The contribution of steel wallposts to out-of-plane behavior of non-structural masonry walls

For years,non-structural masonry walls have received little attention by code developers and professional engineers.Recently,significant efforts have been made to shed more light on out-of-plane(OOP)behavior of non-structural masonry walls.In updated provisions of the Iranian seismic code,bed joint reinforcements(BJRs)and steel wallposts have been suggested for use.BJRs are horizontal reinforcements;steel wallposts are vertical truss-like elements intended to provide additional OOP restraints for a wall.The contribution of BJRs has previously been investigated by the authors.This study is devoted to investigating the contribution of steel wallposts to the OOP behavior of non-structural masonry walls.Using pre-validated 3D finite element(FE)models,the OOP behavior of 180 non-structural masonry walls with varying configurations and details are investigated.The OOP pressure-displacement curve,ultimate strength,the response modification factor,and the cracking pattern are among the results presented in this study.It is found that steel wallposts,especially those with higher rigidity,can improve the OOP strength of the walls.The contribution of wallposts in the case of shorter length walls and walls with an opening are more pronounced.Results also indicate that masonry walls with wallpost generally have smaller modification factors compared to similar walls without wallpost.

Analysis of Stress Concentration Factors due to in-Plane Bending and out-of-Plane Bending Loads on Tubular TY-Joints of Offshore Structures

The aim of this work is to study the stress distributions and the location of hot spots stress in the vicinity of the intersection lines of the tubular elements of the tubular TY-joints.Using the finite element models,we analyze the effects of geometrical parameters on the stress concentration factor in the case of in-plane bending and out-of-plane bending loads,around the weld toe of the tubular joints.Our results reveal the location of the maximum stress concentration factor at the heel or toe in the case of in-plane bending loads and at the saddle point in the case of out-of-plane bending loads.Six parametric equations are established and used to calculate the stress concentration factor at critical locations using the non-linear regression method.The results obtained from the finite element analysis are close to the results of the parametric equations and the experimental data from the previous work.

OH…O Out-of-Plane Bending Band [γ(OH)] and Its Overtone Band of Dimethylol Propionic Acid(DMPA)

In the present paper are reported the OH…O out-of-plane bending band[γ(OH)] between 900—950 cm -1 of dimethylol propionic acid(DMPA), its dependence upon temperature and its overtone band investigated via FTIR spectroscopy. It has been found based on the crystal structure that the band [γ(OH)] may not certainly be the characteristic band of carboxylic dimers, it can also result from another H-bond formed between carboxylic carbonyl and the primary hydroxyl. In addition, the band [γ(OH)] is very sensitive to temperature change but its overtone band can only appear at a low temperature.

Comparison study on calculation methods of bending behavior of Chinese reinforced concrete beams from 1912 to 1949

In order to study the calculation methods of bending behavior of Chinese reinforced concrete beams from 1912 to 1949, tests on the mechanical performance of 66 rebars from different modem Chinese concrete buildings, the concrete compressive strength of 12 modem Chinese concrete buildings, and the concrete cover thickness of 9 modem Chinese concrete buildings are carried out; and the actual material properties and structural conformations of modem Chinese concrete buildings are obtained. Then, the comparison on calculation methods of bending behavior including the original Chinese calculation method, the present Chinese calculation method, the present American calculation method and the present European calculation method is studied. The results show that the original Chinese calculation method of bending behavior is based on the allowable stress calculation method, and the design safety factors are 3.55 to 4. 0. In term of the calculation area of longitudinal rebars of reinforced concrete beams, without considering earthquake action, the original Chinese structural calculation method is safer than the present Chinese structural calculation method, the present European structural calculation method, and the present American structural calculation method. The results can provide support for the structural safety assessments of modem Chinese reinforced concrete buildings.

Deformation behaviors of 21-6-9 stainless steel tube numerical control bending under different friction conditions

For contact dominated numerical control(NC) bending process of tube, the effect of friction on bending deformation behaviors should be focused on to achieve precision bending forming. A three dimensional(3D) elastic-plastic finite element(FE) model of NC bending process was established under ABAQUS/Explicit platform, and its reliability was validated by the experiment. Then, numerical study on bending deformation behaviors under different frictions between tube and various dies was explored from multiple aspects such as wrinkling, wall thickness change and cross section deformation. The results show that the large friction of wiper die-tube reduces the wrinkling wave ratio η and cross section deformation degree ΔD and increases the wall thinning degree Δt. The large friction of mandrel-tube causes large η, Δt and ΔD, and the onset of wrinkling near clamp die. The large friction of pressure die-tube reduces Δt and ΔD, and the friction on this interface has little effect on η. The large friction of bending die-tube reduces η and ΔD, and the friction on this interface has little effect on Δt. The reasonable friction coefficients on wiper die-tube, mandrel-tube, pressure die-tube and bending die-tube of 21-6-9(0Cr21Ni6Mn9N) stainless steel tube in NC bending are 0.05-0.15, 0.05-0.15, 0.25-0.35 and 0.25-0.35, respectively. The results can provide a guideline for applying the friction conditions to establish the robust bending environment for stable and precise bending deformation of tube bending.

