近断层地震动下摇摆-自复位桥墩地震反应分析

为讨论摇摆-自复位（Rocking Self-Centering,RSC）桥墩在近断层地震动下的地震反应,基于OpenSees数值分析平台建立了RSC桥墩抗震分析模型。同时建立了普通钢筋混凝土（Reinforced Concrete,RC）桥墩,配置竖向无粘结预应力筋（Unbonded Prestressed Reinforced Concrete,PRC）桥墩的抗震分析模型作为对比。对各模型输入近断层地震动记录,进行增量动力分析。以墩顶最大位移角、残余位移角、预应力筋最大应力为考察目标,对比分析了不同墩高（剪跨比分别为2、4和6）、不同桥墩类型（RSC、RC和PRC桥墩）时各桥墩的地震反应。结果表明:随着耗能钢筋配筋率增加,RSC桥墩墩顶最大位移角和预应力筋最大应力均减小;RSC和PRC桥墩均可有效减少桥墩震后残余位移角。耗能钢筋配筋率与PRC桥墩纵筋配筋率接近的RSC桥墩,两者的最大墩顶位移角、残余位移角和预应力筋应力水平均接近。无论是RSC桥墩还是PRC桥墩,当剪跨比大于等于6.0时,易发生预应力筋失效。为避免预应力筋失效引起RSC桥墩产生过大的墩顶残余变形,RSC桥墩中耗能钢筋配筋率不宜低于0.75%。     

近断层地震方向脉冲效应对高速铁路桥梁弹塑性反应的影响

基于PEER-NAG强震数据库,采用ANSYS分析软件、ANSYS-APDL语言和弯矩曲率关系计算程序,以高速铁路多跨简支梁桥为研究对象,建立了近断层脉冲型地震作用下的高速铁路桥梁全桥模型,考虑了轨道不平顺的影响,分析了结构的自振特性,计算了近/远断层地震作用下桥梁的弹塑性地震响应。计算结果表明,近断层方向脉冲型地震作用下的墩底的荷载-变形曲线呈现中间加强的特点,此时需要桥墩有更强的能量释放能力和较好的延性要求,相比远断层地震而言,近断层方向脉冲型地震作用下墩底梁体位移、墩顶位移以及墩底弯矩增大,且导致更大的塑形变形;远断层地震趋向于能量的逐渐释放过程并与较少的滞回环损伤疲劳相联系;由于近断层地震动方向脉冲效应的影响,在一些地震动的某些时段内,对结构破坏起控制作用的因素是速度或位移而不是峰值加速度;由于近断层地震较大的竖向地震动,导致梁体竖向挠度比远断层地震增加较多,《铁路工程抗震设计规范》等取竖向地震为横向的2/3左右,会导致竖向动力响应偏小,建议取竖向地震动的合理范围进行计算较为妥当。     

干接缝节段拼装桥墩拟静力试验研究

摘要：为了比较节段拼装桥墩与整体现浇桥墩之间抗震性能的差异,以是否存在预应力钢筋、不同施工方法、预应力筋的位置和粘结状态、是否存在耗能钢筋等为试验参数,设计了一个包含五种不同构造类型混凝土桥墩的试验方案。采用拟静力试验方法比较分析了这五种不同构造类型混凝土桥墩的破坏形态、易损部位、荷载位移滞回曲线、节段拼装桥墩接缝的开展、拟静力残余位移、曲率分布、耗能能力、粘滞阻尼比等,得到了三种节段拼装桥墩、整体现浇钢筋混凝土桥墩和预应力混凝土桥墩之间拟静力行为的异同。试验结果表明：节段拼装桥墩在循环荷载作用下发生接缝的交替开闭,曲率变化集中在接缝附近,没有发生整体现浇混凝土桥墩通常出现的塑性铰现象。耗能钢筋的存在可以延缓接缝的张开,增加构件的极限弯矩和耗能能力,从而有利于增加抗震能力;采用无粘结预应力钢筋和有粘结预应力钢筋连接的节段拼装桥墩的拟静力残余位移比较小,而采用耗能钢筋的节段拼装桥墩的拟静力残余位移较大,基本上与整体现浇桥墩的拟静力残余位移相近。     

