Effects of connection types and elevated temperature on the impact behaviour of restrained beam in portal steel frame

Based on the background of structural protection and Disaster Reduction Engineering, the dynamic behaviour and failure mechanism of restrained beams in portal steel frames in localised fire are investigated via experimental measurement and numerical simulation techniques. Comprehensive parametric studies are carried out to discuss the influence of end connection types, temperature, impact velocity,impact mass and span-to-depth ratio(SDR) on the dynamic response of the beams. The characteristics of deformation, internal force and energy distribution about the restrained beams and its joints are investigated. A temperature dependent criterion for evaluating the frame joint performance is proposed to measure the degree of performance degradation and impact resistance of the joint. The dynamic displacement amplification factor in different temperature environments are proposed for the different beam end constraint types and SDRs. Results of the experimental and numerical analysis show that the welded connection(WC) of three typical joint types is the strongest, and the extended endplate connection(EEC) is the weakest in terms of the impact resistance performance. With regard to the failure mode of the joint, the failure positions of the WC and the welded-bolted connection are located in the inner web of the column. Meanwhile, the EEC is located in the connection position between the beam and the endplate. Three different internal force stages and two obvious critical temperature boundaries of the restrained beams emerge with the increase in temperature, and they have significant characteristics in terms of deformation trend, internal force transfer and energy distribution. During the impact, a phenomenon known as “compression arch action” develops into “catenary action” with the increase in deflection in the frame beam mechanism.

Experimental Study of Moso Bamboo to-Steel Connections with Embedded Grouting Materials

Moso bamboos have attracted excessive attention as a renewable green building material to the concept of sustainable development.In this paper,the 20 bolted Moso bamboo connection specimens with embedded steel plates and grouting materials were designed according to connection configurations with different bolt diameters and end distance of bolt holes,and their bearing capacities and failure modes were analyzed by static tension tests.According to the test results of all connectors,the failure modes of the specimens are divided into four categories,and the effects of bolt diameter and bolt hole end distance on the connection bearing capacity and failure mode are analyzed.The test results show that the deformation and failure process can be divided into four stages.The main influence factor of connector bearing capacity is bolt diameter.Connectors can be divided into four failure modes,and brittle failure can be avoided by adopting certain structural measures.Filling with grouting material can improve the bearing capacity of joints.Due to the large variability of bamboo,further experiments are needed.

Study on the Application of UHVDC Hierarchical Connection Mode to Multi-infeed HVDC System

随着我国特高压交直流技术的广泛应用，多馈入直流集中落入受端负荷中心将是未来我国电网发展所面临的重要问题。为从电网结构上有效解决多馈入直流系统的问题，提出一种特高压直流分层接入交流电网的方式。研究分层接入方式直流多馈入短路比计算方法的适用性，从理论上对比特高压直流不同接入方式下多馈入直流电网的系统特性，证明特高压直流分层接入方式有助于提高多馈入直流系统的电压支撑能力，引导潮流在1000kV与500kV层级间合理分布。结合国家电网规划，仿真验证了特高压直流分层接入方式的优势。

Experimental and Numerical Studies of Failure Modes and Load-Carrying Capacity of Through-Diaphragm Connections

Shear failure in panel zones and plastic hinges in steel beams are the two major failure modes of connections between concrete-filled steel tubular(CFST) columns and steel beams. To investigate the behavior of this type of connection in both modes,two through-diaphragm connections were tested under cyclic and monotonic loadings and the load-carrying capacity,ductility,and strength of degradation of connections were discussed. Using ABAQUS software,we developed nonlinear finite-element models(FEMs) to simulate the load-carrying capacity and failure modes of the connections under monotonic loading. The finite-element(FE) analysis and test results showed reasonable agreement for the through-diaphragm connections,which confirms the accuracy of FEMs in predicting the load-carrying capacity and failure modes of connections. Based on the validated FEM,a parametric study was then conducted to investigate the infl uence of the thicknesses of the tube and diaphragm on the load-carrying capacity and failure modes of these connections. The results indicate that the strength,stiff ness,and load-carrying capacity are infl uenced less by the thickness of the diaphragm,and more by the thickness of the steel tube. According to the FE analysis results,it can be found that the critical condition between the two failure modes is determined by the shear resistance and bending resistance.

