矩形钢管混凝土边框组合剪力墙及筒体结构抗震研究

钢管混凝土边框组合剪力墙及筒体是一种新型抗侧力部件。该文对不同混凝土强度等级,不同轴压比,不同剪跨比,不同强弱抗剪连接键等设计参数的矩形钢管混凝土边框组合剪力墙的抗震性能进行了研究。进行了2个普通钢筋混凝土剪力墙和7个矩形钢管混凝土边框组合剪力墙的低周反复荷载试验,以及2个设置不同形式抗剪连接键的剪力墙节点的低周反复荷载试验。在试验基础上,对比分析了剪力墙的承载力、延性、刚度及其衰减过程、滞回特性、耗能能力及破坏特征。建立了组合剪力墙的承载力计算模型,计算结果与实测结果符合较好。研究表明:这种新型组合剪力墙及筒体可有效地将混凝土剪力墙侧向刚度和承载力大的优势与钢管混凝土柱抗震延性好的优势组合,钢管混凝土边框柱与混凝土剪力墙之间的抗剪连接键能可靠工作。工程应用效果良好。     

Transverse elastic shear of auxetic multi re-entrant honeycombs

The paper describes the transverse shear properties of a novel centresymmetric honeycomb structure evaluated using analytical and finite element models. The cellular structure features a representative volume element (RVE) geometry allowing in-plane auxetic (negative Poisson’s ratio) deformations, and multiple topologies to design the honeycomb for multifunctional applications. The out-of-plane properties are calculated using a theoretical approach based on Voigt and Reuss bounds. The analytical models are validated using a full scale Finite Element technique to simulate transverse shear tests, a quarter FE of the RVE with periodic shear conditions and an FE homogenisation method for periodic structures. The comparison between the analytical and numerical models shows good convergence between the different set of results, and highlights the specific deformation mechanism of the multi re-entrant honeycomb cell.     

Chemical analysis of a single basic cell of porous anodic aluminium oxide templates

We prepared anodic aluminium oxide (AAO) templates with “honeycomb” geometry, i.e. hexagonally ordered circular pores. The structures were extensively studied and characterized by EPMA coupled with FEG-SEM and FEG-TEM coupled with EDX at meso and nanoscopic scales, in other words, at the scale of a single basic cell making up the highly ordered porous anodic film. The analyses allowed the identification of the chemical compounds present and the evaluation of their levels in the different parts of each cell. Of note was the absence of phosphates inside the “skeleton” and their high content in the “internal part”. Various models of porous anodic film growth are discussed on the basis of the results, contributing to a better understanding of AAO template preparation and self-nanostructuring phenomena.     

3D hierarchical computational model of wood as a cellular material with fibril reinforced, heterogeneous multiple layers

A 3D hierarchical computational model of deformation and stiffness of wood, which takes into account the structures of wood at several scale levels (cellularity, multilayered nature of cell walls, composite-like structures of the wall layers) is developed. At the mesoscale, the softwood cell is presented as a 3D hexagon-shape-tube with multilayered walls. The layers in the softwood cell are considered as considered as composite reinforced by microfibrils (celluloses). The elastic properties of the layers are determined with Halpin–Tsai equations, and introduced into mesoscale finite element cellular model. With the use of the developed hierarchical model, the influence of the microstructure, including microfibril angles (MFAs, which characterizes the orientation of the cellulose fibrils with respect to the cell axis), the thickness of the cell wall, the shape of the cell cross-section and the cell dimension (wood density), on the elastic properties of softwood was studied.     

带暗支撑短肢剪力墙及核心筒抗震研究与应用

提出了钢筋混凝土带暗支撑异形截面短肢剪力墙,提出了带暗支撑核心筒。对不同设计参数、不同受力特点的钢筋混凝土带暗支撑异形截面(一字形、T形、L形、Z形)短肢剪力墙及带暗支撑核心筒模型进行了低周反复荷载下的抗震性能试验研究,较系统地分析了其承载力、刚度、延性、滞回特性及耗能能力。在试验研究的基础上,建立了带暗支撑异形截面短肢剪力墙及核心筒的力学模型,提供了抗震设计方法,在实际工程应用中取得了良好的效果。     

考虑反复加载时混凝土损伤积累的RC平板及剪力墙的有限元分析模型的开发

反复荷载作用下的混凝土、钢筋的本构模型是评价和分析钢筋混凝土(RC)结构的承载力-变形特性关键,旨在开发适用于反复荷载作用下RC平板、剪力墙的2维非线性有限元分析的材料本构模型,探讨并推出了反复荷载作用下在混凝土的本构模型中考虑混凝土损伤积累的方法;并对RC平板和剪力墙进行了反复加载的2维有限元模拟。分析结果与实验结果的比较表明,采用所建议的考虑损伤积累的2维非线性有限元分析模型由加载至最大承载力前能很好的模拟反复加载时RC平板、剪力墙的非线性特性。     

