圆钢管混凝土轴压长柱极限承载力的稳定系数法

为完善圆钢管混凝土轴压长柱极限承载力的计算理论,对比分析了中国国家标准GB 50936-2014和CECS 28：2012中轴压短柱极限承载力的N₀计算公式,并把GB 50936-2014中基于套箍系数的N₀计算公式改写成统一的形式,提出了基于正则长细比的轴压长柱的稳定系数计算式,并通过36个试件的对比,对计算式的精度和适用范围进行了分析。研究表明,现行国标GB 50936-2014中基于套箍系数的N₀计算公式更为精确,基于N₀计算公式和本文的稳定系数,可以计算得到更为精确的轴压长柱的极限承载力。     

Axial Bearing Capacity Design Method of Cold-Formed Steel Quadruple-C Built-up Section Members

The finite element model involving geometric large deformation,materials and contact nonlinearity is established.Specimens of cold-formed steel quadruple-C built-up section members are simulated and the finite element models are proved to be valid.Then,numerical analysis on the behavior of specimens with different slenderness ratio and flange flakiness ratio are carried out,and then the axial bearing capacities of specimens are obtained.Based on effective width method and direct strength method (DSM) in related codes,two design methods of cold-formed steel quadruple-C built-up section members under axial compression are proposed:effective length method and correction factor method.It is shown that:the final failure characteristics of all specimens are local buckling and distortional buckling.In the case of not considering the reduction of effective length,the results calculated by each code are slightly lower than those of test and FEM when the slenderness ratio is less than 50,while the results are too conservative when the slenderness ratio is more than 50.     

油菜秸秆灰分混凝土与钢筋之间粘结性能研究

为了探究油菜秸秆灰分的掺入对钢筋-混凝土之间粘结性能的影响。对3种不同油菜秸秆灰分掺量的钢筋-油菜秸秆灰分混凝土试件进行中心拉拔试验,并与钢筋-普通混凝土粘结性能作对比试验。结果表明:钢筋-油菜秸秆灰分混凝土粘结强度与混凝土抗压强度呈正相关。当水胶比一定时,随着油菜秸秆灰分掺量的增加,钢筋-油菜秸秆灰分混凝土的粘结强度降低。水胶比为0.47时的钢筋-油菜秸秆灰分粘结性能与普通混凝土最为接近,为最优配合比。由试验结果可知,在承重要求较低的普通钢筋混凝土结构中,采用适量油菜秸秆灰分等量替代水泥,对于节省水泥生产能源和科学合理利用农业废弃物两方面均具有重要意义。     

方形高强钢管混凝土叠合柱轴压极限承载力分析

对于新提出的方形高强钢管混凝土叠合柱的极限承载力,基于统一强度理论,考虑中间主应力和材料拉压比的影响,引入有效约束系数和非有效约束系数并考虑箍筋对钢管外混凝土约束作用的不同,把钢管外箍筋约束混凝土划分为有效约束区和非有效约束区,将方形截面等效为圆形截面以考虑钢管核心混凝土受到的钢管和外围钢筋混凝土的双重约束效应,提出了方形高强钢管混凝土叠合柱的一种新的轴压极限承载力计算方法。将所得理论计算结果与文献试验结果进行对比,吻合良好,证明了公式的正确性。对各参数的影响规律分析表明,方形高强钢管混凝土叠合柱的承载力随着侧压系数、中间主应力影响系数、材料拉压比和纵向配筋率的增大而增大,随着钢管径厚比的增大而减小。     

Experimental Analysis on Shear Strengthening Capacity of Secondary Dapped end Beams

Because section steel can only be extended to the edge of the support, when a simple support RC beam is reinforced by bonded section steel, a notch comes into being at the end of the beam which is called a secondary dapped end beam, making the stress state of the beam more complex. Through experimental analysis on 21 dapped end beam specimens shear reinforced by steel plate bonded, the deformation process, performing characteristics and failure mechanism of the specimens were investigated. The result shows that two steel bonded forms, including horizontal steel plate and oblique steel plate with angle 45° bonded, delay the appearance of cracks significantly and improve the maximum bearing capacity by 102% and 93%. Due to the impact of stress concentration at the notch, the main modes of damage include concrete tensile or shear failure with the result of bonding failure of a steel plate. By changing the width of steel plates and analyzing different reinforcement effects, formula of bearing capacity of shear reinforcement was proposed based on the method of truss analogue, which provides a reference for engineering application.     