液化场地钢筋混凝土桥墩残余位移分析

为探究场地液化对钢筋混凝土(ReinforcedConcrete,RC)桥墩残余位移影响机理，首先基于OpenSees有限元计算平台阐述了液化场地-结构有限元数值建模方法，通过与离心机试验结果对比验证了建模方法的可靠性。其次以一座实际工程中的单桩单柱式桥墩为原型，发展了液化场地-RC桥墩建模方法，建立非液化场地-桩-RC桥墩数值模型(模型1)和液化场地-桩-RC桥墩数值模型(模型2)，对两模型输入近断层地震动进行非线性动力时程分析。讨论了模型2场地液化情况，并对模型1与模型2的场地位移、桩身位移、桩身最大屈服曲率延性系数、墩顶残余位移及墩顶残余位移随地震动峰值加速度(PGA)变化情况进行对比。结果表明：地震过程中，模型2场地各深度出现不同程度液化现象；且土体中上部均达完全液化状态，土体水平极限抗力损失最大，对桩身侧向约束严重降低。液化导致场地震后残余位移显著增加，场地对桩身震后约束增强，导致桩顶残余位移增大。另外，由于地震过程中中上部液化土体对桩身侧向约束严重降低导致桩身塑性变形显著增大、桩身最大塑性变形位置明显下移以及桩身塑性变形区扩展，引起桩身更为严重的塑性损伤，进而增大桩顶残余位...     

近断层地震作用下曲线桥碰撞效应及影响试验研究

为明晰近断层地震动作用下曲线梁桥碰撞效应及其影响,以某小半径带坡匝道桥为对象,设计制作1/10缩尺模型及可调式碰撞测试装置,选取同次地震中近断层和远场地震动输入,完成了单向和双向激励条件下试验模型桥的振动台试验。结果表明:与远场地震动相比,近断层地震动作用下曲线梁桥的碰撞效应(碰撞次数和碰撞力)有较为显著的增加,而碰撞效应的增大会增大支座的位移响应,进而增加支座失效或落梁风险,且双向地震动影响更大;碰撞对边墩和中墩沿碰撞力方向的切向位移峰值增加显著,对碰撞力方向上试验模型桥的墩顶有效均方根位移响应均有放大作用,碰撞会增加试验模型桥桥墩的破坏风险。曲线桥抗震设计中应考虑近断层地震动诱发的碰撞效应影响。     

地震作用下钢筋混凝土桥墩残余位移研究

为更深入了解地震作用下钢筋混凝土桥墩墩顶残余位移与最大位移关系,提出精度更高的残余位移估算方法。首先利用OpenSees地震仿真软件中的纤维梁柱单元建立了钢筋混凝土桥墩的动力计算模型,通过与已有钢筋混凝土桥墩振动台试验结果的对比,验证了计算模型的可靠性;其次通过研究桥墩轴压比、长细比、纵筋配筋率、体积配箍率、纵筋强度硬化系数、纵筋与混凝土强度比等参数对钢筋混凝土桥墩墩顶残余位移延性指标的影响规律;最后通过回归分析建立了残余位移影响系数随以上参数变化的预测公式,并通过已有振动台试验数据验证了计算公式的合理性。研究结果表明:与日本规范相比,推荐公式对残余位移的估算值与试验值更接近,可用于基于性能抗震设计时初步估算地震作用下钢筋混凝土桥墩的残余位移值。     

预应力双柱式摇摆墩结构体系摇摆谱分析EI北大核心CSCD

摇摆桥墩的损伤和残余位移小,具有良好的震后可恢复性。以预应力双柱式摇摆墩结构体系为研究对象,考虑预应力筋对摇摆刚度的影响,基于拉格朗日方程和动量矩守恒定理给出预应力双柱式摇摆墩的刚体动力分析模型,并进行脉冲型地震动作用下的摇摆谱分析。研究结果表明:在长周期脉冲地震动作用下,预应力筋可以有效减轻低墩的地震反应;随着桥墩高度的增加或地震动频率的增加,预应力筋对桥墩地震反应的影响降低,桥墩依靠自身转动惯量抵抗地震作用;负摇摆刚度既可有效避免桥墩的倒塌,又能减轻脚点处的局部损伤,可在摇摆墩设计时采用。     