Mechanics of plain-woven fabrics for inflated structures

Pressurized fabric tubes, pressure-stabilized beams (known as air beams) and air-inflated structures are considered to be valuable technologies for lightweight, rapidly deployable structures. Design optimization of an inflated structure depends on a thorough understanding of woven fabric mechanics. In this paper the bending response of woven pressure-stabilized beams have been experimentally tested and analytically investigated. Additionally, the micromechanical effects of interacting tows have been studied through finite element models containing contact surfaces and nonlinear slip/stick conditions. Local unit cell models consisting of pairs of woven tows were created to characterize the effective constitutive relations. The material properties from the unit cell models were then used for the global continuum model subjected to 4-point flexure. An experimental set-up was designed and manufactured for testing of Vectran and PEN air beams. The air beam mid-span deflections were measured as functions of inflation pressure and bending load. Plots of the elastic and shear moduli with respect to the pressure and coefficient of friction have been generated. It was determined that the effective elastic and shear moduli were functions of inflation pressure, the material used and the geometry of the weave. It was shown that pneumatic or pressurized tube structures differ fundamentally from conventional metal structures.     

带有橡胶垫层的混凝土接触特性试验及其内聚力模型

针对带有橡胶垫层的混凝土试件,通过直剪试验研究了带有橡胶垫层的混凝土接触摩擦特性。采用PPR内聚力模型表征接触面的接触摩擦特性,对试验结果进行了模拟分析。试验结果表明:在带有橡胶垫层的混凝土接触面剪切过程中,剪切应力与剪切位移的变化过程可分为弹性、弹塑性硬化和应变软化变形阶段。当轴向应力在1.5 MPa~13 MPa范围内时,残余强度与剪切强度比在55%~65%,当轴向应力为17 MPa和21 MPa时,残余强度与剪切强度比大约分别为70%、80%。橡胶垫层在混凝土之间起到良好的缓冲作用。在轴向应力较大时,接触面的应力变形会伴有明显的软化变形阶段。利用Archard非线性幂次准则描绘了剪切峰值应力与轴向应力的关系,准则中常数k和m分别为0.97和0.33。PPR内聚力模型计算表明剪切应力随剪切位移变化关系曲线与试验结果基本吻合,为研究盾构管片块体间的接触摩擦作用研究提供借鉴。     

Analysis of influence of imperfections on stiffness of fully anchored light-frame timber shear walls—elastic model

In order to stabilize light-frame timber buildings against horizontal loads, the diaphragm or in-plane action of roofs, floors and walls is often used. This paper deals with the influence of imperfections such as gaps and uplift on the horizontal displacement of fully anchored shear walls. The significance of analyzing the effects of imperfections is evident when evaluating the stiffness of shear walls; tests of walls show that the horizontal displacement is underestimated in calculations using the stiffness of sheathing-to-framing joints as obtained from experiments. Also, in real structures where hold-downs are used according to the elastic design method, the influence of gaps and uplift should be included in order to obtain realistic displacements in the serviceability limit state. A new elastic model for the analysis, based on linear elastic behaviour of the mechanical sheathing-to-framing joints, is presented and the equations for the stiffness and the deflection versus the number of segments in the wall are derived. The fully anchored condition for the shear walls are modelled by applying a diagonal load to the wall. Three types of imperfections are evaluated: gaps at all studs, a gap only at the trailing stud, and gaps at all studs, except at the trailing stud. It is shown that the effect of imperfections on the stiffness of the wall in the initial stage is considerable. Depending on the distribution of the gaps and the number of segments included in the shear wall, the displacement of the shear wall is increased several times compared to that of a fully anchored shear wall with no gaps; e.g. for a single segment wall more than three times. However, for walls with more than six to ten segments, the effect of imperfections can be neglected. Finally, the theoretical model is experimentally verified.     

Fluidic origami with embedded pressure dependent multi-stability: a plant inspired innovation

Inspired by the impulsive movements in plants, this research investigates the physics of a novel fluidic origami concept for its pressure-dependent multi-stability. In this innovation, fluid-filled tubular cells are synthesized by integrating different Miura-Ori sheets into a three-dimensional topological system, where the internal pressures are strategically controlled similar to the motor cells in plants. Fluidic origami incorporates two crucial physiological features observed in nature: one is distributed, pressurized cellular organization, and the other is embedded multi-stability. For a single fluidic origami cell, two stable folding configurations can coexist due to the nonlinear relationships among folding, crease material deformation and internal volume change. When multiple origami cells are integrated, additional multi-stability characteristics could occur via the interactions between pressurized cells. Changes in the fluid pressure can tailor the existence and shapes of these stable folding configurations. As a result, fluidic origami can switch between being mono-stable, bistable and multi-stable with pressure control, and provide a rapid ‘snap-through’ type of shape change based on the similar principles as in plants. The outcomes of this research could lead to the development of new adaptive materials or structures, and provide insights for future plant physiology studies at the cellular level.     

