钢管混凝土框架的非线性分析

建立数值程序,对钢管混凝土框架进行非线性分析。通过采用轴力和弯矩共同作用下梁柱结构稳定求解中的稳定函数,考虑几何非线性。通过追踪沿杆件长度方向选定的横截面上的纤维单轴应力-应变关系,描述横截面上及杆件长度方向的塑性发展。由于位移控制方法具有数值稳定性和有效性,基于此,采用增量迭代法,求解非线性平衡方程。通过与试验和已有求解结果的比较,验证了本方法的准确性。对于钢管混凝土结构的非线性分析,数值分析是有效的。     

Nonlinear inelastic time-history analysis of truss structures

This paper presents the nonlinear inelastic time-history analysis of truss structures including both geometric and material nonlinearities. The geometric nonlinearity is considered based on an updated Lagrangian formulation, while the material nonlinearity is captured by tracing an empirical stress–strain relationship in the elastoplastic range. The presented truss model is capable of capturing several failure modes of member such as buckling, yielding, inelastic post-buckling, unloading, and reloading. An incremental-iterative solution scheme based on the Newmark method and the Newton–Raphson method is adopted for solving the nonlinear equations of motion. A computer program is developed to predict the nonlinear inelastic responses of truss structures. Numerical examples are presented to demonstrate the capabilities of the proposed program in capturing the nonlinear responses of space truss structures under earthquake loadings.     

Second-order inelastic dynamic analysis of steel frames using fiber hinge method

This paper presents a simple and effective numerical procedure for the nonlinear inelastic dynamic analysis of steel frames under dynamic loadings which considers both geometric and material nonlinearities. The geometric nonlinearities are included by using stability functions obtained from the exact stability solution of a beam-column subjected to axial force and bending moments. The spread of plasticity over the cross section and along the member length is captured by tracing the uniaxial stress-strain relations of each fiber on the cross-sections located at the integration points along the member length. A computer program utilizing the average acceleration method for the integration scheme is developed to numerically solve the equations of motion. The obtained results are compared with those generated by ABAQUS to illustrate the accuracy and the computational efficiency of the proposed procedure.     

Nonlinear analysis of circular concrete-filled steel tubular short columns under axial loading

The confinement effect provided by the steel tube in a circular concrete-filled steel tubular (CFST) short column remarkably increases the strength and ductility of the concrete core. The reliable prediction using nonlinear analysis methods for circular CFST columns relies on the use of accurate models for confined concrete. In this paper, accurate constitutive models for normal and high strength concrete confined by either normal or high strength circular steel tubes are proposed. A generic fiber element model that incorporates the proposed constitutive models of confined concrete is created for simulating the nonlinear inelastic behavior of circular CFST short columns under axial loading. The generic fiber element model developed is verified by comparisons of computational results with existing experimental data. Extensive parametric studies are conducted to examine the accuracy of various confining pressure models and the effects of the tube diameter-to-thickness ratio, concrete compressive strengths and steel yield strengths on the fundamental behavior of circular CFST columns. A new design formula accounting for concrete confinement effects is also proposed for circular CFST columns. It is demonstrated that the generic fiber element model and design formula adequately predict the ultimate strength and behavior of axially loaded circular CFST columns and can be used in the design of normal and high strength circular CFST columns.     

Nonlinear analysis of circular concrete-filled steel tubular short columns under eccentric loading

This paper presents an effective theoretical model for the nonlinear inelastic analysis of circular concrete-filled steel tubular (CFST) short columns under eccentric loading. Accurate material constitutive relationships for normal and high strength concrete confined by either normal or high strength circular steel tubes are incorporated in the theoretical model to account for confinement effects that increase both the strength and ductility of concrete. The predicted ultimate bending strengths and complete moment-curvature responses of circular CFST columns under eccentric loading are compared with existing experimental results to examine the accuracy of the theoretical model developed. The fundamental behavior of circular CFST beam-columns with various diameter-to-thickness ratios, concrete compressive strengths, steel yield strengths, axial load levels and sectional shapes is studied using the verified theoretical model. Based on extensive numerical studies, a new design model for determining the ultimate pure bending strengths of circular CFST beam-columns is proposed. The theoretical model and formulas developed are shown to be effective simulation and design tools for the nonlinear inelastic behavior of circular CFST beam-columns under eccentric loading.     

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.     

