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。     

Experimental Analysis of Size Effect of High-strength Concrete Column Under Small Eccentric Loading

To analyse size effect of high-strength concrete column under small eccentric loading, experimental analysis was carried out on 3 categories of different sizes of high-strength concrete columns under small eccentric loading. The columns' section size was 200 mm × 200 mm, 400 mm × 400 mm and 800 mm × 800 mm, respectively. Failure mode, ultimate strength, deformation capacity and cross-sectional strain distributing rules were compared to get the size effect law. The results show that the compressive failure mode and cross-sectional strain distributing rules of HSC column under small eccentric loading are basically the same, and the size effect isn't obvious. Ultimate strength and deformation capacity of HSC column under small eccentric loading have size effect obviously. With increase of section size, safety reservation of ultimate strength is reduced and deformation capacity also reduces.     

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.     

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。     

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。     

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。     

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.     

Axial Force Stiffness Interaction in Seismic Analysis of RC Double Column Bridges

Earthquake induced dynamic axial force in reinforced concrete (RC) bridge bent columns will not only change the yield strength of the columns but also change their stiffness, which is seldom considered by the common lumped plasticity line model. Based on the fiber element model results that taking into account the influence of dynamic axial force on strength and stiffness simultaneously, the axial force stiffness interaction effect on the seismic responses of RC double column bridges was analyzed. The results show that, axial force stiffness interaction has a large effect on the seismic responses of the double column bridge in the elastic range, and it does not alter the ultimate capacity of the columns. Since the stiffness of the columns under compression and tension dynamic axial forces offset each other, the global displacement of bridge bent with equal columns is relatively unaffected by the axial force stiffness interaction, however, the differences of the column member forces are manifest. For the short column controls the global stiffness, the axial force stiffness interaction has significant influences on both the global displacement and member force responses. The influences become larger as the irregularity of the bridge bent increases, so the interaction between axial force and member stiffness should be sufficiently considered in seismic analyses.     

Experimental Study on Plannar Representative Connections Used in Obliquely Crossing Lattice of One Super Highrise Building

One Super Highrise Building is adopted to a new structural pattern of a reinforced concrete core tube enclosed by an outer lattice tube made of obliquely crossing concrete filled rectangular steel tubular columns.In order to understand the stress state of plannar representative connections used in obliquely crossing lattice and verify the rationality of the details,two 1:3 scale models were respectively applied symmetrical and asymmetrical axial force,and experiment processes were numerical simulated by ABAQUS.The results indicate that the connections are validated to meet the design requirement of the building,with sufficient loading capacity.     

THE STRAIN OF THE BARS IN THE STRUCTURAL COLUMNS OF THE PRESTRESSED EARTHQUAKE-RESISTANT BRICK-WALLS

Through the comparative tests of prestressed and non-prestressed brick-walls un-der the repeated lateral loading,the effect of the prestress-force to the strain distribution in the non-prestressed bars of the structural columns has been investigated.This effect is beneficial:the pre-stress-force will reduce the value of strain in the bars of the lower part in the columns and uniformize the strain distribution along the whole height of the columns.Furthermore,instead of a strainreduction,the strain of prestressed be will increase along with the increasing of the lateral load.Thus,the coefficient of prestress-force-increase could be calculated in the tWo stages of the crack-resistance and ultimate bearing capacity.As a result,both the prestressed and non-prestressed barsare able to give the potential of their bearing capacity a full play,and improve the earthquake-resis-tant property.     

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。     

Effects of Eccentricity on the Ultimate Strength of K joint with Tube gusset Plate Connections

The behavior and strength of tube gusset connections with tube 219×6 and 1/4 annular ribbed plate subjected to eccentric force is investigated. Non dimensionalized ultimate strength interaction relations between the wall moment of tube ,vertical axial force ,and eccentric vertical component force of axial brace force of tube gusset connections with 1/4(1/2) and annular ribbed plate subjected to eccentric force is researched based on the model of equivalent forces of tubular joint. The parameters which influence the ultimate strength of tube gusset joint were analyzed and non dimensionalized ultimate strength interaction relationships were proposed. It is shown that the proposal formula has theoretical and practical significance for design because of comparation with experimentation.     

