Finite element model updating for large span spatial steel structure considering uncertainties

In order to establish the baseline finite element model for structural health monitoring,a new method of model updating was proposed after analyzing the uncertainties of measured data and the error of finite element model.In the new method,the finite element model was replaced by the multi-output support vector regression machine(MSVR).The interval variables of the measured frequency were sampled by Latin hypercube sampling method.The samples of frequency were regarded as the inputs of the trained MSVR.The outputs of MSVR were the target values of design parameters.The steel structure of National Aquatic Center for Beijing Olympic Games was introduced as a case for finite element model updating.The results show that the proposed method can avoid solving the problem of complicated calculation.Both the estimated values and associated uncertainties of the structure parameters can be obtained by the method.The static and dynamic characteristics of the updated finite element model are in good agreement with the measured data.

Three-Dimensional Thermo-Elastic-Plastic Finite Element Method Modeling for Predicting Weld-Induced Residual Stresses and Distortions in Steel Stiffened-Plate Structures

The objective of the present paper is to develop nonlinear finite element method models for predicting the weld-induced initial deflection and residual stress of plating in steel stiffened-plate structures. For this purpose, three-dimensional thermo-elastic-plastic finite element method computations are performed with varying plate thickness and weld bead length (leg length) in welded plate panels, the latter being associated with weld heat input. The finite element models are verified by a comparison with experimental database which was obtained by the authors in separate studies with full scale measurements. It is concluded that the nonlinear finite element method models developed in the present paper are very accurate in terms of predicting the weld-induced initial imperfections of steel stiffened plate structures. Details of the numerical computations together with test database are documented.

A 3-Node Co-Rotational Triangular Finite Element for Non-Smooth,Folded and Multi-Shell Laminated Composite Structures

Based on the first-order shear deformation theory,a 3-node co-rotational triangular finite element formulation is developed for large deformation modeling of non-smooth,folded and multi-shell laminated composite structures.The two smaller components of the mid-surface normal vector of shell at a node are defined as nodal rotational variables in the co-rotational local coordinate system.In the global coordinate system,two smaller components of one vector,together with the smallest or second smallest component of another vector,of an orthogonal triad at a node on a non-smooth intersection of plates and/or shells are defined as rotational variables,whereas the two smaller components of the mid-surface normal vector at a node on the smooth part of the plate or shell(away from non-smooth intersections)are defined as rotational variables.All these vectorial rotational variables can be updated in an additive manner during an incremental solution procedure,and thus improve the computational efficiency in the nonlinear solution of these composite shell structures.Due to the commutativity of all nodal variables in calculating of the second derivatives of the local nodal variables with respect to global nodal variables,and the second derivatives of the strain energy functional with respect to local nodal variables,symmetric tangent stiffness matrices in local and global coordinate systems are obtained.To overcome shear locking,the assumed transverse shear strains obtained from the line-integration approach are employed.The reliability and computational accuracy of the present 3-node triangular shell finite element are verified through modeling two patch tests,several smooth and non-smooth laminated composite shells undergoing large displacements and large rotations.

Eigenanalysis of Electromagnetic Structures Based on the Finite Element Method

This article presents a review of our research effort on the eigenanalysis of open radiating waveguides and closed resonating structures. A two dimensional (2-D) hybrid Finite Element method in conjunction with a cylindrical harmonics expansion is established to formulate the open waveguide generalized eigenvalue problem. The key element of this approach refers to the adoption of a vector Dirichlet-to-Neumann map to rigorously enforce the continuity of the two field expansions along a truncation surface. The resulting algorithm was able to evaluate both surface and leaky eigenmodes. The eigenanalysis of three dimensional (3-D) structures involves vast research challenges, especially when they are electrically large and open-radiating. The effort herein is focused on the electrically large case including the losses due to the finite conductivity of metallic walls and objects as well as the loading material losses. The former is introduced through impedance or Leontovich boundary condition, resulting to a non-linear-polynomial generalized eigenvalue problem. A straightforward linearization solution is adopted along with a more efficient alternative technique which mimics analytical approaches. For this one the linear eigenproblem formulated assuming metals as perfect electric conductors is initially solved and their finite conductivity is accounted through impedance boundary conditions enforced locally on the resulting eigenvectors. Finally, some numerical results are presented to verify the performance of these methodologies along with a discussion on their possibilities for extension to open 3D structures as well as to characteristic modes eigenanalysis.

Structural Analysis and Design of Steel Connections Using Component-Based Finite Element Model

This paper introduces CBFEM （component-based finite element model） which is a new method to analyze and design connections of steel structures. Design focused CM （component model） is compared to FEM （finite elements models）. Procedure for composition of a model based on usual production process is used in CBFEM. Its results are compared to those obtained by component method for portal frame eaves moment connection with good agreement. Design of moment resistant column base is demonstrated by a case loaded by two directional bending moments and normal force. Interaction of several connections in one complex joint is explained in the last example. This paper aims to provide structural engineers with a new tool to effectively analyze and design various joints of steel structures.