RC桥墩残余位移模拟的参数敏感性分析EI北大核心CSCD

为讨论RC桥墩震后残余位移模拟的建模方法,采用Open Sees非线性纤维梁柱单元和零长度转动弹簧单元,建立了桥墩抗震分析模型。以1个足尺RC桥墩振动台试验结果为依据,对桥墩进行动力时程分析和静力滞回性能模拟。结果表明,纤维梁柱单元数量、转动弹簧单元极限滑移量S_u、刚度折减系数b、调整纵筋失效循环次数的延性系数C_f和强度降低系数C_d对残余位移模拟的影响不明显。纵筋滞回关系调整参数R_0和转动弹簧单元捏缩系数R对残余位移模拟结果影响较大,初步识别结果为15和1.0。考虑混凝土抗拉的Concrete 02模型模拟残余位移精度高于Concrete 01模型,考虑纵筋的屈曲GA模型模拟的桥墩残余位移明显偏小。     

RC桥墩残余位移模拟的参数敏感性分析

为讨论RC桥墩震后残余位移模拟的建模方法,采用Open Sees非线性纤维梁柱单元和零长度转动弹簧单元,建立了桥墩抗震分析模型。以1个足尺RC桥墩振动台试验结果为依据,对桥墩进行动力时程分析和静力滞回性能模拟。结果表明,纤维梁柱单元数量、转动弹簧单元极限滑移量S_u、刚度折减系数b、调整纵筋失效循环次数的延性系数C_f和强度降低系数C_d对残余位移模拟的影响不明显。纵筋滞回关系调整参数R_0和转动弹簧单元捏缩系数R对残余位移模拟结果影响较大,初步识别结果为15和1.0。考虑混凝土抗拉的Concrete 02模型模拟残余位移精度高于Concrete 01模型,考虑纵筋的屈曲GA模型模拟的桥墩残余位移明显偏小。     

近断层长周期脉冲型地震动对竖向反应谱影响研究

长周期大幅值脉冲运动是近断层地震动的重要特征,也是引起结构震害的重要因素。在既有的地震动数据库基础上,筛选建立了长周期脉冲型记录的统计样本库,并构建了地震动特征参数的回归关系式。针对竖向反应谱,深入分析了竖向分量与水平向分量的加速度反应谱比值随脉冲周期和结构自振周期的变化规律,结果表明反应谱比值显著大于现行规范取值,进而采用分段线性化方法,建立了竖向反应谱比值随脉冲周期、自振周期变化的简化关系式,并对影响竖向反应谱曲线各拐点周期的特征比值进行统计分析,拟合得到了其随震级和断层距的衰减模型。     

Insertion of triangulated surfaces into a meccano tetrahedral discretization by means of mesh refinement and optimization procedures

In this paper, we present a new method for inserting several triangulated surfaces into an existing tetrahedral mesh generated by the meccano method. The result is a conformal mesh where each inserted surface is approximated by a set of faces of the final tetrahedral mesh. First, the tetrahedral mesh is refined around the inserted surfaces to capture their geometric features. Second, each immersed surface is approximated by a set of faces from the tetrahedral mesh. Third, following a novel approach, the nodes of the approximated surfaces are mapped to the corresponding immersed surface. Fourth, we untangle and smooth the mesh by optimizing a regularized shape distortion measure for tetrahedral elements in which we move all the nodes of the mesh, restricting the movement of the edge and surface nodes along the corresponding entity they belong to. The refining process allows approximating the immersed surface for any initial meccano tetrahedral mesh. Moreover, the proposed projection method avoids computational expensive geometric projections. Finally, the applied simultaneous untangling and smoothing process delivers a high‐quality mesh and ensures that the immersed surfaces are interpolated. Several examples are presented to assess the properties of the proposed method.     

Certification Institutions Expected to Update and Transfer Information on Present Standards

Standards are the basis for production enterprises to organize production, ex-factory inspection, trade (delivery) and technical exchanges, product certification, quality arbitration and supervision.……     

From Industry 4.0 to Research 4.0. Development of High Performance Fibers in the Light of Digitization

We associate a variety of innovations with the term ＂Industry 4.0＂. The pioneer of many 4.0 modifications forms the basisfor the trend towards the integrated di...     

