考虑楼板空间组合效应的组合框架体系纤维模型

将正常使用极限状态和承载能力极限状态有效宽度公式与传统纤维模型相结合，通过修正楼板钢筋和混凝土材料的单轴本构关系，实现了一种改进的考虑楼板空间组合效应的纤维模型，利用该模型可以在组合框架体系非线性分析中采用高效的全杆系单元合理地考虑复杂楼板空间组合效应的影响。基于考虑楼板空间组合效应的纤维模型，开发了一套较为完整的组合结构非线性有限元分析程序COMPONA-MARC (Version 1.0)。最后，将开发程序应用于多个组合框架抗震试验的模拟，结果表明了本文模型可较为准确地模拟组合框架弹塑性全过程的楼板空间组合效应。     

Analysis on shear behavior of high-strength bolts connection

Because of high cost of tests and numerical calculation using solid element of high-strength bolts connection in steel frameworks, it is important to find an accurate and simplified approach to describe the shear behavior of high-strength bolts connection. The paper aims to find a spring element to simulate the shear behavior instead of solid element in structure. Firstly, solid element model of high-strength bolt connection is established, which is proved correct and applicable comparing with existing typical shear tests. Then, base on the reliability of finite element model, the shear behavior of bolts connection is further discussed through a large number of parameter analyses. The three feature points and four stages of the simplified shear model are calibrated according to tests and calculation results. A simplified shear behavior model and hysteretic criterion of high-strength bolts connection are proposed. According to cases study, feasibility of the proposed model is validated. The proposed model gives a simple process to provide quite accurate results, which provides a great tool for engineering applications.     

城市固体废弃物的复合指数应力–应变模型及其应用

在大三轴固结排水剪试验研究的基础上,提出了城市固体废弃物(MSW)的复合指数应力–应变模型。该模型参数少且有明确的物理意义,既可反映MSW在小应变情况下的非线性变形特性,也可反映其在大应变情况下的明显应变硬化特性。采用有限差分程序FLAC内置的Fish语言将复合指数应力–应变模型耦合入FLAC程序,并通过三轴压缩试验数值模拟得到了验证。最后利用该模型分析了某填埋场在竖向扩建堆体荷载作用下的应力压缩沉降、侧向变形以及新老填埋场交界面处中间衬垫系统的应变。结果表明:复合指数模型的计算结果总体上位于莫尔–库仑模型和邓肯–张模型之间;中间衬垫系统的拉伸应变可能导致压实黏土层发生破坏。     

高应变率受压荷载下准各向同性碳纤维复合增强层压板的破环分析

对准各向同性纤维复合材料的动态抗压强度进行试验和数字模拟。采用分离式霍普金森压杆,在应变率400/s左右进行准各向同性层压板的平面压缩试验。与静态值相比,准各向同性层压板的动力强度大大增强。采用ABAQUS软件中实体8结点单元C3D8I和作者自定义的8结点界面单元建立有限元模型。界面单元连接三维实体单元来模拟复合材料层,其包括允许初始剥离和扩展的粘结破坏模式。假定模型在这些条件下的破坏现象主要取决于界面的剥离,这一结论通过试验得到验证。试验显示所有的准各向同性层压板几乎劈裂成完整的几块。模型结果与试验结果十分吻合,证实了假设:层内破坏不是准各向同性层压板破坏的主要原因。     

Random imperfection fields to model the size effect in laboratory wood specimens

The composite nature of a wood continuum prevents one from extrapolating the results of laboratory tests on standard wood specimens to structural elements of significant size. Therefore, these elements are usually tested under standardized loading conditions in order to detect a sort of average material behaviour.

In this paper, the initial step consists, instead, of testing the material specimens. The extension of the results to structural elements is then pursued by introducing a random field, or, in a discretized model, a random array of imperfections.

The calibration of the suitable spatial distribution of the imperfections is then investigated by a mixed experimental–numerical approach, for a reference beam. The analyses on the relative finite elements model are iterated to match the response of the full scale laboratory tests.     

