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.

Improvement of Bending Strength of Carbon Fiber/Thermoplastic Epoxy Composites <br/>—Effects of Molecular Weight of Epoxy on Carbon Fiber/Matrix Interfacial Strength and Connection of Cracks in Matrix

The bending strength of carbon?fiber/thermoplastic epoxy composites?(CF/TP-EP Compo.)?had?bi-linear increasewith increase of weight-average molecular weight (Mw) of matrix. The transition in the bending strength appeared at around 55k of Mw (“k”?means 103). SEM observation of fractured surface of CF/TP-EP Compo. showed that the fracture mode changed from interfacial failure to fiber breakage dominated failure. The smooth surface of carbon fibers appeared at lower Mw than 55k while some resin remained on the fibers indicating good adhesion between carbon fiber and matrix at higher Mw than 55k. The interfacial shear strength between carbon fiber and matrix bi-linearly increased with an increase of Mw similarly to the bending strength of the composite, measured by the micro droplet test. The dynamic loss tanδ?of the matrix measured at 2?Hz also showed a bi-linear relationship with respect to Mw having a knee point at Mw = 55k. The connection probability of two cracks introduced on?each side of specimens also confirmed that the interfacial strength between carbon fiber and matrix is the key for the mechanical performance of CF/TP-EP Compo. in bending.

Effect of the Entrained Air Void on Strength and Interfacial Transition Zone of Air-Entrained Mortar

In order to facilitate the development and application of air entraining agents (AEA) in the high performance concrete, entrained air void structure parameters (air void size range from 10 to 1 600 mu m) of 28 d sifted mortar were measured by image analysis method. The relationship between the air void size distribution and strength of mortar was studied by methods of grey connection analysis and multiple linear regression analysis. The multiple linear regression equation was established with a correlation coefficient of 0.966. The weight of the affection of hierarchical porosity on the compressive strength ratio was also obtained. In addition, the effect of air voids on the paste-aggregate interfacial transition zone (ITZ) was analyzed by microhardness. The results show that the correlation between different pore size range and the compressive strength is negative. The effect of air void size distribution on 28 days compressive strength is different: under the condition of similar total porosity, with the increase of the porosity of the air void size, ranging from 10 to 200 mu m, and the decrease of the porosity, ranging from 200 to 1 600 mu m, the average air void diameter and mean free spacing are decreased; as well as the width of ITZ. On the contrary, the microhardness of the ITZ is increased while the compressive strength loss is decreased.

Network-based structure optimization method of the anti-aircraft system

The anti-aircraft system plays an irreplaceable role in modern combat. An anti-aircraft system consists of various types of functional entities interacting to destroy the hostile aircraft moving in high speed. The connecting structure of combat entities in it is of great importance for supporting the normal process of the system. In this paper, we explore the optimizing strategy of the structure of the anti-aircraft network by establishing extra communication channels between the combat entities.Firstly, the thought of combat network model(CNM) is borrowed to model the anti-aircraft system as a heterogeneous network. Secondly, the optimization objectives are determined as the survivability and the accuracy of the system. To specify these objectives, the information chain and accuracy chain are constructed based on CNM. The causal strength(CAST) logic and influence network(IN) are introduced to illustrate the establishment of the accuracy chain. Thirdly, the optimization constraints are discussed and set in three aspects: time, connection feasibility and budget. The time constraint network(TCN) is introduced to construct the timing chain and help to detect the timing consistency. Then, the process of the multi-objective optimization of the structure of the anti-aircraft system is designed.Finally, a simulation is conducted to prove the effectiveness and feasibility of the proposed method. Non-dominated sorting based genetic algorithm-Ⅱ(NSGA2) is used to solve the multiobjective optimization problem and two other algorithms including non-dominated sorting based genetic algorithm-Ⅲ(NSGA3)and strength Pareto evolutionary algorithm-Ⅱ(SPEA2) are employed as comparisons. The deciders and system builders can make the anti-aircraft system improved in the survivability and accuracy in the combat reality.