Flow calorimeter for enthalpy increment measurements on condensed gases

A flow calorimeter for enthalpy increment measurements on condensed gases is presented. A better knowledge of the properties of the liquefied natural gas is needed, and therefore a liquid loop has been designed for our flow calorimeter. The fluid loop in the calorimeter is designed in order to avoid the two-phase region, since two phases would give compositional disturbances in the measurements. The avoidance of the two-phase region is made possible by increasing the pressure of the test fluid after the measurement section, then heating the fluid at super-critical pressure past the critical point. Finally, the fluid is throttled to the low-pressure gas state at the inlet condition of the compressor that circulates the fluid. To perform the pressure increase, a new cryogenic pump has been designed. To evaluate the new equipment, measurements were taken on liquid ethane over the temperature range 146–256 K at pressure between 0.9 and 5.1 MPa.     

Refrigerators Enter a New Era of Health Preservation Frestech initiates the establishment of China's first standard for household sterilization refrigerators

On November 30, 2007, the China Association for Standardization (CAS) held a press conference at Beijing Diaoyutai State Guest House. Leaders from the China Household Electric Appliance Research Institute, the China Household Electric Appliance Association, and the China Consumers' Association attended and made speeches.……     

Roman iron and steel: A review

ABSTRACT

The production of ferrous metal increased during the Roman Late Republican period, Principate and Empire. The direct bloomery process was used to extract the metal from its ores using slag-tapping and slag-pit furnaces. The fuel was charcoal and an air blast was introduced by bellows-operated tuyères. Iron formed as a bloom, often as a spongy mass of metal, which contained impurities from the smelting process, including unreacted ore, fuel, slag and fragments from the furnace walls, while the metal was often inhomogeneous with varied carbon contents. Blooms were either smithed directly into bars or ingots or they were broken up, which also allowed the removal of gross impurities and a selection of pieces with similar properties to be made. These could then be forge-welded together and formed into characteristically shaped ingots. Making steel in the furnace seems to have been achieved: it depended on the ore and the furnace and conditions within it. Surface carburization was also carried out. Iron and steel were used extensively in construction and for tools and weapons. Fire welding was often used to add pieces of steel to make the edges of tools and weapons, which could be heat-treated by quenching to harden them.     

Optimum-Simulation von Ernteprozessen

Zusammenfassung Bei der Gestaltung von Ernteprozessen — beispielsweise des Prozesses Mähdrusch, Körnertransport und -abnahme — als transportverbundene Fließarbeitsverfahren mit mindestens zwei verschiedenen Arbeitsmitteln gibt es einen großen Optimierungsspielraum. Solche Prozesse sind mehrstufige Bedienungsprozesse mit gemischter Anordnung der Bedienungseinrichtungen. Außerdem besitzen sie stark ausgeprägte räumliche Aspekte. Es wird vor allem gezeigt, welche Merkmale solcher Prozesse in Simulationsmodellen abgebildet sein müssen, welche Zielgrößen in Abhängigkeit von welchen Einflußgrößen unter Berücksichtigung welcher Prozeßbedingungen ermittelt werden sollten und wie der Bewertungsprozeß zur Ermittlung der gewünschten Informationen gestaltet werden muß.     

A study of centrifugal cast high boron high speed steel

In the present study a high‐boron high speed steel (HSS) roll material was designed. Many expensive alloy elements have been substituted by cheap boron alloy, and high‐boron high speed steel roll has been manufactured by centrifugal casting method. The microstructures, mechanical properties and wear resistance of centrifugal casting high‐boron high speed steel roll have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), and X‐ray diffraction (XRD) analysis, hardness test, impact test and wear test. The results indicated that the solidification microstructures of high‐boron high speed steel roll consisted of M₂(B,C), (W,Mo)₂(B,C), M₃(B,C), M₂₃(B,C)₆ type borocarbides and martensite, a small amount of retained austenite. Borocarbides were continuously distributed over the grain boundary. After quenching from 1050 °C, local broken network appeared in partial borocarbides, and fine secondary borocarbide precipitated from the matrix. After tempering from 525 °C, the amount of precipitated borocarbide increased significantly. After heat treatment, the hardness of high‐boron high speed steel roll excelled 60 HRC, and its impact toughness excelled 8.0 J/cm². The single groove steel rolling amount of high‐boron high speed steel rolls increases by 500% than that of bainite cast iron roll, when the rolls are used in K₁ mill housing of bar mill.     

Thixotropy of Systems with Shear Thinning and Plastic Flow Behavior

The definition of the thixotropy is a decrease in viscosity with time in shear and a subsequent recovery of viscosity after the shear deformation is removed.We ...