Numerical evaluation of buckling behavior in space structure considering geometrical parameters with joint rigidity

The buckling behavior of single layer space structure is very sensitive. The joint rigidity, moreover, is one of the main factors of stability which may determine the entire failure behavior. Thus, the reasonable stiffness of joint system, which is neither total pin assumption nor perfect fix condition, is very important to apply to the real single layer space one. Therefore, the purpose of this work was to investigate the buckling behavior of single layer space structure, using the development of the upgraded stiffness matrix for the joint rigidity. To derive tangential stiffness matrix, a displacement function was assumed using translational and rotational displacement at the node. The geometrical nonlinear analysis was simulated not only with perfect model but also with imperfect one. As a result, the one and two free nodal numerical models were investigated using derived stiffness matrix. It was figured out that the buckling load increases in proportion to joint rigidity with rise-span ratio. The stability of numerical model is very sensitive with the initial imperfection, responding of bifurcation in the structure.

Analysis of the Rigidity of a Straight Beam Flexible Hinge with Different Geometrical Parameters

Flexible hinges are widely used in micro motion robotics. Its rigidity directly influences an organization＇s terminal localization. Its actual structure geometry size cannot satisfy the theoretical analysis completely in a theoretical supposition condition. In this paper, we analyzed the rotation rigidity of a corner-filleted straight beam flexible hinge in different parameters using finite element software ANSYS. The errors are discovered and compared with theoretical results. Through the graph of the flexible hinge parameters and its performance, an analysis of changes of parameters on the performance of a corner-filleted flexible hinge was carried out. The key manufacture parameters that affect the performance of a corner-filleted flexure hinge the most and rules of design are given, which can provide directions of design precision for the flexure hinge.

适应高流量车载的装配式路面刚性接缝材料的制备及性能研究

通过聚合物改性水泥基材料探讨改性砂浆的力学性能、抗疲劳能力以及微观结构和产物等,研究满足高流量车载装配式路面的适宜填缝材料。研究结果表明,刚性接缝砂浆28d抗折强度、抗压强度满足填缝主拉应力为0.3 MPa、M10级的水泥砂浆拉应力和抗压强度要求,能快速满足通车需求,减少交通隔断时间。GⅢ刚性砂浆200万次疲劳变形处于材料的抗压疲劳破坏前中期,满足中等交通量车载要求。该类型砂浆在装配式道路板工程中的应用,体现出优异的综合性能和较高的性价比。

新型承插型盘扣式钢管格构支架有限元分析及相关计算理论对比

针对某工程中得到应用的新型承插型盘扣式钢管格构支架,基于有侧移半刚性钢框架计算理论,建立了考虑节点半刚性以及广义初始缺陷的有限元模型,进行数值分析。对于不同文献、规范中现有的几种计算理论进行了对比计算,根据所得结果的不同,分析了各计算理论的局限性与可参考性。通过数值分析与理论计算结果的对比,得到了计算模型最贴近实际、并与数值分析结果最为接近的一种计算理论,以供在实际工程应用中作为设计参考。

海河流域河湖生态环境复苏十年成效评估及展望

海河流域水生态问题突出,一度出现河流断流、湖泊萎缩、水生态系统退化等问题。近年来海河流域大力开展河湖生态环境复苏工作,回顾了2014年以来主要措施及成效,选取流域3大水系52条河流和5个重点湖泊为主要评价对象,围绕河流有水时长、河流有水河长和水面面积、湖泊水位、地下水水位、河湖水质状况、河湖水生态状况6项指标,采用水文监测和遥感解译分析相结合的方法进行河湖生态环境复苏成效评估。结果显示:2014年以来,海河流域河流的有水时长、有水河长和水面面积均有所提升,地下水水位回升,全流域劣Ⅴ类水质基本消除,生物多样性及河湖面貌得到改善。在此基础上分析了当前实现水利高质量发展面临的新要求和新挑战,为巩固河湖生态环境复苏成效,建议严格水资源管理,推进多水源调度,健全生态流量保障体系,完善长效治理机制,加快数字孪生海河建设,提升监管评价能力,努力实现海河流域河湖健康与流域可持续发展目标。