Experimental Study on Shear Strength of High Strength Concrete Columns

On basis of the experiment on sixteen high strength concrete columns, their shear behaviors are analysed. The effects of shear-span ratio and axial compression ratio on failure behavior, cracking shear and shear strength are analysed. The authors have discussed the suitability of the design equations for shear strength in the code. This experimental study on shear strength of high strength concrete frame columns is the first one in this field at home and the results can be served as reference for the code of high strength concrete design.     

Experimental Analysis of Bearing Capacity of Triangle Hollow Flange Beam

On the basis of Hollow Flange Beam (HFB) which is proposed by Australian researchers, a new pattern triangle hollow flange beam (THFB) is presented. According to the experimental test and finite element simulation, the failure processes of THFB and traditional I-beam under concentrated load are compared, and then the obvious differences between the failure modes of these two type beams are founded. The local buckling is easily occurred for the THFB, while overall instability is easily occurred for traditional I-beam, and THFB possesses have better bending performance and twist resistance than those of traditional I-beam. with the experiments, finite element analysis is carried out by FE software ANSYS, and the FE results agree with the test results. Based on FE models, the parameter analysis is carried out for THFB. The parameters mainly include the thickness of top flange, the width of top flange, the thickness of web and the yield strength of steel. The change rule of the bearing capacity of THFB with different parameters can be achieved by parameter analysis. Finally, based on the above results, the applicability of the calculation formula of Eurocode3 to compute the bearing capacity of THFB is discussed. The results show that it is safe and reliable to adopt the calculation formula of Eurocode3 to compute the bearing capacity of THFB, Whilst the estimation is relatively conservative.     

Shear Performance of Steel Plate with Trilateral Constrained

The load carrying test for four steel plate shear walls specimens with various ratio of width thickness are carried out so as to test the failure mode and the shear strength of steel plate with trilateral constrained, and the lateral stiffness and the buckling mode are investigated in the test. The result indicates that the ratio of width thickness of steel plate exerts effects on the shear carrying capacity and failure mode; the buckling of steel plate does not have lateral stiffness. Based on the failure mode of steel plate, the computation model of lateral performance is presented by theoretical analysis. The restraining stiffness of double angle and the buckling restrained stiffness of steel plate are the important design conditions. Formulae to determine the elastic lateral stiffness and the angle type is proposed, which can be used in the preliminary design of steel plate with trilateral constrained.     

Mechanical Model of Steel Plate Composite Shear Walls

Based on concepts of mechanics, a mechanical model of novel type of steel plate composite shear wall is presented. The novel type of structure is formed by steel plate shear wall and T-shaped solid-web composite columns. Flexural stiffness of steel beams, lateral stiffness of the T-shaped solid-web composite columns, shear stiffness of steel plate composite shear wall and shear stiffness of beam-column connection are taken into account in the mechanical model. And the equivalent damping between steel plate and boundary is considered. Based on the deformation features of structures and the calculation hypothesis, the lateral stiffness model and the energy dissipation model of structures are developed. Meanwhile, the calculation equations of elastic ultimate and plastic ultimate of shear strength of structures are set up. The theoretical analysis results inosculate better with the results of experiment. The comparison between the result calculated from the formula and the experimental result shows that the calculation precision is high enough to meet the demand of theoretical analysis. The difference, including equivalent model, stress states, manufacturing defect and installation error, between the formula and the experiment has been further discussed.     