Experimental characterization of microstructure development during loading path changes in bcc sheet steels

Interstitial free sheet steels show transient work hardening behavior, i.e., the Bauschinger effect and cross hardening, after changes in the loading path. This behavior affects sheet forming processes and the properties of the final part. The transient work hardening behavior is attributed to changes in the dislocation structure. In this work, the morphology of the dislocation microstructure is investigated for uniaxial and plane strain tension, monotonic and forward to reverse shear, and plane strain tension to shear. Characteristic features such as the thickness of cell walls and the shape of cells are used to distinguish microstructural patterns corresponding to different loading paths. The influence of the crystallographic texture on the dislocation structure is analyzed. Digital image processing is used to create a “library” of schematic representations of the dislocation microstructure. The dislocation microstructures corresponding to uniaxial tension, plane strain tension, monotonic shear, forward to reverse shear, and plane strain tension to shear can be distinguished from each other based on the thickness of cell walls and the shape of cells. A statistical analysis of the wall thickness distribution shows that the wall thickness decreases with increasing deformation and that there are differences between simple shear and uniaxial tension. A change in loading path leads to changes in the dislocation structure. The knowledge of the specific features of the dislocation structure corresponding to a loading path may be used for two purposes: (i) the analysis of the homogeneity of deformation in a test sample and (ii) the analysis of a formed part.     

Horizontaltragfähigkeit von zusammengesetzten Mauerwerksquerschnitten

Zusammengesetzte Schubwandquerschnitte weisen unter kombinierter Beanspruchung aus Normalkraft und Schub mit Scheibenbiegung bezüglich der Steifigkeit und Tragfähigkeit ein deutlich günstigeres Verhalten auf als gerade Wandabschnitte ohne entsprechende Flansche. Insbesondere im Hinblick auf Erdbeben beanspruchungen wurde an der Technischen Universität München ein Versuchsprogramm an im Grundriss T‐förmigen Schubwandbauteilen unter realistischen Randbedingungen durchgeführt und mit rechnerischen Untersuchungen begleitet. Der Beitrag stellt die Ergebnisse auszugsweise dar, insbesondere im Hinblick auf numerische Vergleichsberechnungen. Masonry shear walls with flanges: Behaviour under combined loadings. Concering the load bearing capacity and the stiffness characteristics of shear walls with flanges, a significant better behaviour under combined shear loadings, compared to walls with rectangular shape, can be found. Within a research project, several tests on full‐scale walls with T‐shaped ground plan view and different execution detaillings (e. g. connection between shear wall and intersecting wall with shear ties or interlocking) under combined N‐M‐V loadings (static‐cyclic and pseudo‐dynamic) have been performed. In the following some results of the tests and numerical investigations are presented.     

Machine locking of degenerated thin shell elements

The degenerated shell element is one of the most efficient elements for analysing shell structures. However, it is known to result in rather stiff models when used in thin element applications. The phenomena associated with this behaviour are known as locking phenomena. This paper analyses the machine locking mechanism developed in thin to very thin Lagrangian and serendipity elements. The machine related locking phenomenon is distinguished from the shear and membrane locking phenomena. A remedy for the pure machine locking problem is developed for the two elements. The proposed remedy is based on the technique of the modified transverse shear modulus. It is also extended to control shear locking. The proposed technique is shown to completely eliminate machine locking. Also, it is shown to effectively alleviate stiffening effects due to the presence of spurious shear strain.     

A coupled experimental and numerical approach to the integrity of friction-grip connections in glass structures

The growing use of glass as structural building material gives rise to structural integrity and safety problems. As a contribution to solving these problems, this work investigates the mechanical behaviour of friction-grip bolted connections, which are probably the most commonly used assembling technique for glass beams and plates. The mechanical problems relative to friction-grip bolted connections are complex because highly nonlinear phenomena such as unilateral contact and dry friction are involved. To achieve the objective, a coupled experimental and numerical approach is developed in this work. Firstly, an experimental tribological study is carried out to propose a law capable of describing the friction phenomenon relevant to glass bolted joints. Next, the unilateral frictional contact problem posed by friction-grip bolted connections is numerically analyzed by using the MSC MARC^® finite element code in which an experimentally-identified time-dependent friction law is implemented. Finally, full scale tests are performed for glass structures to validate the numerical simulations.     

