高温下钢管约束型钢混凝土柱的受力性能

火灾下无防火保护的结构构件温度会迅速上升，从而造成钢材和混凝土的强度明显下降。为了研究火灾下钢管约束型钢混凝土柱的受力性能，考虑火灾下钢管约束型钢混凝土柱的不均匀温度分布及温度对材料力学性能的影响，提出了火灾下受轴心荷载作用的钢管约束型钢混凝土柱承载力的计算方法。利用有限元软件ABAQUS对提出的计算方法进行了验证，结果吻合较好。进而采用该计算方法对影响高温下承载力的参数进行了分析，研究表明：随着构件截面尺寸的增加以及混凝土强度和钢材强度的提高，构件的承载力逐渐增加，而钢管壁厚的改变对承载力并无太大影响。利用有限元软件ABAQUS分析了荷载比、构件尺寸、钢管壁厚等因素对构件耐火极限的影响，发现耐火极限随着荷载比和钢管壁厚的增加而减小，随着构件尺寸的增加而增大。     

Fire Resistance Analysis of High Strength Q460 Steel Beams-Part I：Theoretical Analysis

In order to investigate the fire resistance of high strength steel beams made from Q460, the method to compute temperature distribution of high strength Q460 steel beams was derived and the temperature distribution was calculated by using finite difference method. The modified equations of temperature for components of steel beam were proposed. According to critical moment at room temperature and mechanical properties of high strength Q460 steel at elevated temperature, the critical moment and stability checking coefficient were obtained by analysis. The load bearing capacity and critical temperature as well as stability factor were studied by using equivalent stiffness method through considering the effect of temperature gradient on stiffness.     

焊接加固热作用对工形截面压弯钢构件承载性能的影响

为研究焊接加固热作用及不同初始负载对工字形压弯钢柱承载性能的影响,基于考虑热影响的热结构耦合分析方法进行了热源模型热输入改进,并考虑初始几何缺陷、初始残余应力及摩擦等,完成了不同负载下焊接加固的3个工字形压弯钢柱的模拟分析。研究了焊接位移时程、腹板应力应变重分布及荷载位移关系,通过有限元分析与相应试验结果对比验证,进而获得了试验无法获得的焊接温度场、翼缘与加固板间的焊接应力应变重分布以及翼缘边缘屈服承载力等结果,并将承载力结果与规范计算结果对比,考察了现有设计方法。结果表明,焊接顺序决定焊接变形的发展过程,焊接热输入和初始负载共同决定持载焊接的位移变化范围和焊接残余变形的大小;初始负载越大,应力应变重分布往偏心受力方向发展更多,承载力越低,而初始残余应力不影响极限承载力;采用考虑热影响的有限元方法具有一定可行性和总体安全性,规范设计方法仍有可提升空间。     

Experimental study on the mechanical behavior of eccentrically loaded steel tubular columns filled with structural steel and concrete

Considered strength classes of concrete, ratio of structural steel to concrete, ratio of steel tube to concrete and eccentricity ratio of load, 6 test specimens of steel tubular columns filled with structural and concrete are designed. The damage phenomena of specimens are described in detail and the failure mechanism is analyzed. The results show the initial failure of the specimens are began from the yield of steel tube, the ultimate failure are ended from the buckling of steel tube caused by the expansion of core concrete. Due to the existence of structural steel, the ductility of specimens is superior to steel tubular columns. Before the yield of steel tube, the plane cross-section assumption of specimens can be put into use. The ultimate bearing capacity of specimens is increased with the increase of strength classes of concrete, ratio of structural steel to concrete and ratio of steel tube to concrete. But the ultimate bearing capacity and ductility are decreased with the increase of eccentricity ratio.     

Factors Affecting the Ultimate Bearing Capacity of Cold-Formed Steel Portal Frames

The FEM simulation analysis method was studied to identify the ultimate bearing capacity of cold-formed steel portal frames.In this study,the beam-spring system was used to simulate the performance of joints.The initial imperfection of frame components was considered.The deformation performance and failure features of portal frame structures under vertical loads also were studied.The analytic results of the FEM simulation analysis method are close to the values obtained by experimentation.The ultimate bearing capacity of portal frames were computed by changing parameters such as the web plate thickness,the flange width,the plate thickness of brackets,the portal frame roof inclination,and the column footing stiffness.The analytic results indicate that the ultimate bearing capacity may be improved when the parameters mentioned above are increased.     