Shaking test research on connection modes between block infill wall and frame beam

In order to achieve an optimal anti-seismic behavior,or rather stability,the out-of-plane stability of infill wall in frame has been researched with the shaking test of four sets of two-layer infill wall,in which four different connection modes of filled with inclined bricks on the top,disconnection,flexibility and semi-flexibility were adapted.The acceleration and displacement response of the specimens were analyzed under the seismic load.Also,some feasible connection modes were gained by comparing the response of infill walls.Finally,the calculation of earthquake of infill wall was held.The results showed that seismic responses of the infill walls whose connect with frame in form of flexibility and semi-flexibility modes are weaker than others obviously,and their integrality is better.Thus the conclusion could be drawn that out-of-plane stability of the specimens with connection modes of flexibility and semi-flexibility are better than those with the connection modes of filled with inclined bricks on the top and disconnection.The research results can provide evidence for establishing specifications and directing the construction and therefore help reduce the casualties and property loss caused by earthquake disasters.

Influence of the column-to-beam flexural strength ratio on the failure mode of beam-column connections in RC frames

The column-to-beam flexural strength ratio(CBFSR)has been used in many seismic codes to achieve the strong column-weak beam(SCWB)failure mode in reinforced concrete(RC)frames,in which plastic hinges appear earlier in beams than in columns.However,seismic investigations show that the required limit of CBFSR in seismic codes usually cannot achieve the SCWB failure mode under strong earthquakes.This study investigates the failure modes of RC frames with different CBFSRs.Nine typical three-story RC frame models with different CBFSRs are designed in accordance with Chinese seismic codes.The seismic responses and failure modes of the frames are investigated through time-history analyses using 100 ground motion records.The results show that the required limit of the CBFSR that guarantees the SCWB failure mode depends on the beam-column connection type and the seismic intensity,and different types of beam-column connections exhibit different failure modes even though they are designed with the same CBFSR.Recommended CBFSRs are proposed for achieving the designed SCWB failure mode for different types of connections in RC frames under different seismic intensities.These results may provide some reference for further revisions of the SCWB design criterion in Chinese seismic codes.

Resting-state connectivity in the default mode network and insula during experimental low back pain

Functional magnetic resonance imaging studies have shown that the insular cortex has a signif- icant role in pain identification and information integration, while the default mode network is associated with cognitive and memory-related aspects of pain perception. However, changes in the functional connectivity between the defauk mode network and insula during pain remain unclear. This study used 3.0 T functional magnetic resonance imaging scans in 12 healthy sub- jects aged 24.8 ± 3.3 years to compare the differences in the functional activity and connectivity of the insula and default mode network between the baseline and pain condition induced by intramuscular injection of hypertonic saline. Compared with the baseline, the insula was more functionally connected with the medial prefrontal and lateral temporal cortices, whereas there was lower connectivity with the posterior cingulate cortex, precuneus and inferior parietal lobule in the pain condition. In addition, compared with baseline, the anterior cingulate cortex exhibited greater connectivity with the posterior insula, but lower connectivity with the anterior insula, during the pain condition. These data indicate that experimental low back pain led to dysfunction in the connectivity between the insula and default mode network resulting from an impairment of the regions of the brain related to cognition and emotion, suggesting the impor- tance of the interaction between these regions in pain processing.

Comparison the Performances of Three Earthing Systems for Micro-Grid Protection during the Grid Connected Mode

This paper presents, tests and compares three earthing systems (TT, TN and IT) for Micro-Grid (MG) protection against various fault types during the connected mode. The main contribution of this work is including the models of all the micro sources which interfaced to the MG by power electronic inverters. Inverters in turns are provided with current limiters and this also included in the inverter models to exactly simulate the real situation in the MG during fault times. Results proved that the most suitable earthing system for MG protection during the connecting mode is the TN earthing system. That system leads to a suitable amount of fault current sufficient to activate over current protection relays. With using TN system, Touch voltages at the faulted bus and all other consumer’s buses are less than the safety limited value if current limiter is included with the transformer of the main grid which connects MG. For the two others earthing systems (TT and IT), fault current is small and nearly equal to the over load current which make over current protection relay can not differentiate between fault current and overload current. All models of micro sources, earthing systems, inverters, main grid and control schemes are built using Matlab?/Simulink? environment.

Mechanical Properties of Moso Bamboo Connections with External Clamp Steel Plates

The Moso bamboo,a renewable green building material used in various new green buildings,have received exten-sive attention with the promotion of the concept of green buildings.To explore the mechanical properties of Moso bamboo connections with external clamp steel plates,the 16 specimens were designed by changing the bolt diameters and the end distances of the bolt holes.Their static tension tests were conducted to investigate bearing capacities and failure modes of different connection configurations.Based on test results,three failure modes of these connections were obtained,including the shear failure of bolt shank,bearing failure of bolt hole and punch-ing shear failure of the Moso bamboo.The influence of bolt diameters and end distances of bolt holes on bearing capacities of the connections was quantitatively analyzed.Based on a simplified mechanical model,the analytical models were deduced for the bolt shear failure and the bearing failure of bolt holes.The results showed that the predictive values are in substantial agreement with the experimental results.Finally,the design and manufacturing suggestions are recommended for this Moso bamboo connections.