考虑初始缺陷的桥梁高大施工支架整体稳定性能研究

高大施工支架是大跨度复杂桥梁工程中常用的钢结构支撑系统。实际工程中由于受到高大施工支架加工安装误差、超限受力或不均匀受力等因素影响,因此钢结构施工支架存在节点连接不牢固、杆件弯曲变形等初始缺陷。为明确初始缺陷对桥梁高大施工支架整体稳定性能的影响规律,首先开展了桥梁高大施工支架的线性屈曲分析,进而探讨了节点半刚性、杆件初弯曲等初始缺陷对桥梁高大施工支架极限承载力的影响规律。为提高桥梁高大施工支架极限承载力的求解精度,引入刚度系数来衡量节点半刚性,综合考虑节点体对杆件计算长度的影响,并提出模拟节点三向六自由度的方法以简化计算。研究表明,结构的极限承载力与刚度系数相关,实际工程中应保障刚度系数在4以上。以第一阶整体屈曲模态作为结构初始几何缺陷时,缺陷对于结构的极限承载力和跨中平面外位移的影响更显著;以第二阶屈曲模态作为结构初始几何缺陷时,缺陷对于结构的边杆平面外位移的影响更显著。

装配式钢结构全栓接刚节点的抗震性能分析

地震时强烈振动可能导致栓接节点的螺栓松动、滑移甚至断裂,影响节点的整体承载能力和稳定性,增加结构倒塌的风险。为减轻对主体结构的破坏,对装配式钢结构全栓接刚节点的抗震性能进行分析。计算出高强螺栓的用量并构建结构的几何模型,输入Abaqus有限元软件,考虑节点参数构建有限元模型,确定加载制度,以及地震载荷影响下该结构节点的抗震性能。模拟结果表明:相比于普通钢结构节点,用高强螺栓连接的装配式钢结构栓接节点,翼缘塑性铰外移,地震时稳定性更高;不同阶段该节点上的螺栓均发挥较强作用,不会出现严重应力集中,节点不易开裂;峰值载荷后该节点骨架曲线平滑稳定地下降,不会失去稳定性,具有较强抗震性能。

基于MDEM的非线性半刚性空间钢框架的弹塑性动力分析

基于三维杆系离散元法(MDEM)提出了一种能够有效地进行具有半刚性节点的三维钢框架结构动力分析的计算方法,该法可同时考虑结构的几何非线性、材料非线性以及梁柱节点连接的半刚性非线性。其中,几何非线性行为利用刚体运动学进行处理,而材料非线性行为则通过引入精细塑性铰模型进行考虑。与此同时,该文中在半刚性节点处设置了虚拟的具有3个平动自由度和3个转动自由度的空间弹簧单元,该弹簧单元以线性分配的方式将三维梁柱节点的半刚性特性量化到与之相邻的接触单元各方向刚度,进而根据能量等效原理推导了上述接触单元刚度的修正公式,且通过独立硬化模型考虑了半刚性节点的非线性滞回性能。多个数值结果与已有研究成果的对比验证了该文所提方法的正确性和精确性。

Pushover analysis of reinforced concrete frames considering shear failure at beam-column joints

Since most current seismic capacity evaluations of reinforced concrete （RC） frame structures are implemented by either static pushover analysis （PA） or dynamic time history analysis, with diverse settings of the plastic hinges （PHs） on such main structural components as columns, beams and walls, the complex behavior of shear failure at beam-column joints （BCJs） during major earthquakes is commonly neglected. This study proposes new nonlinear PA procedures that consider shear failure at BCJs and seek to assess the actual damage to RC structures. Based on the specifications of FEMA-356, a simplified joint model composed of two nonlinear cross struts placed diagonally over the location of the plastic hinge is established, allowing a sophisticated PA to be performed. To verify the validity of this method, the analytical results for the capacity curves and the failure mechanism derived from three different full-size RC frames are compared with the experimental measurements. By considering shear failure at BCJs, the proposed nonlinear analytical procedures can be used to estimate the structural behavior of RC frames, including seismic capacity and the progressive failure sequence of joints, in a precise and effective manner.

Analysis of the Micro-Rotation Compliant Mechanism Based on the Corner-Filleted Flexure Hinges

The purpose of this thesis is to derive the flexibility formula of the corner-filleted flexure hinge easily and conveniently and use it to design a micro-rotation compliant mechanism. Firstly,we get the corner-filleted flexure hinge flexibility formula by methods of symmetry transformation and coordinates translation. The correctness of this formula is validated on the basis of the finite element method and under the premise that the effects of shear stress are taken into consideration. Then a micro-rotation compliant mechanism is designed in accordance with the corner-filleted flexure hinge,and the deduction and analysis of its working moment/rigidity are conducted. Moreover,this theoretical formula is proved to be accurate and reliable through the finite element analysis and the experimental verification,based on which the structural design and optimization can be made on the rotating part of a micro adjustment device. The results illustrate that designing and optimizing the structures by the analysis model is convenient and reliable so that complicated 3D modeling and finite element analysis are not needed.