Finite Element Modelling of Steel Beams with Web Openings

Height limitations are not uncommon in multi-storey buildings due to economic requirements and esthetical considerations. Substantial spaces are normally required to enable the passage of large pipes and ducts beneath steel beams leading to uneconomic floor heights. The most adopted solution for this issue is the use of steel beam web openings to provide the required space for services. These openings could lead to a significant decrease of the beam load carrying capacity depending on the adopted openings shape, size and location. These aspects motivated the present study based on FE simulations calibrated against numerical and test results. The results accuracy enabled a comprehensive parametric analysis of beams with web openings to be made focused on the profile size, web opening location, among others. The study also investigated the efficiency of longitudinal stiffeners welded at the opening region and benefits of using an adequate edge concordance radius in beams with rectangular and square openings. The obtained results showed the need of using welded longitudinal stiffeners in order to increase the beams ultimate load carrying capacity. This adoption can double or even triple the ultimate load of beams with rectangular and square opening heights equal to 0.75 H, respectively.

Wind-Induced Effect of a Spatial Latticed Dome Structure Using Stabilized Finite Element Method

A stabilized finite element algorithm potential for wind-structure interaction(WSI) problem is presented in this paper. Streamline upwind Petrov-Galerkin(SUPG) scheme of the large eddy simulation(LES) of dynamic sub-grid scale(DSGS) is developed under the framework of arbitrary Lagrangian-Eulerian(ALE) description to solve the governing equations. High stabilization is achieved by a three-step technique in the temporal discretization. On the other hand, the partitioned procedure is employed for the consideration of the coupled WSI problem. Newmark integral method is introduced for the computation of structure domain, while spring analogy method is used for the grid update of the mesh domain. The developed computational codes are applied to the analysis of wind-induced effect of a spatial latticed structure. The numerical predictions of the three-dimensional wind flow features, the wind pressures and the wind-induced effect of spatial structures are given. Comparisons are made between the effects of rigid structure in view of the WSI.

Time Domain Simulation of Transient Responses of Very Large Floating Structures Under Unsteady External Loads

A time domain finite element method （FEM） for the analysis of transient elastic response of a very large floating structure （VLFS） subjected to arbitrary time-dependent external loads is presented. This method is developed directly in time domain and the hydrodynamic problem is formulated based on linear, inviscid and slightly compressible fluid theory and the structural response is analyzed on the thin plate assumption. The time domain finite element procedure herein is validated by comparing numerical results with available experimental data. Finally, the transient elastic response of a pontoon-type VLFS under the landing of an airplane is computed by the proposed time domain FEM. The time histories of the applied force and the position and velocity of an airplane during landing are modeled with data from a Boeing 747-400 jumbo jet.

Numerical Simulation of Dynamic Response and Collapse for Steel Frame Structures Subjected to Blast Load

The progressive collapse of steel frame structures under the blast load was investigated using LS-DYNA. The multi-material Eulerian and Lagrangian coupling algorithm was adopted. A flu-id-structure coupling finite element model was established which consists of Lagrange element for simulating steel frame structures and concrete ground, multiple ALE element for simulating air and TNT explosive material. Numerical simulations of the blast pressure wave propagation, struc-tural dynamic responses and deformation, and progressive collapse of a five-story steel frame structure in the event of an explosion near above ground were performed. The numerical analysis showed that the Lagrangian and Eulerian coupling algorithm gave good simulations of the shock wave propagation in the mediums and blast load effects on the structure. The columns subjected to blast load may collapse by shear yielding rather than by flexural deformation. The columns and joints of steel beam to column in the front steel frame structure generated enormous plastic defor-mation subjected to intensive blast waves, and columns lost carrying capacity, subsequently lead-ing to the collapse of the whole structure. The approach coupling influence between struc-tural deformation and fluid load well simulated the progressive collapse process of structures, and provided an effective tool for analyzing the collapse mechanism of the steel frame structure under blast load.

Coupled BEM-FEM Analysis of the Large-Diameter Cylinder Structure System

A method of coupled BEM-FEM analysis for the elastic spatial structure system is presented. It can be applied to the calculation of the stress and deformation of the large-diamater cylinder structure system and it is suitable for symmetric or non-symmetric structures under the distributed or concentrated load. Numerical examples show that the proposed method and computer program BEFEM are quite efficient in the analysis of the large-diameter cylinder structure problems in ocean engineering.

