钢筋混凝土开洞剪力墙极限承载力分析模型的改进

以建立基于抗剪抵抗机构的钢筋混凝土(RC)有开洞剪力墙的极限承载力分析模型为目的,在已有抗剪抵抗机构基础上(文中称之为“M-M”模型)提出改进“M-M”模型,其抗剪机构可简化为:洞口右侧倾角为1θ的斜向混凝土压杆a1、洞口左侧倾角为2θ的斜向混凝土压杆a2、纵向分布钢筋和洞口下方横向分布钢筋4部分.基于“M-M”模型和改进“M-M”模型推导了RC有开洞剪力墙极限承载力计算公式,并编制了计算程序.对23片不同配筋、不同几何尺寸和受力状态的RC有开洞剪力墙进行了2种模型的承载力试验值和计算值的分析比较,分析结果表明,改进“M-M”模型的理论计算结果和实验结果吻合较好,具有较高的计算精度,可以得出改进“M-M”模型能够较好地反映RC有开洞剪力墙的承载力特性,可供RC有开洞剪力墙抗剪强度验算参考.     

轻钢与泡沫混凝土组合墙体抗剪承载力有限元分析

对轻钢与泡沫混凝土组合墙体应用于建筑结构进行推广,对6面组合墙体进行抗剪承载力试验,对其水平荷载峰值、开裂荷载、极限荷载、破坏形态进行测定,建立了轻钢与泡沫混凝土组合墙体ABAQUS有限元计算模型,有限元计算结果与试验结果吻合度较高,该模型可用于轻钢与泡沫混凝土组合墙体抗剪承载力的计算与分析。     

无腹筋BFRP筋玄武岩纤维混凝土深梁抗剪性能试验研究

为研究玄武岩纤维对无腹筋BFRP筋混凝土深梁裂缝开展、破坏形态、跨中挠度、剪切开裂承载力及抗剪极限承载力的影响,以玄武岩纤维体积掺率和纤维长度为参数,设计并制作了5根试验梁,通过四分点集中力加载研究深梁的抗剪性能。结果表明:随着纤维特征参数的增大,构件破坏形态出现由斜压破坏向剪压破坏转变的趋势;与普通混凝土深梁相比,相同荷载作用下,玄武岩纤维混凝土深梁跨中挠度和裂缝宽度均随着纤维特征参数的增大而减小;构件剪切开裂承载力和抗剪极限承载力随着纤维特征参数的增大均有所提高。在考虑玄武岩纤维增强作用的基础上,参照GB 50010—2015规范对玄武岩纤维混凝土深梁抗剪极限承载力进行计算,实测值与计算值基本吻合。     

低周反复荷载下混杂纤维混凝土柱抗剪承载力研究

通过低周反复荷载试验,研究了钢纤维混凝土、钢-聚丙烯混杂纤维混凝土柱的破坏现象、破坏形态,分析了纤维掺量对抗剪承载力的影响规律;利用桁架+拱的模型理论推导了钢纤维混凝土柱在低周反复荷载作用下的抗剪承载力计算公式,并将试验值与理论计算值进行了比较.结果表明:钢纤维混凝土柱呈现弯曲破坏、钢-聚丙烯混杂纤维混凝土柱呈现弯剪破坏;掺量为1.0％、1.5％、2.0％的三种钢纤维混凝土柱的抗剪承载力比基准混凝土分别提高14.10％、19.87％和12.18％;钢纤维掺量为1.0％、1.5％、2.0％,聚丙烯纤维掺量均为0.1％的三种混杂纤维混凝土柱的抗剪承载力比基准混凝土分别提高19.23％、23.72％、16.03％;抗剪承载力试验值与理论推导计算值有较好的一致性和适用性.     

剪跨比对腹板增强复合材料夹层梁受剪性能影响试验研究

对不同剪跨比(a/d)的纤维腹板增强复合材料夹层梁进行四点弯试验,得到其荷载-位移曲线和典型破坏模式,分析了不同剪跨比和纤维腹板厚度对其受剪机理影响规律。结果表明:剪跨比为1的试件承载力最大;随着剪跨比增加,腹板增强夹层梁极限承载力降低,延性性能降低,比强度降低;当夹层梁剪跨比小于3时,试件发生上面板压陷/芯材剪切破坏,当剪跨比大于3时,试件发生上面板受压屈服破坏;对具有相同剪跨比试件,纤维腹板能显著提高其极限承载力和延性性能,厚度越大,极限承载力提高效果越明显。     

格栅剪力键的FRP板与混凝土粘结性能试验研究

针对不同界面连接形式的FRP板与混凝土进行单剪试验,重点研究破坏形式、极限承载力及破坏机理等内容,研究表明:布置单向剪力连接件时,增加连接件数量、减小连接件间距可以提高界面抗剪承载力,也可改善构件弹性阶段整体刚度;提出的双向格栅剪力连接件可明显提高界面整体抗剪承载力,并可增强弹性阶段构件整体刚度。     

CFS加固RC梁正截面承载力的设计计算

基于平截面假定的抗弯承载力计算理论，提出了一种考虑二次受力时的碳纤维预浸料(CFS)加固钢筋混凝土(RC)梁抗弯极限承载力的实用计算方法，该方法理论计算值和实验结果比较吻合，可供工程计算参考。     

