Experimental research on the development of residual strain in seasonal frozen soil under freezing-thawing and impact type traffic loads

Vehicle load is among the main factors affecting the deformation of subgrade soil.In this research study,the concept of impact type traffic load is introduced to investigate the effects of vehicle load based on the dynamic stress and displacement time histories acquired from seasonal frozen subgrade soils.Using freezing-thawing and dynamic triaxial tests and considering the amplitude and loading sequence of impact type traffic load,the residual deformation characteristics of subgrade soil under impact type traffic loads and freezing-thawing cycles is studied.It was found that under impact type traffic load,the residual deformation of soils increased sharply as the amplitude of impact type traffic load increased.It was also found that the increase in the amplitude of impact type traffic load led to the increase of residual deformation in a scale of power and exponential function.The amplitudes of impact type traffic load affect the development stress-strain path of the residual strain.After the soil experienced the proper amount of pre-vibration of the light load,residual deformation decreased by 15%.After freezing-thawing,the residual strain of soil increased as the amplitude of the impact type traffic loads increased.Also,when the amplification effect of freezing-thawing on the residual strain was basically stable,the residual deformation increased by about 10%.The peak impact type traffic load had a large effect on soil deformation after the freezing-thawing process,leading to the observation that of the earlier the peaks,the stronger the effect of freezing-thawing.After the soil was subjected to preloading with a small load,the influence of the freezing-thawing cycles gradually stabilized.The results may be useful in preventing and controlling the risk of subgrade soil failure when construction takes place spring thaw periods.

Energy-balanced clustering protocol for data gathering in wireless sensor networks with unbalanced traffic load

Energy-efficient data gathering in multi-hop wireless sensor networks was studied,considering that different node produces different amounts of data in realistic environments.A novel dominating set based clustering protocol (DSCP) was proposed to solve the data gathering problem in this scenario.In DSCP,a node evaluates the potential lifetime of the network (from its local point of view) assuming that it acts as the cluster head,and claims to be a tentative cluster head if it maximizes the potential lifetime.When evaluating the potential lifetime of the network,a node considers not only its remaining energy,but also other factors including its traffic load,the number of its neighbors,and the traffic loads of its neighbors.A tentative cluster head becomes a final cluster head with a probability inversely proportional to the number of tentative cluster heads that cover its neighbors.The protocol can terminate in O(n/lg n) steps,and its total message complexity is O(n2/lg n).Simulation results show that DSCP can effectively prolong the lifetime of the network in multi-hop networks with unbalanced traffic load.Compared with EECT,the network lifetime is prolonged by 56.6% in average.

An investigation on the strain accumulation of the lightly EICP-cemented sands under cyclic traffic loads

Industrial production of chemical cement leads to extreme emissions of greenhouse gases.Biological or bioinspired sustainable materials for soil treatment projects can be employed instead of chemical cement to heal the carbon cycle in the ecosystem.The enzyme-induced calcite precipitation(EICP)method is one of the novel bio-inspired technologies that can be employed in soil treatment projects to increase desired properties of soils.While the monotonic and cyclic behavior of the enzymatically treated sands has been investigated comprehensively,the strain accumulation pattern in these improved soils under cyclic traffic loads has not been evaluated yet.In this paper,confined and unconfined cyclic compression tests are applied to the enzymatically lightly cemented sands,and the effects of the different parameters on their strain accumulation pattern are investigated for the first time in the literature.This study uses two types of specimens with unconfined compression strengths(UCS)equal to 42 kPa and 266 kPa.It is shown that the treated specimens have a rate-dependent behavior where cyclic loads with low frequencies lead to more resilient and plastic strains in the specimens.The results show that by approaching the maximum applied stresses to the UCS of the specimens(by breaking more calcite bonds between sand particles),the rate dependency behavior of specimens will reduce.Investigation of the effects of the cementation level demonstrated that by increasing the amount of the precipitated calcite from 0.38%to 0.83%,accumulated plastic strains are reduced almost 95%under the same loading condition.Effects of the initial static loads,confining pressures,the number of cycles,and amplitudes of the cyclic loads are also evaluated.

