拱结构空间几何非线性分析的曲梁单元

利用势能原理和插值函数推导了一种供结构空间几何非线性分析的曲梁单元。采用固定Lagrange坐标系和Newton-Raphson求解法。使用本文的方法与其他方法相比，该方法将轴向应变的非线性部分取平均值，提高了结果的精确性，而且单元数量大大减少。     

An effective four node degenerated shell element for geometrically nonlinear analysis

The development of a new four node degenerated shell element is presented for the analysis of the shell structures undergoing large deformations. In the formulation of the new element, the assumed covariant transverse shear strains are used to avoid the shear locking problem, and the assumed covariant membrane strains which are separated from the covariant inplane strains by mid-surface interpolation, are applied to eliminate the membrane locking problem and also to improve the membrane bending performance. This element is free of serious shear and membrane locking problems and undesired spurious kinematic deformation modes. An incremental total Lagrangian formulation is presented which allows the calculation of arbitrarily large displacements and rotations. The resulting nonlinear equilibrium equations are solved by the Newton-Raphson method combined with load or arc-length control. The versatility and accuracy of this new degenerated shell element is demonstrated by solving several numerical examples.     

Buckling analysis design of steel frames

Steel design codes do not provide sufficient information for the efficient design of steel structures against out-of-plane failure, and what is provided is often overly conservative. The method of design by buckling analysis (DBA) specified in one code corrects this situation for beams, but the extension of this method to columns is only referred to, while there is no guidance on how to apply this method to the design of beam-columns and frames.Beam DBA uses the design code formulation for the member nominal design strengths in terms of the section moment capacities and the maximum moments at elastic buckling, accurate predictions of which may be determined by computer programs. Column DBA is similar, in that it uses the design code formulation for the column nominal design strengths in terms of the section compression capacities and accurate predictions of the elastic buckling.However, design codes do not provide formulations for the direct buckling design of beam-columns, but instead use the separate results of beam design and column design in interaction equations. The further extension to frames is not directly possible, because frames are not designed as a whole (except through the rarely used methods of advanced analysis), but as a series of individual members. This paper shows how the method of DBA can be used to design beam-columns and frames as well as beams and columns. Two example frames are designed and very significant economies are demonstrated when the DBA method is used.     

Shallow shell finite element for the large deflection geometrically nonlinear analysis of shells and plates

An investigation into the large deflection, geometrically nonlinear behaviour of shells is carried out in the present paper. The finite element method is used in conjunction with linearised incrementation and the Newton-Raphson iterative technique.The finite element used is based on independent strain assumptions insofar as it is allowed by the compatibility equations. Strain-displacement relationships based on shallow shell formulation are used and applied to an element having three principal curvatures. The resulting element has the only essential external degrees of freedom, satisfies the exact requirement of strain free rigid body modes of displacements and can be used for the representation of cylindrical, spherical and hyperbolic paraboloid shells.Complex load-deflection curves are obtained for cylindrical and spherical shells by incrementing loads as well as deflections. The relative behaviour of cylindrical and spherical panels having the same overall dimensions are also discussed in terms of stiffness, instability and snap-through phenomena.     

Buckling analysis of stiffened circular cylindrical panels using differential quadrature element method

Differential quadrature element method (DQEM) for buckling analysis of stiffened circular cylindrical panels subjected to axial uniform compressive stresses is presented for the first time. The methodology and procedures are worked out in detail. The circular cylindrical panel and the stiffeners are treated separately. Governing differential equations are derived based on the equilibrium of the panel and the stiffener, and on compatibility conditions along the interface of panel elements and stiffeners. Torsional stiffness of the stiffener is ignored. Circular cylindrical panels with a stringer stiffener or a chordwise stiffener are analyzed by the DQEM, and the results are compared with previously published data to verify the established methodology and procedures. Some new results are presented for the circular cylindrical panels with two orthogonal stiffeners.     

Nonlinear analysis of masonry-infilled steel frames with openings using discrete element method

Nonlinear numerical modeling of masonry-infilled frames is one of the most complicated problems in structural engineering field. This complexity is attributed to the existence of joints as the major source of weakness and material nonlinearities as well as the infill-frame interaction which cannot be properly modeled using the traditional finite element methods. Although there are many numerical studies available on solid masonry-infilled steel frames’ behavior, however, few researches have been conducted on infilled frames with openings. In this paper a two-dimensional numerical model using the specialized discrete element method (DEM) software UDEC (2004) is developed for the nonlinear static analysis of masonry-infilled steel frames with openings subjected to in-plane monotonic loading. In this model, large displacements and rotations between masonry blocks are taken into account. It was found that the model can be used confidently to predict collapse load, joint cracking patterns and explore the possible failure modes of masonry-infilled steel frames with a given location for openings and relative area. Results from the numerical modeling and previous experimental studies found in the literature are compared which indicate a good correlation between them. Furthermore, a nonlinear analysis was performed to investigate the effect of door frame on lateral load capacity and stiffness of infilled frames with a central opening.     

