某薄壁型钢屋架厂房倒塌事故分析

介绍一起采用双C型薄壁型钢屋架的厂房雪灾倒塌事故。通过ANSYS软件,对该屋架梁进行数值模拟,分别选用壳单元和梁单元对其进行非线性受力分析,并考虑材料非线性和几何非线性,同时考虑大变形效应,根据数值模拟结果分析屋架梁倒塌的原因,得出对工程设计有益的结论,从而为工程设计提供一定的参考。     

Modelling steel frame behaviour under fire conditions

A formulation for the noblinear analysis of two-dimensional steel frames under fire conditions using the finite element method is presented. Deterioration in material strength with increasing temperature is represented by a set of nonlinear stress-strain-temperature relationships using a Ramberg-Osgood equation in which creep effects are implicitly included. Structures subject to increasing loads or temperatures are analysed using an incremental Newton - Raphson iterative procedure. The analysis permits deformation history and either collapse load or critical temperature to be calculated at a specified temperature or load level respectively. It includes the effects of geometric nonlinearity, temperature dependent nonlinear material behaviour and variations in temperature distributions both along and across each member. The effects of thermal strains, residual stresses and thermal bowing are also considered and different material models may be used. Comparisons are made with fire test results on frames and columns that represent a wide range of problem parameters such as slenderness, end conditions, load levels and temperature distributions. In all cases, the agreement is very satisfactory. An example two-bay frame is analysed to illustrate the potential of the analysis and to show the influence of various forms of partial protection on the collapse temperature of sway frames.     

Second-order distributed plasticity analysis of steel frames with semi-rigid connections

This paper proposes an accurately and efficiently numerical procedure for distributed plasticity analysis of semi-rigid steel frames. Both geometric and material nonlinearities are included in the proposed analysis. Geometric nonlinearities due to the large and small P-Delta effects are respectively captured using the corotational formulation and curvature-based displacement procedure. Material nonlinearities due to residual stresses and inelastic behaviour of materials are taken into account using a fibre model. The nonlinear semi-rigid behaviour of beam-to-column connections is simulated using a zero-length connection element. The validity of the present analysis is verified by comparing the obtained predictions with existing solutions. A case study of a very large-scale steel frame indicates that the present analysis is very reliable and computationally efficient and thus would be a valuable tool for daily use in office engineering design.     

Practical advanced analysis software for nonlinear inelastic dynamic analysis of steel structures

This paper presents a practical advanced analysis software which can be used for nonlinear inelastic dynamic analysis of space steel structures. The proposed software can predict accurately the nonlinear response of a steel structure by using only one element per member in structural modeling. Three types of element including both geometric and material nonlinearities are implemented in the proposed software: (1) catenary cable element; (2) truss element; and (2) beam-column element. An incremental-iterative solution scheme based on the Newmark method and the Newton-Raphson method is adopted for solving the nonlinear equations of motion. Several numerical examples are presented to verify the accuracy and efficiency of the proposed software in predicting the nonlinear response of steel structures. The proposed program is shown to be an efficient and reliable tool for daily use in design.     

Nonlinear analysis of 3-D steel frames

In this paper, a nonlinear analysis of three-dimensional steel frames is developed. This analysis accounts for material and geometric nonlinearities. The material nonlinearity considers the gradual yielding associated with member forces. The geometric nonlinearity includes the second-order effects associated with P-δ and P-Δ. The material nonlinearity at a section is considered using the concept of the P–M hinge consisting of many fibers. The geometric nonlinearity is considered by the use of stability functions. The modified incremental displacement method is used as the solution technique. The load–displacement relationships predicted by the proposed analysis compare well with those given by other approaches.     

Nonlinear inelastic analysis of space frames

In this paper, a fiber beam-column element which considers both geometric and material nonlinearities is presented. The geometric nonlinearities are captured using stability functions obtained from the exact stability solution of a beam-column subjected to axial force and bending moments. The material nonlinearities are included by tracing the uniaxial stress-strain relationship of each fiber on the cross sections. The nonlinear equilibrium equations are solved using an incremental iterative scheme based on the generalized displacement control method. Using only one element per member in structure modeling, the nonlinear responses predicted by the proposed element compare well with those given by commercial finite element packages and other available results. Numerical examples are presented to verify the accuracy and efficiency of the proposed element.     

空间框架的非线性塑性分析

介绍一种纤维梁柱单元,考虑几何和材料非线性。通过轴力和弯矩作用下构件稳定方程中的稳定函数来表示几何非线性,通过跟踪横截面上各纤维的单轴应力-应变关系来模拟材料非线性。基于广义位移控制方法,采用增量迭代法求解非线性平衡方程。用1个单元模拟1根杆件,该单元的非线性性能与有限元软件分析结果及其他有效结果比较吻合,并举例证明了该单元的准确性和有效性。     

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.     

