型钢混凝土节点受力性能及承载能力计算方法比较

对型钢混凝土梁柱节点的受力机理和影响因素进行了分析研究.根据已有的节点试验资料,对YB规程、JGJ规程、我国梁柱节点专题组建议公式、AISC规范以及AIJ规范关于节点抗剪承载力计算公式进行分析比较,结果表明:JB规程直接考虑了轴力的有利作用,计算值与试验值整体吻合较好,但对于轴压比较大的试件以及高强混凝土试件,还需要进一步修正;我国梁柱节点专题组建议公式未对型钢混凝土柱-钢梁节点以及型钢混凝土柱-型钢混凝土梁节点做深入研究,应通过更多的试验数据对其进行修正完善.     

3×35m连续钢-混组合梁桥施工期受力性能的分析

为了解连续钢-混组合梁桥在施工架设过程当中钢主梁顶底板和桥面板钢筋的受力状态,检验设计的合理性,选取(3×35+3×35)m的连续钢板组合梁桥为研究对象,在施工阶段,通过在边跨3L/8位置和墩顶位置布置应力传感器来测量钢主梁顶底板的应力,在墩顶、距墩顶0.15L和边跨3L/8位置埋设应力传感器测量桥面板钢筋应力;并在成桥阶段对该桥进行了荷载试验。建立(3×35+3×35)m连续钢板组合梁桥有限元模型,获取桥梁在不同施工阶段的理论应力值。结果表明:施工阶段墩顶负弯矩钢主梁最大拉应力为91.9MPa,小于理论计算值,边跨桥面板钢筋最大压应力为30.9MPa,大于理论计算值;在等效设计荷载作用下,该桥试验跨的强度和刚度满足设计要求,结构处于弹性工作状态。     

浅谈钢筋混凝土双向受弯构件斜截面承载力计算方法

根据钢筋混凝土受弯构件斜截面的受力特点,破坏形态和影响斜截面受剪承载力的主要目因素性态和影响斜截面受剪承载力的主要目因素;把《混凝土结构设计规范》(GB50010-2010)规范中规定的单向受弯构件正截面承载力计算方法转换成双向受弯构件计算公式,从而简化计算过程。同时,按照规范要求,采用混凝土轴心抗拉强度表达构件的承载力。通过计算比较表明:此计算方法可行,且比较安全。     

中国、美国、欧洲混凝土规范的裂缝宽度计算

运用国内外钢筋混凝土受弯构件的短期裂缝宽度试验资料,从计算方法、计算参数及计算精度3个方面对中国、美国、欧洲混凝土规范的裂缝宽度计算模式进行了比较分析.在此基础上,结合我国规范的裂缝宽度计算模式,提出了钢筋混凝土受弯构件最大裂缝宽度计算的建议公式.结果表明,建议公式计算值与实测值符合得更好.     

不同截面钢管混凝土结构承载力分析

本文对不同截面钢管混凝土受力特点进行分析和比较,重点分析圆形、方形及多边形钢管混凝土柱受力特点。根据工程中不同截面钢管混凝土承载力公式不同,本文对部分理论公式进行简化,提出不同钢管混凝土截面承载力统一公式,公式计算结果与实验值符合良好。     

桥塔刚度对混凝土自锚悬索桥动力特性的影响分析

以国内某混凝土加劲梁自锚悬索桥为研究背景,在总结前人研究成果的基础上,采用Midas Civil程序建立"脊骨梁"式有限元模型,研究结构基础自振特性与桥塔抗弯刚度变化对混凝土加劲主梁自锚悬索桥动力特性的影响。结果表明桥塔顺桥向抗弯刚度对自锚悬索桥的1阶纵向漂移、竖弯振动、横弯振动与扭转振动频率均有影响,但桥塔横向抗弯刚度仅对自锚悬索桥横弯振动频率影响较大。     

T型方钢管相贯节点轴压性能有限元研究与试验验证

利用通用有限元软件ABAQUS对T型方钢管相贯节点进行了建模及非线性有限元计算.将试件的破坏模式、变形过程、极限承载力与试验进行了校核.研究结果表明:试件在轴向压力作用下,发生弦杆相贯面凹陷和侧壁鼓凸的现象;试件在加载全过程具有较强的变形能力;β值越小,试件的应力强化越时显,延性也越小;试件极限承载力随着β值的增大而增大;有限元模拟与试验吻合度较高.     

方支管-H型钢主管T型节点轴压性能数值分析

为研究方支管-H型钢主管平面T型节点的轴压性能,利用有限元软件ABAQUS,对方支管-H型钢主管平面T型节点进行模拟计算,以得到破坏模式和极限承载力.试验结果表明,破坏模式为支管根部屈曲破坏,极限承载力为242 kN,模拟结果和试验结果误差10.5%,有限元能够较好地模拟实验节点,工程中应适当增加支管壁厚以避免支管过快发生屈曲破坏.     

