Role of Nb in 14MnNbq Steel

In order to meet the needs of China-made gigantic bridges with long spans, 14MnNbq steel was developed . It is a new type of microalloyed steel. In this paper, simulated controlled rolling and cooling is taken. The role of microalloyed element Nb and Nb(CN) in the process of deformation and their effects on microstructures and mechanical properties of 14MnNbq steel are analysed by means of optical microscope, TEM, electrical chemical phase extraction analysis and micrography analysis.It is pointed out that in period of non-recrystallization of finish rolling should increase the deformation increment as great as possible to give full play to Nb, The cooling speed after rolling and the temperature of finish cooling should be controlled properly according to working condition to ensure Nb(CN) to separate out adequately. It is proved that Nb possesses good fine-grain strenghening and medium precipitate-hardening effects.     

Hysteretic Behavior of Composite Deep Beam Infilled Steel Frame

The Quasi static tests of one steel frame and two the composite deep beams infilled steel frames were carried out. The effects of the deep beams on the load capacity, ductility, hysteretic property and energy dissipation of pure steel structure were analyzed. It is found that the hysteresis curve is a straight line with the constant of the stiffness at the beginning and without residual deformation. And the hysteresis curve of specimen was full after yielding, and the skeleton curves had a clear plastic flow phase with triple linear. The lateral drifts of the beam specimens at failure were 1/25 and 1/22. The composite deep beams enhance the initial stiffness, yield load and maximum load bearing capacity of steel frame. Therefore, seismic performance of the composite deep beams is better.     

Nonlinear numerical simulation of steel reinforced concrete truss joints

This paper analyzes the steel reinforced concrete large span transfer truss joints using the finite element analysis software ANSYS, and get the joints deformation and the mechanics increase, such as deformation properties, stress distribution. The monitoring results during construction phase show that nonlinear numerical simulation analysis, which is in good agreement with the test results, is an effective method for the mechanical property analysis on this kind of structural components.     

Research on Deformation Equation and Dynamic Properties of Hybrid Structure

Based on the principle of interactive analysis,the deformation equation of hybrid structure which contains rigid character value is established using the analysis of the frame - shear wall structure for reference, considering the rigid zone between concrete beam and concrete - tube, the shear deformation of concrete - tube, axial deformation of steel frames and semi - rigid connection between steel columns and concrete beams. Assuming the hybrid structure to be a continuous elastic structure with infinite degree of freedom, a free vibration equation has been built and the formula for calculating free vibration period has been deduced. The influences of various parameters to the coefficient of free vibration period relating to rigid character value are discussed according to some diagrams. It is shown that the rigid zone can lessen the free vibration period but the shear deformation of concrete - tube, axial deformation of steel frames, and the semi -rigid connection between steel columns and concrete beams can enhance the free vibration period.     

SEPARATION OF THE SECOND PHASE IN STEEL AND DETERMINATION OF SOLIDIFIED VANDIUM

In this paper, the dissolving condition of iron and vandium solidified in iron and the collecting method of the second phase vandium compounds in alloy steel are studied, the existing possibility of spreading phase vandium compounds in steel is discussed, which provide the possible conditions for concentration and electrochemical separation of the second phase vandium compounds. Using this method, quite reliable results in measuring vandium solidified in iron can be obtained.     

A Strain-equivalent Non-local Constitutive Model for Lamellar Dual-Phase Materials

Pearlitic steel is composed of numerous pearlitic colonies with randomly distributed orientations,and each colony is composed of many alternatively arranged parallel lamellas of ferrite and cementite.The pearlitic steel with fine interlamellar spacing possesses excellent mechanical properties,such as high strength,good resistance against wear,and high fatigue life,etc. Based on the inconsistency of the deformation between the two phases,a strain_equivalent and non_local constitutive model is proposed. Using this model,the effect of the interlamellar spacing of peailitic steel,a fundamental parmeter of the microstructure of pearlitic material, on its macroscopic mechanical behavior can be described without changing the local material parameters for each phase of the material.The asymmetrical cyclic plasticity of both the hot_rolled and the off_line full_length quenched pearlitic steel PD3 is analyzed.The comparison between the computational and the experimental results shows satisfactory agreement.     

THE STUDY OF DELAMINATION IN THE STRUCTURAL STEELS

The influence of temperature and stress state on delamination in the pipe-line steel has been studied by tensile tests at different temperature and stress states. It is found that the' delamination always takes place along the centerline segregation band in pipe-line steel produced by continuous casting and then controlled rolling. At room temperature, the delamination appears to be caused by micrbvoid nucleation and coalecence. And the delamination appears to be caused by the cleavage cracking along (100) plane at low temperatur.e. The best way to eliminate the delamination is to reduce the degree of centerline segregation.     