Molecular dynamics analysis on bending mechanical behavior of alumina nanowires at different loading rates

The molecular dynamics(MD)model ofα-Al_(2)O_(3) nanowires in bending is established by using LAMMPS to calculate the atomic stress and strain at different loading rates in order to study the effect of loading rate on the bending mechanical behaviors of theα-Al_(2)O_(3) nanowires.Research results show that the maximum surface stress−rotation angle curves ofα-Al_(2)O_(3) nanowires at different loading rates are all divided into three stages of elastic deformation,plastic deformation and failure,where the elastic limit point can be determined by the curve symmetry during loading and unloading cycle.The loading rate has great influence on the plastic deformation but little on the elastic modulus ofα-Al_(2)O_(3) nanowires.When the loading rate is increased,the plastic deformation stage is shortened and the material is easier to fail in brittle fracture.Therefore,the elastic limit and the strength limit(determined by the direct and indirect MD simulation methods)are closer to each other.The MD simulation result ofα-Al_(2)O_(3) nanowires is verified to be valid by the good agreement with the improved loop test results.The direct MD method becomes an effective way to determine the elastic limit and the strength limit of nanoscale whiskers failed in brittle or ductile fracture at arbitrary loading rate.

INFLUENCE OF COMPRESSION-BENDING COUPLING ON THE STABILITY BEHAVIOR OF ANISOTROPIC LAMINATED PANELS

Dynamic-Relaxation Method (DRM) is applied to studying the influence of compression-bending coupling on nonlinear behavior of cylindrically slightly curved panels of unsymmetric laminated composite materials subjected to uniform uniaxial Compression during loading and unloading. Numerical results are given for cross-ply plates and panels under S4S4 and S4S2 boundary conditions. The results show that the effects of absolute value and the sign of the coupling coefficient on the stability behavior of the panles are significant.

窄幅钢箱-UHPC组合梁负弯矩下抗弯性能试验研究

为改善钢-混凝土组合梁负弯矩下的受力性能,提出一种新型窄幅钢箱-超高性能混凝土(UHPC)组合梁。通过6根试验梁的反向静力加载试验,得到试验梁受力全过程跨中荷载-挠度、荷载-应变、荷载-最大裂缝宽度关系曲线、裂缝发生发展及破坏形态等,基于简化塑性理论推导出了组合梁极限抗弯承载力计算公式。结果表明:窄幅钢箱-UHPC组合梁在负弯矩下具有良好的受力性能;提高配筋率、钢纤维掺量和UHPC相对板厚都可在一定程度上改善组合梁延性,提高其极限抗弯承载力;翼板配筋率对承载力影响较大,配筋率由1%增加至2%时,其极限抗弯承载力提高了15%;钢纤维掺量和UHPC相对板厚对初始开裂荷载影响较大,钢纤维掺量从1%增加到2%时,初始开裂荷载提高32%,UHPC相对板厚由0增加到0.5时,初始开裂荷载提高56%;增加钢纤维掺量和UHPC相对板厚可有效控制裂缝宽度,减少结构主裂缝数量,改善组合梁耐久性;组合梁极限抗弯承载力计算公式计算值与试验值吻合较好,表明塑性理论适用于窄幅钢箱-UHPC组合梁的承载力计算。

柔性立管限弯器高效设计方法

目的考虑聚氨酯材料非线性的影响,建立一种简单高效的柔性立管限弯器设计方法。方法首先确定限弯器的初始尺寸,在此基础上进行参数分析,并根据分析结果绘制设计图谱,然后通过插值获得最佳的设计尺寸。结果针对深水与浅水2种典型环境,分别采用本方法与基于遗传算法的优化设计方法进行限弯器设计,通过结果对比验证了方法的有效性。同时发现,深水环境条件设计出的限弯器相对短粗,而浅水条件设计出的限弯器则较为细长,且考虑材料非线性后,2种环境下限弯器的设计尺寸均有所减小。结论本文建立的限弯器设计方法具有广泛的适用性,且能够在确保得到理想设计方案的前提下,显著提高设计效率。与基于遗传算法的优化设计方法相比,采用线性材料和考虑材料非线性时的设计效率可分别提高约10倍和20倍。

