况及轴向速度的分布规律。研究结果表明:炸药威力变大,会增加起爆端轴向稀疏波的作用区域,该区域的壳体在轴向上与径向上破碎加剧;增大起爆端装药威力,不增大轴向稀疏波影响的区域,但会加剧起爆端轴向稀疏波区域内的壳体破碎程度及增大破片速度;增大非起爆端装药威力,不影响壳体的破碎程度,但会降低起爆端稀疏波影响区域内的破片速度;当B炸药(Comp.B)装药长度不在起爆端稀疏波影响区域时,壳体会在装药交界处发生断裂。

轴压荷载作用下双钢板-混凝土组合剪力墙中钢板屈曲性能研究

双钢板-混凝土组合剪力墙作为建筑物中的抗侧力构件,具有承载力高、耗能能力强和延性好等优点。在高层和超高层建筑结构中,双钢板-混凝土组合剪力墙需要承担一定的竖向荷载,钢板在正常使用阶段要求不发生弹性屈曲。钢板初始几何缺陷是影响双钢板-混凝土组合剪力墙轴压荷载下钢板屈曲应力的重要指标,而在以往的研究中,钢板屈曲应力的计算方法并未予以考虑。基于前期的双钢板-混凝土组合剪力墙轴压试验研究,采用分析软件ABAQUS建立了双钢板-混凝土组合剪力墙轴压试件有限元模型,模型中引入了钢板的初始几何缺陷,从钢板屈曲应变、荷载-位移曲线和破坏模态等方面与试验结果进行对比,验证了模型分析结果的合理性。在此基础上进行参数分析,系统研究了钢板初始几何缺陷、钢板距厚比和钢材屈服强度等参数对钢板屈曲性能的影响规律,基于试验和数值模拟分析结果,提出了考虑钢板初始几何缺陷影响的双钢板-混凝土组合剪力墙钢板屈曲应力计算方法。

钢筋PVA-ECC柱复合受扭性能试验研究及损伤分析

为研究复合受力状态下钢筋PVA-ECC构件的受扭性能,进行了9根PVA-ECC柱和1根普通混凝土(RC)柱的单调加载试验,考虑不同轴压比、扭弯比、剪跨比、纵筋配筋率和箍筋间距等参数,研究其破坏特征、扭矩-扭率曲线特征,并进行了损伤演变分析。结果表明,PVA-ECC试件受力过程均经历了弹性阶段、弹塑性阶段和破坏阶段;PVA-ECC试件在受扭承载能力和扭转变形方面与RC试件相比有很大提升;降低轴压比、增大扭弯比和剪跨比可有效提高试件的扭转延性,减小箍筋间距和剪跨比、增大轴压比可有效延缓试件开裂;采用PVA-ECC材料能有效抑制试件的损伤发展;剪跨比、纵筋配筋率和箍筋间距对复合受扭作用下试件的损伤有较大影响;纵筋配筋率越大和剪跨比、箍筋间距越小,试件复合受扭的损伤程度越小。

Axial segregation characteristics and size-induced flow behavior of particles in a novel rotary drum with curved sidewalls

Particle mixing and segregation are common phenomena in rotary drums,which are challenging to be controlled and driven artificially in powder technology.In this work,the discrete element method(DEM)was applied to construct the novel rotary drum composed of different shaped curved sidewalls.By varying the operation parameters of particle and sidewall shapes as well as the length-to-diameter(L/D)ratio of drums,the axial mixing and segregation processes of binary size-induced particles were investigated.The results show that the axial flow velocity of the particle mixtures is noticeably weakened once the particle angularity increases,making the non-spherical particles to mix better in rotary drums compared to the spherical particles.Besides,in the short drums with size-induced spherical particles,the axial segregation characteristics are significantly enhanced by the convex sidewalls while suppressed by the concave sidewalls.However,for size-induced non-spherical particles,the axial segregation structure can be present in rotary drums with plane and concave sidewalls while not in drums with convex sidewalls.Moreover,the axial segregation band structure of spherical particles eventually increases proportionally with the increased drum L/D ratios.In contrast,the non-spherical particles cannot form obvious multi-proportional segregation bands.

On the calibration of a shear stress criterion for rock joints to represent the full stress-strain profile

Conventional numerical solutions developed to describe the geomechanical behavior of rock interfaces subjected to differential load emphasize peak and residual shear strengths.The detailed analysis of preand post-peak shear stress-displacement behavior is central to various time-dependent and dynamic rock mechanic problems such as rockbursts and structural instabilities in highly stressed conditions.The complete stress-displacement surface(CSDS)model was developed to describe analytically the pre-and post-peak behavior of rock interfaces under differential loads.Original formulations of the CSDS model required extensive curve-fitting iterations which limited its practical applicability and transparent integration into engineering tools.The present work proposes modifications to the CSDS model aimed at developing a comprehensive and modern calibration protocol to describe the complete shear stressdisplacement behavior of rock interfaces under differential loads.The proposed update to the CSDS model incorporates the concept of mobilized shear strength to enhance the post-peak formulations.Barton’s concepts of joint roughness coefficient(JRC)and joint compressive strength(JCS)are incorporated to facilitate empirical estimations for peak shear stress and normal closure relations.Triaxial/uniaxial compression test and direct shear test results are used to validate the updated model and exemplify the proposed calibration method.The results illustrate that the revised model successfully predicts the post-peak and complete axial stressestrain and shear stressedisplacement curves for rock joints.