Behaviour of cellular materials under impact loading

The paper describes experimental and computational testing of regular open‐cell cellular structures behaviour under impact loading. Open‐cell cellular specimens made of aluminium alloy and polymer were experimentally tested under quasi‐static and dynamic compressive loading in order to evaluate the failure conditions and the strain rate sensitivity. Additionally, specimens with viscous fillers have been tested to determine the increase of the energy absorption due to filler effects. The tests have shown that brittle behaviour of the cellular structure due to sudden rupture of intercellular walls observed in quasi‐static and dynamic tests is reduced by introduction of viscous filler, while at the same time the energy absorption is increased. The influence of fluid filler on open‐cell cellular material behaviour under impact loading was further investigated with parametric computational simulations, where fully coupled interaction between the base material and the pore filler was considered. The explicit nonlinear finite element code LS‐DYNA was used for this purpose. Different failure criteria were evaluated to simulate the collapsing of intercellular walls and the failure mechanism of cellular structures in general. The new computational models and presented procedures enable determination of the optimal geometric and material parameters of cellular materials with viscous fillers for individual application demands. For example, the cellular structure stiffness and impact energy absorption through controlled deformation can be easily adapted to improve the efficiency of crash absorbers.     

带暗支撑剪力墙体系抗震研究及应用 第十三届全国结构工程学术会议特邀报告

提出了钢筋混凝土带暗支撑剪力墙。对不同高宽比、不同暗支撑型式、不同暗支撑倾角和配筋比的带暗支撑低矮、中高剪力墙模型和双肢剪力墙模型进行了低周反复荷载下的抗震性能试验研究。进行了带暗支撑剪力墙结构模型与不带暗支撑剪力墙结构模型的振动台对比试验研究。在试验研究的基础上,建立了带暗支撑剪力墙的力学模型和抗震设计方法,在实际工程应用中取得了良好的效果。     

结构抗震消能控制的试验与应用研究

为了改善高层剪力墙结构的抗震性能,根据结构控制的原理提出了一种新型剪力墙—沿竖向消能的带竖缝剪力墙。首先,进行了竖缝处消能装置的剪切—摩擦试验,研究了这种消能装置的受力机理和消能机理,给出了荷载—位移骨架曲线的理论计算方法。其次,进行了带有此消能装置的一层带竖缝剪力墙和普通实体墙的低周反复荷载试验,对比研究了这两类剪力墙的破坏机理和滞回特性,试验表明这种新型消能剪力墙具有良好的抗震性能。接着,讨论了这种剪力墙的消能计算方法。最后,介绍了消能剪力墙的一个工程应用实例。     

Distinct simulation of earth pressure against a rigid retaining wall considering inter-particle rolling resistance in sandy backfill

The focus of this paper is to analyze earth pressure against a rigid retaining wall under various wall movement modes with a contact model considering inter-particle rolling resistance implemented into the distinct element method (DEM). Firstly, a contact model considering rolling resistance in particles was generally explained and implemented into the DEM. The parameters of the contact model are determined from DEM simulation of biaxial tests on a sandy specimen. Then, the influence of inter-particle rolling resistance in the backfill is discussed by comparing the active and passive earth pressure against a rigid wall subjected to a translational displacement with and without inter-particle rolling resistance in the material. Third, the DEM model considering the rolling resistance is used to investigate active and passive earth pressures while the rigid wall moves in a more general manner such as rotation or translation. The influence of rolling resistance on the earth pressures is examined from the microscopic particle scale (e.g., shear strain field) as well as the macroscopic scale (e.g., the magnitude and action point of resultant earth pressures). Finally, the effect of the initial density and the particle size of the backfill are discussed. The results show that when rolling resistance in the particles is taken into account in the DEM simulation, the simulation results are more appropriate and are in line with practical situation. Hence, particles rolling resistance should be taken into account to get more realistic results in DEM analyses.     

A numerical modelling of non linear 2D-frictional multicontact problems: application to post-buckling in cellular media

In this paper a numerical modelling of non linear problems involving large deformations and frictional contact conditions is proposed. The motivation of this work comes from the study of the cellular materials (such as wood or foams) undergoing strong deformations. We restrict our study to a regular cellular network of hexagonal cells with thin walls. Strong loadings can generate at first buckling phenomena, then self-contact in the cell. Renouncing homogenization procedures, not always pertinent in this case, we have developed direct simulations. After giving the mechanical and mathematical formulations of the problem, we present two advanced numerical tools to solve large non linear frictional multicontact problems. This numerical modelling is based on an arc-length continuation method which permits to snap through singular points due to buckling phenomena and on an optimal domain decomposition method adapted to frictional contact problems. Finally, mechanical investigations of the contactless buckling and the post-buckling provide some pertinent parameters controlling the deformation process.This work was supported in part by CINES, Centre Informatique National de lEnseignement Supérieur, (Montpellier-FRANCE), Project mgc2547. The different simulations run on the SGI3800 computer based at the CINES.