编织碳纤维复合材料加强铝合金帽型薄壁梁动态弯曲特性研究

金属/复合材料混合薄壁结构可同时满足汽车车身抗撞性和轻量化的要求。旨在对比研究不同纤维铺层方式铝/碳纤维复合材料(Aluminum/Carbon Fibre Reinforced Plastic,Al/CFRP)混合帽型薄壁梁的动态弯曲特性。通过三点弯曲试验比较分析各试件的弯曲失效行为与耐撞性能,结合试验结果建立有限元模型且验证其准确性,并进一步分析压头尺寸、压头形状和冲击位置对混合梁弯曲性能的影响。结果表明,铺层角度较铺层顺序对试件弯曲性能影响更大,压头尺寸越大、压头形状越相对扁平或冲击位置越远离中间时可获得较好的耐撞特性。研究所用方法与所得结论可为类似抗弯结构耐撞性设计提供参考。

U型组合再生混凝土-高强混凝土梁抗火性能

为突破单一混凝土材料在受力和抗火两方面的性能难以协同优化的难题,该文创新性地提出U型组合再生混凝土-高强混凝土梁(简称为RAC-HSC组合梁),系统地开展了火灾试验和常温、火后受弯试验,综合分析了不同工况下组合梁的性能表现。研究表明:火灾下,RAC-HSC组合梁的耐火性能显著优于高强混凝土整浇梁,其梁内温度较低,跨中挠度较小,跨中未出现明显裂缝,且未观察到爆裂现象;常温及高温后的受弯试验中,RAC-HSC组合梁的屈服荷载、极限承载力及初始刚度均显著优于再生混凝土梁,基本达到或超过普通混凝土整浇梁和高强混凝土整浇梁的水平。该文所提出的U型组合再生混凝土-高强混凝土梁是混凝土构件“抗火-受力一体化设计”的有益尝试。

不同模具角度下反复弯曲-压平变形工艺对AZ31镁合金板材显微组织演变和变形行为的影响

采用不同角度模具的反复弯曲-压平变形工艺制备AZ31镁合金板材。通过FEM、OM、EBSD和硬度计研究AZ31镁合金在反复弯曲-压平变形过程中的显微组织演变和变形行为。结果表明,150°/150°模具在所有三组实验中都表现出最佳性能。随着道次的增加,合金的等效应变由于剪切和弯曲作用而显著提高。经过4道次后,合金的平均晶粒尺寸显著细化至1.7μm,基面织构被弱化,这是非基面滑移、动态再结晶和孪生引起的;尤其是锥面滑移有利于引发动态再结晶和孪生。合金的硬度值达到HV 77,这是滑移、孪生和动态再结晶竞争产生的显微组织和织构综合作用的结果。

泡沫混凝土-混凝土双层叠合墙板受弯性能研究

泡沫混凝土-混凝土双层叠合墙板具有轻质、保温隔热和强度高等优点,主要应用于建筑物的墙体结构。浇筑了3组12块桁架钢筋结构叠合板,考虑筋材直径和不同类型混凝土受荷面等因素进行抗弯性能试验研究。结果表明:随钢筋直径的增大,泡沫混凝土-混凝土双层叠合板的抗弯性能得到明显改善,但受荷面为混凝土层的叠合墙板抗弯能力较弱,裂缝出现稍早且加载后期挠度较大,设计时应以泡沫混凝土面为受力面并控制裂缝的开展。对叠合墙板极限弯矩计算值与实测值进行比较发现:实测弯矩值远高于理论计算值,现有的规范计算方法不适用于混凝土叠合墙板,但泡沫混凝土板基本能满足工程的需要,可作为轻型承重构件。

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。

中、下承式索支承人行桥动力特性的对比分析

为了研究中承式人行索桥的动力特性与弯扭耦合特征,以某下承式人行索桥为蓝本,在相同设计条件下变化桥面高度,构造了中承式人行索桥模型,采用Midas/Civil软件建立有限元模型,通过自振特性分析并定义弯扭耦合系数,从动力特性的角度对中、下承式人行索桥进行对比分析,并对中承式索桥桥面位置和抗风缆参数对其动力性能的影响进行了研究。结果表明,同等设计条件下,两种桥型均存在横向弯扭振型耦合,中承式耦合程度更大。撑杆高度增大会使扭转主振型延后,频率增大,但各阶竖弯频率和一阶横弯主振型频率减小。随抗风缆矢跨比的增大,结构竖弯和扭转频率略有减小,对称横弯频率增大,反对称横弯频率减小。随抗风缆倾角的增大,结构竖弯、扭转和高阶横弯频率增大,但会降低结构横弯基频。抗风缆矢跨比和倾角的增大均使中承式索桥振型的弯扭耦合程度增强。

Experimental and numerical investigation of mechanical behavior of plain woven CFRP composites subjected to three-point bending