Experimental Investigation of Steel Frames with Infill Prefabricated Reinforce-Concrete Shear Walls

In order to improve seismic performance of steel frame with prefabricated reinforce-concrete infill shear walls (SFCW), the ear bar device was used in the connection between the steel frame and the infill wall. Two one-bay, two story and one-third scaled models of SFCW were tested with low cyclic load. The working performance of ear bar connection, the cracks development in infill walls and deformation performance of SFCW were investigated. And the failure mode, hysteretic behavior,stiffness degradation,deformation and ductility and energy dissipation of composite structure were analyzed. The comparison study of steel frame with prefabricated, cast-in-place and silt reinforce-concrete infill shear walls was carried out. The results show that no failure occurs in the connection between the steel frame and the infill wall because ear plates below and up the beam-to-column connections are added in the specimens, and the connection device of ear plate presents good working performance. The properly designed SFCW has good ductility.     

Experimental analysis of strengthening effect of corroded reinforced concrete beams strengthened with bolted steel plates

In order to study the mechanical behavior of corroded reinforced concrete beams strengthened with bolted steel plates, this paper designed 12 reinforced concrete beams. These beams were corroded by using accelerated electrochemical corrosion method with a designed corrosion ratio of 10%. The pre-compression experiments were performed for all RC beams before strengthening and the maximum crack width was controlled as 0.2 mm. According to the thickness of concrete cover, the beams were divided into 3 groups. Each group was composed of one comparative beam and three tested beams strengthened by steel plates bolted with study according to the thickness of steel plates which were 3 mm, 4 mm and 5 mm, respectively. It was shown that the strain distributions along the height of the strengthened beams at middle-span were in good agreement with the plain section assumption basically. The serviceability performances of corroded RC beams were significantly improved and these ultimate bearing capacities increased obviously. The steel plate bolted with stud effectively reduced the crack width and the extension height of reinforced concrete beams. It was indicated that an increase of steel plates with 35 mm resulted in a decrease of deflection by 13%51% when beams had the same thickness of concrete cover and corrosion ratio. Influence of the thickness of concrete cover on the ultimate bearing capacity was not obvious.     

GBT-based Buckling Loads Formula of Non-linear Thin-walled Compressed Members

A buckling loads formula based on Generalised Beam Theory (GBT) was proposed, which could be used in non-linear elastic metallic materials thin-walled compressed members, such as stainless steel. By introducing non-linear stress-strain relations and instantaneous elastic modulus, the modifications were incorporated in the conventional GBT, and the expressions were formulated to calculate buckling loads of stainless steel members buckling in local, distortional and global modes. Compared with the existed test results, it is shown that linear elastic method cannot deal with stainless steel, while the results of proposed method are much more reliable. Moreover, the modified GBT method with deformation plasticity theories produces safer results, which could be used in determining buckling loads of non-linear metallic materials thin-walled members in compression, as well as structural design and further researches.     

Analysis of the Mechanical Behavior of Gusset Plate to CHS KK joints

A nonlinear finite elements analysis was carried out to investigate the failure modes and the ultimate strength of gusset plate to CHS KK joints. The effects of web loading proportion, geometric parameters and axial stress in chord on the ultimate strength were considered. It was found that the ultimate strength of gusset plate to CHS KK joints was greatly decreased with the increase of web loading proportion when the proportion value was positive; however, the web loading proportion had less effect on the ultimate strength when the proportion value was negative. And with the varying of web loading proportion, the effect of the axial stress in chord on the ultimate strength of KK joints had a complex effect on the joint mechanic behavior. Based on the regression analysis, a formula was proposed for predicting the ultimate strength of gusset plate to CHS KK joints.     

PRACTICAL DESIGN OF PROBABILISTIC LIMIT STATES FOR STEEL STRUCTURES OF TALL BUILDING

For design purposes, this paper presents performance coefficients for steel structures of tall building, and furthermore design values of strength of heavy plates. The calculated results show that suggested coefficients meet the requirements of probabilistic limit states design method. They can serve as a supplement to GBJ17-88 and the expression of limit states design provided in this paper is available for reference in compilation of concerned standard.     