Analyzing the Form-Finding of a Large-Span Transversely Stiffened Suspended Cable System: A Method Considering Construction Processes

The precise control of the shape of transversely stiffened suspended cable systems is crucial. However, existing form-finding methods primarily rely on iterative calculations that treat loads as fixed known conditions. These methods are inefficient and fail to accurately control shape results. In this study, we propose a form-finding method that analyzes the load response of models under different sag and stress levels, taking into account the construction process. To analyze the system, a structural finite element model was established in ANSYS, and geometric nonlinear analysis was conducted using the Newton-Raphson method. The form-finding analysis results demonstrate that the proposed method achieves precise control of shape, with a maximum shape error ranging from 0.33% to 0.98%. Furthermore, the relationships between loads and tension forces are influenced by the deformed shape of the structures, exhibiting significant geometric nonlinear characteristics. Meanwhile, the load response analysis reveals that the stress level of the self-equilibrium state in the transversely stiffened suspended cable system is primarily governed by strength criteria, while shape is predominantly controlled by stiffness criteria. Importantly, by simulating the initial tensioning process as an initial condition, this method solves for a counterweight that satisfies the requirements and achieves a self-equilibrium state with the desired shape. The shape of the self-equilibrium state is precisely controlled by simulating the construction process. Overall, this work presents a new method for analyzing the form-finding process of large-span transversely stiffened suspended cable system, considering the construction process which was often overlooked in previous studies.

Numerical Analysis of the Structure of High-Strength Double-Layer Steel Plate Concrete Shaft by Drilling Method of Water-Bearing Weak Rock Formation

In order to ensure the safety of coal mine shaft construction, a double-layer steel plate concrete composite shaft wall structure was proposed. However, fewer studies were conducted on this structure, which made engineers too confused to fully recognize its feasibility of this structure. Hence, based on the previous experimental research on the Taohutu mine construction project in Ordos in Inner Mongolia, this research paper aims to provide a widely deep numerical analysis by the usage of the finite element software, in fact, to establish the corresponding numerical analysis model and make a comparison with the experimental data to get the rationality of the verified model. The influence of the composite characteristics of the steel plate and concrete on the ultimate bearing capacity and stress field of the shaft wall structure is studied here through the method of multi-factor analysis. Also, the optimal design scheme of the double-layer steel plate and concrete composite shaft wall structure is proposed in this research paper.

Influence of local geometric parameters on fatigue performance of orthotropic steel deck

Fatigue has become critical issue for bridge with orthotropic steel deck.Number of stress cycle and equivalent stress amplitude were adopted as two investigated fatigue effects.As presented from fatigue monitoring comparison of two series-lined bridges,three local geometric parameters of steel box girder have significant influence on fatigue performance of two welded joints.They are thickness of longitudinal ribs(Tr),longitudinal spacing of transverse floor plate(Sc)and longitudinal truss(LT).Fatigue analytical models were created for parametric study of fatigue effects under wheel load.Consequently,three local parameters have exhibited insignificant influence on number of stress cycle.Compared with Tr and Sc,configuration of LT has brought about foremost effect on the equivalent stress amplitude.For equivalent stress amplitude of rib-to-deck and rib-to-rib welded joints,the influence regions of LT are respectively longitudinal strap and quadrate with the geometric length of 600 mm.Enough attention ought to be paid for local stiffen structure on fatigue performance of orthotropic steel deck in fatigue design and monitoring.

Ductility and Ultimate Capacity of Concrete-Filled Lattice Rectangular Steel Tube Columns

A kind of concrete-filled lattice rectangular steel tube(CFLRST)column was put forward.The numerical simulation was modeled to analyze the mechanical characteristic of CFLRST column.By comparing the load-deformation curves from the test results,the rationality and reliability of the finite element model has been confirmed,moreover,the change of the section stiffness and stress in the forcing process and the ultimate bearing capacity of the column were analyzed.Based on the model,the comparison of ultimate bearing capacity and ductility between CFLRST column and reinforced concrete(RC)column were also analyzed.The results of the finite element analysis show that the loading process of CFLRST column consists of elastic stage,yield stage and failure stage.The failure modes are mainly strength failure and failure of elastoplastic instability.CFLRST column has higher bearing capacities in comparison with reinforced concrete columns with the same steel ratio.In addition,the stiffness degeneration of CFLRST column is slower than RC column and CFLRST column has good ductility.