Lower Bound on de Bruijn Graphs Out-degree for Lower Traffic Load in Peer-to-peer Networks

Designers search for N-nodes peer-to-peer networks that can have O （1） out-degree with O （log2 N） average distance. Peer-to-peer schemes based on de Bruijn graphs are found to meet this requirement. By defining average load to evaluate the traffic load in a network, we show that in order to decrease the average load, the average distance of a network should decrease while the out-degree should increase. Especially, given out-degree k and N nodes, peer-to-peer schemes based on de Bruijn graphs have lower average load than other existing systems. The out-degree k of de Bruijn graphs should not be O（1） but should satisfy a lower bound described by an inequality κ^κ≥N^2, to ensure that the average load in peer-to-peer schemes based on de Bruijn graphs will not exceed that in Chord system.

Influence of erosion voids and traffic loads on buried large-diameter reinforced concrete pipes

Geotechnical centrifuge tests were conducted to examine the influence of invert voids and surface traffic loads on 1400 mm diameter reinforced concrete pipes buried with a shallow soil cover depth of 700 mm.Void formation beneath the pipe was simulated during centrifuge testing.The test results revealed that before void formation,the surface load directly above the middle of the pipe caused a significant increase in not only the circumferential bending moments but also the longitudinal bending moments,the latter of which was considerable and could not be ignored.Void formation beneath the middle of the pipe led to a reduction in both the circumferential bending moments and longitudinal bending moments at all measuring positions,i.e.,crown,springline,and invert.The most significant reduction occurred at the invert,and there was even a reversal in the sign of the invert longitudinal bending moment.A comparison was made between centrifuge tests with erosion voids and surface loads at different horizontal positions,which had a marked influence even when the positions differed by half a pipe length.Joint rotation played an important role in relieving large bending moments of pipe barrels in a jointed pipeline when the void and surface load were located at the joint.

Application of semi-analytical finite element method to analyze asphalt pavement response under heavy traffic loads

Accurate assessment of the impact of heavy traffic loads on asphalt pavements requires a computational model which is able to calculate the response of the pavement fast and precisely. Currently the most finite element analysis programs based on traditional methods have various limitations. A specific program SAFEM was developed based on a semi-analytical finite element method to overcome the problems. It is a three-dimensional FE program that requires only a two-dimensional mesh by incorporating the semi- analytical method using Fourier series in the third dimension. The computational accuracy and efficiency of the program was verified by analytical verification previously. The experimental verification is carried out in this paper and the results show that the SAFEM is able to predict the mechanical responses of the asphalt pavement. Using the program SAFEM, the impact of heavy traffic loads was analyzed in terms of stress and strain dis- tribution, surface deflection and fatigue life. The results indicate that if the asphalt pave- ment is subjected to the heavy traffic load more, the thicknesses and stiffness of the pavement structural layers should be increased adequately in order to support the surface deflection, The compressive stress in asphalt binder course is relatively large and increases more significantly compared with that in the other asphalt layers when the axle load becomes larger. With comparison of the predicted fatigue life, the increase of the axle load will lead to the destruction of the asphalt pavement extremely easily.

A Traffic-Aware and Cluster-Based Energy Efficient Routing Protocol for IoT-Assisted WSNs

The seamless integration of intelligent Internet of Things devices with conventional wireless sensor networks has revolutionized data communication for different applications,such as remote health monitoring,industrial monitoring,transportation,and smart agriculture.Efficient and reliable data routing is one of the major challenges in the Internet of Things network due to the heterogeneity of nodes.This paper presents a traffic-aware,cluster-based,and energy-efficient routing protocol that employs traffic-aware and cluster-based techniques to improve the data delivery in such networks.The proposed protocol divides the network into clusters where optimal cluster heads are selected among super and normal nodes based on their residual energies.The protocol considers multi-criteria attributes,i.e.,energy,traffic load,and distance parameters to select the next hop for data delivery towards the base station.The performance of the proposed protocol is evaluated through the network simulator NS3.40.For different traffic rates,number of nodes,and different packet sizes,the proposed protocol outperformed LoRaWAN in terms of end-to-end packet delivery ratio,energy consumption,end-to-end delay,and network lifetime.For 100 nodes,the proposed protocol achieved a 13%improvement in packet delivery ratio,10 ms improvement in delay,and 10 mJ improvement in average energy consumption over LoRaWAN.