STRENGTH DESIGN OF PREMIUM THREADED CASING CONNECTION

Using premium casing connections instead of API ones is one of the mosteffective technique to prevent casing failure. The factors contribute to the strength of premiumcasing connections are studied with FEA and full-scale test. The criterions are presented thatensure the connection's strength higher than the pipe. At the same time, the method is given todecrease the peak stress of the connection so as to improve its anticorruption property. At last,full-scale tests are done to test the strength of the connections designed with the methoddescribed, the results show that the connection's strength is higher than the pipe. This indicatedthat the method described is effective in designing premium casing connection.

Investigation on the dynamic behaviors of the coupled memcapacitor-based circuits

In this paper, by referring to the concept of coupled memristors （MRs） and considering the flux coupling connection, the constitutive relations for describing the coupled memcapacitors （MCs） are theoretically deduced. The dynamic behaviors of dual coupled MCs in serial and parallel connections are analyzed in terms of identical or opposite polarities for the first time. Based on the derived constitutive relations of the two coupled MCs, the modified relaxation oscillators （ROs） are obtained with the purpose of achieving controllable oscillation frequency and duty cycle. In consideration of different parameter configurations, the experimental investigation is carried out by using practical off-the-shelf circuit components to verify the correction of the theoretical calculation with numerical simulation of the coupled MCs and its application in ROs.

On the Correlations among Affective Variables,Learning Strategies and Language Proficiency

Affective variables and learning strategies are two important factors that influence language proficiency. In the investigation conducted by the author,there is no sure causal connection being found among the three factors. Further,affective variables seems prevail over learning strategies of the influence on language proficiency and it is the primary element in language study process.

Effects of Anesthesia on Effective Connectivity in the Brain

The brain constitutes a formidably complicated structural network. There are three main types of connectivity used to describe neuronal networks, which reflect three parallel levels of investigation: anatomical connectivity, functional connectivity and effective connectivity. Effective connectivity indicates the direct influence that a node exerts on another, and in the context of neuronal?circuits, a causal relationship between the activities of two nodes. Since its definition, effective?connectivity analysis has been used to describe causal relationship across multiple spatial scales in?PET imaging, fMRI, electroencephalography (EEG) and magnetoencephalography (MEG), single-unit, and local field potential. There are diverse literatures which probe the anesthetized state?using effective connectivity analysis over the past two decades. The examination of effective connectivity in the anesthetized state is of relevance to both anesthesiologists and neuroscientists, as it has the potential to elucidate still unclear mechanisms of anesthesia while offering insight into intrinsic functional activity in the brain. The present review attempts to examine, elucidate, and integrate the insight that effective connectivity analysis of the anesthetized state has generated thus far.

Seismic Behavior of Steel Reinforced Ultra High Strength Concrete Column and Reinforced Concrete Beam Connection

To investigate the seismic behavior of connections composed of steel reinforced ultra high strength concrete (SRUHSC) column and reinforced concrete (RC) beam, six interior strong-column-weak-beam connection specimens were tested subjected to reversal cyclic load. Effects of applied axial load ratio and volumetric stirrup ratio on ductility, energy dissipation capacity, strength degradation and rigidity degradation were discussed. It was found that all connection specimens failed in bending in a ductile manner with a beam plastic hinge. The ductility and energy dissipation capacity increased with the decrease of applied axial load ratio or increase of volumetric stirrup ratio. The displacement ductility coefficient and equivalent damping coefficient lay between those of steel reinforced ordinary concrete connection and those of reinforced concrete connection. The applied axial load ratio and volumetric stirrup ratio had less influence on the strength degradation and more influence on the stiffness degradation. The stiffness degraded sharply with the decrease of volumetric stirrup ratio or increase of applied axial load ratio. The experimental results indicate that SRUHSC column and RC beam connection exhibited better seismic performance and can provide reference for engineering application.

Residual Capacity of Friction⁃Type High⁃Strength Bolted T⁃stub Connection with Nut Corrosion Damage