大型履带吊上楼面板施工过程有限元分析

珠海某项目由框架、核心筒及双层交叉桁架结构体系组成,采用在地下室顶板上铺设路基箱的加固方式,部分构件先地面拼装再吊装等施工工艺,同时对履带吊行走路线进行严格的规划。在现有结构上进行钢结构吊装,对下部混凝土结构影响较大,采用MIDAS GEN有限元分析软件对下部混凝土结构的裂缝和应力变化情况进行有限元分析,模拟履带吊全施工过程。分析结果表明:在地下室顶板上铺设路基箱的加固方式,可以有效降低下部混凝土结构的最大变形及应力,满足国家规范要求。

The mechanical response of multi-tower continuous-span suspension bridge deck pavement based on whole bridge analysis

The effect of multiple span suspension structure on the mechanical response of bridge deck pavement was studied, and finite element analysis (FEM) of stress and strain of pavement according to the bridge floor system features of super-long and high flexibility was made. Meanwhile, the FEM results were compared with those of the single span suspension structure. Three-stage analytic hierarchy process (AHP) is developed to analyze the mechanical response including whole bridge analysis, partial beams section analysis and orthotropic plate analysis. The most unfavorable load position was determined by the numerical solutions acquired from each stage to study the main mechanical index of multiple span suspension structure. The FEM results showed that the mechanical response numerical solutions by using the three-stage AHP are greater than those by simplified boundary condition, and the force condition of multiple span suspension structure is worse than that of the single span suspension structure.

西安城市展示中心长悬挑、大跨度钢结构设计

西安城市展示中心由南馆、北馆和连桥组成,其中南馆悬挑长度62m,连桥跨度150m。结合建筑方案特点,南馆与连桥采用整层钢桁架结构体系,结构布置与建筑形态高度契合。介绍了南馆、连桥、穹顶、屋面等位置的结构布置情况,明确了超限项和抗震性能目标,对于多杆件复杂交汇钢节点进行有限元分析。针对南馆、连桥屋楼盖振动舒适度不足,设计布置了调谐质量阻尼器(TMD),实测减振效果显著。对连桥提升过程进行施工模拟,结果表明该过程增加了连桥挠度,需要考虑提前起拱。对超长连体结构温度和地震行波效应进行分析,根据结果对连桥楼板配筋和局部框架柱进行了加强。大震弹塑性分析与防连续倒塌分析结果表明,结构满足“大震不倒”的性能目标,结构冗余度较高,具有良好的防连续倒塌能力。

合肥新桥国际机场T2航站楼结构设计

新建合肥新桥国际机场T2航站楼采用下部为混凝土结构、顶部屋盖为大跨钢结构的结构形式,结构设计基于建筑特点和场地条件展开。介绍了基于场地表面起伏较大、需进行大面积回填条件下的桩基选型过程和桩基施工流程,详细阐述了基于建筑结构一体化理念的大跨屋盖结构体系及其支承结构的确定过程。根据航站楼的功能特点,通过比选确定主楼采用速度型减震装置的消能减震方案,提高结构的耗能能力并实现良好的抗震性能。通过抗连续倒塌分析和抗火分析确定钢屋盖及其支撑柱的防护方法,对钢管混凝土柱与下部钢筋混凝土柱等截面的连接节点进行了数值分析,最后对屋盖钢桁架的管-管相交节点确定原则进行了介绍。结果表明:该航站楼结构设计可靠,满足各项要求。

预应力在我国大跨度结构中的应用研究综述

为了提高大跨度结构的正常使用性能,通常在混凝土结构中施加预应力.结果表明,预应力混凝土结构具有更好的使用性、耐久性和大跨度适用性,其中预应力混凝土空心板结构在不显著降低承载力和刚度的前提下明显减小结构自重,预应力型钢混凝土梁(板)结构采用较小的截面尺寸即可满足承载力和刚度的需求.开发城市地下空间是解决城市用地紧张的有效手段,我国地下大跨空间常用的结构形式主要包括密排框架(肋梁)结构、折板或拱形结构、变截面(加腋)板结构、预应力混凝土结构、型钢-混凝土组合结构和Y形柱结构6种形式,相比之下,跨度较大时宜采用预应力结构.

常泰长江大桥组合索塔锚固结构钢-混传剪构造足尺模型试验研究

常泰长江大桥索塔锚固结构采用钢箱-核芯混凝土组合结构,为研究该新型组合索塔锚固结构钢-混传剪构造的受力特性,进行钢-混传剪构造足尺模型试验研究。制作2个锚固结构足尺节段试验模型,通过压剪试验研究锚固结构的荷载~滑移曲线及应力、应变分布等受力特性,并通过有限元模型分析锚固结构的传力机理和各组件的内力分配比例,推导剪力钉剪力计算方法。结果表明:在2.14倍单索最大索力荷载作用下,锚固结构保持弹性状态,钢壁板未产生明显滑移,钢-混界面最大滑移不超过0.25 mm,该锚固结构中钢-混传剪构造至少具有2.14倍的安全系数;荷载作用下,剪力钉剪力从上至下逐渐增大,锚腹板附近底部3排剪力钉剪力较大,钢-混传剪构造至少存在剪力钉和界面摩擦力2种传剪机制,钢-混传剪构造的承载能力显著提高;钢-混传剪构造受力过程分为粘结力传力阶段和局部滑移阶段,剪力钉剪力分布不仅与沿剪切方向长度分布有关,也与荷载的大小线性相关。