Durability of Bridge Expansion Joints with Perforated Dowels Under Traffic Impact Loading

In design phases, expansion joints are required to have movement capacity, bearing capacity for static and dynamic loading, watertight, low noise emission and traffic safety. On the basis of the fact that failure due to dynamic loading is the main reason for the observed damages, attention is focused on the bearing capacity for dynamic loading governed by impact, because it differs from the static loading. In this study, from the viewpoint of durability, experimental studies for dynamic behavior were conducted for aluminium alloy expansion joints with perforated dowels. The validity of the perforated dowels against traffic impact loading was confirmed by both experimental and numerical studies.

Review of Load Balancing Mechanisms in SDN-Based Data Centers

With the continuous expansion of the data center network scale, changing network requirements, and increasing pressure on network bandwidth, the traditional network architecture can no longer meet people’s needs. The development of software defined networks has brought new opportunities and challenges to future networks. The data and control separation characteristics of SDN improve the performance of the entire network. Researchers have integrated SDN architecture into data centers to improve network resource utilization and performance. This paper first introduces the basic concepts of SDN and data center networks. Then it discusses SDN-based load balancing mechanisms for data centers from different perspectives. Finally, it summarizes and looks forward to the study on SDN-based load balancing mechanisms and its development trend.

广西某高速公路沥青路面车辙病害影响因素分析

对实体依托工程的现场调研、室内试验和建立模型进行分析,从重载交通、路面结构、抗压强度、压实度等因素分析了对广西高速公路沥青路面车辙病害的影响,提出加强对重载、超载的管制,进行针对性路面结构设计,提高沥青路面施工质量稳定性的对策建议。

Energy-Efficient Resource Optimization for Massive MIMO Networks Considering Network Load

This paper investigates the resource optimization problem for a multi-cell massive multiple-input multiple-output(MIMO)network in which each base station(BS)is equipped with a large number of antennas and each base station(BS)adapts the number of antennas to the daily load profile(DLP).This paper takes into consideration user location distribution(ULD)variation and evaluates its impact on the energy efficiency of load adaptive massive MIMO system.ULD variation is modeled by dividing the cell into two coverage areas with different user densities:boundary focused(BF)and center focused(CF)ULD.All cells are assumed identical in terms of BS configurations,cell loading,and ULD variation and each BS is modeled as an M/G/m/m state dependent queue that can serve a maximum number of users at the peak load.Together with energy efficiency(EE)we analyzed deployment and spectrum efficiency in our adaptive massive MIMO system by evaluating the impact of cell size,available bandwidth,output power level of the BS,and maximum output power of the power amplifier(PA)at different cell loading.We also analyzed average energy consumption on an hourly basis per BS for the model proposed for data traffic in Europe and also the model proposed for business,residential,street,and highway areas.

Design of Bridge Expansion Joints with Perforated Dowels Under Impact Loading

The expansion joints are expected to have movement capacity, bearing capacity for static and dynamic loading, water-tightness, low noise emission and traffic safety. In particular, the failure due to impact loading is the main reason for the observed damages. The problem of dynamic behavior of the expansion joints is so complex that we shall focus our attention on the impact factor for vehicle load that is governed by traffic impact. In order to overcome this difficulty, the cantilever-toothed aluminum joint (finger joint) is one of the promising joints under impact loading. In this study, from the viewpoint of design methodology, numerical studies for impact behavior were conducted for aluminum alloy expansion joints with perforated dowels. The design impact factor for the expansion joints with the perforated dowels against traffic impact loading was examined by using numerical simulations.

