Test and simulation of full-scale self-centering beam-to-column connection

A new type of beam-to-column connection for steel moment flames, designated as a ＂self-centering connection,＂ is studied. In this connection, bolted top-and-seat angles, and post-tensioned （PT） high-strength steel strands running along the beam are used. The PT strands tie the beam flanges on the column flange to resist moment and provide self-centering force. After an earthquake, the connections have zero deformation, and can be restored to their original status by simply replacing the angles. Four full-scale connections were tested under cyclic loading. The strength, energy-dissipation capacity, hysteresis curve, as well as angles and PT strands behavior of the connections are investigated. A general FEM analysis program called ABAQUS 6.9 is adopted to model the four test specimens. The numerical and test results match very well. Both the test and analysis results suggest that： （1） the columns and beams remain elastic while the angles sustain plastic deformations for energy dissipation when the rotation of the beam related to the column equals 0.05 tad, （2） the energy dissipation capacity is enhanced when the thickness of the angle is increased, and （3） the number of PT strands has a significant influence on the behavior of the connections, whereas the distance between the strands is not as important to the performance of the connection.

Shake-table testing of a self-centering precast reinforced concrete frame with shear walls

The seismic performance of a self-centering precast reinforced concrete （RC） frame with shear walls was investigated in this paper. The lateral force resistance was provided by self-centering precast RC shear walls （SPCW）, which utilize a combination ofunbonded prestressed post-tensioned （PT） tendons and mild steel reinforcing bars for flexural resistance across base joints. The structures concentrated deformations at the bottom joints and the unbonded PT tendons provided the self-centering restoring force. A 1/3-scale model of a five-story self-centering RC frame with shear walls was designed and tested on a shake-table under a series of bi-directional earthquake excitations with increasing intensity. The acceleration response, roof displacement, inter-story drifts, residual drifts, shear force ratios, hysteresis curves, and local behaviour of the test specimen were analysed and evaluated. The results demonstrated that seismic performance of the test specimen was satisfactory in the plane of the shear wall; however, the structure sustained inter-story drift levels up to 2.45%. Negligible residual drifts were recorded after all applied earthquake excitations. Based on the shake-table test results, it is feasible to apply and popularize a self-centering precast RC frame with shear walls as a structural system in seismic regions.

Self-centering seismic retrofit scheme for reinforced concrete frame structures:SDOF system study

This paper presents the results of a parametric study of self-centering seismic retrofit schemes for reinforced concrete (RC) frame buildings. The self-centering retrofit system features flag-shaped hysteresis and minimal residual deformation. For comparison purpose,an alternate seismic retrofit scheme that uses a bilinear-hysteresis retrofit system such as buckling-restrained braces (BRB) is also considered in this paper. The parametric study was carried out in a single-degree-of-freedom (SDOF) system framework since a multi-story building structure may be idealized as an equivalent SDOF system and investigation of the performance of this equivalent SDOF system can provide insight into the seismic response of the multi-story building. A peak-oriented hysteresis model which can consider the strength and stiffness degradation is used to describe the hysteretic behavior of RC structures. The parametric study involves two key parameters -the strength ratio and elastic stiffness ratio between the seismic retrofit system and the original RC frame. An ensemble of 172 earthquake ground motion records scaled to the design basis earthquake in California with a probability of exceedance of 10% in 50 years was constructed for the simulation-based parametric study. The effectiveness of the two seismic retrofit schemes considered in this study is evaluated in terms of peak displacement ratio,peak acceleration ratio,energy dissipation demand ratio and residual displacement ratio between the SDOF systems with and without retrofit. It is found from this parametric study that RC structures retrofitted with the self-centering retrofit scheme (SCRS) can achieve a seismic performance level comparable to the bilinear-hysteresis retrofit scheme (BHRS) in terms of peak displacement and energy dissipation demand ratio while having negligible residual displacement after earthquake.