Influence of Control Modes of Grid-Connected Solar Photovoltaic Generation on Grid Power Flow

Integration of Solar Photovoltaic (PV) generation into an existing distribution system has many impacts on the system, with the power flow being one of the major issues. This impact is not generic for any network, but it may manifest itself either positively or negatively, depending on the grid configuration, interface control modes, operation mode, and load profile. Grid-connected PV systems have three control options of the local voltage controller of the interface DC-AC converter. These control modes are Power Factor control, voltage control, and Droop Voltage control. This paper aims at evaluating and comparing the impacts of those control modes on the grid power flow. A set of evaluation criteria and indices is defined and mathematically formulated. Based on the requirements of the used program (Power Factory Dig Silent V14.1.3), a computation plan (algorithm) has been proposed. The algorithm has been applied to a typical weak network and a wide range of simulations has been carried out. Simulation results have been thoroughly discussed and important findings have been concluded.

部分包覆钢-混凝土组合梁柱节点抗震性能试验研究

为研究不同连接构造的部分包覆钢-混凝土组合梁柱节点(PEC梁柱节点)的抗震性能,对2个PEC梁柱节点试件进行了拟静力加载试验,研究了低周往复荷载作用下PEC梁柱节点试件的破坏现象、滞回曲线、骨架曲线、延性、耗能能力和刚度退化等抗震性能。结果表明:强轴连接PEC梁柱节点的滞回曲线呈梭形和弓形,在达到极限承载力后仍能保持一定的延性和耗能能力;弱轴连接PEC梁柱节点牛腿与梁间的焊缝处发生破坏,未展现出预期的耗能能力,PEC梁仍在弹塑性状态,没有达到极限状态;PEC梁柱节点核心区混凝土替换为加劲肋板后,试件仍具有较好的承载力、延性和耗能能力,刚度退化规律无明显变化,且强轴连接节点与弱轴连接节点刚度变化规律基本一致;PEC柱牛腿设计过短会导致焊缝连接处断裂,试件延性和耗能能力得不到发挥,剩余刚度较大。

大规模可再生能源发电友好并网与运行调控技术研究综述

“双碳”目标下大规模可再生能源系统的友好并网与稳定运行问题被广泛关注,但受精确的发电不确定性建模技术与科学的并网调控策略制约.为解决这一问题,从可再生能源发电预测与不确定性建模、可再生能源系统并网运营模式、可再生能源系统并网控制方法三个方面进行梳理和总结,讨论了不同时间尺度下发电不确定性预测技术、针对多场景运行需求的不确定性建模技术;从可再生能源-储能系统、可再生能源集群-独立储能系统、多能源互补系统三个角度分析总结了目前并网运营模式;在此基础上,分析总结了跟网型与构网型两种并网控制策略.最后展望了高比例可再生能源系统在未来电网形态演变中的发展方向,以期为新型电力系统中可再生能源与电网协同发展的研究和技术应用提供借鉴.

跨国公司东道国和母国制度距离对企业创新绩效的影响——基于上市公司数据的实证分析

基于制度理论和行为者能动性视角,研究跨国公司东道国和母国制度距离如何对企业创新绩效产生不对称的影响,并考察企业政治关联和海外进入模式的调节作用。研究发现,正向制度距离对企业创新绩效产生正向影响,而负向制度距离越大,越不利于企业创新绩效提高;与没有政治关联的企业相比,企业具有政治关联则使得正向制度距离与企业创新绩效之间的正相关关系降低,并削弱了负向制度距离对企业创新绩效的负向影响;此外,企业选择跨国并购或绿地新建的进入模式也会调节制度距离方向与企业创新绩效之间的关系。研究结论不仅丰富了制度距离视角下企业创新绩效的研究,而且为政府制定相关政策和企业国际化决策提供了有益的实践启示。

适应并离网模式切换的DFIG电磁暂态仿真建模

目前,常用的商业仿真软件中的双馈式感应发电机(double-fed Induction Generator,DFIG)模型通常不支持离网运行模式,难以实现风力发电系统由离网到并网的全过程电磁暂态仿真,对电力系统仿真分析工作带来极大不便。研究适应并离网模式切换的DFIG电磁暂态仿真建模方法。基于模块化思想分别对风力机、异步电机、变流器以及断路器进行建模,在系统组装形成DFIG风力发电系统电磁暂态仿真模型。提出了适应并离网模式切换的DFIG受控源等效电路模型和离散时间域实现方法,通过设计状态变量矩阵元素的截取和扩充算法实现了模型在并离网模式下的无缝衔接。在MATLAB/Simulink中搭建DFIG发电系统模型对所提方法和模型进行验证,仿真结果表明,所提建模方法能够很好地支持DFIG离网运行模式,实现DFIG由离网到并网的全过程电磁暂态仿真。