偏心荷载下钢管混凝土圆形短柱的非线性分析

提出了一个有效的理论模型,用于钢管混凝土圆形短柱在偏心荷载作用下的非线性弹塑性分析。理论模型中考虑了普通或高强钢管中填充的普通和高强混凝土的精确材料构成关系,用于计算混凝土强度和延性升高时对约束效应的影响。将偏心荷载下对钢管混凝土圆柱预测的极限抗弯强度和完整的弯矩-曲率曲线,与现有的试验数据进行对比以验证理论模型的准确性。利用经过验证的理论模型对圆形钢管混凝土梁柱的基本性能包括径厚比、混凝土抗压强度、钢筋屈服强度、轴向荷载水平和截面形状进行了研究。基于大量的数值研究,针对圆形钢管混凝土梁柱提出了一个用于确定极限纯弯强度的设计模型。理论模型和公式可以对偏心荷载下圆形钢管混凝土梁柱的非线性弹塑性性能进行有效的模拟和设计。     

Nonlinear analysis of concrete-filled square stainless steel stub columns under axial compression

Concrete-filled stainless steel tubes (CFSST) can be considered as a new and innovative kind of composite construction technique, and have the potential to be used extensively in civil engineering. This paper employs a nonlinear analysis of square CFSST stub columns under axial compression. A three-dimensional nonlinear finite element (FE) model is developed using ABAQUS, where nonlinear material behaviour, enhanced strength corner properties of steel, and initial geometric imperfections are included. Close agreement is achieved between the test and FE results in terms of load-deformation response and ultimate strength. In light of the numerical results, the behaviour of stainless steel composite columns is compared with that of carbon steel composite columns. A simple model is proposed to calculate the ultimate strength of square CFSST stub columns.     

Nonlinear inelastic analysis of building frames with thin-walled cores

A second-order inelastic analysis by combining the theories of stability and plasticity is proposed for studying frames with thin-walled cores. In the proposed approach, steel frameworks surrounding the cores are modelled by using the plastic hinge beam-column approach, and core walls modelled by using the thin-walled beam-column approach. Transformation procedures are proposed to consider the kinematic relationship between beams, columns, core walls and floor diaphragm. Nonlinear solution procedures are incorporated for the incremental analysis. The proposed inelastic analysis is used to investigate the inelastic behaviour and ultimate strength of core-braced frames.     

High strength circular concrete-filled steel tubular slender beam-columns, Part I: Numerical analysis

High strength circular concrete-filled steel tubular (CFST) slender beam-columns are frequently used in high-rise composite buildings because they possess higher strength and stiffness than normal strength ones. Most nonlinear inelastic methods of analysis for circular CFST slender beam-columns have not considered the effects of high strength materials and concrete confinement that significantly increases the strength and ductility of the concrete core. As a result, these methods produce computational solutions that deviate considerably from experimental results. This paper presents a new numerical model for predicting the nonlinear inelastic behavior of high strength circular CFST slender beam-columns under axial load and bending. The numerical model developed not only accounts for confinement effects on the concrete core and circular steel tubes but also incorporates initial geometric imperfections of beam-columns. Axial load-moment-curvature relationships obtained from the fiber element analysis of column cross-sections are utilized to determine the equilibrium states in the inelastic stability analysis of slender beam-columns. Computational algorithms are developed for determining the axial load-deflection and axial load-moment interaction curves for slender beam-columns. The numerical model is implemented in a computer program, which is shown to be an efficient and accurate simulation tool that can be used to investigate the fundamental behavior of high strength circular CFST slender beam-columns. The verification and applications of the numerical model are given in a companion paper.     

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。     

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.     

高强圆钢管混凝土压弯构件(1):数值分析

由于具有比普通构件强度高、刚度大等特点,高强圆钢管混凝土压弯构件被广泛用于高层建筑中。然而,针对此类构件的大多数非线性分析方法都没有考虑高强材料属性和混凝土约束的影响,这很大程度上高估了核心混凝土的强度和韧性。因此,这些方法的求解结果与试验结果相差很大。针对高强圆钢管混凝土压弯构件的非线性性能,提出新的数值模型。该模型不仅考虑了混凝土约束对核心混凝土和钢管的影响,还考虑了压弯构件的初始几何缺陷。根据通过有限元分析求得的轴力-弯矩曲线,确定压弯构件非线性稳定分析中的平衡状态。为确定轴力-变形及轴力-弯矩曲线,提出了计算准则。在计算机程序中应用该数值模型,可研究高强圆钢管混凝土压弯构件的基本性能。在后续文章中,将验证该模型的正确性,并应用此模型。     

High strength circular concrete-filled steel tubular slender beam-columns, Part II: Fundamental behavior