Corrosion is a primary cause of the slippage of friction⁃type high⁃strength bolted(FHSB)T⁃stub connections.This paper attempts to quantify the residual capacity of FHSB T⁃stub connections with corroded nuts.Firstly,corrosion simulation tests were conducted on 48 manually cut nuts to find out the relationship between the damage degree of nut section and the residual clamping force(RCF)of bolt.Then,static load tests were carried out on 24 FHSB T⁃stub connections with nuts of different degrees of damage to obtain the failure modes.By finite⁃element(FE)models,a comparative analysis was performed on the initial friction load(IFL)and ultimate strength(US)of each connection with corroded nuts.Finally,the parameters of 96 FE models for FHSB T⁃stub connections were analyzed and used to derive the calculation formulas for the degree of damage for each nut and the IFL and US of each connection.The results show that the RCF decay of a bolt is a quadratic function of the equivalent radius loss ratio and the shear failure after nut corrosion;the IFL of each connection had a clear linear correlation with the RCF of the corresponding bolts,and the correlation depends on the applied load and static friction on connecting plate interface induced by the clamping force;the static friction had little impact on the US of the connection;the proposed IFL and US formulas can effectively derive the residual anti⁃slip capacity of FHSB T⁃stub connections from the degree of damage of the corroded nut section.The research results provide a scientific basis for the replacement and maintenance of corroded bolts of FHSB T⁃stub connections.

Topological probability and connection strength induced activity in complex neural networks

Recent experimental evidence suggests that some brain activities can be assigned to small-world networks. In this work, we investigate how the topological probability p and connection strength C affect the activities of discrete neural networks with small-world （SW） connections. Network elements are described by two-dimensional map neurons （2DMNs） with the values of parameters at which no activity occurs. It is found that when the value of p is smaller or larger, there are no active neurons in the network, no matter what the value of connection strength is; for a given appropriate connection strength, there is an intermediate range of topological probability where the activity of 2DMN network is induced and enhanced. On the other hand, for a given intermediate topological probability level, there exists an optimal value of connection strength such that the frequency of activity reaches its maximum. The possible mechanism behind the action of topological probability and connection strength is addressed based on the bifurcation method. Furthermore, the effects of noise and transmission delay on the activity of neural network are also studied.

Multi-scale strength analysis of bolted connections used in integral thermal protection system

Efficient and accurate strength analysis of bolted connections is essential in analyzing the integral thermal protection system（ITPS） of hypersonic vehicles, since the system bears severe loads and structural failures usually occur at the connections. Investigations of composite mechanical properties used in ITPS are still in progress as the architecture of the composites is complex. A new method is proposed in this paper for strength analysis of bolted connections by investigating the elastic behavior and failure strength of three-dimensional C/C orthogonal composites used in ITPS. In this method a multi-scale finite element method incorporating the global–local method is established to ensure high efficiency in macro-scale and precision in meso-scale in analysis.Simulation results reveal that predictions of material properties show reasonable accuracy compared with test results. And the multi-scale method can analyze the strength of connections efficiently and accurately.

Microstructures and mechanical properties of semi-solid squeeze casting ZL104 connecting rod

Semi-solid squeeze casting（SSSC） and liquid squeeze casting（LSC） processes were used to fabricate a ZL104 connecting rod, and the influences of the process parameters on the microstructures and mechanical properties were investigated. Results showed that the tensile strength and elongation of the SSSC-fabricated rod were improved by 22% and 17%, respectively, compared with those of the LSC-fabricated rod. For SSSC, the average particle size（APS） and the shape factor（SF） increased with the increase of re-melting temperature（Tr）, whereas the tensile strength and elongation increased first and then decreased. The APS increased with increasing the mold temperature（Tm）, whereas the SF increased initially and then decreased, which caused the tensile strength and elongation to increase initially and then decrease. The APS decreased and the SF increased as squeezing pressure（ps） increased, and the mechanical properties were enhanced. Moreover, the optimal Tr, ps and Tm are 848 K, 100 MPa and 523 K, respectively.

State-of-the-art on resistance of bearing-type bolted connections in high strength steel