改性再生混凝土梁受剪性能试验研究

以不同掺和物为试验参数,对1组取代率为50%的普通RAC梁和3组不同掺和物含量的改性RAC梁进行对比试验,研究在相同剪跨比和配箍率下,不同砖粒、硅粉和混杂纤维含量对RAC梁的破坏形态、纵箍筋应变和受剪承载力的影响.结果表明:改性RAC梁与普通RAC梁的破环过程与形态基本相同,相对来说掺入硅粉对于RAC性能影响不大,而随着砖粒的掺入,抗剪承载力降低,相反,混杂纤维的掺入使RAC梁的抗剪承载力明显提高;最后通过对试验数据对比分析得出,改进的经验回归公式计算出的极限承载力更加适用于改性再生混凝土.     

表层嵌贴CFRP板条加固混凝土梁抗剪性能的研究

为研究采用表层嵌贴法加固后钢筋混凝土梁的抗剪性能,推导加固梁抗剪承载力设计公式。本文基于Abaqus软件,构建表层嵌贴CFRP板条的T型梁模型,研究混凝土强度、配箍率、剪跨比、嵌贴角度、嵌贴间距对加固梁抗剪性能的影响,通过回归得到相关影响因素下的CFRP板条的有效应力表达式,建立表层嵌贴法的加固梁抗剪承载力表达式。研究表明:混凝土强度、剪跨比、板条的嵌贴间距和嵌贴角度对加固梁抗剪性能影响较大,配箍率对加固效果有一定的影响。表层嵌贴法对加固梁的挠度和极限承载力均有提高。将采用本文抗剪承载力表达式计算的结果与相关试验值对比,吻合较好。     

无腹筋BFRP筋混凝土深梁受剪性能研究

在对称集中荷载作用下,对7根无腹筋BFRP筋混凝土深梁进行受剪试验,分析了构件的裂缝发展、破坏形态及不同剪跨比、BFRP筋配筋率、玄武岩纤维体积掺率对构件跨中挠度、开裂荷载和极限荷载的影响。试验结果表明:各试验梁均发生剪切破坏;相同荷载作用下,跨中挠度随着剪跨比的增大而增大,随着配筋率及玄武岩纤维体积掺率的增大而减小;开裂荷载与极限荷载均随着剪跨比的增大而减小,随着配筋率及玄武岩纤维体积掺率的增大而增大。参照相关规范对试验梁抗剪承载力进行计算,研究结果表明美国ACI 440. 1R-06规范计算值与试验值比较吻合,加拿大CSA. S 806-12规范稳定性较好,中国GB 50608—10规范相对保守,建议采用美国ACI440. 1R-06规范对无腹筋BFRP筋混凝土深梁进行抗剪承载力计算。     

Epoxy adhesive shear mechanism on the molecular level

The tensile and shear performances of epoxy adhesive were evaluated both experimentally and using molecular dynamics (MD) simulations to understand the shear mechanism operating at the atomic level. A sandwich structure composed of pure epoxy and two copper layers was established based on the standard stretching mode. This three-layer model was first stretched in the perpendicular direction to examine the dynamic evolution of the epoxy molecules. The epoxy was then adhered onto both smooth and rough copper surfaces to determine their shear strengths. Adhesive failure involving interfacial slippage and slight shear deformation of the epoxy matrix was observed on the smooth copper surface, while the epoxy was strongly bound to the rough surface and fractured under shear stress. MD simulations provided data that are consistent with experimental values. Finally, the shear mechanism was investigated by calculating the interaction energies between the epoxy and copper. This study provides significant insight into the shear-failure mechanisms of epoxy adhered to copper surfaces.     

低模量硅橡胶剪切性能研究

研究了低模量硫化硅橡胶在-40～50℃范围内剪切性能及其与复合材料粘接性能。研究结果表明，低模量硫化硅橡胶室温下的剪切模量稳定区域在剪切应变为80％～220％之间，剪切应变在0～150％区间加载-卸载时硅橡胶剪切滞后损失为34．7％；低模量硫化硅橡胶各在-40℃和50℃下保温2h后，其剪切模量G0与室温下相近，满足-40～50℃温度范围内弹性材料使用要求；低模量硫化硅橡胶在-40℃～50℃范围内与复合材料粘接质量良好。满足粘接技术要求。     

Ultrasonic determination of the effect of shear on lipid crystallization

The design and calibration of a novel rheometer incorporating ultrasonic sensors are described. The instrument is capable of the simultaneous measurements of torque, rate of temperature change, and ultrasonic properties of a liquid as a function of time, temperature, and shear rate. The effect of shear rate on the crystallization onset temperature of a sample of confectionery coating fat is studied using this device. The instrument detected the phase transition in the sheared sample as abrupt changes in all of the measured parameters. The onset temperature increased significantly with shear rate, implying lipid crystallization can be accelerated by mixing. There were also significant differences between sensing modalities.     