Numerical simulation of the seismic behavior of self-centering steel beam-column connections with bottom flange friction devices

A new type of steel moment resisting frame with bottom flange friction devices （BFFDs） has been developed to provide self-centering capacity and energy dissipation, and to reduce permanent deformations under earthquakes. This paper presents a numerical simulation of self-centering beam-column connections with BFFDs, in which the gap opening/closing at the beam-column interfaces is simulated by using pairs of zero-length elements with compression-only material properties, and the energy dissipation due to friction is simulated by using truss elements with specified hysteretic behavior. In particular, the effect of the friction bolt bearing against the slotted plate in the BFFDs was modeled, so that the increase in lateral force and the loss of friction force due to the bolt bearing could be taken into account. Parallel elastic-perfectly plastic gap （ElasticPPGap） materials in the Open System for Earthquake Engineering Simulation （OpenSees） were used with predefined gaps to specify the sequence that each bolt went into the bearing and the corresponding increase in bending stiffness. The MinMax material in OpenSees is used to specify the minimum and maximum values of strains of the ElasticPPGap materials. To consider the loss of friction force due to bok bearing, a number of parallel hysteretic materials were used, and the failure of these materials in sequence simulated the gradual loss of friction force. Analysis results obtained by using the proposed numerical model are discussed and compared with the test results under cyclic loadings and the seismic loading, respectively.

OPTIMIZING DESIGN OF MECHANICAL SELF-CENTERING DEVICE FOR SUSPENSION HEIGHT

Firstly, in view of the respective defects of existing self-centering devices for vehicle suspension height, the design scheme of the proposed mechanical self-centering device for suspension height is described. Taking the rear suspension of a certain light bus as a research example, the structures and parameters of the novel device are designed and ascertained. Then, the road excitation models, the performance evaluation indexes and the half-vehicle model are built, the simulation outputs of time and frequency domain are obtained with the road excitations of random and pulse by using MATLAB/Simulink software. So the main characteristics of the self-centering suspension are presented preliminarily. Finally, a multi-objective parameter design optimization model for the self-centering device is built by weighted sum approach, and optimal solution is obtained by adopting complex approach. The relevant choosing-type parameters for self-centering device components are deduced by using discrete variable optimal method, and the optimal results are verified and analyzed. So the performance potentials of the self-centering device are exerted fully in condition of ensuring overall suspension performances.

Prediction-based Manufacturing Center Self-adaptive Demand Side Energy Optimization in Cyber Physical Systems

Cyber physical systems（CPS） recently emerge as a new technology which can provide promising approaches to demand side management（DSM）, an important capability in industrial power systems. Meanwhile, the manufacturing center is a typical industrial power subsystem with dozens of high energy consumption devices which have complex physical dynamics. DSM, integrated with CPS, is an effective methodology for solving energy optimization problems in manufacturing center. This paper presents a prediction-based manufacturing center self-adaptive energy optimization method for demand side management in cyber physical systems. To gain prior knowledge of DSM operating results, a sparse Bayesian learning based componential forecasting method is introduced to predict 24-hour electric load levels for specific industrial areas in China. From this data, a pricing strategy is designed based on short-term load forecasting results. To minimize total energy costs while guaranteeing manufacturing center service quality, an adaptive demand side energy optimization algorithm is presented. The proposed scheme is tested in a machining center energy optimization experiment. An AMI sensing system is then used to measure the demand side energy consumption of the manufacturing center. Based on the data collected from the sensing system, the load prediction-based energy optimization scheme is implemented. By employing both the PSO and the CPSO method, the problem of DSM in the manufac^ring center is solved. The results of the experiment show the self-adaptive CPSO energy optimization method enhances optimization by 5% compared with the traditional PSO optimization method.

Self-access Centers’Effects on College English Learning

This paper aims to investigate self-access centers'effects on college English learning. Data, collected in the form of questionnaires and interview, were analyzed. Results demonstrate that the self-access center(SAC)does help students to promote learner autonomy, lower their anxiety and encourage their interest in college English learning.

A Local Property of Hausdorff Centered Measure of Self-Similar Sets

We analyze the local behavior of the Hausdorff centered measure for self- similar sets. If E is a self-similar set satisfying the open set condition, thenC^s（E∩B（x,r））≤（2r）^sfor all x ∈ E and r〉 0, where Cs denotes the s-dimensional Hausdorff centered measure. The above inequality is used to obtain the upper bound of the Hausdorff centered measure. As the applications of above inequality, We obtained the upper bound of the Hausdorff centered measure for some self-similar sets with Hausdorff dimension equal to 1, and prove that the upper bound reach the exact Hausdorff centered measure.