With the recent development of material science,high strength steel(HSS)has become a practical solution for landmark buildings and major projects.The current codes for design of bearing-type bolted connections of steel constructions were established based on the research of conventional steels.Since the mechanical properties of HSS are different from those of conventional steels,more works should be done to develop the appropriate approach for the design of bearing-type bolted connections in HSS.A review of the research carried out on bearing-type bolted connections fabricated from conventional steel and HSS is presented.The up-to-date tests conducted at Tongji University on four connection types fabricated from three grades of HSS with nominal yield strengths of 550,690,and 890 MPa are presented.The previous research on failure modes,bearing resistance and the design with consideration of bolt hole elongation are summarized.It is found that the behavior of bolted connections in HSS have no drastic difference compared to that of conventional steel connections.Although the ductility is reduced,plastic deformation capacity of HSS is sufficient to ensure the load redistribution between different bolts with normal construction tolerances.It is also found that behavior of each bolt of multi-bolt connections arranged in perpendicular to load direction is almost identical to that of a single-bolt connection with the same end distance.For connections with bolts arranged in parallel to load direction,the deformation capacity of the whole connection depends on the minimum value between the end distance and the spacing distances in load direction.The comparison with existing design codes shows that Eurocode3 and Chinese GB50017-2017 are conservative for the design of bolted connections in HSS while AISC 360-16 may overestimate the bearing resistance of bolted connections.

针刺治疗单侧基底节缺血性卒中后抑郁相关脑区效应连接变化:基于fMRI的格兰杰因果分析

目的:基于静息态fMRI探讨手足十二针疗程干预对单侧基底节缺血性卒中后抑郁相关脑区的影响和经穴特异性。方法:纳入42例卒中后抑郁患者,随机分为真穴组23例、假穴组19例;另招募28例健康人作为对照组。真穴组行手足十二针治疗,假穴组在经穴旁开1寸针刺,2组在针刺前后行MRI扫描;对照组未行针刺干预,仅行MRI扫描。选取双侧梭状回、丘脑、小脑前下、基底神经节、小脑后下作为ROI,比较真穴组、假穴组针刺前后及真穴组、假穴组针刺后与对照组间格兰杰因果关系(GC)。结果:假穴组针刺后右侧梭状回→左侧基底节的GC减弱,差异有统计学意义(P<0.05);真穴组针刺后左侧丘脑→右侧梭状回、右侧梭状回→右侧基底节、左侧丘脑→左侧小脑后下的GC增强,左侧小脑前下→左侧梭状回、左侧小脑前下→右侧基底节、左侧基底节→右侧小脑后下、左侧小脑后下→右侧小脑后下的GC减弱,差异均有统计学意义(均P<0.05);假穴组针刺前右侧丘脑→左侧梭状回、左侧小脑前下→右侧梭状回、左侧小脑前下→左侧丘脑、右侧小脑后下→右侧丘脑、右侧梭状回→左侧小脑前下、右侧丘脑→右侧小脑后下的GC强于对照组,右侧梭状回→左侧基底节、右侧丘脑→左侧小脑后下的GC弱于对照组,差异均有统计学意义(均P<0.05);真穴组针刺前右侧丘脑→左侧梭状回、左侧基底节→左侧小脑前下、左侧小脑前下→左侧基底节强于对照组,右侧丘脑→左侧小脑后下弱于对照组,差异均有统计学意义(均P<0.05)。结论:手足十二针对左半球抑郁相关脑区存在激活驱动属性和优先激活倾向;假穴对脑区间效应连接激活效率低于真穴,且存在半球间激活代偿、激活滞后,提示穴位有特异性。

基于BP神经网络的复合材料螺栓连接强度预测

针对复合材料螺栓连接强度预测问题,设计拉伸试验并记录极限载荷。将试验变量数值化抽象为神经网络输入神经元参数,基于BP神经网络理论,建立强度预测模型。使用三组预留的试验结果验证模型的准确性,三个测试组预测误差分别为6.13%、1.63%、3.34%。调整训练组的组成并重新训练模型,结果表明,本文模型针对训练组未出现参数值有着较好的预测能力。最后建立有限元分析模型进行对比分析,结果表明,针对复合材料螺栓连接强度预测问题,相比有限元方法,神经网络方法精度相当,且具有明显的速度优势。

SOFIM连杆螺栓的有限元分析

针对SOFIM连杆螺栓出现的早期疲劳断裂现象,建立了连杆螺栓的有限元模型,利用ANSYS软件对该连杆螺栓进行了有限元分析,并与疲劳试验结果进行了对比,吻合较好。分析结果表明,该连杆螺栓早期疲劳断裂的原因是由于杆部与头部的过渡圆弧处产生的应力集中所导致的。该结论为以后的改进工作提供了理论依据。

