轴心受压杆件的弯曲屈曲

全面梳理了轴压杆弯曲屈曲的理论分析过程和工程应用方法。欧拉公式解决了轴压杆弹性区的弯曲屈曲问题。欧拉之后的学者完善了非弹性区的问题,建立了以切线模量理论为基础的轴压杆非弹性区弯曲屈曲的欧拉公式。其后的学者通过考虑安全度的方式将其用于工程设计。新版《钢结构设计标准》(GB 50017—2017)沿用我国自88钢规以来的做法,以等效初挠度综合考虑初始缺陷,按压弯杆计算给出轴压杆弯曲屈曲的设计公式。     

高强钢焊接箱形柱力学性能研究(Ⅱ)：二阶非弹性分析

高强钢的焊接残余应力分布和普通钢材的有较大差异,现有的切线模量和刚度退化函数不适合用于高强钢焊接箱形截面的二阶非弹性分析。而精炼塑性铰模型通过切线模量和刚度退化函数可合理考虑残余应力的影响和塑性渐进发展,达到与塑性区模型相近的精度。基于此,提出适合高强钢焊接箱形截面的二阶非弹性分析方法。通过稳定函数考虑单元二阶效应,基于杆端部转动引起的构件弯曲及其导致的轴向应变,考虑弯曲效应。在精炼塑性铰模型中,采用高强钢焊接箱形截面的残余应力统一分布模型,通过截面分析法构建不同强度等级的焊接箱形截面切线模量计算公式。同时,分析轴力和弯矩共同作用下的渐进屈服对箱形截面刚度退化的影响,从而建立可模拟截面塑性发展的刚度退化函数。结合塑性铰的产生与发展对平衡微分方程解的影响,建立梁柱单元的弹塑性刚度矩阵。结果表明,所提出的二阶非弹性分析方法可准确分析高强钢焊接箱形截面轴压构件的力学性能,可应用于高强钢框架结构设计,为二阶非弹性分析方法的工程应用提供参考。     

部分包覆钢-混凝土组合柱单向压弯面内整体稳定承载力的工程计算

利用有限元方法建立部分包覆钢-混凝土组合柱(PEC柱)模型,对比既有试验数据,校核其可行性.经大量参数计算,在多高层建筑结构常见的柱子长细比范围内考察了压弯构件极限状态下轴力-弯矩相关曲线的特点.提出了采用轴力-弯矩相关方程表达的PEC柱单向面内压弯整体稳定承载力计算公式,利用既有试验数据、有限元计算数据对该公式的适用性、可靠性进行校核.结果表明,在绕强轴失稳与绕弱轴失稳的情况下公式均偏安全且经济,可用于实际工程中.     

截面轴力与弯矩屈服面在钢框架动力弹塑性分析中的应用

为了在现行规范下考虑轴力与弯矩的相互作用,并兼顾计算精度与计算效率,研究了截面屈服面在钢框架动力弹塑性分析中的新应用。首先选用截面组合思想构建轴力与弯矩的屈服面。接着,基于经典塑性理论建立截面恢复力模型,并给出了截面状态确定方法。然后阐述了基于力的梁柱单元状态确定过程及其对截面恢复力模型的调用。最后采用alpha-OS积分算法,对一个四层两跨钢框架开展了动力弹塑性分析。结果表明：截面轴力弯矩屈服面能很好地考虑轴力存在及变化对截面弯矩承载力的影响,基于屈服面的恢复力模型在计算精度上远高于塑性铰模型并逼近纤维模型,在效率上远高于纤维模型,可以用于钢框架的动力结构弹塑性分析。     

考虑不同残余应力分布的热轧Ⅰ型钢轴向构件的切线模量

提出各种残余应力分布下热轧I型钢截面有效切线模量的计算公式。因为存在残余应力,即使在均匀轴向应力作用下,横截面也会逐渐屈服。在弹塑性阶段,能够采用构件的有理正切模量得到其结构响应历史。在这项研究中,基于力学平衡的一般原理,推导出弹塑性阶段热轧I型钢构件的有理正切模量方程。为用于工程实际,给出传统热轧I型钢构件残余应力分布下的切线模量方程。利用壳单元模拟钢轴向构件,对其进行了一系列材料非线性分析,通过数值方法对所提出的公式进行了验证,并将所提出的公式与目前最常用的CRC切线模量方程进行了比较。对比研究表明,所提出的公式无需使用复杂的壳单元模型,能够以最简单的方式,精确分析轴心受压构件的弹塑性性能。     