摩擦耗能型摇摆柱节点抗震性能研究

基于可恢复功能的概念,提出了一种摩擦耗能型摇摆柱节点。阐述了该节点的构造形式并研究了其抗震性能。通过试验和数值模拟,分析了轴压比、弹簧刚度等参数对节点抗震性能的影响及节点在余震和修复情况下的韧性。研究结果表明,在±3%层间位移角内,节点呈现出低损伤特性,摇摆柱始终保持弹性。在轴向力作用下,滞回曲线呈明显的“旗帜形”,节点具有良好的自复位性能,最大残余转角仅为0.23%。通过重新拧紧螺栓,节点性能即可恢复至震损前水平,实现抗震韧性。弹簧刚度的增大可以显著提高节点的抗弯承载力;增大轴压比可以提高节点的“屈服”弯矩和极限弯矩。在轴向力作用下节点属于典型的半刚性连接,并确定了节点初始转动刚度的取值范围。针对该节点提出了一个简化的恢复力模型,理论结果与试验结果吻合度较好,为进一步对整体结构进行分析和设计奠定了基础。

自复位转动摩擦阻尼器弯矩-转角恢复力性能研究

为了满足减震结构对可恢复功能的要求,针对传统摩擦阻尼器不具备自复位能力震后存在较大残余变形的问题,提出了一种基于形状记忆合金的自复位转动摩擦阻尼器,由摩擦耗能装置和形状记忆合金自复位装置组合而成。介绍了该SCRF(self-centering rotating friction)阻尼器的构造形式、工作原理,通过理论推导建立了SCRF阻尼器的弯矩-转角恢复力模型,通过ABAQUS软件有限元数值分析结果对弯矩-转角恢复力模型进行了验证,分析了低周往复荷载作用下SCRF阻尼器的滞回性能,并进行了参数分析。结果表明:有限元计算结果与阻尼器恢复力模型结果吻合良好;提高接触面间的摩擦因数与斜面高度可以提高阻尼器的最大承载力、耗能能力、有效刚度,但是超过一定限值的斜面高度会降低阻尼器的自复位能力;施加SMA螺栓预紧力可以提高阻尼器的摩擦启动弯矩,对于阻尼器的耗能能力与最大承载力影响不大。

变滞回性能阻尼器的抗震性能及其在RC排架墩中的应用

为了实现分级保护主体结构同时减小传统耗能阻尼器在强震作用下的残余变形的目的,提出一种基于形状记忆合金(shape memory alloy,SMA)板环的新型变滞回性能阻尼器(variable hysteresis performance damper based on shape memory alloy,SMA-VHD)。首先阐明了新型阻尼器的基本构造,揭示了其变滞回性能工作机理和自复位原理。通过对SMA板材进行材性试验确定了SMA板材的关键性能参数,进而建立阻尼器精细化有限元模型,系统研究阻尼器的滞回性能及参数影响规律。最后将新型阻尼器应用于RC排架墩中,通过动力时程分析研究附加阻尼器桥墩结构的分阶段抗震性能。研究结果表明:SMA板材应力应变关系呈“旗帜型”,具有良好的自复位能力;SMA-VHD滞回曲线呈现明显分级平台,随着阻尼器变形的增加,其滞回曲线由饱满的矩形变为具有自复位功能的“旗帜型”,表明该阻尼器具有变滞回性能的特性;将SMA-VHD应用到RC排架墩中,可有效实现结构的分级抗震,提高桥墩结构的抗震性能水平。

高速铁路自复位摇摆桥墩抗震性能分析

基于OpenSEES平台分别建立4跨高速铁路传统简支梁桥和摇摆桥墩简支梁桥系统的有限元模型,并依据摇摆桥墩的基本抗震设防目标,设计摇摆桥墩耗能构件的面积和承载力。在考虑地震动随机性基础上,进行自复位摇摆桥墩在高铁桥梁系统中的抗震性能研究。结果表明:罕遇地震下自复位摇摆耗能装置能够有效降低墩底最大弯矩,减震率达20.26%,进而减少墩身损伤,但碰撞效应使墩底最大轴力放大了74.7%;墩底耗能构件基本进入塑性但未完全被破坏,可实现震后快速修复;摇摆桥墩的最大墩顶位移比传统桥墩增加了66%,但位移组成中可自复位的刚体旋转变形远大于弯曲变形,因此震后残余位移减少了35%;摇摆耗能机制对支座最大变形的减震率达12.3%,使主梁最大变形增大了约49%,但对其残余变形的影响在1 mm内;轨道约束会削弱桥墩摇摆行为,使墩顶最大位移减少了14%,但对墩顶残余位移无明显影响。