Use of the equivalent continuum approach to model the behavior of a rock mass containing an interlayer shear weakness zone in an underground cavern excavation

An interlayer shear weakness zone (ISWZ) is a weak zonal geotechnical system of variable thickness that occurs between different rock strata (e.g., tuff and basalt). At the site of the future Baihetan hydropower station, Sichuan Province, China, because of the relatively poor ISWZ mechanical properties, the overall stability of the underground powerhouse is potentially at risk. In this study, to evaluate the effects of ISWZs on the stability of the future underground powerhouse by means of three-dimensional continuum modeling (3-D continuum modeling), the concept of a virtual rock mass composed of ISWZ and host rock is proposed. An equivalent continuum approach, including a rock–soil composite material (RSCM) model, is elaborated, with corresponding expressions for the input parameters. Comparisons were made between the predictions from the RSCM model, the results obtained by an analytic method, and existing data from physical model tests. The comparison showed that all three types of information showed good consistency in terms of failure mode and strength. This indicates the suitability of the RSCM model for describing the behavior of a rock mass containing discontinuities. Furthermore, comparison between the predictions of the proposed equivalent continuum approach, the joint element approach, and the solid element approach for a deformation of a test tunnel section containing an ISWZ show that the results produced by the first two approaches are similar, but much smaller than that using the third approach. Further comparison of the actual state of the ISWZ-containing rock mass in the test tunnel section confirmed the applicability of the proposed equivalent continuum approach to prediction of deformation of the rock masses containing ISWZs at the future Baihetan underground powerhouse site.     

Experimental and numerical study on restrained composite slab during heating and cooling

In this paper, a series of fire tests on restrained composite slabs, carried out at the University of Manchester, is presented. A total of six composite slabs were tested under different fire scenarios, with different load ratios. The tests were particularly concerned with the variation of internal forces within the slabs during both heating and cooling phases. In addition to the testing programme, two separate nonlinear finite element models have been developed to simulate the thermal and mechanical behaviour of composite slabs during heating and cooling, which is introduced in detail in this paper. In the thermal analysis model, plane elements were adopted to obtain a detailed thermal behaviour. In the structural analysis model, the concrete, steel deck and mesh were simulated by solid elements, shell elements and truss elements respectively. The interaction between the concrete and steel sheet was simplified to spring elements. According to the experimental results and FE modelling, the behaviour of composite slabs was analysed in detail. At last, the parametric study was performed where the effect of concrete strength, steel deck thickness and mesh size was analysed.     

加热和冷却过程中约束复合板的试验及数值研究

在曼彻斯特大学,对约束复合板进行一系列耐火试验。在不同火灾场景下,对6块不同荷载比下的复合板进行试验,观察加热和冷却过程中板内力的变化。设计试验方案,建立两种不同的非线性有限元模型,模拟复合板在加热和冷却过程中的热学和力学性能。在热分析模型中,采用平面单元模拟。在结构分析中,混凝土、钢板、锚钉分别采用实体单元、壳单元、桁架单元模拟。混凝土和钢板间的连接简化为弹簧单元。根据试验结果和有限元计算结果,详细分析了复合板的性能。最后,进行参数研究,分析了混凝土强度、钢板厚度和锚钉尺寸的影响。     

Effects of partial shear connection on the behavior of semi-continuous composite beams

In this paper, the effects of partial shear connection on the behavior of semi-continuous composite beams were studied numerically using two-dimensional finite element model with plane stress elements. The finite element model takes into account the nonlinearity of the different materials involved. For the shear connectors, a non-linear (shear-slip) relation, drawn from the push-out tests, was used. The accuracy of the proposed finite element model was verified against test results available in the literature. A simplified method to predict load capacity and deflection of the semi-continuous composite beams was also proposed. Based on the results obtained from the finite element analysis, the concept of partial shear connection in the hogging moment regions can be accepted provided that the shear connectors are sufficiently ductile.     

Design and behavior of recentering beam-to-CFT column connections with super-elastic shape memory alloy fasteners

This study investigates the performance of new composite (steel-concrete) moment connections through numerical simulations. The innovative aspects of this research lay in the use of end-plate connections between steel beams and concrete-filled tube (CFT) columns that utilize a combination of low-carbon steel and shape memory alloy (SMA) components. In these new connections, the intent is to use the recentering effect provided by super-elastic SMA tension bars to reduce the level of building damage and residual drift after a major earthquake. The low-carbon steel components provide excellent energy dissipation. The analysis and design of these structures is complicated because the connections cannot be modeled as being simply pins or full fixity ones; they are partial restraint (PR). A refined finite element (FE) model with sophisticated three dimensional (3D) solid elements was developed to perform numerical experiments on the PR-CFT joints with a view to obtaining the global behavior of the connection. Based on the behavioral information obtained from these FE tests, simplified connection models were formulated using 2D joint elements with nonlinear spring components. The behavior of entire connections under cyclic loads was examined. The results were compared with the connection behavior obtained from the 3D FE simulations and corresponding connection tests. Good agreement was found between the simple and sophisticated models, confirming the robustness of the approach.     