纤维增强工程塑料板橡胶隔震支座力学性能理论研究

针对适用于村镇地区的纤维增强工程塑料板橡胶隔震支座，提出基本力学性能的解析公式。基于隔震支座橡胶应力的静水压力假定，同时考虑了橡胶可压缩性及加劲层泊松比的影响，建立隔震支座单层分析单元在轴压及纯弯曲状态下的平衡方程，求得静水压力的解析解，进而通过积分求得单层分析单元的压缩模量及弯曲模量的解析解，并进行了参数分析。进一步推导出支座水平等效刚度的解析公式。基于abaqus软件建立一组支座单层分析单元的有限元模型，进行轴压和纯弯曲分析。将有限元结果与文献中两种解析公式以及本文中解析公式进行了对比。结果表明，推导的解析公式具有较高的精度，且较其他解析解具有明显的优势，为在村镇地区推广此类隔震支座提供理论分析基础。     

初始扭转轴压杆弹性弯曲屈曲性能研究

初始扭转杆在工程设计中有着广泛的应用.通过对初始扭转轴压杆弹性弯曲屈曲性能的研究表明,初始扭转轴压杆弹性弯曲屈曲位移在两截面主轴平面上相互耦合.初始扭转角使得强轴对压杆绕弱轴的屈曲位移产生"抵抗"作用,从而提高了杆的弹性弯曲屈曲临界荷载.同时,提出基于初始扭转轴压杆弹性弯曲屈曲变形后的位移曲线是平面位移曲线的假定,提出需进一步验证分析.     

不锈钢热轧槽钢压弯构件绕弱轴面内稳定性能研究

为研究S30408(EN1.4301)不锈钢热轧槽钢压弯构件绕弱轴的面内稳定性能，对18个中长柱进行偏心加载试验，分析其绕弱轴的失稳破坏模态和面内稳定承载力。试验前测量试件初始几何缺陷、荷载初偏心及截面残余应力分布。采用有限元软件ABAQUS建立不锈钢热轧槽钢压弯构件有限元模型，经与试验结果对比验证后开展参数分析，研究了初始几何缺陷及纵向残余应力对不锈钢热轧槽钢压弯构件绕弱轴面内稳定性能的影响。基于试验及有限元分析结果对现行规范CECS 410:2015《不锈钢结构技术规程》(简称规范)设计方法进行评估，并提出了改进设计建议。研究结果表明：中长柱的破坏模态均为绕弱轴整体弯曲失稳；按照规范计算得到的不锈钢热轧槽钢压弯构件绕弱轴面内稳定承载力较试验值总体偏于保守，对于试验及有限元分析结果与规范公式计算结果比值，正偏心工况下为1.31,负偏心工况下(弯矩作用使槽钢翼缘肢尖受拉)为1.21且部分试件偏于不安全；改进的设计方法能较合理地预测不锈钢热轧槽钢压弯构件绕弱轴的面内稳定承载力，对于试验及有限元结果与改进设计方法计算结果比值，正偏心工况下为1.07,负偏心工况下为1.05。     

初始扭转轴压杆弯曲屈曲性能有限元验证分析

通过对初始扭转轴压杆弹性弯曲屈曲性能的研究表明:初始扭转轴压杆弹性弯曲屈曲位移在两截面主轴平面上相互耦合.初始扭转角使得强轴对压杆绕弱轴的屈曲位移产生"抵抗"作用,从而提高了杆的弹性弯曲屈曲临界荷载.以有限元法对初始扭转角不同的轴压杆进行参数分析表明,弹性弯曲屈曲变形后,其位移曲线是一条空间曲线,随着初始扭转角的增加,屈曲后位移曲线偏离同一平面的幅度变大.     

工字钢-混凝土组合梁弹性约束畸变屈曲研究

约束畸变屈曲是不同于侧向屈曲和畸变屈曲的一类特殊的屈曲形式,通常发生在组合梁负弯矩区。基于弹性地基压杆方法对组合梁弹性约束畸变屈曲进行了研究。将Svensson压杆模型进行改进,考虑了腹板参与部分,并推导了两种基于改进压杆模型的变轴力稳定计算表达式。借助于有限元方法,分析了现有变轴力弹性地基压杆方法用于组合梁约束畸变屈曲的求解精度,研究结果表明：弹性地基压杆方法对组合梁作用纯弯矩及三角形负弯矩情况符合良好,但对非线性弯矩分布情况精度较差。对约束畸变屈曲引入等效弯矩假设,并对其适用性进行了分析,提出了约束畸变屈曲等效弯矩假设临界长度简化公式,进而通过三步简化实现了连续组合梁弹性约束畸变屈曲计算。图16表7参17     

