Strength of shear keys used in pre-cast prestressed composite beams

This work investigates the shear strength of shear keys used in slab–web connections in pre-cast bridge systems. In pre-cast systems where the slab is also a pre-cast element, the slab–web connection is discontinuous and usually made by casting concrete plugs (shear keys) through holes left over on the line of connection with the web at prescribed spacing. The contribution of the slab to the flexural strength of the composite beam is highly dependent on the individual shear strength of the keys and the spacing between them. In this work a test program was developed to estimate the shear strength of full scale shear keys used in practice to combine pre-cast reinforced concrete slab bridge deck to pre-cast prestressed pretentioned concrete girders, as a function of the amount and type of connection steel. On the basis of test results and the shear-friction model, an equation for the estimation of the shear strength of the shear keys is here proposed.     

基于近场动力学方法的混凝土板侵彻问题研究

由于近场动力学(Peridynamics)用统一空间积分-时间微分方程描述物体连续或不连续区域,改进常用微观弹脆性模型对势本构力函数,给出刚性体与变形体冲击问题接触算法;编制计算程序,验证经典简支梁变形及Kalthoff-Winkler试验;数值模拟刚性弹丸侵彻混凝土矩形板破坏过程,揭示损伤累积及裂纹扩展全过程与最终破坏形态。结果表明,改进的近场动力学模型及算法合理、可靠,能有效模拟混凝土结构冲击破坏及侵彻问题。     

装配式干式连接剪力墙结构中楼板性能试验研究

装配式剪力墙结构中存在大量竖向拼缝,竖向拼缝采用干式连接可减少现场湿作业,提升建筑装配率。竖向拼缝采用干式连接后,由于拼缝宽度较小,拼缝两侧的剪力墙相对变形较大,而楼板在竖向拼缝处通常保持连续,因此在地震作用下,竖向拼缝处楼板局部将受到较强的剪切作用而发生严重破坏。针对上述问题,提出一种带局部加强构造的楼板做法,通过试验研究楼板在干式连接拼缝处的破坏现象和机理,并与现浇剪力墙进行了对比。试验结果表明:对于带竖向拼缝的剪力墙,楼板表现出明显的剪切破坏特征,在无干式连接节点时,楼板局部破坏严重,大震后难以修复;采用干式连接后,墙体的承载力和延性均有提升。由于干式连接节点的贡献,墙肢间相对变形减小,楼板损伤程度较轻,大震后更容易修复。     

Numerical model for composite structures with experimental confirmation

The paper briefly presents a numerical model for the simulation of composite structures. The main structure is modeled with two‐dimensional plane finite elements. The composite surface is modeled with two‐dimensional interface elements for the continuous connection simulation and modified beam elements for the discrete connection simulation. The applied material model’s primary purpose is the simulation of reinforced concrete structures. It includes the most important nonlinear effects of reinforced concrete behavior: yielding in compression and opening and propagation of cracks in tension, with tensile and shear stiffness of cracked concrete, as well as the nonlinear behavior of reinforced steel. It also includes nonlinear behavior of the composite surface and the connection elements. The model was confirmed in experimental tests of composite concrete Omnia slabs, which are in common usage. The achieved test results were compared with the results obtained through the developed numerical model.     

A design model for punching shear of FRP-reinforced slab-column connections

The overall aim of this paper is to develop a unified design method for the punching shear resistance of slab-column connections irrespective of the type of internal reinforcement. In the first part of the paper a design model for the punching shear resistance of concrete slab-column connections reinforced with fibre-reinforced polymers (FRP) is proposed. This design model is based on the authors’ theoretical analysis for such slabs, which considers the physical behavior of the connections under load. The effects of the inherent linear brittle response, the lower elastic modulus and the different bond features, as compared to steel, of the FRP reinforcement are all accounted for in the present study. The proposed model does not incorporate any fitting factors to match the theory to the trend of the available FRP slab test results. The excellent agreement between the predicted and published test results should give confidence to engineers and designers in using FRP as a sound structural reinforcement for slab-column connections.

It is then shown that the proposed design model for FRP slabs and the previous model of the authors for steel reinforced slabs are both identical in nature and structure, thus constituting a unified approach to design for punching shear in slabs. On the basis of the unified model comparison and correlation between an FRP slab and a reference steel reinforced slab, confirmed by the available test results, are presented. The unified model also enables the development of a more rational and reliable equivalent steel reinforcement ratio which can be applied to existing code equations for steel reinforced slabs to estimate the punching resistance of FRP-reinforced slabs.     