Two-dimensional computational framework of meso-scale rigid and line interface elements for masonry structures

In this paper, rigid elements along with nonlinear line interface elements are utilized to model masonry structures. The modeling approach focuses on two dimensions (2D) whereby the in-plane behavior of components is represented by rigid elements and nonlinear line interfaces instead of modeling by a traditional finite element method. In this approach, the component will be allowed to crack in predefined paths which have more likelihood for propagation. The paper discusses the model derivation and implementation. Moreover, the mesh sensitivity of this method is assessed by using different mesh sizes, and it is shown that the model captures response obtained by the experimental tests. The traditional finite element method is indeed capable of predicting the behavior of large scale masonry component, but the computational time is very high. In this study it has been shown that using rigid elements along with nonlinear line interfaces leads to a reduced number of degrees-of-freedom, which consequently reduces the computational time. The material model is implemented in a user-defined subroutine that is compiled with DIANA. The algorithms and material models are validated with well-documented experimental studies, and results clearly show the capabilities of the proposed procedures.     

Moment resistance of composite steel and concrete connection in sinusoidal-web girders

Steel girders have been successfully used for many years in the composite steel and concrete construction market. Further developments and advances in manufacturing technology have led to a new generation of structural shapes. One of these developments, the composite sinusoidal-web girders, has been recently introduced in the construction of Brazilian buildings. In spite of the advantages this type of composite construction may offer, there are no design standards dealing with the behavior of such girders. As a result, there is a need to develop design recommendations that properly address the flexural and rotation capacities and initial stiffness of these elements and their connections to the adjacent members. To this end: (i) experimental tests of connections on cruciform arrangements were performed, (ii) finite-element models for the connections and the composite girders have been developed, using the commercial finite element software ANSYS, (iii) finite element models were validated by experimental data, (iv) a parametric study was carried out and (v) a theoretical model is proposed. It is shown that the proposed theoretical model, despite all the complexities involved, is in compliance with both experimental and numerical analyses.     

正弦腹板网格结构中复合钢和混凝土连接节点的受弯承载力

多年来,钢梁已经被成功地运用于复合钢及混凝土结构领域中。制造技术的进一步发展和改进导致了新型结构型材的产生。其中复合正弦腹板网格结构在近些年被运用于巴西建筑结构中。尽管这种复合结构有很多优点,仍然缺少技术规范来计算这种梁结构的性能。因此,仍需要更多的设计建议妥善处理这些构件及它们与相邻构件连接处的弯扭承载力和初始刚度问题。所以:1)试验测试中所用构件按十字形排列;2)使用有限元分析软件AN-SYS构建构件和组合梁的有限元模型;3)有限元模型通过试验数据的验证;4)对其进行参数研究;5)提出一个理论模型。所提出的理论模型虽然包含了很多复杂因素,仍与试验和数值分析结果相吻合。     

推出试验中摩擦接触效应的数值分析

建立精确有效的2D非线性有限元模型,以研究组合桥梁中预制混凝土板和钢梁间抗剪连接件的力学性质。考虑材料非线性本构关系,采用4节点平面单元,该模型还对大梁翼缘与混凝土板以及混凝土板底部双头螺柱与混凝土之间的摩擦接触面进行了有限元分析。将数值分析结果与试验结果进行比较。每个试件中含有4个或9个双头螺柱。首先,给出能够精确模拟经典3D实际问题的2D数值分析法:等值法。然后,进行数值计算,研究摩擦系数对试件加载滑动性能的影响以及试件的内部变形与内力分布情况。最后,利用参数研究法和实际经验更好地进行连接件设计。     

A simplified FE simulation method with shell element for welding deformation and residual stress generated by multi-pass butt welding

In order to propose a simplified simulation method using finite element (FE) model for predicting deformation and residual stress generated by multi-pass butt welding, a series of experiments and numerical analyses were carried out. 3-pass butt welding of steel plates was simulated by the thermal elasto-plastic analysis with shell elements and with solid elements respectively. A heat input model for considering the temperature distribution in the thickness direction in shell elements was proposed. The validity of the heat input model was verified by comparing analytical results with experimental results or other analytical results using solid elements. Furthermore, the effectiveness for saving computing time by using shell elements was confirmed from the comparison with the case using solid elements. It was confirmed that the welding out-of-plane deformation and residual stress could be predicted with high accuracy by the proposed method. The computing time was around 14% of that by the precise model with solid elements.     