三维多向编织复合材料T型梁抗弯应力分析

针对三维多向编织复合材料结构件承载细观结构优化设计的问题,以三维编织复合材料T型梁为对象,对其抗弯性能进行模拟分析。基于细观结构单胞模型,采用刚度体积平均法计算具有不同编织角的三维四向、五向和六向编织复合材料的弹性常数;利用有限元软件Patran/Nastran计算T型梁承受弯曲载荷的应力与应变,分析纤维束交织结构和细观结构参数对T型梁抗弯性能的影响。结果表明,纤维体积含量一定时,三维六向较三维四向、五向编织复合材料的弹性性能更接近各向同性,同时选择比较大的编织角,可提高T型梁抗弯的承载能力。此方法可为异型三维编织复合材料构件细观结构的选型与参数设计可供参考。     

三维多向编织复合材料T型梁抗弯应力分析

 针对三维多向编织复合材料结构件承载细观结构优化设计的问题,以三维编织复合材料T型梁为对象,对其抗弯性能进行模拟分析。基于细观结构单胞模型,采用刚度体积平均法计算具有不同编织角的三维四向、五向和六向编织复合材料的弹性常数;利用有限元软件Patran/Nastran计算T型梁承受弯曲载荷的应力与应变,分析纤维束交织结构和细观结构参数对T型梁抗弯性能的影响。结果表明,纤维体积含量一定时,三维六向较三维四向、五向编织复合材料的弹性性能更接近各向同性,同时选择比较大的编织角,可提高T型梁抗弯的承载能力。此方法可为异型三维编织复合材料构件细观结构的选型与参数设计可供参考。     

Derivation of the shear strength of continuous beams

The elastic??full plastic loading curve is for all materials sufficient to explain the strength of beams and beam columns loaded by bending and compression. This theory is extended for the influence of shear stress, and it is shown to be the only way to explain the combined bending-shear strength from test results. Also, the in the past derived bearing strength theory is extended here for bracing action. It will be shown for continuous beams as example, that besides moment redistribution by plastic flow in bending, a plastic shear flow mechanism exists that is also able to cause full moment redistribution. The derivations lead to requirements for the design rules and show how the shear stress may reduce the ultimate bending capacity.     

Mechanical performance curves for the strength grading of maritime pine

Finite element models (FEM) were used to simulate beam sections in bending with a knot. They aim at evaluating the mechanical behaviour of timber considering the effect of this singularity on resulting bending strength. By using linear elastic theory and an adapted failure criterion (Tsaï–Hill), an equivalent state can be deduced, giving information about the influence of knot on the load bearing capacity of the element. Several 2D-FEM were then developed using the free software Castem^® by considering plane strain. The beam section was considered like a composite material with two materials; the wood and the knot. The slope of grain around the defect was implemented by using a simple exponential equation parameterized as a function of the radius of the singularity. The location and the size of the defect and the longitudinal modulus of elasticity of wood were investigated in this study. Results exhibit performance curves specific to bending strength. These numerical performance curves were not used to predict the bending strength but to identify some thresholds, function of the size and the location of a critical knot and the stiffness of structural beams. 188 beams with a length of 4.5 m and a cross-section of 200?×?100 mm² were tested to study the efficiency of numerical thresholds. This study shows that it is possible, by identifying only the geometrical properties of the critical defect and the stiffness of the structural beam, to improve the prediction of the bending strength of beams with a large cross-section in Maritime pine up to C40.     

Einfluß der Trägerhöhe auf die Biegefestigkeit von Brettschichtholz

The influence of beam height on the bending strength of glued laminated timber was investigated. Tests showed that with increasing beam height the bending strength decreases for glued laminated timber beams without finger joints (wood failure). Theoretical values confirm calculated values of Eurocode 5. There is not a dependence of strength from the beam height by glued laminated timber beams with finger joints in the outer core. In most cases, glued laminated beams have finger joints in the outer core. Therefore, it is not useful to introduce a height factor in design of glued laminated beams in codes.     

Verifikation von Festigkeitsmodellen für die Brettschichtholz-Biegefestigkeit

The aim of the study was to validate predictive values of new strength models for the characteristic glulam bending strength. Softwood glulam beams were tested in bending. In order to exactly assess the structural and mechanical properties of the laminations used for the production of glulam beams, representative samples were taken from the boards and the finger joints and tested in tension. The experimental investigation was conducted on two different strength levels in order to obtain two independent comparisons between predictive and empirical values. The experimental values of the board and finger joints were used as input data for the strength models to calculate the predictive values of the glulam beams. The predictive values for the characteristic glulam bending strength and the experimental ones differed not more than??6%. This indicates that the new strength models are suitable to reliably determine the characteristic glulam bending strength.     