Sliding state stepping algorithm for solving impact problems of multi-rigid-body system with joint friction

Impact dynamics of multi-rigid-body systems with joint friction is considered. Based on the traditional approximate assumption dealing with impact problem, a general numerical method called the sliding state stepping algorithm is introduced. This method can avoid difficulties in solving differential equations with variable scale and its result can avoid energy inconsistency before and after impact from considering complexily of tangential sliding mode. An example is given to describe details using this algorithm.

大直径盾构隧道新型纵缝接头抗弯性能试验研究

纵缝接头是盾构隧道受力性能的薄弱部位,管片接头的形式直接影响盾构隧道的力学性能。目前国内的盾构隧道纵缝接头使用的连接件多为螺栓,新型纵缝接头使用了一种新的连接件—滑入式连接件,此种接头在大直径盾构隧道中的受力性能有待研究。本文以新型纵缝接头为研究对象,针对两种不同型号的滑入式连接件,采用模型试验的方法探究了大直径盾构隧道新型纵缝接头的受力性能,通过理论分析计算了新型纵缝接头的极限承载力,并比较分析了传统螺栓纵缝接头和新型纵缝接头的受力性能。结果表明:新型接头衬砌管片的薄弱部位在连接件周围的混凝土区域;滑入式连接件的型号直接影响新型纵缝接头的受力性能,两种接头中连接件尺寸较大的接头转角刚度相较于连接件尺寸较小的接头转角刚度增加了7.2~169.5%,极限承载能力增加了69.9%;新型纵缝接头比螺栓接头有更高的转角刚度,受力性能更好,适用于大直径盾构隧道。

Static behavior of semi-rigid thin-walled steel-concrete composite beam-to-column joints with bolted partial-depth flush end plate:experimental study

A new type of semi-rigid thin-walled steel-concrete composite beam-to-column joint has been proposed in this paper.Five semi-rigid composite beam-to-column joint specimens subjected to hogging moments under monotonic loading were tested to study the static behavior of this new type of joint.The main variable parameters for the five joint specimens were the longitudinal reinforcement ratio and the joint type.The experimental results designated that the magnitude of extension of the longitudinal reinforcement is the most important factor that influenced the moment-rotation characteristic of the new type of joint.The concrete slabs could resist 3.8%-19.1% of the total shear load applied to the cross-sections near the beam-to-column connection.The edge stiffened elements,such as the flange of the lipped I-section thin-walled steel beam,were capable of having considerable inelastic deformation capacity although they had comparatively large width-to-thickness ratios.The shear failure of the concrete cantilever edge strip must be taken into account in practical design because it has significant influence on the anchorage of the longitudinal reinforcement in the new type of external joints.

钢管混凝土柱-钢梁外加强环螺栓连接节点抗震性能有限元分析

为深入研究钢管混凝土柱-钢梁外加强环螺栓连接节点的抗震性能,建立了螺栓连接节点的精细化三维实体有限元模型。在对已有试验成果进行验证分析的基础上,研究加劲肋、螺栓连接数量对节点塑性耗能分配机制的影响。结果表明:当钢材本构后期考虑韧性损伤后,有限元计算结果与已有拟静力试验结果更吻合;CFST-1节点(梁高300 mm,有螺栓垫板)耗能能力最优,但仅达到相应焊接节点的一半;与CFST-1节点相比,CFST-3节点(梁高300 mm,无螺栓垫板)及CFST-2节点(梁高250 mm,有螺栓垫板)的总耗能更低;各螺栓节点的塑性耗能分配机制主要依靠梁耗能,而相应的加强环焊接节点主要依靠梁与加强环耗能;当螺栓节点采用环板加劲肋、4排螺栓以及腹板加劲肋构造优化后,刚度、承载力、延性与相应焊接节点一致,总塑性耗能达到刚接节点的79.1%,基本达到刚接节点的抗震水平。

Seismic Behavor of RC Beam-Column Joint with Additional Bars under Cyclic Loading

The behavior of Beam-Column Joints in moment resisting frame structures are susceptible to damage caused by seismic effects due to poor performance of the joint.A good number of researches were carried out to understand the complex mechanism of RC joints which are considered in seismic design code practices presently adopted.The traditional construction detailing of transverse reinforcement have shown serious joint failure. This paper introduces a new design philosophy involving the use of additional diagonal bars within the joint particularly suitable for low to medium seismic effects in earthquake zones throughout the world.In lieu to this study,ten(10) full-scale interior beam-column specimens were constructed with various additional reinforcement details and configurations as will be discussed in the later.The experiment provided adequate results to proof the idea of additional bars as suitable approach in reinforced concrete structures where earthquake is eminent.While compared with overall cracking observation during the test,the specimen with additional bars (diagonal and straight) had shown few cracks on the column than the ones without.Furthermore,concrete confinement is certainly an important design method as recommended by certain international codes.