风力发电机轮毂-主轴连接螺栓强度影响因素分析

基于VDI2230的基本理论,从螺栓刚度、螺栓组参数、夹紧件结构3个方面对轮毂-主轴连接螺栓的极限和疲劳性能进行研究。采用有限元的计算方法,基于大型计算软件模拟了不同规格、不同节圆、不同边距等不同方案下轮毂主轴连接螺栓的力学性能。结果表明:对于无缩径螺栓,增大螺栓规格可以改善极限强度但不能改善螺栓疲劳强度。在缩径相同的条件下,增大螺栓规格可以改善抗疲劳性能。增加螺栓数量及增大节圆直径均可以提升轮毂-主轴连接螺栓的极限强度。夹紧件结构对螺栓疲劳损伤值影响明显,增大轮毂-主轴连接螺栓的边距可以大幅度改善螺栓的抗疲劳性能。

An Overview and Perspectives On Bidirectional Intelligence: Lmser Duality, Double IA Harmony,and Causal Computation

Advances on bidirectional intelligence are overviewed along three threads,with extensions and new perspectives.The first thread is about bidirectional learning architecture,exploring five dualities that enable Lmser six cognitive functions and provide new perspectives on which a lot of extensions and particularlly flexible Lmser are proposed.Interestingly,either or two of these dualities actually takes an important role in recent models such as U-net,ResNet,and Dense Net.The second thread is about bidirectional learning principles unified by best yIng-yAng(IA)harmony in BYY system.After getting insights on deep bidirectional learning from a bird-viewing on existing typical learning principles from one or both of the inward and outward directions,maximum likelihood,variational principle,and several other learning principles are summarised as exemplars of the BYY learning,with new perspectives on advanced topics.The third thread further proceeds to deep bidirectional intelligence,driven by long term dynamics(LTD)for parameter learning and short term dynamics(STD)for image thinking and rational thinking in harmony.Image thinking deals with information flow of continuously valued arrays and especially image sequence,as if thinking was displayed in the real world,exemplified by the flow from inward encoding/cognition to outward reconstruction/transformation performed in Lmser learning and BYY learning.In contrast,rational thinking handles symbolic strings or discretely valued vectors,performing uncertainty reasoning and problem solving.In particular,a general thesis is proposed for bidirectional intelligence,featured by BYY intelligence potential theory(BYY-IPT)and nine essential dualities in architecture,fundamentals,and implementation,respectively.Then,problems of combinatorial solving and uncertainty reasoning are investigated from this BYY IPT perspective.First,variants and extensions are suggested for AlphaGoZero like searching tasks,such as traveling salesman problem(TSP)and attributed graph matching(AGM)that are turned into Go like problems with help of a feature enrichment technique.Second,reasoning activities are summarized under guidance of BYY IPT from the aspects of constraint satisfaction,uncertainty propagation,and path or tree searching.Particularly,causal potential theory is proposed for discovering causal direction,with two roads developed for its implementation.

Application of an interpretable artificial neural network to predict the interface strength of a near-surface mounted fiber-reinforced polymer to concrete joint

Accurately estimating the interfacial bond capacity of the near-surface mounted(NSM)carbon fiber-reinforced polymer(CFRP)to concrete joint is a fundamental task in the strengthening and retrofit of existing reinforced concrete(RC)structures.The machine learning(ML)approach may provide an alternative to the commonly used semi-empirical or semi-analytical methods.Therefore,in this work we have developed a predictive model based on an artificial neural network(ANN)approach,i.e.using a back propagation neural network(BPNN),to map the complex data pattern obtained from an NSM CFRP to concrete joint.It involves a set of nine material and geometric input parameters and one output value.Moreover,by employing the neural interpretation diagram(NID)technique,the BPNN model becomes interpretable,as the influence of each input variable on the model can be tracked and quantified based on the connection weights of the neural network.An extensive database including 163 pull-out testing samples,collected from the authors’research group and from published results in the literature,is used to train and verify the ANN.Our results show that the prediction given by the BPNN model agrees well with the experimental data and yields a coefficient of determination of 0.957 on the whole database.After removing one non-significant feature,the BPNN becomes even more computationally efficient and accurate.In addition,compared with the existed semi-analytical model,the ANN-based approach demonstrates a more accurate estimation.Therefore,the proposed ML method may be a promising alternative for predicting the bond strength of NSM CFRP to concrete joint for structural engineers.