新型自复位钢框架-复合墙连接节点研究

内填RC复合墙钢框架结构在框架与内嵌墙之间设置开缝并安装耗能连接件能减小结构损伤,改善结构力学性能。提出在内填RC复合墙和钢框架结构之间采用新型折板型耗能连接件,并采用ABAQUS对连接件的受力性能进行分析,研究了节点的受力过程和破坏模式。将耗能连接件应用于两侧开缝的密肋复合墙-钢框架结构中实现滑移连接。结果显示:折板连接件在竖向拉压荷载和水平侧向荷载作用下的变形损伤模式存在差异,折板角和折板弯折数目对连接件受力性能影响显著。折板连接件用于结构中时,结构加载前期滞回曲线表现出残余变形小的特点,具有自复位性能,因此折板连接件是一种具有自复位能力的连接形式。

预应力耗能钢框架抗连续倒塌机制研究

针对预应力耗能(PTED)钢框架结构的连续倒塌问题,采用ABAQUS软件建立精细化有限元模型,对框架结构拆除承重构件后不平衡荷载重分配的行为展开研究。并将有限元结果与1/3缩尺PTED钢框架的准静态试验结果进行对比分析,验证了模型的准确性。在此基础上,进一步开展了PTED钢框架抗连续倒塌受力机制的研究,并分析了初始预应力、预应力钢绞线数量、钢构件材料强度和梁翼缘宽厚比四种因素对钢框架抗连续倒塌机制的影响。结果表明:PTED钢框架抗连续倒塌过程主要包括三个阶段:初始阶段、压拱机制有利阶段和压拱机制不利阶段;倒塌抗力由预应力钢绞线拉力和梁柱之间的竖向作用力共同提供;提高初始预应力、预应力钢绞线数量、钢材屈服强度和降低梁翼缘宽厚比,均会使峰值荷载增大;钢绞线数量的增多使框架在失效柱位移较小时可以提供较大的抗力;增强梁柱构件抵抗局部屈曲变形的能力会提升预应力钢框架抗连续倒塌能力。

近场脉冲型地震作用下附加支撑双柱式摇摆桥墩的抗震性能研究

为了解决摇摆桥墩承载力和耗能能力不足的问题,该文提出一种附加人字形支撑的双柱式摇摆桥墩结构,支撑为纯耗能支撑或自复位耗能支撑,支撑通过连接装置安装在双柱式摇摆桥墩的盖梁和承台之间。为了研究新型附加人字形支撑双柱式摇摆桥墩的抗震性能,对其进行拟静力分析,将双柱式现浇桥墩和双柱式纯摇摆桥墩作为对比模型,研究附加纯耗能支撑和自复位耗能支撑双柱式摇摆桥墩的滞回性能;分别对这四种桥墩结构进行动力时程分析,探究这四种桥墩在近场对称脉冲、近场非对称脉冲和远场无脉冲地震动作用下的动力响应。研究结果表明:附加支撑的双柱式摇摆桥墩中的墩柱仍具有摇摆机制,可有效避免墩身出现塑性铰发生严重的损伤破坏,同时附加的支撑可以显著提高桥墩的承载能力和耗能能力,有效降低桥墩结构的位移响应,特别是自复位耗能支撑还可额外为桥墩提供自恢复力,有效提高结构的抗震性能。

新型铁路桥梁自复位体系抗震性能研究

针对铁路桥梁震后损伤重、修复难的问题,提出了基于新型自复位减震装置的铁路桥梁自复位体系,并开展了抗震性能研究。提出了具有低损伤、变刚度等特点的新型自复位减震装置,阐明了装置工作机理,建立了滞回分析模型。提出了“活动型支座+新装置”的减隔震与复位系统,明确了装置布置与安装方案。随后基于非线性时程分析方法,对比了传统非减隔震桥梁与自复位桥梁的抗震性能。研究结果表明:所提出的自复位体系具有极佳的抗震性能和可恢复性能,相比于原型桥梁,最大位移可降低27%,残余位移基本消除,仅最大剪力有所增加。