Fire Resistance Analysis of High Strength Q460 Steel Beams-Part II：Theory Validation

In the previous companion paper, the fire resistance of high strength steel beams made from Q460 was theoretically studied. The methods to obtain temperature distribution, critical moment, critical temperature and stability coefficient were presented. The temperature distribution and load bearing capacity was analyzed by finite element method, and the validation was evaluated by comparison of results between theoretical computation and finite element analysis as well as experimental results. The comparison was made between Q460 steel beam and mild Q235 steel beam and the difference on fire resistance was obtained. A simplified approach for fire resistance of high strength Q460 steel beams was proposed and an example was given to show the application and reference of the approach.     

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。     

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。     

Experimental Analysis of the Behavior of Steel Plate-masonry Composite Wall-beams

When steel plate-masonry composite structure used in the existing masonry structure with load bearing walls is removed for a large space, composite action should be considered between the beam and the supported masonry wall due to the arch effect formed in the supported wall. In order to investigate the working mechanism, failure mode, and load-carrying capacity, strain distribution in critical sections and mid-span defcection of this type of composite wall-beam, five steel plate-masonry wall-beams were tested under concentrated loads and analyzed, which considered variables of height-span-ratio of supported masonry wall, height-span-ratio of composite beam and thickness of steel plate. The results show that steel plate-masonry composite wall-beam starts failure from the masonry located at the line between loading point and supporting point; strain distribution of steel plate along section height meets the plane section assumption; the height-span-ratio of supported wall can directly influence the failure mode of masonry wall, buckling load corresponding to steel plate experiencing local buckling and ultimate load of tested specimens; the reasonable height of supported masonry wall is beneficial to the formation of composite action between supported masonry wall and composite beam, and the excessive high masonry wall will reduce the ultimate load of the tested specimen. Finally, the reasonable range for height-span-ratio of supported masonry wall was presented, and the proposed value representing the flexural stiffness of the steel plate-composite beam relative to the in-plane stiffness of the supported masonry wall was at least more than 79.     

Experimental Analysis on Axial Compressive Behavior of R- CFTStub Columns with Prestressed Binding Bars

In order to investigate the effect of prestressed binding bars on axial compressive behavior of rectangular concrete-filled tubular (CFT) short columns, five rectangular CFT short columns, three with prestressed binding bars, one with ordinary binding bars, the other with no binding bars, were constructed and tested under axial compressive loads. The binding bars were made up with high-strength bolts. As used for ordinary binding bars, the high-strength bolts were welded to the steel tube before the column was loaded to axial compressive force. As used for prestressed binding bars, the high-strength bolts were first tensed by screwed screw cap down to bring force to prestress the steel tube and its core concrete, then welded to the steel tube before the column was loaded to axial compressive force. Test results indicate that the bearing capacity and ductility of rectangular CFT short columns are increased by setting binding bars. Compared to ordinary binding bars, the prestressed binding bars can decrease the longitudinal displacements corresponding to ultimate strength, but have little effect on the ultimate strength and displacement capacity after ultimate strength of the columns. The longitudinal displacements corresponding to ultimate strength of the columns decrease with the decreasing of space between binding bars. With the same section width and amount of binding bars, the bearing capacity of the columns improves with the increase of section long-broad-ratio, while displacement capacity after ultimate strength decreases with the increase of section long-broad-ratio.     

Bearing capacity of composite columns reinforced by concrete filled steel tube

In this study, nine simplified short composite columns consisting of core CFST (concrete filled steel tube) of different diameters and outer reinforced concrete were constructed to study their compressive performance under axial or eccentric compression. The failure mode is characterized by the crush of the outer concrete. The bearing capacity increases at first and then decreases with further increase of the position coefficient. It can be concluded that position coefficient is an important structural parameter that has considerable influences on the ultimate bearing capacity of the composite columns. The outer concrete, steel tubes and longitudinal reinforcement are found to work in a cooperative manner under axial or eccentric compression when the position coefficient is about 0.5. An improved bearing capacity algorithm that takes the position coefficient into account has been proposed based on the experimental and simulation results and current technical specification in China. It has been proven to be precise and safe.     

Bearing Capacity of Bar-Reinforced Concrete-Filled Square Steel Tubular Short Columns After Fire

Based on the determined stress-strain relationship of steel and concrete after fire, a temperature field and mechanical model of bar-reinforced concrete-filled square steel tubular columns after fire was set up with using ABAQUS, and the model has been validated by testing results. Then this paper analyzed the side of section, bar ratio, fire duration time, steel ratio and material strength parameters on the bearing capacity of bar-reinforced concrete-filled square steel tubular columns after fire. It is found that fire duration time and side of section is the dominant factor. Lastly this paper puts forward a theoretical formula of bearing capacity of bar-reinforced concrete-filled square steel tubular columns after fire, for the post-disaster restoration and provides references for the reinforcement.     