将弧长法应用于结构的几何非线性有限元分析

首先介绍了弧长法的发展及基本理论，随后根据笔者的研究，对其中的几个问题提出了相应的参考意见，最后给出了几个算例。     

Geometric and material nonlinear analysis of three-dimensional steel frames

Results obtained through theoretical and empirical studies which examined the nonlinear behaviour of construction members enabled us to characterize the behaviour of construction systems under external effects more closely. The calculation methods that took into consideration the nonlinear behaviour of the construction members and the nonlinear effects of their geometrical variations had to be developed in order to evaluate these phenomena and to design structures according to their collapse load principle. In the presented study, a computer program was developed for the characterization of structural systems by taking into consideration the nonlinear conditions of material behaviours under increasing loads and by considering the second-order effects. A matrix-replacement method was used as the basis for developing the program, which takes into consideration the effects of axial forces on the stiffness of the member by using the stability functions and the effects of plastic hinges by systematically changing the stiffness matrix in each occurrence of the plastic hinges. In the study, based on the results obtained from the examples, which were solved by the developed program, it was identified that the program could yield rapid and reliable results depending on the user-defined values (number of nodes, error limit for the iteration) and it is observed that the results are consistent with the literature. The obtained results in this study have contributed to capability of converting two dimensional analyses to three-dimensional analysis of stability functions developed.     

使用非线性有限元法对张力膜结构找形分析

首先介绍了张力膜结构找形分析的基本原理,然后讨论非线性有限元法中的几种索单元和膜单元力学模型,并建立相应的几何方程、物理方程和平衡方程,最后提出以极小曲面作为找形分析的最终平衡状态。     

Buckling analysis of structural steel frames with inelastic effects according to codes

Steel building frames are often analyzed for stability in an elastic way, while most of their columns behave inelastically at the buckling stage. Most column design provisions allow for inelastic behavior, but overall inelastic stability analysis is rarely performed. In this study the analysis philosophy is centered on the overall frame stability and its true safety factor. As many columns show inelastic behavior at the buckling stage, the proposed procedure takes due consideration of this fact. Once the overall buckling factor for the frame is obtained, individual column effective length factors, and their true slenderness ratios are computed, and used in the design relationships. This procedure circumvents the use of design nomographs and numerous formulas proposed in the past to alleviate their shortcomings. The procedure proposed based on the overall safety factor concept is an iterative one. It starts with a stability analysis and gradually modifies the structural properties to take account of inelasticity and eventually converges to the final buckling factor and mode shape. Any type of lateral restraint can be exactly modeled and taken into consideration without the need for approximate simplifying assumptions. The design philosophy proposed herein is that all columns must have their design parameters as related to buckling capacity must be derived from a single buckling analysis valid for the whole structure, and not considered separately and isolated from the rest of the structure as is currently practiced. Examples are worked out to illustrate the procedure and the results are compared to those of others.     

Buckling of frames braced by flexural bracing

This paper investigates the buckling of multistory frames braced by vertical beams. The sectional properties of the frames and the bracing beam are assumed to vary linearly along the height; the axial forces in the columns and the bracing beam are also assumed to linearly change along the height. A relationship between the buckling load and the bracing rigidity is established. The threshold rigidity for the vertical bracing beam which is just enough to make the frames buckle in a non-sway mode is obtained. The result may be used as a rational basis for classifying sway frames and non-sway frames after taking the influence of initial imperfections and lateral loads into account.     

Design of tapered member portal frames

Non-uniform steel frames, incorporating tapered or haunched members, have proved to be economical solutions for warehouses and factory buildings over a wide range of spans. Design rules, however, deal only with uniform member frames and therefore attempts have been made to convert the non-uniform frame into an equivalent uniform frame. One such method appears in the AISC Specification for the Design of Steel Buildings^(l) but it is relatively complex and of limited application.A simpler and more general procedure, based on a parametric study and using a limit state interaction equation, is presented. In the study, elastic instability computer programs were used and changes were made to the values of the principal variables. The results were subjected to an analysis of variance and equations of best fit were obtained for the conversion to an equivalent uniform frame. At this stage of the research program only completely symmetrical taper member frames have been investigated. The proposed conversion enables the designer to use all the currently available design aids dealing with the effective length factors of uniform members. The method is illustrated by two numerical examples.     