新型冷弯薄壁型钢墙体立柱轴压性能研究

为了研究喷涂式轻质砂浆-冷弯薄壁型钢墙体立柱的轴压性能,文章采用有限元分析和真实试验对比测试了立柱间距、立柱壁厚、截面尺寸、钢材强度等级、两侧砂浆厚度、横撑数量、立柱长度等参数对立柱轴压承载力的影响;结合新型墙体立柱的试验特征,构建基于弹性稳定理论的力学模型,采用能量法和变分原理求解新型墙体立柱弹性屈曲荷载,进一步求解极限屈曲应力修正参数,得到新型墙体立柱轴压承载力的计算方法。结果表明:有限元分析的极限荷载、破坏模式、荷载位移曲线与试验结果较为接近;新型墙体立柱轴压承载力受两侧砂浆厚度、立柱间距影响不大,但随立柱高度增大而减小,横撑个数对纯龙骨立柱轴压承载力影响较大,而对新型墙体立柱影响较小;新型墙体立柱轴压承载力计算时,采用中国规范修正弹性屈曲应力并计算有效面积求得的极限荷载值小于试验值,建议按照中国规范计算的轴压承载力可乘以1.25的修正系数。

内置异形箍筋矩形钢管混凝土柱的轴压力学性能

钢管混凝土作为一种发展前景广阔的结构形式,具有较好的承载力和塑性变形能力。矩形钢管混凝土柱作为其中常见的一种形式,在实际工程中的应用较为广泛。该研究基于矩形钢管混凝土在实际应用中存在的长短边约束不一致和对核心混凝土约束不足两个问题,探究一种新型的矩形钢管混凝土构件,即内置异形箍筋矩形钢管混凝土柱。为此,对11根内置异形箍筋矩形钢管混凝土柱、2根内置跑道形箍筋的矩形钢管混凝土柱、2根普通矩形钢管混凝土柱开展了轴压力学性能试验,重点分析了并束距、钢管壁厚、混凝土强度等级、箍筋间距、箍筋直径、内置用钢量等重要参数对内置异形箍筋矩形钢管混凝土柱的轴压承载力和延性的影响规律。结果表明:在总用钢量不变的情况下,将矩形钢管的壁厚减薄,并加工成异形箍筋内置于核心混凝土中,能够有效地提高试件的轴压承载力和延性;内置异形箍筋矩形钢管混凝土柱的轴压过程可以分为4个阶段——弹性阶段、弹塑性阶段、塑性强化段、下降段;相比于普通矩形钢管混凝土柱,内置异形箍筋矩形钢管混凝土柱有更为饱满的塑性强化段。在试验和参数分析结果的基础上,采用已有的约束混凝土本构模型,推导得到内置异形箍筋矩形钢管混凝土柱的轴压承载力计算公式。该研究可为实际工程应用提供科学依据和数据参考。

矩形节理界面对花岗岩—混凝土组合体轴压细观力学行为影响

岩体表面施工时会形成可观的随机不规则节理界面,而界面又是影响岩石—混凝土组合体稳定的关键。基于水平光滑界面的花岗岩—混凝土组合体材料单轴压缩试验,采用颗粒离散元程序PFC2D进行建模与参数标定,考虑不同节理倾角与高宽比的矩形节理界面,利用正交设计方法,开展不规则矩形节理对花岗岩—混凝土组合体轴压力学行为的细观模拟研究。结果表明:随着节理倾角的增加,组合体峰值应力与弹性模量呈现出“V”字的变化趋势,节理倾角的增加对应力—应变曲线有着显著的影响,而角度一定时高宽比的增加会改变同角度时的峰值应力与应变;节理倾角的增加会改变裂隙的数量与分布区域,组合体的最终破坏模式也随着倾角的改变从压缩破坏逐渐转变为剪切滑移破坏,且贯通主裂隙集中在矩形节理的角点处,沿角点处向外扩展导致模型的最终破坏;建立了考虑高宽比、节理倾角的本构方程。

盾构输水隧道C-T快速连接件纵缝受弯特性试验研究

C-T快速连接件纵缝应用于盾构输水隧道时,隧道中的内水压使接缝处轴力减小,进而影响接缝的抗弯性能,但轴力变化对快速连接件纵缝抗弯性能的影响研究还不充分。因此,开展较小轴力正弯矩下C-T快速连接件接缝足尺压弯试验,并将试验结果与既有相同接缝的较大轴力工况试验对比,总结不同轴力下C-T件纵缝压弯力学特性。结果表明:1)较小轴力下,C-T件纵缝的受弯过程可以分为混凝土单独承弯阶段和混凝土连接件共同承弯阶段。单独承弯阶段弯矩首先呈线性增长,之后接缝抗弯刚度不断减小。当C-T件搭接时接缝抗弯刚度增大,之后连接件快速屈服,抗弯刚度不断降低直至连接件断裂接缝破坏。2)较小轴力下,影响接缝抗弯能力的主要因素为C-T件的搭接、屈服及断裂,需要提高C-T件的抗拉性能以防止其过早屈服;较大轴力下,外侧混凝土的搭接和压溃是影响接缝抗弯能力的主要因素点。在不同轴力下连接件周围均出现裂缝。