Inelastic second order analysis of steel frame elements flexed about minor axis

Frame elements may be subjected to significant bending moments about cross-sectional minor axis such as space frame elements and struts that buckle about minor axes. In some cases such as columns with compound cross-sections, the major bending moment acts about minor axes of cross-sectional components. The present paper proposes a simplified model for predicting the second order inelastic behavior of steel frame elements under axial compression force and bending moment about minor axis. New formulae are proposed to describe the plastic strength surface for steel I- and H-shaped cross-sections under axial force and bending moment about minor axis. Moreover, empirical formulae are developed to predict the tangent modulus for those cross-sections. The tangent modulus formulae are extended to evaluate the secant stiffness that is used for internal force recovery. The formulae are derived for steel sections considering the residual stresses as recommended by the European Convention for Construction Steelwork (ECCS). A finite element program is prepared to predict the inelastic second order behavior of plane frames using the derived formulae. The derived model exhibits good correlations when compared with the fiber model results. The analysis results indicate that the new model is accurate, furthermore it saves a lot of calculation time that may be consumed by iterations on the cross-sectional level.     

New method of inelastic buckling analysis for steel frames

In general, the concept of bifurcation stability cannot be used to evaluate the critical load of typical steel frames that have geometric imperfections and primary bending moment due to transverse loads. These cases require a plastic zone or plastic hinge analysis based on the concept of limit-load stability instead. However, such analyses require large computation times and complicated theories that are unsuitable for practical designs. The present paper proposes a new method of inelastic buckling analysis in order to determine the critical load of steel frames. This inelastic analysis is based on the concept of modified bifurcation stability using a tangent modulus approach and the column strength curve. Criteria for an iterative eigenvalue analysis are proposed in order to consider the primary bending moment as well as the axial force by using the interaction equation for beam-column members. The validity and applicability of the proposed inelastic buckling analysis were evaluated alongside elastic buckling analysis and refined plastic hinge analysis. Simple columns with geometric imperfections and a four-story plane frame were analyzed as benchmark problems. The results show that the proposed inelastic buckling analysis suitably evaluates the critical load and failure modes of steel frames, and can be a good alternative for the evaluation of critical load in the design of steel frames.     

An inelastic model for low cycle fatigue prediction in steel braces

This paper presents a nonlinear inelastic cyclic model to predict the effect of low cycle fatigue on the behavior of steel brace elements. This brace element is assumed as a beam-column element with pinned ends and a plastic hinge at mid-span. The kinematic hardening rule, based on the concept of a yielding surface in the theory of plasticity, together with the tangent modulus of elasticity, have been taken into account. Furthermore, a simplification of the linear cumulative damage theory is used to represent the low cycle fatigue deterioration of the brace element during the inelastic cyclic behavior. In the presented method, as an expansion of physical model theory, the governing yield function of the plastic behavior of the brace element is transformed mathematically by different factors. Then the yield surface which is defined in resultant stresses space, is changed and diminished by separately altering the axial load and bending moment terms of the yield function in each step of loading history to manifest low cycle fatigue deterioration. Comparison of the results of the proposed model with two existing experimental results has shown that this model was capable of predicting the low cycle fatigue of brace elements, and in one example, the rupture point of the brace element was predicted well by the model. It is advised that the model should be further expanded to more precisely include the effect of local buckling and distortion of brace elements with different cross-sectional geometries at the plastic hinge.     

轴力和双向弯曲下工字钢承载力

确定钢横断面抵抗力的塑性准则常基于一些基本假设,例如,取决于内力和截面形状相互作用的塑性铰的发展,因此,需要对每种截面形式提出相应的特定方程。该文提出新的相互作用准则分析轴力或双向弯曲下工字钢的弹性和塑性极限状态(不包括屈曲现象)。首先,针对一些特殊的内力组合(例如:单向弯矩-轴力组合和双向弯矩),给出相应的塑性相互作用准则。这二种情况都给出了精确的计算公式(包含采用该研究假设的框架),将所有塑性相互作用准则与EC3中相应的塑性准则进行比较。然后,提出适用于轴力和双向弯曲共同作用时的简化且总的准则。新的简化的塑性准则及EC3中采用的相应的塑性准则与精确的数值解相比较,结果显示,简易塑性准则的计算结果较为精确。对EC3提出改进建议。     