There is relatively little experimental and numerical research on the fundamental behavior of high strength circular concrete-filled steel tubular (CFST) slender beam-columns. In a companion paper, a new numerical model for predicting the nonlinear inelastic behavior of high strength circular CFST slender beam-columns under axial load and bending was presented. The numerical model developed accounts for confinement effects on the strength and ductility of the concrete core and on circular steel tubes as well as initial geometric imperfections of beam-columns. This paper presents the verification of the numerical model and extensive parametric studies on the fundamental behavior of high strength circular CFST slender beam-columns. The ultimate strengths and axial load-deflection responses of circular CFST slender beam-columns under eccentric loading predicted by the numerical model are verified by corresponding experimental results. The computer program implementing the numerical model is used to investigate the fundamental behavior of high strength circular CFST slender beam-columns in terms of load-deflection responses, ultimate strengths, axial load-moment interaction diagrams, and strength increase due to concrete confinement. Parameters examined include column slenderness ratio, eccentricity ratio, concrete compressive strengths, steel yield strengths, steel ratio and concrete confinement. It is demonstrated that the numerical model developed is an efficient computer simulation and design tool for high strength circular CFST slender beam-columns. Benchmark numerical results presented in this paper are valuable in the development of composite design codes for high strength circular CFST slender beam-columns.     

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.     

悬索桥的非弹性动力分析

提出一种精确的计算方法,用于地震作用下悬索桥的非线性时程分析。该方法考虑了几何非线性和材料非线性。利用稳定函数分析桥塔和主梁的几何非线性,而用弹性悬链线的精确解析方程分析索杆的几何非线性。利用切线模量概念和精细塑性铰模型按构件长度和截面划分屈服等级。给出一种基于Newton-Raphson法的Newmark平均加速算法。计算结果与商业软件SAP2000的分析结果吻合,说明该计算程序准确有效。     

高强圆钢管混凝土压弯构件(2):基本性能

目前,有关高强圆钢管混凝土压弯构件基本性能的试验及数值研究相对较少。在之前文章中,已经提出评估此类压弯构件非线性性能的数值模型,考虑约束和初始几何缺陷对核心混凝土强度和韧性及钢管的影响。验证该模型的正确性,并进行压弯构件基本性能的参数化研究。通过相应的试验结果,验证根据此模型求得的偏心荷载作用下极限承载力和轴力-变形性能的正确性。在计算机程序中应用该模型,研究高强圆钢管混凝土压弯构件的基本性能,如:荷载-位移曲线,极限承载力,轴力-弯矩曲线及由混凝土约束引起的强度增量。参数包括:构件长细比,偏心率,混凝土抗压强度,钢材屈服强度,钢材百分比,混凝土约束条件等。结果表明:提出的数值模型能有效模拟和设计高强圆钢管混凝土压弯构件。本基准数值结果对完善组合结构设计规范中有关高强混凝土压弯构件的规定很有意义。     

预应力斜拉网格结构的非线性静力分析

对预应力斜拉网格结构的线性和非线性进行了对比分析。分析结果表明：当斜拉索跨度较大或垂度比较大时,不宜忽略斜拉索的非线性影响,应选用合理的方法进行非线性分析,综合考虑斜拉索由于自重垂度对刚度和索力的效应。     

Behavior of biaxially-loaded rectangular concrete-filled steel tubular slender beam-columns with preload effects

In composite construction, rectangular hollow steel tubular slender beam-columns are subjected to preloads arising from construction loads and permanent loads of the upper floors before infilling of the wet concrete. The behavior of biaxially loaded thin-walled rectangular concrete-filled steel tubular (CFST) slender beam-columns with preloads on the steel tubes has not been studied experimentally and numerically. In this paper, a fiber element model developed for CFST slender beam-columns with preload effects is briefly described and verified by existing experimental results of uniaxially loaded CFST columns with preload effects. The fiber element model is used to investigate the behavior of biaxially loaded rectangular CFST slender beam-columns accounting for the effects of preloads and local buckling. Parameters examined include local buckling, preload ratio, loading angle, depth-to-thickness ratio, column slenderness, loading eccentricity and steel yield strength. The results obtained indicate that the preloads on the steel tubes significantly reduce the stiffness and strength of CFST slender beam-columns with a maximum strength reduction of more than 15.8%. Based on the parametric studies, a design model is proposed for axially loaded rectangular CFST columns with preload effects. The fiber element and design models proposed allow for the structural designer to efficiently analyze and design CFST slender beam-columns subjected to preloads from the upper floors of a high-rise composite building during construction.     

某超限高层框筒结构弹塑性动力时程分析

应用MIDAS BUILDING结构软件对一个高层框筒结构进行了罕遇地震下的动力弹塑性分析,给出了结构在实际地震作用下的动力响应及各部位、构件的塑性发展情况,对结构的抗震性能做出评价,并对工程设计提出改进建议。