Elastoplastic large deformation analysis of a lattice steel tower structure and comparison with full-scale tests

The objective of this paper is to develop a numerical model for simulating ultimate behavior of lattice steel tower structures. We present the elastoplastic large deformation analysis of a lattice steel tower structure using finite element analysis and we compare the numerical results with full-scale destructive tests. A 2-node three-dimensional L-section beam finite element proposed in our previous work is used. The beam finite element can consider eccentricities of loading and boundary conditions as well as material and geometrical nonlinearities. We model a real tower structure section using the beam elements and perform a nonlinear static analysis to obtain the limit behavior of the tower in two different load cases. The numerical results are discussed in detail.     

采用纤维铰法的钢框架二阶非线性动力分析

考虑几何非线性和材料非线性,建立了适用于钢框架非线性动力分析的简洁且有效的数值程序。通过采用拉弯或压弯下梁柱节点稳定性求解中的稳定函数来考虑几何非线性。通过追踪横截面上整合点处沿杆长方向每个纤维的单轴应力-应变关系,确定横截面上沿杆长方向的的塑性发展。通过采用平均加速度方法的计算机程序,求解动力方程。与ABAQUS程序计算结果对比,验证了本程序的准确性和计算效率。     

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.     

钢管混凝土框架结构力学性能非线性有限元分析

在考虑材料非线性和几何非线性的基础上进行了钢管混凝土柱-钢梁平面框架结构力学性能的非线性有限元分析,核心混凝土采用考虑钢管约束效应的应力-应变关系,钢材采用二次塑流模型或线性强化模型,通过在有限元公式中引入几何刚度矩阵,并在荷载步中更新坐标描述二阶效应来反映框架结构的几何非线性效应。基于近似修正的拉格朗日表述来反映框架结构变形前后位形之间的关系,利用虚功原理建立相应的增量平衡方程,并采用位移增量法求解非线性有限元方程,理论计算结果得到试验结果的验证。分析表明,基于非线性纤维梁-柱单元理论的分析方法可以反映钢管混凝土框架在受力过程中构件屈服和塑性分别沿截面和杆长两个方向扩展的分布塑性特征,并考虑初始缺陷、残余应力等,因此可较好地反映钢管混凝土框架的力学性能。在此基础上对影响钢管混凝土框架力学性能的主要因素进行了参数分析,分析的具体结果可供有关研究或工程应用参考。     

方钢管混凝土柱穿心高强螺栓-端板节点性能研究

提出一种新型穿心高强螺栓-端板方钢管混凝土柱-钢梁节点,并对3个节点试件进行柱端加载的伪静力试验研究。利用三维实体单元,建立同时考虑几何、材料及接触等三重非线性的有限元模型,采用有限元程序ANSYS对节点进行单调荷载和循环荷载作用下的有限元分析。试验及有限元计算结果表明,节点具有很好的强度、刚度、延性和耗能能力。     

Loss-of-stability induced progressive collapse modes in 3D steel moment frames

This paper deals with the progressive collapse analysis of a tall steel frame following the removal of a corner column according to the alternate load path approach. Several analysis techniques are considered (eigenvalue, material nonlinearities, material and geometric nonlinearities), as well as 2D and 3D modelling of the structural system. It is determined that the collapse mechanism is a loss-of-stability-induced one that can be identified by combining a 3D structural model with an analysis involving both material and geometric nonlinearities. The progressive collapse analysis reveals that after the initial removal of a corner column, its two adjacent columns fail from elastic flexural-torsional buckling at a load lower than the design load. The failure of these two columns is immediately followed by the failure of the next two adjacent columns from elastic flexural–torsional buckling. After the failure of these five columns, the entire structure collapses without the occurrence of any significant plastification. The main contribution is the identification of buckling-induced collapse mechanisms in steel frames involving sequential buckling of multiple columns. This is a type of failure mechanism that has not received appropriate attention because it practically never occurs in properly designed structures without the accidental loss of a column.     

基于有限质点法的结构倒塌破坏研究Ⅱ:关键问题与数值算例

采用有限质点法求解结构倒塌破坏的关键问题，包括结构动力反应、几何非线性和材料非线性分析以及构件断裂。采用虚拟运动分离单元的刚体运动和纯变形，用以模拟结构的几何非线性行为；根据不同的本构模型计算质点内力，求解材料非线性问题；为模拟构件的断裂，建立了杆单元和梁单元的断裂准则，提出了断裂发生后的结构计算方法；综合考虑各关键问题，给出结构倒塌过程模拟的分析流程。通过对一个空间刚架的几何非线性、材料非线性和断裂行为的模拟和分析，验证了有限质点法在结构复杂行为计算中的正确性；最后对某悬挑网架结构在台风作用下的倒塌破坏过程进行研究，并将分析结果与现场破坏情况进行对比和分析。研究表明，该方法适用于结构的倒塌破坏研究，可以对倒塌全过程进行模拟，计算结果能够揭示结构的倒塌破坏机理。     