Railway Traffic Vibration Impact Analysis on Surrounding Buildings by FEM—Case Study: TER (Regional Express Train) Dakar—AIBD

The vibrations induced by railway traffic can affect the stability of structures, buildings and buried structures. To evaluate this impact, this study was carried out considering the case of the Regional Express Train which will connect Dakar to Blaise Diagne International Airport. For that, the modeling software Plaxis dynamic [1], able to generate harmonic loads, is used and permitted to have a dynamic analysis and comparison between static and dynamic load for one passage of the train for 2.56 s. In the modeling, two behavior laws were used those of Mohr Coulomb for the layers of soil, embankments and the form layer, and then the linear elastic model for the rest of the elements. The results obtained showed extreme vertical displacements 40.18 mm for the building and when no load is applied on the track, there was 40.24 mm for a static load, and 40.17 mm for a dynamic load. Also, it was observed for the track a displacement of 33.73 mm for a static load and 19.83 mm for a dynamic load. However, further studies are necessary to take into account the permanent deformation after an accurate cycle of train passage in order to better evaluate the railway traffic impact.

OpenFIow Based Flow Slice Load Balancing

Today's data center networks are designed using densely interconnected hosts in the data center.There are multiple paths between source host and destination server.Therefore,how to balance traffic is key issue with the fast growth of network applications.Although lots of load balancing methods have been proposed,the traditional approaches cannot fully satisfy the requirement of load balancing in data center networks.The main reason is the lack of efficient ways to obtain network traffic statistics from each network device.As a solution,the OpenFlow protocol enables monitoring traffic statistics by a centralized controller.However,existing solutions based on OpenFlow present a difficult dilemma between load balancing and packet reordering.To achieve a balance between load balancing and packet reordering,we propose an OpenFlow based flow slice load balancing algorithm.Through introducing the idea of differentiated service,the scheme classifies Internet flows into two categories:the aggressive and the normal,and applies different splitting granularities to the two classes of flows.This scheme improves the performance of load balancing and also reduces the number of reordering packets.Using the trace-driven simulations,we show that the proposed scheme gains over 50%improvement over previous schemes under the path delay estimation errors,and is a practical and efficient algorithm.

Load Balancing in IP/MPLS Networks: A Survey

The present era has witnessed tremendous growth of the Internet and various applications that are supported by it. There is an enormous pressure on Internet Service Providers (ISPs) to make available adequate services for the traffics like VoIP and Video on demand. Since the resources like computing power, bandwidth etc. are limited, the traffic needs to be engineered to properly exploit them. Due to these limitations, terms like Traffic Engineering, Quality of Service (QoS) came into existence. Traffic Engineering broadly includes techniques like multipath routing & traffic splitting to balance the load among different paths. In this document, we survey various techniques proposed for load balancing that are available on the Internet. We here try not to be exhaustive but analyze the important techniques in the literature. Present survey would help to give a new direction to the research in this realm.

多层交通荷载下非对称一体化地下结构的动力响应

地下结构在交通荷载作用下的动力响应对其运营期的安全稳定有重要影响。为了探究大断面非对称一体化地下结构在多层交通荷载作用下的动力响应特征,依据工程典型断面建立有限元模型,模拟施加路表、市政、轨道三层交通荷载,分析了非对称一体化地下结构的振动响应和应力分布特征,探究了多层交通荷载共同作用产生的结构动力响应叠加规律。结果表明:非对称一体化结构的振动响应在市政交通层的左幅顶板中部最大,达0.5~0.7 m/s^(2),动应力在轨道交通层底角处最大,达0.08~0.10 MPa;地铁列车荷载是结构动应力的主要影响源,但土钉支护与桩基支撑能够有效降低动应力的影响;作用于地面的车辆荷载会对一体化结构的振动响应产生较显著影响,运营期应重点关注位于地面车辆行驶密集路段的结构。研究结果可为地下非对称一体化结构的优化设计、运营期养护提供参考。