复合材料纤维张力缠绕预应力场动态特性

复合材料纤维张力缠绕技术通过提高纤维的张力水平可充分发挥纤维高强、高模优势,在成型过程中对结构进行预紧,成为解决高速转动部件径向变形大、界面强度低等问题新的有效途径。将每一层纤维的张力缠绕等效为一个含预应力复合材料薄环的叠加,基于正交各向异性复合材料缠绕层和各向同性金属芯模弹性变形理论,建立了纤维张力缠绕力学解析模型,得到芯模和缠绕层预应力场随缠绕层数及缠绕张力的变化规律,并通过复合材料纤维张力工艺试验验证了力学解析模型的正确性。研究发现了纤维张力缠绕中预应力“饱和”现象,并确定了影响张力缠绕预应力场的两个主要参数:缠绕层环径向刚度比E_θ/E_r和张力大小T（r）,为复合材料纤维张力缠绕成型工艺提供理论支撑。      

冷弯薄壁方钢管梁柱加腋节点抗震性能研究

摘要：汶川地震后冷弯薄壁方钢管在灾区重建过程中得到了大量使用,但其梁柱节点的连接方式和力学性能等尚需进一步研究。为此,文中基于结构实际受力情况设计了一种三维双节点试验模型,对不同轴压比下冷弯薄壁方钢管梁柱加腋节点和普通节点的8个试件进行了足尺试验,通过对比分析研究了低周往复荷载作用下加腋节点的破坏模式、滞回曲线及评价节点抗震性能的主要参数（承载力、延性、刚度退化和能量耗散系数等）。同时,利用ANSYS对各节点进行了有限元数值计算,并与试验结果进行了对比分析进一步对加腋节点进行了研究。结果表明：试验与有限元数值计算结果吻合良好,验证了理论分析的正确性;加劲腋板提高了节点的初始刚度和承载力,钢管梁的弹塑性性能得到了充分发挥,不同轴压比下均出现了塑性铰,导致加腋节点各试件的最终破坏均是由钢管梁塑性变形过大出现局部屈曲引起;加劲腋板提高了节点的延性系数及往复变形次数,延长了变形时间,增大了节点的粘滞阻尼和耗能性性能,改善了节点的抗震性能;随轴压比增加,加腋节点塑性变形减小,脆性破坏特征增加,各耗能系数均相应降低。     

Numerical and experimental distribution of temperature and stress fields in API round threaded connection

Thread galling is one of the main failure forms for oil tubing and casing connections, and it leads to deterioration of seal performance and connection strength of oil tubing and casing directly. A series of full-scale tests were performed on samples of API J55 steel grade non-upset tubing threaded connections. The temperature and stress field distributions of the tubing threaded connection were measured dynamically under the action of different make-up and break-out torque and velocity. Major factors, which affect the distributions of temperature and stress fields of tubing connections, were studied and their effects on thread galling failure were summarized with friction-wear theory. The FEA models of tubing threaded connections are validated by comparing the numerical results with the full-scale tests. The validated models are afterwards used to perform parametric studies on the connection behaviour.     

Shear behavior model for steel fiber-reinforced concrete members without transverse reinforcements

Due to the complex shear mechanism of steel fiber-reinforced concrete (SFRC) members, there is lack of comprehensive shear behavior models for SFRC members. The shear behavior model, based on a smeared crack model, requires the tensile stress–strain constitutive equation of SFRC membrane subjected to biaxial stresses. After SFRC panel tests under biaxial stresses were recently conducted, it has been possible to create a more complete smeared crack model for estimating the shear behavior of SFRC members. It is, however, very difficult to conduct such experiments for different types of steel fibers, various amount of steel fibers, different ranges of concrete strengths, etc. Thus, in this study, steel fibers are modeled as average direct tensile contribution elements in a modified smeared crack truss model, considering directionality and distribution of fibers. In this way, only simple bond tests are required to reflect the effects of different characteristics of SFRC. In addition, the shear contribution of steel fibers can be obtained considering the bond failure of steel fibers. The proposed model was compared to the test results of 8 SFRC panels and 80 SFRC beams, and the shear behavior of the SFRC members was well estimated.     