Simplified nonlinear progressive collapse analysis of welded steel moment frames

In this study, two nonlinear analysis methods are proposed that can be used for a simplified but accurate evaluation of progressive collapse potential in welded steel moment frames. To this end, the load-resisting mechanism of the column-removed double-span beams in welded steel moment frames was first investigated based on material and geometric nonlinear parametric finite element analysis. A simplified tri-linear model for the vertical resistance versus chord rotation relationship of the double-span beams was developed. The application of the developed model to energy-based nonlinear static progressive collapse analysis was then proposed. The relationship between the gravity loading and the maximum dynamic chord rotation or the concept of collapse spectrum was also established for a quick assessment of the maximum deformation demands.     

钢筋混凝土构件不同有限元模型对比分析

通过采用三种模型对钢筋混凝土梁进行对比分析,发现在完全弹性阶段不同模型的计算结果并无显著差别,进入塑性阶段后简化模型会带来较大误差,如果整体结构分析中梁柱采用一维线单元模型,应对计算结果进行折减。     

Buckling analysis of thin-walled open members—A finite element formulation

In a companion paper, a variational principle based on the principle of stationary complementary energy was developed for the buckling analysis of thin-walled members with open cross-sections. In this paper, the variational principle is adopted to formulate a finite element buckling solution. The formulation successfully incorporates shear deformation effects, a feature that is neglected in most available buckling solutions. By adopting a non-orthogonal coordinate system, the solution successfully captures the transverse load position effect relative to the shear center. A series of examples demonstrate the validity of the finite elements formulated and their applicability to a wide variety of buckling problems. Examples include column flexural and torsional buckling, lateral torsional buckling of beams with a variety of end conditions and subjected to a variety of moment gradients. The formulation is shown to be applicable to beams with mono-symmetric sections. In all cases, the validity of the new solution is assessed and established through comparisons to well-established closed-form and/or numerical solutions.     

Buckling analysis of cracked plates using hierarchical trigonometric functions

The present paper deals with the estimation of buckling loads of plates with cracking damages. The hierarchical trigonometric functions are used to define the displacement function of the cracked plate. Selective choosing of the trigonometric functions satisfies the various boundary conditions of a plate bounded by support members in a continuous plated structure. Moreover, the analysis of the cracked plate can be carried out with a minimum number of equations accurately. In the present paper, the buckling loads of plates with various types of cracks, such as edge crack and central crack, are estimated under uniaxial compressive load, biaxial compressive load and in-plane shear load. The results are found to correlate well with those obtained using a finite element method.     

Y型偏心支撑钢框架受力性能有限元分析

建立了四种Y型偏心支撑钢框架有限元模型,对平面模型框架和三种空间模型框架进行了单向加载和循环加载试验,并对比分析了模型框架的屈服强度、极限承载力、侧向刚度、延性和耗能能力等方面的受力性能差异,得到的结果为工程设计提供了参考。     

预应力胶合木梁受弯性能的有限元分析

采用ABAQUS软件,建立了有限元分析模型,探求力臂对于胶合木梁受弯性能的影响,得到随着力臂的增加胶合木梁的极限承载力随之增加的结果,有助于优化后续的试验。     

Numerical analysis of the nonlinear performance of concentrically braced frames under cyclic loading

Concentrically braced frames (CBFs) are widely used as lateral-load resisting system in steel structures. This study examines the effects of different parameters especially those associated with connections, on the behavior of CBFs. A single bay, singlestory frame is used to evaluate the interaction between structural members. Nonlinear analyses using a detailed inelastic finiteelement model (FEM) are carried out to study the behavior of frames subjected to cyclic loading. Models are designed based on seismic codes and analyzed to evaluate the performance of both SCBFs and OCBFs. The equivalent plastic strain concept is used to determine the ductility capacity and to predict fracture and failure in these models. Results show that the seismic performance of CBFs, which are designed according to current provisions can be improved by configuring the details of gusset plate connections in a way that inelastic demands are balanced in middle of brace and gusset plate corners.     

导流隧洞进水口结构非线性有限元分析

对龙滩导流隧洞进水结构进行三维有限元分析,求得整体结构的应力、位移,并确定结构中的薄弱环节.针对薄弱环节进行二维有限元分析,确定钢筋应力,裂缝开展情况.在此基础上对现有的设计做出评价,并提出相应的建议.