柱失效方程中荷载相关特性对承载力抗震设计可靠度的影响

以竖向荷载和水平地震作用组合下的钢筋混凝土柱和钢柱为对象,研究了失效方程中荷载相关特性对柱承载力抗震可靠性的影响。根据现行《混凝土结构设计规范》和《钢结构设计规范》分析了不同柱弯矩轴力相关曲线的特性。结合多个框架结构实例,对比了柱失效方程中荷载相关曲线与规范考虑情形的异同。实例分析表明:水平地震和竖向荷载组合作用下,小偏压RC柱和工字型钢柱的荷载相关曲线与规范考虑的情形较为符合,均近似为负相关的直线;水平地震和竖向荷载组合作用下,大偏压RC柱的荷载相关曲线则与规范考虑的情形有较大出入,存在明显的正相关段部分。在此基础上,考虑失效方程复杂特性,依据已有的荷载和抗力变量概率模型,采用Monte Carlo法分析了水平地震和竖向荷载组合作用下柱的可靠性。结果表明:钢柱和小偏压RC柱的承载力抗震可靠度随轴压力荷载效应比值的变化幅度较小,与规范模式计算结果较接近;大偏压RC柱的承载力抗震可靠度随轴压力荷载效应比值的变化会有较大幅度波动,与规范模式计算结果差异较大;当轴压力荷载效应比值为负时,大偏压RC柱的承载力抗震可靠度会低于规范计算值较多,现行柱可靠性设计方法会偏于不安全。     

Numerical Method for Load Bearing Capacity of High Strength Steel Columns at Elevated Temperature

In order to make fire resistance design of high strength steel columns in building structures, the numerical calculation method on load bearing capacity of high strength steel columns at elevated temperature was investigated. By taking the mechanical property of high strength steel at elevated temperature into consideration, extension was made on the inverse calculation segment length method and the program to compute the load bearing capacity of high strength steel columns at elevated temperature was performed. The program was adopted to compute the load bearing capacity. The results obtained by the program and the finite element analysis were compared and good agreement had been found. The influence of magnitude, distribution mode of residual stress and initial geometry imperfection on ultimate load bearing capacity was analyzed by employing the program. It is shown that the extended method can be is shown used to calculate the load bearing capacity of high strength steel columns at elevated temperature; the magnitude and distribution mode of residual stress had little influence but the geometry imperfection have significant influence on ultimate load bearing capacity.     

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.     

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.     

冻融环境下钢筋与粉煤灰混凝土的粘结性能

通过对内贴应变片钢筋的直接拔出试验,分析冻融作用下粉煤灰掺量对钢筋与粉煤灰混凝土间粘结性能的影响,得出冻融循环作用对钢筋与粉煤灰混凝土之间粘结性能的影响规律。试验结果表明：钢筋与粉煤灰混凝土的粘结强度随粉煤灰掺量的增加而降低;当粉煤灰掺量一定时,随着冻融循环次数的增加,混凝土强度有所下降,钢筋与粉煤灰混凝土间极限粘结强度降低;当粉煤灰掺量较大,达到40%时,随冻融次数的增加,钢筋粉煤灰混凝土试件极限粘结强度的下降幅度明显减缓,极限粘结强度对应的滑移量增大。表明掺入较多粉煤灰可使试件的冻融损伤现象得到缓解,冻融环境下钢筋混凝土的粘结性能得到提高。     

The Effect of Axial Compression on the Prestressed Concrete Frame under Vertical load

For prestressed frames, the axial compression ratio will affect not only the ductility of structures but also the structural internal force.Based on the computer-calculation for four groups of 24 prestressed frames combined with the references, in this paper, the effects of axial compression ratio on the prestressed frames are studied and discussed through three aspects: the second-order effect, the axial deformation of frame-columns and the comparison with ordinary concrete frames.The study results show that the effects of axial compression ratio on the prestressed frames and the ordinary concrete frames are basically consistent, but there are some self-born characteristics.As a whole, the effect of axial compression ratio on the prestressed frames is more notable than that on the ordinary concrete frames, but under common situation the effect is small.     

Experimental Analysis on Bending Capacity of Unbonded Prestressed Concrete Beams with HRBF500 Steel Bars

The bending capacity tests on ten simple supported beams were conducted to investigate the damage characteristics, prestress increment, beading capacity and displacement ductility of unbounded prestressed concrete beams with HRBF500 steel bars. The results show that the HRBF500 steel bars has yielded before the limit state. The concrete in compression zone crushes upon the broken of the beams, which shows a sudden damage mode. The measured ultimate stress increments of unbounded tendons are in linear relationship with the comprehensive reinforcement ratio index, while the values of the ultimate stress increments are obviously higher than those values specified in the code GB50010-2010, and the average ratio of predicted values to testing values is about 0.35. The mid span deflection upon yielding of the beams is large, while the displacement ductility is bad and the average value of the displacement ductility ratio is 1.67. The displacement ductility ratio decreases with the increases of the comprehensive reinforcement ratio index. Based on the experimental results, the proposed calculation formula of ultimate stress increments of unbounded tendons was established, and it is in good agreement with the experimental results when the testing value is less than 450 MPa.     

Theoretical Analysis of Load Capacity of EccentricalReinforced Concrete Columns with Concerete Cover

Based on the plane_section hypothesis of combination section,this paper describes the section strains of reinforced concrete columns with concrete cover under initial axial pressure and analyses the height of relative limit compression area and the stress of concrete and reinforcing bar of combination section in ultimate state.Meanwhile,the paper proposes practical calculation method of load capacity.