Critical Temperature of Axially Restrained Steel Columns withPartial Fire Retardant Coating Damage

In order to investigate the fire resistance of steel columns with partial fire retardant coating damage in fire, based on the differential equation of equilibrium on each portion of steel column, the deflection of steel column after the fire retardant coating damage was derived, with the pined ends and rigid ends of the columns at elevated temperatures. The critical temperature calculation method was proposed for partial fire protection damage and axial restrained steel columns by taking the edge yielding criteria. The deflection and axial displacement were verified by finite element method at elevated temperature. With a case study, the critical temperature and relationship of axial force and temperature were obtained for pined column with axial restraint. It was shown that the axial force of the steel column at elevated temperatures was increased and the critical temperature was decreased by the axial restraint. The longer the fire retardant coating damage was and the higher the axial restraint was, the lower the critical temperature was.     

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.     

Stability Behavior of Shuttle-Shaped Steel Lattice Columns With Bending Moment

The stability behavior of shuttle-shaped steel lattice columns subject to combined axial force and bending moment was examined through elastic buckling analysis and geometrically and materially nonlinear analysis. Firstly, the concept of section stiffness variation ratio is proposed for shuttle-shaped lattice columns and the elastic buckling behavior is discussed. Then, the effect of bending moment on the stability behavior of lattice columns is investigated, with the emphasis on the development of axial stress, bending stress and shear stress. The influence of column component spacing and diaphragm thickness on the stability bearing capacity is also analyzed. It is shown that the elastic buckling mode of the lattice column is dependent on its section stiffness variation ratio; for lattice columns with C-shaped buckling mode, the reduction in stability bearing capacity caused by bending moment is smaller than that of columns with S-shaped buckling mode; the maximum stability bearing capacity of the lattice column can be achieved by adjusting the column component spacing, and the spacing corresponding to the maximum capacity is basically consistent with the critical spacing for transformation of C-shaped buckling mode and S-shaped mode; and it is more effective to increase the thickness of columns with S-shaped buckling mode to get larger bearing capacity.     

轴心受压钢构件高温下局部稳定设计方法

为了得到钢构件高温下局部稳定设计方法,通过试验对建立的有限元模型进行了验证。采用验证后的有限元模型,分析了温度、板件宽厚比、初始几何缺陷、腹板和翼缘相互作用等因素对H形截面轴心受压钢构件局部屈曲应力的影响,提出了Q235钢和Q460钢H形截面轴心受压构件高温下的局部稳定承载力简化计算公式和高温下防止局部屈曲的翼缘宽厚比和腹板高厚比限值。研究表明：当板件宽厚比较小时,构件的局部屈曲应力随宽厚比的增大迅速减小,宽厚比较大时,构件屈曲应力降低不明显;初始几何缺陷对构件局部屈曲应力影响较小;高温下翼缘对腹板屈曲的约束作用比常温下明显;高温下防止局部屈曲的宽厚比限值与常温下宽厚比限值不同。     

Experimental Analysis of Extension Length of Shape Steel in SRC-RC Transfer Column

Seismic performance of SRC-RC transfer column was analyzed based on experiment of 12 specimens of transfer columns and 1 RC specimen under low cyclic reversed loading, which mainly focused on the extension length of shape steel. Analysis and comparison on skeleton curves of specimens was carried out. Analysis was completed for ductility, bearing capacity, energy dissipation capacity and degeneration ratio of strength. Displacement ductility changes with the increase of extension length of shape steel, enhancing at first, then reducing, and reaching peak value when extension length is close to three fifths of column height. Extension length of shape steel has little effect on bearing capacity. Energy dissipation capacity of transfer columns has relationship with many factors. Three fifths of column height is rational for extension length of shape steel, and specimens have not only advanced performance of energy dissipation but also good stability of stiffness and strength in this condition. The bond performance between concrete and shape steel decreases with the increment of extension length of shape steel, and hence stability of strength decreases.     

Finite Element Analysis of the Influence of Steel Strength on Beam-to-column Composite Connections

Because high material strength and composite load-bearing are emphasized in constructing members for high-rise steel frame structures, in a composite connection, steel strength has a dramatic influence on both the bearing performance and the composite action of the concrete slab. Based on a finite element analysis, we discuss the composite effect and the connection breaking mode, focusing on the performance change of the composite effect in adopting high strength steel. It can be found from the results that, along with the improvement of the steel strength, the elastic and plastic ultimate strength of the composite connection will increase, the ductility will decrease to a certain extent, and the composite effect of the concrete slab will diminish. The collapse of the concrete in a positive moment side contacting the column flange is viewed as the limiting state of the connection.     

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。     

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.