监察互涉案件管辖模式的反思与调整--以《监察法》第34条第2款为视角

监察互涉案件在实践中产生了三类管辖模式,分案管辖模式应为此类案件管辖模式的“天然形态”,并案管辖模式是管辖制度灵活与变通的产物,专案组管辖模式则是折中后的特殊模式。三类管辖模式在实践中存在着适用规范与范围不明的问题,且并案管辖模式的适用并未受到职能管辖范围的限制。应当回归《监察法》第34条第2款的本义,该条款应为分案管辖模式,且未为并案管辖模式的适用留下解释空间,“为主”与“协助”之界需以法定职能管辖为红线。对此,并案管辖模式仅可适用于监检型互涉案件,《监察法》第34条第2款例外情形的判断应引入“主罪”的考量因素,具体管辖模式的适用应权衡案件的关联性、复杂性、社会影响力、各案之间的办理进度等因素。

NFTSM控制的光伏并网系统低压穿越控制策略

针对现有PI与ISMC控制下光伏并网系统LVRT过程响应速度慢、不对称故障时控制效果较差或抖振效果明显等问题,提出一种NFTSM控制的LVRT控制策略。考虑光伏并网系统外部条件多变的特性,采用双指数滑模超平面与控制率,选取指数趋近律加速趋近速率,构造出具有调节有功、无功输出的非奇异快速滑模控制器,并验证其稳定与收敛性,简单且有效地实现了光伏并网LVRT。Matlab/Simulink仿真结果表明,NFTSM控制的光伏并网LVRT具有收敛速度快、谐波含量低、抗外界干扰与抖振抑制能力强等优点。

双流制式下四分裂式变压器用作双回路滤波电感的特性分析

对一台运行于双流制下的机车进入直流电网时其变压器(四分裂式)用作电抗器的电感值进行了分析和计算.机车运行于直流电网时变压器同一铁心柱上的2个低压绕组串联接入回路滤波,而4个高压绕组并联开路.4个低压绕组两两串联有4种接法,且同一接法还有双边工作和单边工作的情况.利用在分析磁场的基础上获得的四分裂式变压器8个绕组的电感矩阵,列写4种不同接法时电路方程,将其等效为两端口网络,进行等效阻抗及电感计算,且对结果进行了讨论,给出了有关建议.

特高压直流分层接入方式下抑制连续换相失败的直流电流控制策略

特高压直流分层接入系统逆变侧交直流间均存在耦合,单一换流站发生连续换相失败容易导致电网发生连锁故障。针对这一问题,从层间交互作用机理出发,深入分析了高低端换流器控制响应差异以及其动态无功特性。分析表明:故障恢复阶段的无功交互量增加会导致非故障层换流母线电压的跌落,并直接引起该层换流器关断角的减小,从而引发连续换相失败。在此基础上,提出一种抑制连续换相失败的直流电流控制策略。该策略综合考虑无功交换量与换流母线电压的波动特征,通过系统实际运行状态实时计算直流电流指令来实现对高低端换流器的连续换相失败抑制。最后,建立了分层接入系统电磁暂态模型,通过多工况对比验证了策略的有效性。所提策略能够降低分层接入系统发生连续换相失败的概率,同时改善两层交流系统电压恢复特性,有利于系统安全稳定运行。

伴有童年创伤的重症抑郁患者异常全脑功能连接:一项静息态功能磁共振研究

【目的】童年创伤(CT)被认为是成年后发展为重度抑郁(MDD)的主要危险因素之一。然而,伴有CT的MDD(CT-MDD)患者的神经基础仍然知之甚少。因此,本研究的目的是探讨CT-MDD患者静息态全脑功能连接(FC)。【方法】对34名CT-MDD患者和34名健康对照组进行静息态功能磁共振扫描。进行全脑体素水平度中心性(DC)分析,选取两组间显著差异的脑区作为感兴趣区(ROI),进一步计算全脑FC。随后,将异常脑区DC,FC值与临床量表进行相关性分析。【结果】CT-MDD组右侧额中回(MFG)的DC值高于健康对照组。基于种子点的脑功能连接分析发现,与健康对照组相比,CT-MDD组右侧MFG与右内侧前额叶和左侧楔前叶之间的FC增加(P<0.05)。此外,右侧MFG的DC值与CT严重程度相关。【结论】我们的结果表明,以右侧MFG作为ROI,其与默认网络(DMN)中的两个重要脑区右内侧前额叶和左侧楔前叶之间的FC增加,这可能表明CT-MDD患者的认知执行网络与DMN之间的同步性增加。这些发现可能为深入了解CT-MDD的病理生理机制提供了见解。