Resistance of steel I-sections under axial force and biaxial bending

The plastic criteria for the verification of steel cross-sections resistance are usually based on some basic hypotheses such as the development of plastic hinges, which depend on the interaction between the internal forces and the cross-section shape; therefore, specific equations are required for each type of cross-section.This paper presents new alternative interaction criteria for the analysis of steel I-sections subjected to an axial force and biaxial bending moments, at the elastic or the plastic limit states (as long as buckling phenomena are not involved).The plastic interaction criteria are presented, in a first step, for some particular combinations of the internal forces, such as axial loading with bending about a main axis, and biaxial bending without axial loading. In these cases, they are given by exact equations (within the frame of the hypotheses adopted in this study). All these plastic interaction criteria are compared with the corresponding plastic criteria adopted in the Eurocode 3 (EC3).Afterwards, a simplified global criterion is proposed for the simultaneous combination of an axial force and bending moments about both the main axes of inertia. This new simplified plastic criterion and the corresponding plastic criterion adopted in the EC3 are compared with the exact solution, obtained by a mixed numerical and analytical integration procedure. This comparison shows that this simplified criterion usually leads to results closer to the exact solutions. Some suggestions are then presented to improve the results given by the EC3.     

Combined MVP failure criterion for steel cross-sections

This study determines failure criterion for steel member cross-sections, subjected to combined bending moment M, shear force V, and axial force P (MVP). The principle of maximum plastic strain energy is employed to develop the strain-stress relationship for plastic flow, and the expression for the MVP yield surface of the cross-section. A linear distribution of shear strain over the cross-section is assumed. The influence of plastic deformation on bending moment, shear force and axial force, at full yield of the cross-section, is investigated. Results predicted by the derived MVP failure surface, are compared with those obtained by other studies in the literature. The derived MVP yield surface can serve as a basis to identify the failure of steel members, such as during seismic or progressive-failure analysis of building frameworks.     

Analytical formulation for the deformations of I-shapes and RHS at the plastic strain ultimate limit state

The development of “full plastic hinges” in the most stressed cross-sections is a common hypothesis considered in the elastic-plastic design of steel structures. The equations for the internal forces at the plastic limit state are then based on equilibrium conditions only, and they do not allow the global deformations corresponding to each combination of internal forces at this ultimate limit state to be estimated.This paper presents a simplified analytical model for the elastic-plastic analysis of rectangular hollow sections and bisymmetrical I-sections bent about their strong axis. This model states the relations between the global deformations (axial deformation and bending curvature) and the corresponding internal forces (axial force and bending moment) at the cross-section plastic strain ultimate limit state. It allows a realistic evaluation of the cross-section ductility, based on a relevant strain limitation at the most strained cross-section fibres.     

自复位方钢管混凝土框架-薄钢板剪力墙结构的水平边缘构件受力分析

基于薄钢板剪力墙在目标位移下充分屈服并形成拉力带,对绕梁腹板销轴转动的自复位方钢管混凝土框架-薄钢板剪力墙结构的水平边缘构件（中梁和顶梁）进行受力分析。分别对水平边缘构件在钢绞线预应力和薄钢板剪力墙拉力带作用下的受力进行分析,推导了钢绞线在目标位移下的拉伸预应力计算公式;基于薄钢板剪力墙极限破坏形态,研究了薄钢板剪力墙拉力带产生的水平边缘构件端部的轴力和剪力;提出了水平边缘构件的弯矩、剪力及轴力计算公式,明确了水平边缘构件的内力分布。结果表明:水平边缘构件内力公式计算值与有限元分析值吻合较好,可为水平边缘构件的设计提供参考。     

A computer method for nonlinear inelastic analysis of 3D semi-rigid steel frameworks

This paper presents an efficient computer method for inelastic and large deflection analysis of steel space frames with non-linear flexible joint connections, based on the most refined type of second order inelastic analysis, the plastic zone analysis. The method employs modeling of structures with only one element per member, which reduces the number of degree of freedom involved and the computational time. Gradual yielding of cross-sections is modeled using the nonlinear inelastic force strain relationships, and then using the flexibility approach the elasto-plastic tangent stiffness matrix and equivalent nodal loads vector of 3-D beam-column element is developed. The method ensures also that the plastic bending moment is nowhere exceeded once a full plastified section develops. A zero-length rotational spring element is used for incorporating the connection flexibility into the element tangent stiffness matrix and equivalent nodal forces. The combined effects of material, geometric and connection behaviour nonlinearity sources are simulated into an object oriented computer program automatically. This program was used to study the ultimate response of several steel frames, which have been studied previously by other researchers. The example of computations and the comparisons made have proved the robustness, accuracy and time saving of the proposed analysis method.