输电钢管塔空间KK型管板连接节点极限承载力

空间KK型管板连接节点作为输电钢管塔中最主要的节点型式,其安全性是整个塔架结构安全的重要保证。相比较于平面K型节点,在考虑实际结构中节点空间效应后的KK型节点的受力性能更为复杂。在平面K型管板节点的试验研究基础上,对两类空间KK型管板节点展开参数化分析,重点讨论了节点几何尺寸参数和主管轴压应力比等因素对节点极限承载力的影响变化规律。结合大量有限元参数分析所得计算结果,并综合考虑各种因素对节点极限承载力的影响,提出了空间KK型管板连接节点在主管管壁局部屈曲破坏模式下的极限承载力建议计算方法。     

Phase Transformation Diffusion Bonding of Titanium Alloy to Stainless Steel

Jointing of titanium alloy and stainless steel is very often in the fields like aviation, chemical plants etc. The combination of materials has the advantages of both titanium alloy and stainless steel and will reduce the consumption of titanium resource. The phase transformation diffusion bonding of TA17 titanium alloy to 0CriSNigTi stainless steel are carried out on Gleeble - 1500D. The effcet of maximum thermal cycle temperature, the tensile strength, the fracture surface and microstruture of the joints are investigated. The results show that TiFe and TiFe2 intermetallics and some solid solutions are formed along the interface, when maximum thermal cycle temperature increase, the area proportion of intermetallics in the fracture surface increase, which are detrimental to the mechanical properties of the transition joints.     

配置600 MPa级高强钢筋T形柱抗震性能试验研究

600 MPa级钢筋是一种新型高强度钢筋,为研究该钢筋应用于异形柱结构体系的可行性,对7根不同轴压比、体积配箍率和钢筋强度的混凝土T形柱试件进行低周往复荷载试验,分别对其承载力、位移、滞回曲线、骨架曲线、刚度退化和耗能性能进行研究,综合评估其抗震性能。研究结果表明：配置600 MPa级钢筋的混凝土T形柱具有良好的变形能力和承载能力,提高配箍率能有效提高试件的抗震性能,提高轴压比可以提高试件的承载力,但降低其变形能力。随着钢筋强度的提高,试件的承载力显著提高。     

混凝土拉压强度尺寸效应的细观非均质机理

为了从材料细观非均质角度揭示混凝土强度尺寸效应机理,建立了混凝土细观单元等效非均质力学模型,开展了立方体抗拉、抗压强度尺寸效应细观数值模拟研究。研究结果表明：混凝土强度尺寸效应根源于材料细观非均质性,随着模型尺寸的增加,混凝土材料细观单元弹性模量变异系数增大,材料细观非均质性增强,大尺寸模型内部存在更多的低强度单元或缺陷,导致混凝土立方体抗拉、抗压强度降低,极限应变减小,脆性增大;混凝土损伤破坏由少量集中区域,发散扩展形成多条非贯通的裂纹带;数值模拟结果与尺寸效应实验数据相吻合。     

Experimental Analysis of Cracking Behavior of ConcreteBeams Reinforced with High Strength Bars

Eight concrete beams reinforced with 500MPa steel bars and four reinforced with 400MPa ultra fine grain steel bars were tested under two point symmetrical concentrated static loading to observe the details of crack pattern development on these beams and investigate their cracking characteristics. It was shown that the cracking behavior of the beams with high strength bars was essentially similar to that of common RC flexural members, whereas the computed crack widths using the formula adopted in the Code for Design of Concrete Structures GB 50010 2002 exceeded that of the experiment under the normal service. Furthermore, the formulas for crack spacing and crack width specified in GB 50010 2002 were evaluated through the experimental results and previous studies of sixty seven concrete beams reinforced with high strength bars. On the basis of the calculation model in GB 50010 2002, revised formulas for crack spacing and crack width were proposed. The values calculated by revised formulas were in good agreement with the test results.     

Experimental Research on Mechanical Behavior of High-strength Concrete Short Columns Confined with Stirrups

Based on the test of high strength concrete (HSC)short columns confined with stirrups 8 under axial loads and 6 under small eccentric loads, the influence of stirrups confinement on stressstrain relationship and related parameter under monoaxial compression are studied, and the effect of the type of stirrups, stirrup ratio, etc. on the HSC columns ductility is analysed. Besides, the strength and deformation behavior of HCS columns under small eccentric compression are explored.Based on the experimental study, the complete stress-strain curves of confined HSC and the formula for calculating the related parameter are presented in this paper.