加强型翼缘-波纹腹板组合隔板贯通式节点抗震性能研究

为克服隔板贯通式节点易发生脆性断裂而导致结构破坏的不足,结合“加强”和“削弱”的措施,使塑性铰外移,提出了加强型翼缘-波纹腹板组合隔板贯通式梁柱新型节点,并利用有限元软件ABAQUS探究了该新型节点在低周往复荷载作用下的破坏模式、应力分布情况。研究波纹数量、波纹厚度、加强板厚度、加强板长度这4种参数对该新型节点的滞回曲线、骨架曲线、耗能能力的影响规律。结果表明:新型节点有较好的承载力,应力主要集中在梁翼缘上波纹腹板削弱处,破坏发生在远离削弱处一侧,且腹板未发生屈曲变形。随着波纹厚度、加强板长度的增大,新型节点的承载力增加,耗能能力下降;随着波纹数量的增多,新型节点承载力和耗能能力增加;随着加强板厚度的增大,承载力增加,耗能能力先减小后增大。

钢筋混凝土薄壁空心高墩塑性铰长度计算方法

针对我国现行抗震设计规范尚未明确给出钢筋混凝土(RC)薄壁空心高墩塑性铰长度计算方法的问题,首先收集整理了既有RC桥墩塑性铰长度计算方法以及试验数据,分析影响塑性铰计算长度的主要因素;同时对实际桥梁工程采用的RC薄壁空心墩构造参数进行统计归纳.在验证有限元建模方法准确性后,采用ABAQUS软件建立了高度为40~120 m的8种典型RC薄壁空心高墩的精细化有限元模型,并开展非线性推覆分析,得到不同高度桥墩的等效塑性铰长度.最后讨论不同塑性铰长度计算方法的适用性,发现Eurocode 8规范的计算公式精度最高,可用于计算RC薄壁空心高墩的塑性铰长度.

露出式刚接箱型柱混合节点的抗震性能分析

运用ABAQUS有限元软件,分析了用于RC框架-钢结构加层混合结构的露出式刚接箱型柱节点的非线性受力性能,并在验证有限元模型正确性的基础上,深入研究了相关参数对露出式刚接节点抗震性能的影响规律,并提出设计建议。结果表明:露出式刚接箱型柱混合节点为梁塑性铰破坏,具有较强的耗能能力和塑性变形能力,但刚度退化较为严重;根据相关参数研究提出合理的设计建议,上部钢柱应尽可能采用平面内、平面外等稳定性的箱型或■字形截面柱;就论文所研究的试件来看,轴压比控制在0.16~0.40之间比较合理。

基于总安全系数法的隧道支护“强度-变形-时机”一体化设计方法研究

为解决宜兴高铁兴山东隧道含炭质页岩段大变形问题,基于总安全系数法理论体系,以围岩变形和多层结构协同承载控制为目标,建立适用于主动和被动支护体系的支护“强度-变形-时机”一体化设计方法。在强度满足承载要求的前提下,通过调整支护构件本身的变形能力和支护时机,使支护可变形能力大于设计支护力下围岩必需的变形量(防止支护刚度过大),并小于最小支护力下围岩必需的变形量(防止支护刚度过小),从而使整体支护结构按设计意图以最经济的方式“工作”。采用该设计理论,设计“双层初期支护+可缩钢架方案”和“预应力锚索主动支护方案”2种支护体系,提出各分项支护构件的施作时机和安全控制要求,并在现场开展试验。试验结果表明:1)2种支护方案均有效实现了设计意图,解决了隧道含炭质页岩段大变形问题。2)采用双层初期支护+可缩钢架方案时初期支护安全系数最小值为1.83,隧道最大水平收敛为588 mm,满足设计要求;采用预应力锚索主动支护方案时围岩最大水平收敛为372 mm,锚索最大轴力为310 kN,满足设计要求。