改性聚乙烯醇纤维增强水泥基复合材料制备及其力学性能

为提高聚乙烯醇(PVA)纤维与水泥基体间的界面强度,采用化学接枝法在PVA纤维表面接枝一层纳米二氧化硅颗粒(SiO₂ NPs),制备改性PVA纤维增强水泥基复合材料(PVA-FRCC)。通过三点弯曲试验测试改性前后PVA-FRCC的抗弯强度,并研究纤维铺排方向和层数对水泥基复合材料抗弯性能的影响。结果表明:纤维交叉铺排时,PVA-FRCC的抗弯强度优于纵向和横向铺排,且改性PVA-FRCC的抗弯强度高于未改性PVA-FRCC的;当纤维铺排层数为3层时,改性PVA-FRCC的抗弯强度最好。对PVA-FRCC的弯曲过程进行有限元模拟分析,含有横向铺排纤维的PVA-FRCC断裂失效时,纤维的桥连作用突显。同时,交叉铺排的PVA-FRCC中除横向铺排的纤维承力外,纵向纤维也有一定的承力,且试样失效后无界面损伤。     

Biegefestigkeit von Brettschichtholzträgern in Abhängigkeit von den festigkeitsrelevanten Einflußgrößen

The reliability of the statistical model of part 1 and of size effect factors of part 2 was verified by bending tests. These tests showed, that more severe visual requirements only partly lead to higher bending strength values of glulam beams. High bearing capicities can only be garanteed with high density and/or MOE of the laminations, because these wood properties control the strength of wood as well as the strength of finger joints. A very good agreement could be stated between calculation results and test results.     

Mechanical properties improvement of silane addition epoxy/3D orthogonal woven composite material

In this study, the influence of silane addition on mechanical properties of epoxy/3D orthogonal glass fiber woven composite was studied. The KH560 silane modification composite specimen reinforced with 3D orthogonal woven fabric/epoxy was manufactured by means of Resin Infusion under Flexible Tooling. The mechanical properties of the epoxy/3D glass fiber woven composites were characterized by tensile and bending tests. The tensile and bending properties of silane-modified 3D orthogonal woven glass composite in warp and weft directions were compared with the pristine or epoxy/glass composite material not coupled using silane. The results show that the tensile and bending properties in warp and weft directions have been improved due to the silane addition. The bonding strength between the fiber and matrix was improved and the delamination and debonding between fiber and matrix was retarded and shifted to cohesive failure of the matrix due to the silane modification. Electron microscopy of the fracture and failure modes of the test specimens were used to support the results and conclusions.     

Einige Holzeigenschaften erkrankter Fichten und Tannen aus Baden-Württemberg,als Ergebnis einer flächendeckenden Erhebung

During investigations of forest disease hitherto, 128 spruce and 127 fit trees from 20 stands in Baden-Württemberg with different degrees of disease have been examined with respect to some wood properties. In addition to tests with small clear specimens the investigation included tests of the bending strength of wooden beams. The test results for bending strength, compression strength parallel to the grain, impact bending and modulus of elasticity do not shown significant differences of mean values and variations as compared to known values of healthy trees. Negative changes in the properties investigated were not found to be dependent upon the degree of disease. No relation was found between nutrition element content of needles, degree of infection with needle fungi, and the degree of disease. In contrast to fir the green sapwood of spruce with more than 70% loss of needles showed a declining moisture content and an increase in moisture content deficit.     

The Tensile and Flexural Properties of Textile Composites

The mechanical properties of thermoset (glass-fibre-reinforced epoxy, polyester, and vinylester) and thermoplastic (glass-fibre-reinforced poly(ethylene terephthalate)) composite laminates manufactured from novel textile fabrics are investigated. The tensile and flexural properties of warp-knitted and woven composites were determined for glass-fibre-reinforced epoxy, polyester, and vinylester. The tensile strength and modulus were slightly lower than expected, mainly owing to fibre misalignment. The flexural failures of the thermoplastic laminates initiated on the compression face, and they were stable and gradual, i.e. a large amount of energy absorption was possible.

Thermoplastic and thermoset box-beams were manufactured by using compression moulding and resin-transfer moulding, respectively. Woven and warp-knitted fabrics, together with braiding, were used for the preforming. The load-bearing capabilities of the beams were tested in three-point bending. Failures initiated at the compression side of the beams, more noticeably so for the thermoplastic beams. The experimental results are compared with those of a finite-element analysis, and the agreement is reasonably good.     

马来酸酐偶联剂对麦秸／废旧聚丙烯复合材料性能的影响

以麦秸和废旧聚丙烯为原料,以马来酸酐作为偶联剂,异氰酸酯(MDI)作为胶黏剂,采用热压工艺压制麦秸/废旧聚丙烯复合材料,通过正交实验研究了偶联剂对该复合材料力学性能的影响。结果表明:单独施用马来酸酐偶联剂,内结合强度极低,静曲强度较低,吸水厚度膨胀率较高,板材性能差;与施用马来酸酐偶联剂相比较,单独施用MDI胶黏剂,内结合强度提高,吸水厚度膨胀率值降低,材料的综合性能好于施用马来酸酐偶联剂的情况,但还不能完全达到刨花板国家标准(GB/T4897.1-4897.7-2003)要求;同时施用马来酸酐偶联剂和MDI胶黏剂时,除密度对内结合强度影响较大外,聚丙烯含量对内结合强度、马来酸酐用量对内结合强度、施胶量对静曲强度和吸水厚度膨胀率均有显著影响,其中马来酸酐用量对内结合强度的影响最为显著。但过多的马来酸酐不但起不到促进作用,反而影响了胶黏剂的胶结性能。