钢框架平端板连接组合节点弯矩-转角关系

端板连接节点是多高层钢框架结构体系中经常采用的梁柱连接形式,当考虑现浇钢筋混凝土楼板的作用并有足够的抗剪连接件时则形成了端板连接组合节点,楼板对组合节点承载力和刚度都有贡献。基于ABAQUS软件建立了考虑楼板组合作用影响的端板连接梁柱组合节点的三维有限元数值分析模型,并分别用有关研究者完成的无楼板钢框架端板节点及考虑楼板作用的组合节点的试验结果对理论模型进行了验证,总体上数值模拟结果和试验结果吻合良好。基于该数值模型进行了平端板连接组合节点力学性能影响因素的参数分析,探讨了楼板、柱腹板加劲肋、楼板配筋率、端板厚度、梁截面高度等参数对组合节点力学性能的影响,在此基础上对欧洲规范建议的弯矩-转角关系模型进行了必要修正,最终提出了可反映楼板作用的平端板连接组合节点弯矩-转角关系实用模型。本文模型计算结果与有限元结果吻合良好,可为进一步研究该类节点的设计方法提供参考。     

Experimental testing of wood‐concrete and steel‐concrete composite elements in comparison with numerical testing

The paper presents the results of experimental tests with a numerical comparison of some typical composite element systems. Two different kinds of elements were tested: composite steel‐concrete and composite wood‐concrete elements. Deflections at midspan under monotonously increasing static load on simply supported beams were measured. The affects of different types of composite connections on the results were researched. In numerical tests the structure was modeled with two‐dimensional plane elements. The composite surface was modeled with two‐dimensional contact (interface) elements for the continuous connection simulation and modified beam elements for the discrete connection simulation. The applied material models include the most important nonlinear effects of concrete, steel and wood behavior, as well as the nonlinear behavior of the composite surface at the connection. The achieved results of the developed numerical model were compared with the results obtained through the experimental test.     

全装配式RC楼盖板缝节点拉剪复合受力性能试验研究

为研究分布式连接全装配RC楼盖(DCNPD)板缝节点在拉剪复合作用下的受力性能,进行了12个板缝节点在纯剪和拉剪复合作用下受力性能试验,对板缝节点的承载能力、裂缝模式、破坏形态、位移延性和应变规律等进行了较为系统的研究。结果表明:拉力的存在减小了由剪切作用引起的连接件与相邻混凝土间的承压作用,致使板缝节点抗剪承载力不同程度的降低,并且拉剪比越大,拉力对板缝节点屈服荷载和峰值荷载的削弱作用越明显;拉剪复合作用下,板缝节点较早呈现出非线性受力特征;拉力对板缝节点位移延性有较大的削弱,尤其对于楼盖中高拉剪比区域应采取措施避免节点发生脆性破坏;综合考虑板缝节点的荷载-位移响应、位移延性特征和破坏模式等因素,HPC、CPC和HP-CPC三种节点是较为理想的DCNPD板缝节点形式,SPC锚筋与锚板间焊缝在拉剪复合作用下易发生断裂,需改进措施以提高其拉剪复合受力性能。     

非API套管接头完整性评估计算方法

针对非API套管接头的连接和密封性能提出一套完整的解析评估计算方法。首先建立具有密封和内外螺纹啮合结构的非API套管接头力学分析模型,依据API套管接头失效形式(螺纹跳扣、螺纹剪切破坏和接头断裂)及其机理结合弹塑性力学理论,推导出非API套管接头发生相应连接失效时的临界轴向载荷计算公式。然后,依据螺纹啮合对变形协调方程和单个螺纹牙轴向弹性变形分析,推导出套管接头螺纹牙啮合法向接触力计算方程组,从而获得非API套管接头各个螺纹牙轴向变形量及其承载轴向载荷分布情况数值解。最后,通过对比各个螺纹牙承载轴向载荷与连接失效临界载荷对非API套管接头进行连接性能评估;通过计算轴向载荷和气体内压作用下,套管接头螺纹轴向变形量及其对接头密封过盈配合值的影响,对非API套管接头进行密封性能评估。通过对3种典型非API套管接头完整性评估计算结果表明:在螺距、螺纹啮合中径、螺纹高度等螺纹参数相同情况下,非API套管接头的螺纹牙型设计参数(承载面角度与导向面角度)对其连接和密封性能影响显著。     