Nonlinear analysis of multi-cell reinforced concrete box girder bridges

A numerical method of analysis is developed to determine the nonlinear response, collapse mechanisms and ultimate failure loads of multi-cell RC (reinforced concrete) box girder bridges under stepwise increasing static loads. Nonlinearities considered are material nonlinearities inherent in RC members such as cracking of the concrete, yielding of the reinforcement and formation of plastic hinges due to shear and flexure. The analytical model, based on a three-dimensional grillage, is developed for multicellular structures of arbitrary plan geometry and constant height. Realistic but simple assumptions for the interaction of internal forces due to flexure, shear and torsion in the cellular structure, as well as idealized trilinear force-deformation characteristics for the individual members comprising the grillage, result in a very economical nonlinear analytical model. The proposed analytical scheme, which is based on a mixed model formulation at the element level, is demonstrated and tested on a series of numerical examples and the analytical results indicate good agreement with experimental results obtained from large scale model tests on RC box girder bridges.     

A finite element analysis model for the behaviour of cold-formed steel members

A finite element analysis model for the post-local buckling behaviour of cold-formed steel (CFS) members subjected to axial compression has been developed. The finite element model consists of a Total Lagrangian nonlinear 9-node “assumed strain” shell finite element, and experimental-based material properties models to represent the body of the CFS sections. Experimentally derived residual stress variations, and initial geometric imperfections have also been incorporated. A special loading technique and a displacement solution algorithm were employed to obtain a uniform displacement condition at the loading edges. Details of a test program involving 20 non-perforated, and perforated cold-formed stub-column steel sections have been presented in the second part of the paper. The comparison between the test results, and the finite element results was performed for axial and lateral displacement behaviour, buckling loads, ultimate loads, and axial stress distribution. The comparison forms the basis for the evaluation of the efficiency, and the accuracy of the finite element model, and it indicated that the finite element analysis model constructed herein gives accurate and consistent results for the behaviour of the cold-formed steel members subjected to axial compression.     

Computational modeling of cold-formed steel

The objective of this paper is to provide an overview of computational modeling, both elastic buckling and nonlinear collapse analysis, for cold-formed steel members. Recent research and experiences with computational modeling of cold-formed steel members conducted within the first author's research group at Johns Hopkins University are the focus of the presented work. This admittedly biased view of computational modeling focuses primarily on the use of the semi-analytical finite strip method and collapse modeling using shell finite elements. Issues addressed include how to fully compare finite strip and finite element solutions, and the importance of imperfections, residual stresses, material modeling, boundary conditions, element choice, element discretization, and solution controls in collapse modeling of cold-formed steel. Examples are provided to demonstrate the expected range of sensitivity in cold-formed steel collapse modeling. The paper concludes with a discussion of areas worthy of future study that are within the domain of cold-formed steel modeling.     

Advanced analysis of hybrid steel and concrete frames: Part 2: Refined plastic hinge and advanced analysis

Robust geometric and material nonlinear analysis of buildings under ultimate loads is a key to success of advanced analysis, performance-based seismic design and progressive collapse analysis. This is the second part of two companion papers about the advanced analysis of hybrid steel and concrete frames allowing for various effects such as initial imperfections, gradual cracking effect and geometrical and material nonlinearities. Besides the use of Pointwise–Equilibrium–Polynomial (PEP) element allowing for initial imperfections and the P–Δ–δ effects by one element per member, the plastic hinge approach is refined for modelling of material yielding. In order to assess the sectional strength, the cross-section analysis technique described in the companion paper is utilized in this paper for analysis of steel reinforced concrete (RC) and steel-concrete composite (SCC) sections. Cracking in concrete component, which has significant influence on structural deformation and internal force distribution, is considered by using the Branson's model combined with the concrete cracking fracture surface. The distinct feature of the proposed method is that it integrates the accurate cross-sectional analysis technique to the refined lumped plasticity approach such that a feasible and reliable solution can be obtained. Members with previous experimental results and a portal frame are studied and compared for validation of the proposed method.     

蜂窝钢梁屈曲模型的相互影响

基于侧扭屈曲模型,采用三维非线性有限元法,考虑初始几何缺陷和材料非线性,研究普通和高强蜂窝钢梁的性能。通过不同跨度和横截面的蜂窝梁试验,对模型进行验证。研究了蜂窝钢梁的破坏荷载、屈曲模型间的相互影响、荷载-侧移曲线。采用有限元模型进行参数分析,研究横截面尺寸、梁长、型钢强度对蜂窝钢梁承载力和屈曲性能的影响。腹板的畸变屈曲较大地降低了细长蜂窝钢梁的承载力。将有限元分析得到的侧扭屈曲下钢梁破坏荷载与澳大利亚规范进行比较,结果表明:规范对侧扭屈曲下普通蜂窝钢梁的破坏分析偏保守,对腹板屈曲下蜂窝钢梁的破坏分析较合理,而对侧扭屈曲下高强蜂窝钢梁的破坏分析非常保守。