A Treatment to the Isoline for Finite Element Solution to Ferrite-Martensite Microstructure

The numerical solution of sample point stress field in finite element network of ferrite-martensite microstructure under finite deformation has a high-gradient distributive characteristic whose stress gradient between ferrite and martensite crystalline element is very high. If the interpolation method is used in the whole region,the isogram will be seriously smooth so that the original high-gradient sample point stress field will become untrue. This paper presents a new method for drawing isogram of ferrite-martensite microstructiire stress field by interpolating sample points in an element one by one. This method can make the post-treatment of high-gradient discrete stress field in crystalline network approach to a truer condition and solve the problem of arbitrary curve boundary of the deformed two phase steel.     

Full-Scale Test and Analysis of Mechanical Behavior of Concrete Filled Steel Tubular Column Node in Space Truss Structure

To investigate mechanical behavior and seismic behavior of concrete filled steel tubular column node (CFSTCN) in space truss structure, both full-scale test and Finite Element Method (FEM) were employed. The test load was 1.6 times of design load and by incremental step loading. Meanwhile, stress and deformation in CFSTCN were observed to monitor bearing capacity of the node. The results show that steel tubular works in elastic state and a small part of concrete beyond of compressive stress limits; steel tube and concrete adhesive well. The hysteretic energy dissipation capacity and failure mode under cyclic loading were revealed by nonlinear FEM. weakest position and ultimate bearing capacity of the node were obtained from FEM results. The method of combining full-scale test and FEM can well reveal the mechanical behavior and the seismic behavior of the node.     

Experimental Analysis for Steel Box Concrete Composite Beam of Arch Bridge

A new steel concrete composite structure was proposed which composed of steel box beam, PC beam and PBH Shear connection. Bend test was carried out for the performance study of deformation and stress. It was found that Material advantages of steel and concrete were fully used and crack of concrete and local instability of steel box were avoided. And the deformation between steel box and concrete can be smoothed with PBH shear connection. As the calculated values showed good agreements with the test results, the proposed formulas can be reliably applied to the practice analysis. With the different parameters analysis, mechanic performance of the composite was obtained.     

蠕变模型对约束钢梁抗火性能分析的影响

钢材在高温和荷载作用下产生明显蠕变变形,影响火灾中结构的变形和受力性能。现有的蠕变模型较多,但没有一个广泛适用的蠕变模型。不同的蠕变模型对钢结构抗火分析结果有很大影响。为了量化蠕变模型对约束钢梁抗火性能分析的影响,对5种常用的蠕变模型进行了对比分析。采用编写的约束钢梁计算程序,分别计算5种蠕变模型下约束钢梁的抗火性能并与试验数据进行对比。结果表明,采用Norton蠕变模型的计算结果与试验数据吻合最好。最后对影响约束钢梁抗火性能参数进行了研究,研究发现,Harmathy蠕变模型对约束梁抗火性能分析结果影响最大;不同蠕变模型对不同荷载比、约束刚度下的约束钢梁抗火性能影响程度均不同。     

THERMAL TORSION ANAL1SIS OF USE CHARACTERS FOR SEVERAL HIGH SPEED STEELS

The elastic deformation work(EDW) and elastic-plastic deformation work (EPDW) of M2 high speed steel ,M2A1 high speed steel and 301 high speed steel are neasured be simulating the real use situations and using the thermal torsion analysis. It is found that the reason that the M2A1 high speed steel' s use characters are superior to those of the M2 one is that the former has higher EDW and EPDW.Howerer,the EDW and EPDW of 301 high speed steel are much lower than those of M2 one . So mechanical cutting tools can't be made from it. The results show that the EDW and EPDW measured with the thermal torsion analysis are the main criteria to evaluate the use characters of high speed steels.     

Design Approach on Flexural Load-carrying Capacity of Steel Beam to CFST Column Joints with External Stiffening Ring

A 3-D finite element model is established by ABAQUS to simulate the behavior of the joints with concrete-filled steel tubular (CFST) column to steel beam using external stiffening ring.The load versus deformation curves of this type of joints are compared between theoretical and experimental results,and in good agreement.Parametric analysis is performed to study the flexural load-carrying capacity of the joint.The width of external stiffening ring,the steel ratio of CFST column,the ultimate strength of steel beam,the strength of steel tube and beam,the concrete strength,the axial load ratio,and the beam to column linear stiffness ratio are considered as parameters.The simplified practical design approach is proposed based on parameter analysis of the flexural load-carrying capacity of these joints.The practical calculated values are in good agreement with the FEM results.     