Finite elements in space and time for generalized viscoelastic maxwell model

 The generalization of a new numerical approach with simultaneous space–time finite element discretization for viscoelastic problems developed in the papers by Buch et al. (1999) and Idesman et al. (2000) is presented for the case of the generalized viscoelastic Maxwell model. New non-symmetric variational and discretized formulations are derived using the continuous Galerkin method (CGM) and discontinuous Galerkin method (DGM). Viscoelastic behaviour described by the generalized Maxwell model is represented by means of internal variables. It allows to use only differential equations for the constitutive equations instead of integrodifferential ones. The variational formulation reduces to two types of equations with total displacements and internal displacements (internal variables) as unknowns, namely to the equilibrium equation and the evolution equations for the internal displacements which are fulfilled in the weak form. Using continuous test functions in space and time, a continuous space–time finite element formulation is obtained with simultaneous discretization in space and time. Subdividing the total observation time interval into appropriate time slabs and introducing discontinuous trial functions, being continuous within time slabs and allowing jumps across time interfaces, a more general discontinuous finite element formulation is obtained. The difference between these two formulations for one time slab consists in the satisfaction of initial conditions which are fulfilled exactly for the continuous formulation and in a weak form for the discontinuous case. The proposed approach has some very attractive advantages with respect to semidiscretization methods, regarding the possibility of adaptive space–time refinements and efficient parallel processing on MIMD-parallel computers. The considered numerical examples show the effectiveness of simultaneous space–time finite element calculations and a high convergence rate for adaptive refinement. Numerical efficiency is an advantage of DGM in comparison with CGM for discontinuously changing (e.g. piecewise constant) boundary conditions in time and for solutions with high gradients. Received 7 February 2000     

销轴连接结构的接触应力分析

销轴连接结构是工程中最为常用的一种传力结构,对其进行细致的接触应力分析,研究各参数对接触应力大小和分布的影响,对此类传力结构的设计与应用显得尤为重要。该文以佛山东平大桥为例,在验证有限元模型接触参数设置的基础上,计算东平大桥在竖转脱架状态下销轴连接结构的接触应力,计算结果与实测结果相比,基本反应了接触应力的大小和分布,证明了有限元模型的可靠性。在此基础上,研究了提升力大小、材料本构关系等参数对销轴连接结构接触应力大小和分布的影响,得到以下结果:材料本构关系和提升力大小的选取是影响销轴连接结构接触应力大小和分布的关键因素;接触区域的摩擦因数对计算结果几乎无影响。     

基于组件法的超大承载力端板连接节点弯矩-转角曲线计算方法

超大承载力端板连接节点是一种可以应用于大跨或重载钢结构中的新型梁柱节点形式。为了在结构分析中准确考虑该节点的抗弯承载力和转动刚度,需要确定其弯矩-转角曲线。在已有试验和有限元分析结果的基础上提出了超大承载力端板连接节点的组件模型,引入一种新组件形式并提出了其承载力和刚度的分析方法,基于组件法提出了超大承载力端板连接节点的抗弯承载力和转动刚度的计算方法。综合现有典型的节点弯矩-转角曲线模型的优点,以节点抗弯承载力和转动刚度为基本参数提出了适用于超大承载力端板连接节点的弯矩-转角曲线模型。通过与已开展的试验研究和有限元分析结果进行比较,所提方法得到的节点抗弯承载力和转动刚度较为准确,所提弯矩-转角曲线模型与试验曲线吻合良好,可以应用于采用该节点形式结构的分析和设计中。     

半刚性钢框架实用非线性分析

介绍了在钢框架分析中考虑连接柔性的方法以及常用的连接M–θr模型,建立了能够同时考虑几何、材料和连接非线性的精细塑性铰法三维梁柱单元。单元采用稳定函数考虑二阶效应和剪切变形,采用切线模量和抛物线函数考虑沿单元长度和截面的逐渐屈服,采用Kishi-Chen幂函数模型和修正梁单元方法模拟半刚性连接的非线性行为。利用ANSYS软件的用户可编程特性(UPFs)编写了单元程序,并将用户单元添加至ANSYS软件单元库中。半刚性框架算例分析表明:用户单元分析的荷载-位移曲线与试验结果吻合较好,与采用COMBIN 39单元模拟连接所分析的结果非常接近。     