卫星网络混合负载均衡策略下的多径流量分配算法

为均衡卫星网络流量分配,满足用户QoS需求,提出一种全局和局部结合的混合负载均衡策略下的多径流量分配算法(HLB-MTD)。根据QoS业务需求进行部分路径筛选,基于表的散列算法进行流量的初次分配;在初次分配的基础上针对突发拥塞进行局部调整,建立重映射目标函数,通过改进交叉和变异概率的遗传算法求出最优解;求得局部优化的,流到路径的映射策略。仿真结果表明,该算法可有效缓解卫星网络拥塞,实现流量均衡分配,在丢包率、平均排队时延、等指标上有更好的提升。

基于Topsis改进因子分析的公路隧道入口段视觉负荷研究

为探究直线公路隧道入口段驾驶者的视觉负荷,首先,通过实车试验采集5种视觉指标,采用Topsis改进因子分析法建立视觉负荷评价模型;然后,分析不同时间及位置下视觉负荷的变化特征,基于构建的视觉负荷曲线提出行车舒适评价标准,并运用已发表数据验证构建负荷模型的泛化能力;最后,通过敏感度分析探究视觉指标对视觉负荷的影响程度。结果表明:当驾驶者位于距洞口-13~55 m(12:00)、-10~49 m(15:00)时,视觉负荷超过临界值(0.906),驾驶者的行车舒适度和安全性极低;洞口驾驶者的视觉负荷值和接近度远大于洞内和洞外;18:00的视觉负荷和接近度远低于12:00和15:00。视觉指标的敏感度参数从大到小依次为注视时间、瞳孔面积、注视次数、扫视幅度、扫视速度。

Estimating the frequency of traffic overloading on road bridges

Load limits,which appear to be routinely exceeded by trucks,occasionally result in road bridge failures.Therefore,predicting failures is crucial for safeguarding road safety.Past studies have largely focused on forecasting bridge failure event probability using the reliability analysis method,whilst occasionally accounting for vehicular overloading effects.Only recently,a study has investigated design traffic overloading event frequency using generalised linear regression models(GLRMs),including a power component and negative binomial regressions(NBRs).However,as far as the authors know,artificial neural network models(ANNMs)have never been applied to this field.This paper is an attempt to fill in these gaps.First a frequencybased metric of traffic overloading was adopted as a driver of failure probability.Second,two alternative‘frequency'models were specified,calibrated,and validated.The former was based on a GLRM,the latter on ANNMs.Then,these models were compared using regression plots(RPs),measures of errors(Mo Es)and the ratio between the number of observed vs predicted design load overcoming events to evaluate their performance.The models analysed more than 2 million weigh-in-motion(WIM)data records from a pilot station on a bridge on a heavily used ring road in Brescia(Italy).Results showed that ANNMs outperformed GLRMs.ANNMs have a higher correlation coefficient(between predicted and target frequencies),lower Mo Es,and a closer-to-unity ratio(between predicted and target frequencies).These findings may increase prediction accuracy of design traffic overloading events and give road authorities more effective traffic management to protect bridges from load hazards.

废弃橡胶轮胎在路桥过渡段沉降影响因素研究

为了研究废弃橡胶轮胎作为路基的加筋材料改善道路桥梁过渡段差异沉降的影响因素,建立了ABAQUS有限元数值模型。通过施加单一与交通荷载,对不同加筋层数、筋材特性、交通荷载的幅值、频率、循环次数等因素对土体沉降量的影响进行分析。结果表明,3层加筋效果优于2层,远优于1层。加筋后的桥头路基抵抗沉降的能力有显著提高,且随着模量的提高,效果更明显。在交通荷载作用下,随深度的增加,轮胎的影响深度逐渐减小;随荷载频率的增大,交通荷载作用在土层的次数增加,荷载的影响深度随之增大;随循环次数的增加,土体塑性位移递增。轮胎通过将软土层分层,提高了土体的整体性和连续性,减小了差异性沉降,使路桥的过渡段平稳过渡。