Calculation Methods for Steel Frame Structure Based on the Structural Ultimate Bearing Capacity

The existing problems in calculation approach for multi-story and high-rise steel frame structure are summarized. As the shearing deformation is considered, the analysis methods for steel frame structure are put forward based on the structural ultimate bearing capacity, which is on the basis of second order inelasticity analysis for steel structure. In the approach, the tangent module brought forward by Bleich, F. is used, the second-order refined plastic hinge method presented by Liew, J. Y. R. is modified.     

THE STUDY OF ANTI-SEISMIC BEHAVIOR OF THE TOP CORNER JOINTS OF REINFORCED CONCRETE FRAME WITH THE INCLUSION OF STEEL FIBRES

This paper first discusses the limited effect of steel fibre reinforcement on plain concrete and reinforced concrete. Then, making a comparison among the test results of three full-scale top corner joint assemblies of frame, in which only two of them are added with steel fibres in joint zone. The advantageous and disadvantageous influence in anti-seismic aspect is investigated after adding steel fibres in the joint zone. Finally, this paper gives an overall comment on the application future of using the steel fibres in every kinds of joint of anti-seismic reinforced concrete frame.     

Grinding Hardening Experiments of Non-quenched and tempered Steel Piece

By comparison with quenching and tempering steels the non-quenched-tempered steels not only decrease produetion cost but also can avoid deformation of parts by heat treatment. Grinding hardening, the technology of hardening steel piece surface with grinding heat instead of high or medium frequency induction hardening heat, can integrate grinding surface hardening. This paper tries to carry out test study on grinding hardening of non- quenched and tempered steel. Through carrying out the grinding experiments with variable cut depths and feed speeds, the changing law of depth of hardening layer is studied, and the mierostrueture of test-piece is analyzed. Experimental results show the feasibility of grinding hardening of non- quenched and tempered steel, and the conclusion of this paper can lay the foundations of grinding hardening technology of non-quenched and tempered steel piece.     

The Analysis on Quenching 50CrMn Steel Leaf Spring in the Polymer Cooling Medium

To eliminate the environment pollution and fire disaster caused by using oil for quenching cooling medium,cooling property of polymer cooling medium is analyzed in this article.Then quenching technology is experimented with 281A agueous solution of three different concentrations for 50CrMn steel leaf springs.Metallographic analysis and hardness testing are done for sample.After that,this is compared with the quenching deformation and medium management used for 20 # machine oil.Then,it is found out the reason that the spring over-deviation of the bending deformation of leaf spring:the cooling speed is faster than oil's when this cooling medium is below the M S point temperature of steel. At last,this paper summarizes that the problems required to be solved are decreasing the cooling speed of this medium in low temperature,adjusting concentration and decomposition when extending the use of the polymer cooling medium in the leaf spring industry.     

Analysis of ultimate load and mechanismsof failure in large cast steel joints

Based on a project of pipe truss roof framing in Chengdu, the ultimate limit state analysis is performed on cast steel joints by using FEM, in which Linear hardening elastic-plastic constitutive model is considered. The results show that, the joint has a great accumulation of plastic strain in ultimate loads, and the point of maximum stress is different from that in elastic with the development of the yielding zone. The paper propoes to use rate-type tensor for the large strain geometric nonlinear problem, shows the criterion of failure formation , and indicates that its essential to apply limit state analysis to the determination of the weakest location on cast steel joint design, which provides basis for understanding the failure modes and failure mechanism of cast steel joint and the cast steel joint design.     

Experimental studies on the energy absorption property of aluminum foam filled steel pipe under transverse compression

To understand the energy absorption property of aluminum foam-filled steel pipes and the energy absorption property affected by aluminum foam filler, the energy absorption ability and transverse compression property of steel pipes and aluminum foam-filled steel pipes are tested. The results show that the normal stress-strain curve of steel pipes is similar with that of cellular materials. The normal yield stress of a steel pipe with a large diameter under transverse compression is lower than that with the same wall thickness but a small diameter. The deformation mode of steel pipes can be changed by the filling of aluminum foam. The aluminum foam filler improve the energy absorption ability of steel pipes. The effect of aluminum foam density on the energy absorption ability of steel pipe is small, and the effect of pipe diameter on the energy absorption ability of aluminum foam-filled steel pipes is large.     

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.