Three dimensional modeling for steel-concrete composite bridges using systems of bar elements — Modeling of skewed bridges

A new improved way for modeling steel composite straight bridges has been presented (Vayas, 2009; Vayas, 2010). The proposed model is based on the representation of steel I-girders through the use of equivalent trusses. The concrete slab is suitably represented by a set of bar elements. Diaphragms and stiffeners may also be taken into account. In contrast to the grillage model, which is usually used for the analysis of bridges, the recommended three dimensional model allows for a more reliable prediction of deformations and internal forces. This paper discusses the extension of the model to skewed composite bridges. The presence of skew makes the analysis complicated and for this reason the grillage analysis is not always recommended. Phenomena like differential deflections of the main girders during concreting and lateral displacements of the flanges can be adequately predicted using the proposed model. The new way for modeling composite bridges, using a spatial system of beam-like structural elements, can also be used for stability analysis of skewed bridges. Worked examples are provided to illustrate the set up procedure of the proposed modeling and to compare the different ways of analysis.     

实心和空心钢管混凝土的统一纤维模型

采用纤维模型是进行结构整体分析的一种有效手段,目前已有部分学者给出了实心钢管混凝土的纤维模型计算方法,但是缺乏关于空心钢管混凝土的纤维模型计算方法。为了给钢管混凝土的整体分析提供数值分析手段,在统一强度承载力公式的基础上,给出了实心和空心、圆形和多边形完全统一的基于材料的钢管混凝土纤维模型,并给出了考虑截面形状和空心率影响的约束混凝土的滞回本构及参数取值方法。通过对不同截面形式的钢管混凝土长短柱轴压试验、侧推试验以及滞回试验的比较和分析,证明了基于材料的纤维模型和相关参数取值的适用性。     

基于改进应变楔模型的固体-散体串联组合桩鼓胀变形及沉降分析

针对传统碎石桩易在桩顶1~3倍桩径的深度范围内发生鼓胀破坏的现象,首先,在现有工艺的基础上提出一种固体（混凝土）-散体（碎石散体材料）串联组合桩,并简要阐述其承载特性、施工工艺及破坏模式;其次,建立了串联组合桩鼓胀变形的计算模型,探讨串联组合桩的鼓胀变形机理;然后,对应变楔模型进行修正,并结合广义胡克定律,计算固体-散体串联组合桩的鼓胀变形值及桩身沉降值;最后,通过传统碎石桩及筋箍碎石桩鼓胀变形及沉降试验验证所提理论方法的合理性,结果表明：理论计算值与试验结果吻合较好,可为碎石桩复合地基设计提供一定的参考,具有理论及工程应用价值。     

Theoretical study on the confine-stiffening effect and fractal cracking of square concrete filled steel tubes in tension loads

Tension stress in steel-concrete composite is widely observed in engineering design. Based on an experimental program on tension performance of three square concrete-filled tubes (SCFT), the tension theory of SCFT is proposed using a mechanics-based approach. The tension stiffening effect, the confining strengthening effect and the confining stiffening effect, observed in tests of SCFTs are included in the developed tension theory model. Subsequently, simplified constitutive models of steel and concrete are proposed for the axial tension performance of SCFT. Based on the MSC.MARC software, a special fiber beam-column element is proposed to include the confining effect of SCFTs under tension and verified. The proposed analytical theory, effective formulas, and equivalent constitutive laws are extensively verified against three available tests reported in the literature on both global level (e.g., load-displacement curves) and strain level. The experimental verification proves the accuracy of the proposed theory and formulations in simulating the performance of SCFT members under tension with the capability to accurately predict the tensile strength and stiffness enhancements and realistically simulate the fractal cracking phenomenon.     

Modeling of curved composite I-girder bridges using spatial systems of beam elements

A new way of modeling steel composite bridges has been presented by Vayas et al. (in press, 2010)  [3.] and [4.]. The proposed model is based on the representation of steel I-girders by equivalent trusses. The concrete slab is suitably represented by a set of bar elements, and the bearings by appropriate springs. Diaphragms and stiffeners may also be taken into account. In comparison to the grillage model, which is usually used for the analysis of bridges, the proposed three-dimensional model allows a more reliable prediction of deformations, internal forces, and stresses. Curved bridges display unique behavior characteristics, and for this reason a grillage analysis is not always suitable. The new way of modeling composite bridges, using a spatial system of beam-like structural elements, is applied in this paper for the modeling of curved composite bridges. Worked examples are provided to illustrate the set-up procedure of the proposed modeling and to compare its results with those of corresponding finite element models.