Effects of plasticizer on shear modification of polystyrene

The elastic and viscous properties of polymer melts may be affected by the shear history of the polymer. The extrudate swell of a polymer melt is primarily a manifestation of the elasticity of the polymer melt. In this study, a single screw extruder was used to impose different shear histories on a polystyrene polymer which was processed with and without added plasticizer. The extrudate swell and apparent viscosity of these melts were measured with a capillary rheometer. These characteristics of unplasticized polystyrene are almost not affected by the various preshearing processes. However, the extrudate swell and viscosity of polystyrene containing plasticizer are affected by plasticizer level, shear history and thermal history. After most of the plasticizer in the presheared plasticized polystyrene was extracted, the extrudate swell was still lower than that of the parent sheared polystyrene with the same shear history and the same plasticizer content. These results were obtained without significant changes in molecular weight. Shear modification by conventional process equipment may become impractical if the shear field intensity or dwell time of the material in the apparatus is limited. In such cases, shear refinability by standard process equipment may be observed if the coupling density in the polymer is reduced by some additional means, such as blending with a plasticizer.     

Effect of high shear stress on microbial viability

Escherichia coli and Saccharomyces cerevisiae suspensions were submitted to controlled shear stress. Above a threshold value shear stress induced a decrease in micro‐organism viability. The threshold of shear stress efficiency depended on the micro‐organisms, being between 1292 Pa and 2770 Pa for S cerevisiae, and about 1250 Pa for E coli. Above 1810 Pa, E coli cells were disrupted whereas the S cerevisiae cells remained intact. The higher the cellular concentration, the greater the rate of decrease in viability. Viability loss was influenced by the number of passages through the experimental shear stress device and by exposure time. © 2001 Society of Chemical Industry     

用旋转剪切法测量聚合物熔体零切粘度时应注意的几个问题

本文研究了不同测试条件下用旋转剪切法测量聚合物熔体零切粘度值的变化规律,并通过比较旋转剪切法所得数据与蠕变法及动态法数据,得出对于均聚物或均相共混体系零切粘度的测量,旋转剪切法与蠕变法及动态法同样适用。     

The thermodynamics of high shear blending

As a key constituent in many aerosol powder formulations, the properties of inhaled lactose greatly influence the overall performance of the pharmaceutical powder in inhalers. The interparticle forces defining pharmaceutical performance are markedly affected by the energy input during the high shear blending process. By conducting a number of lactose blending experiments in a small-scale pharmaceutical high shear blender, heat generation in lactose during blending was studied and shown to be consistently predictable. Experiments were then conducted in a larger high shear blender to quantify the energy input into powder using an energy balance equation. A set of relations were developed requiring only the powder temperature and jacket water temperature to approximate energy input into lactose at a given impeller speed and blend time in a high shear blending process. Additionally, this study sets out to substantiate the assumptions made in the proposed energy balance model. These experiments could not identify all possible sources of error; however, evidence is presented suggesting that energy input due to impeller shaft heating is negligible. As a result, the set of relations should be applicable for any high shear blender, given a constant blade size and shape. This analysis of powder heating with respect to blending parameters could be applied to tune blending parameters to minimize powder heating and the resulting change in powder properties. These experiments have provided the framework to understand power input in high shear blending for a range of blend parameters.     

Rheology of crosslinked entangled polymers: Shear stiffening in oscillatory shear

Polyborosiloxane (PBS) was synthesized from boric acid and hydroxyl-terminated polydimethylsiloxane (PDMS). The oscillatory shear behavior of PBS formed by PDMS with different molecular weight was studied. The relaxation time of PBS was calculated by Doi-Edwards model. Finally, the shear-stiffening mechanism of reversibly crosslinked entangled polymer was obtained. Shear stiffening occurs at lower shear frequencies, which is mainly due to crosslinking bonds and friction between molecules hindering the movement of molecules. The increase in storage modulus at high frequencies is attributed to the resistance caused by entanglement in the stretching process of molecular chains. In addition, the molecular weight is greater and the degree of shear stiffening is higher. Such a conclusion is useful to further study the application of shear stiffening. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48421.     

不同体系剪切增稠液体的流变行为研究

剪切增稠液体是指其表观粘度随剪切速率增加而变大的一类流体。工业生产中,剪切增稠的出现会阻碍输送管道,破坏生产设备。针对这种情况,人们对如何降低流体粘度造成的不利影响进行了大量研究。另一方面,剪切增稠液体是“液体防弹材料”的关键组成部分,并且在减震、控制方面也具有可观的应用潜力。该文采用原生粒径为50 nm 的SiO2和80～100 nm 的 CaCO3分别作为分散相,聚乙二醇（PEG）200为分散介质,采用超声分散法制备得到不同固含量的剪切增稠液。并通过纳米粒度仪和扫描电镜对分散相粒子团聚情况进行分析;通过应力控制流变仪分别对 SiO2/PEG200和 CaCO3/PEG200悬浮分散体系的稳态流变性能进行分析。结果表明,两种体系试样在测试中均出现剪切增稠现象,并且分散相质量分数越高,剪切增稠效果越明显;而高质量分数的 SiO2/PEG200体系的粘度变化范围更大,增稠现象更为明显。