The mechanical behavior of plain woven Carbon Fiber-Reinforced Polymer(CFRP)composites under Three-Point Bending(TPB)is investigated via experimental and numerical approaches.Multiscale models,including microscale,mesoscale and macroscale models,have been developed to characterize the TPB strength and damages.Thereinto,Representative Volume Elements(RVEs)of the microscale and mesoscale structures are established to determine the effective properties of carbon-fiber yarn and CFRP composites,respectively.Aimed at accurately and efficiently predicting the TPB behavior,an Equivalent Cross-Ply Laminate(ECPL)cell is proposed to simplify the inherent woven architecture,and the effective properties of the subcell are computed using a local homogenization approach.The macroscale model of the TPB specimen is constructed by a topology structure of ECPL cells to predict the mechanical behavior.The TPB experiments have been performed to validate the multiscale models.Both the experimental and numerical results reveal that delamination mainly appears in the top and bottom interfaces of the CFRP laminates.And matrix cracking and delamination are identified as the significant damage modes during the TPB process.Finally,the quasi-static and dynamic behaviors of plain woven composites are discussed by comparing the results of Low-Velocity Impact(LVI)and TPB simulations.

基于静态三点弯曲超高强钢硬化行为模型分析

选取HC700/980DHD+Z、 HC780/980CPD+Z和HC700/980DPD+Z进行分析,对比了3种材料力学性能和极限冷弯性能的差异;基于5种硬化模型对材料性能曲线进行拟合,选取两类拟合度较高的模型构建了组合硬化模型,并采用R5缺口拉伸试验进行了验证;基于前防撞梁静态三点弯曲测试和仿真对标分析,对组合硬化模型进行验证,并对3种材料的承载性能进行对比分析。结果表明:HC700/980DHD+Z和HC780/980CPD+Z的极限冷弯角分别为109.8°和109.6°,优于HC700/980DPD+Z;前纵梁静态三点弯曲试验测试与仿真分析中关键参数的最大误差在6%左右,表明材料本构模型的精度较高;HC780/980CPD+Z的承载力峰值最大,达到15.1 k N;HC700/980DHD+Z达到承载力峰值的位移最大,达到52 mm;屈强比对静态承载过程的峰值力产生重要影响,而断后伸长率的增加提升了材料的强塑积和塑性应变变形,使得承载力峰值的位移增大。

行为建模技术(Behavioral Modeling)在零件设计中的应用

为更好地把握设计意图,在Pro/ENGINEER软件中需要人工创建各种"关系",这种"关系"只能向前引用"尺寸参数",如果需要向后引用"尺寸参数"则要应用行为建模技术。行为建模技术通过建立"分析特征"实现优化目标的建立,以尺寸参数或用户自定义参数为变量对优化目标进行优化。本文通过一个轮胎模型,例证了上述方法的应用过程,得出了优化结果。

折弯翼缘剪切型钢板阻尼器力学特性研究分析

针对目前剪切型钢板阻尼器翼缘根部焊缝处容易断裂问题,本文试验模型采用一种折弯结构形式的翼缘,并提出一套适用于折弯翼缘剪切钢板阻尼器的基本性能参数(弹性刚度、屈服荷载、屈服位移)理论计算式;然后通过Abaqus有限元建模,模拟阻尼器单调加载和滞回受力性能,模拟结果显示腹板应力分布均匀,全截面基本屈服,阻尼器整体稳性良好;最后对设计的阻尼器进行足尺试验,包括阻尼器的基本力学和疲劳性能,基本力学试验中滞回曲线面积饱满,且与模拟滞回曲线吻合度高,试验结果表明阻尼器屈服承载力、屈服位移和弹性刚度的计算值、有限元分析值和试验结果基本吻合,最大误差为5.83%;低周疲劳试验结果表明折弯结构有效解决了翼缘端部的断裂失效问题,提高了阻尼器的抗疲劳性能,且疲劳曲线平滑饱满,重合度高,表明其疲劳稳定性好,耗能能力强。

销钉式抗拔管桩接头抗弯性能试验研究

为提高预制混凝土桩的桩间连接质量,研发了一种销钉式机械连接接头。通过销钉式机械连接、销钉式机械连接与焊接连接组合的预制桩桩间接头的抗弯性能试验,对比分析了两种连接方式的受弯承载力、破坏特性与裂缝分布情况。结果表明:两种连接方式的管桩接头试件的开裂弯矩与极限弯矩试验值均大于理论值,满足设计要求;销钉式连接的管桩接头试件破坏形式为销钉受拉脱落,销钉式连接和焊接组合的管桩接头试件破坏形式为接头受压面混凝土破坏;两种连接方式的管桩接头试件在桩身裂缝出现前,各混凝土测点应变呈线性增长,试件跨中截面应变分布基本满足平截面假定。