摩擦耗能型SMA杆自复位梁柱节点滞回性能分析

在梁柱节点中引入NAO（非石棉）摩擦耗能器和超弹性形状记忆合金（SMA）杆,形成摩擦耗能型SMA杆自复位梁柱节点（NAO-SMA-SC）,可有效解决传统梁柱节点震后残余变形较大和耗能较低的问题。该文分析了其构造和工作机理,针对节点中SMA杆大应变需求,基于Lagoudas模型提出SMA杆的应变强化段改进本构模型,并将其嵌入到有限元软件OpenSees;建立了NAO-SMA-SC节点的杆系分析模型,考察了循环加载机制下SMA杆、NAO摩擦耗能器、间隙单元随节点转动时的受力行为;系统分析了耗能器摩擦力F_f、SMA杆直径D、SMA杆预应变P等关键参数对NAO-SMA-SC节点滞回性能的影响。结果表明:在节点中引入摩擦耗能器,能明显地提高节点抗弯能力和耗能能力,但同时会增大节点残余变形;随着SMA杆直径的增大,节点抗弯能力和自复位性能均显著提高;SMA杆预应变的施加能有效降低节点的残余变形。     

Influence of snowpack layering on human-triggered snow slab avalanche release

Dry-snow slab avalanches involve the release of a cohesive slab over an extended plane of weakness. In most fatal avalanches, the triggering of the initial failure occurred by localized rapid near-surface loading by people — followed by fracture propagation. Whereas a limit-equilibrium (LE) approach to snow slope failure only takes into account slab depth, slab density and weak layer strength, it omits properties such as the stiffness of adjacent layers and the fracture propagation process. Nevertheless, LE has been applied with some success to the frequency of skier triggering, suggesting that it is relevant to failure initiation. Since field studies have shown that, for a given slab thickness, stiffer slabs are less likely to be triggered, slab properties influence failure initiation, fracture propagation or both. A highly simplified finite element (FE) model of static skier loading was used to assess the effect of slab and substratum properties on skier-induced stresses in the weak layer. Compared to a uniform slab, the skier-induced stress at the depth of the weak layer varied by a factor of 2 due to layering. In particular, the simplified FE model suggests that while stiffer layers in the slab will reduce the skier-induced stress in the weak layer, stiff layers just below the weak layer can increase the shear stress. These results were incorporated into a modified stability index and compared to stability test results. However, by taking into account snowpack layering the correlation between the modified stability index and stability test results did not improve. While our simulations suggest that less stress penetrates through stiffer slabs and thus fracture initiation is less likely, other studies show that, once initiated, fractures under stiffer slabs have high propagation propensity.     

Layered plate with discontinuous connection: Exact mathematical model

The subject of this paper is the plate composed of two identical layers connected to each other in a discontinuous way, i.e. via discontinuous elements (connectors). This paper presents a model that describes the mechanical behavior of this plate by a system of exact, analytical (explicit) equations. The discrete distribution of discontinuous connectors is replaced by a fictitious continuous medium (interlayer). Accordingly, the plate is modeled as an equivalent three-layered plate: Two outer layers and a connecting inner interlayer. In order to obtain a fast and easy to use tool, something that is necessary for an analytical model to be chosen over finite elements and empirical formulas, modeling process is developed within the framework of two-dimensional elasticity. In so doing, the model also represents a means for attaining full comprehension of the mechanical phenomena that are involved, something that neither three-dimensional elasticity nor finite elements and empirical formulas can attain. The transition from three to two-dimensional behavior is obtained by relating the normal stress in the direction transverse to the plate to the distortion in the interlayer. The two-dimensional behavior is governed using kinematic and force assumptions that do not impose appreciable constraints on the stress–strain state and structural behavior. Starting from these assumptions, the paper develops the relationships between displacements and interface stresses, for both continuous and discontinuous connection. The latter relationships, which are used in this model, and the former relationships, which were used in a previously presented model, are discussed and compared to each other. The subsequent sections of the paper describe the model and present some real case applications of discontinuously-connected layered plate.