变摩擦装配式自复位复合墙抗震性能研究

针对自复位墙体耗能不足及大位移角时损伤严重的问题,介绍了一种变摩擦装配式自复位复合墙.墙体由变摩擦阻尼器、钢脚、预应力筋和复合墙构成:变摩擦阻尼器的摩擦力随滑移量的增加而增加,具有良好的耗能能力;钢脚提高了墙角抗压强度并提供了变摩擦阻尼器安装空间;预应力筋为墙体提供了自复位能力和部分承载能力;复合墙具有轻质、高强、绿色环保的特点.为进一步研究该墙体的抗震性能,对3块自复位复合墙进行了低周往复试验,分析不同初始预应力、碟簧组合形式对试件破坏形态、滞回特征、承载力、刚度退化、自复位能力和耗能能力的影响.研究结果表明:试件仅在墙底部出现少量混凝土表皮剥落,表现出良好的低损伤特点;试件在1.0%位移角时最大残余位移角为0.85%,表现出自复位特点;各试件的单圈耗能随着位移角的增加而迅速增加,表现出良好的耗能能力;初始预应力提高至1.9倍,导致承载力增加至1.3倍,而残余位移角降低至60%;阻尼器碟簧组合的并联数量增加至2倍,导致墙体的承载力增加至1.5倍,耗能能力增加至2倍,残余位移角增加至4.6倍.此外,建立了自复位复合墙数值分析模型,数值模型分析结果与试验结果较为吻合.随后进行了参数分析,发现预应力筋根数、螺栓初始预紧力和钢脚宽度对墙体的承载能力或耗能能力具有较大影响.

带有拼缝阻尼器的自复位预制双肢剪力墙的耗能能力研究

为提升自复位预制双肢剪力墙的耗能能力,针对预制双肢剪力墙提出了一种拼缝阻尼器,该阻尼器可适应接缝附近的大变形,帮助结构同时实现自复位和耗能的性能。通过拟静力试验,获得了该阻尼器的滞回曲线,验证了所提阻尼器具备良好的耗能性能;使用Opensees把阻尼器放入预制双肢剪力墙中进行数值分析,发现所提阻尼器在不降低结构原本自复位性能的同时,大大提升了结构的耗能能力。同时,耗能主要由拼缝阻尼器承担,结构自身的耗能和损伤较小,有利于实现结构在震后的快速修复。

基于Pushover方法的耗能自复位铰节点框架结构抗震性能分析

基于Pushover分析方法研究设置耗能自复位铰节点(EDSC-HJ)的钢筋混凝土框架结构的抗震性能.首先介绍EDSC-HJ框架的结构形式,并建立了EDSC-HJ框架结构的有限元模型,通过与振动台试验结果对比验证数值模拟的正确性;其次使用Pushover方法计算EDSC-HJ框架有控结构与无控结构的抗震性能并设计节点弹性恢复装置和耗能装置的力学参数.结果表明:EDSC-HJ框架结构节点相对转动刚度比的合理取值区间为0.05~0.5;设置节点阻尼器的EDSC-HJ有控结构的层间位移响应下降了76%,且满足限值要求;由于节点阻尼器的设置提高了结构的附加抗侧刚度,有控结构的基底剪力响应提高了23%.EDSC-HJ框架结构的抗震性能明显优于钢筋混凝土框架(RCF)结构,具有良好的韧性结构特征.

自复位复合阻尼耗能支撑滞回性能研究

为解决自复位支撑耗能能力不足且来源单一、耗能材料成本高昂的问题,提出了一种新型自复位复合阻尼耗能支撑。支撑由金属屈服阻尼装置、黏弹阻尼装置并联预压碟簧自复位装置组成。对其基本构造和工作原理进行阐述,通过精细化模拟研究了支撑的耗能、复位、承载和变形能力。结果表明,在往复荷载作用下,支撑的滞回响应具有稳定饱满的旗形特征,拉压对称、无残余变形,能够兼顾不同加载频率下的性能需求。揭示了支撑加载制度和设计参数对其滞回性能的影响规律,结果表明:加载频率从0.3 Hz增加到2.0 Hz,黏弹阻尼装置提供的阻尼力增大,支撑耗能量由8.32 kJ增加到11.93 kJ;随着碟簧预压力的增加,支撑激活力从378.98 kN增加到562.67 kN,复位性能始终得到充分发挥;支撑耗能能力主要受三角形钢板个数和黏弹材料剪切面面积影响,增加4个三角形钢板或将黏弹材料剪切面面积从140 mm×140 mm增加到300 mm×140 mm,支撑的等效黏滞阻尼比分别同比增长39.93%和16.09%。