Stability Reliability of the Lateral Vibration of Footbridges Based on the IEVIE-SA Method

Research on the lateral vibrational stability of footbridges has attracted increasing attention in recent years. However, this stability contains a series of complex mechanisms, such as nonlinear vibration, random excitation, andrandom stability. The Lyapunov method is regarded as an effective tool for analyzing random vibrational stability;however, it is a qualitative method and can only provide a binary judgment for stability. This study proposes anew method, IEVIE–SA, which combines the energy method based on the comparison between the input energyand the variation of intrinsic energy (IEVIE) and the stochastic averaging (SA) method. The improved Nakamuramodel was used to describe the lateral nonlinear stochastic vibration of a footbridge, whereby the IEVIE methodwas used to establish the criteria for judging the lateral vibrational stability. Additionally, the SA method was usedto deduce the corresponding backward Kolmogorov equation. Subsequently, the backward Kolmogorov equationwas combined with the stability criterion established by the IEVIE method to analyze the first passage stability. Theproposed method is a semi-analytical, quantitative method that only requires a small calculation. By applying theproposed method to the Millennium Bridge, method effectiveness was verified by comparing it with the MonteCarlo and traditional Lyapunov methods.

Random stability for lateral vibration on footbridge based on IEVIE-PDE method

The pedestrian-induced lateral vibration of footbridges is essentially classified as a nonlinear stochastic vibration.Accordingly,bridge vibration stability falls within the field of nonlinear stochastic vibration stability.At present,the Lyapunov method is mainly used to analyze such stability.However,this method is qualitative,and it cannot quantitatively analyze the vibration stability probability.In this study,a new analytical method based on a comparison of the input energy and the variation of intrinsic energy(IEVIE)is used to analyze the nonlinear stochastic vibration stability of the lateral vibration of the footbridge.The improved Nakamura model is used to describe the lateral nonlinear stochastic vibration of the footbridge.A combination of the IEVIE method and the probability density evolution(PDE)method is then proposed,in which the IEVIE method is utilized to determine vibration stability.The PDE method is used to obtain the reliability of vibration stability.The proposed method is successfully applied to the Millennium Bridge,and its effectiveness is verified by comparing the Monte Carlo and Lyapunov methods.The proposed method can obtain the dynamic probability of the vibration as stable or instable and provide a reference for quantitative analysis of lateral nonlinear stochastic vibration stability of footbridges.

Dynamic Characteristic of the Medium Span Concrete Footbridges

Concrete footbridges, due to their mass, stiffness and damping, are perceived as strucaires more resistant to vibration caused by dynamic action of the users. In order to verify the dynamic behaviour of concrete footbridges, a series of field tests and numerical analyses have been carried out. In the paper, the results of the dynamic field tests of three medium span concrete footbridges with different structural systems （frame, beam and arch footbridges） and their dynamic characteristics （mass, stiffness and damping） are presented. The field tests were carried out for different types of vibration excitation caused by walking, running and jumping persons. Furthermore, the vibrational comfort criteria for footbridges are shortly described and verified for examined structures. The study were supplemented by numerical calculation of natural mode shapes and frequencies of the structures using the 3D FEA （finite element analysis） models with elastic supports elements in order to ensure the compatibility of the calculated and measured mode shapes of the footbridges.

One-of-a-Kind Footbridge, Lublin, Poland

The paper presents the construction of a steel footbridge in the People’s Park in Lublin.The initiation and development of the architectural design of an interesting and,as it eventually turned out,aesthetically pleasing footbridge is discussed.Two teams of architects and bridge engineers worked in parallel on the design.The design process of the footbridge structure is discussed along with its trial installation and on-site construction.The span of the footbridge is short,but its structure is innovative.For this reason its numerical model was developed used as a basis for an analysis of the dynamic response of the designed structure.The basic element of the acceptance procedure was constituted by a dynamic test load and an analysis of the pedestrian footbridge user comfort.Last but not least,the final section reviews the aesthetic canons of bridges and focuses on the footbridge in question in this context.A statistical measure of the aesthetic impression induced by a visit to the footbridge was applied resulting in a predictable and obvious final aesthetical assessment.

Damage Identification in Footbridges from Natural Frequency Measurements

The present study aims to develop a robust structural damage identification method that can be used for the evaluation of bridge structures. An approach for the structural damage identification based on the measurement of natural frequencies is presented. The structural damage model is assumed to be associated with a reduction of a contribution to the element stiffness matrix equivalent to a scalar reduction of the material modulus. A computational procedure for the direct iteration technique based on the non-linear perturbation theory is proposed to identify structural damage. The presented damage identification technique is applied to the footbridge over the Slunjcica River near Slunj to demonstrate the effectiveness of the proposed approach. Using a limited number of measured natural frequencies, reduction in the stiffness of up to 100% at multiple sites is detected. The results indicate that the proposed approach can be successful in not only predicting the location of damage but also in determining the extent of structural damage.

The Ołowianka Bascule Footbridge in Gdansk-A Bridge That Makes the Difference

In the city of Gdansk in Poland,in the very center of the Baltic capital,on 17th of June 2017,a new draw footbridge was ceremoniously opened to the public.The Olowianka footbridge represents the long-time much needed link between the highly tourist-visited historical old town and Ołowianka Island,where further cultural,tourist and recreation facilities are located.The bridge spans a very busy navigable channel of the Motława River,leading inward towards other city channels,a harbor for many tourist ships and the Gdansk Marina.Being the main navigable entrance to the city center,the Motława is constantly under nautical traffic,so the Ołowianka footbridge operates 24/7,according to a 30-min schedule.The Ołowianka footbridge is an extraordinary acquisition for the city of Gdansk,which immediately became a new landmark and much more in the already very picturesque historic city center.Not just its design,but also its carefully chosen location and its realization at the right moment,has made this bridge indispensable to the inhabitants,visitors and the administration of the city of Gdansk,decisively contributing to further development in the Ołowianka Island area and its surroundings.

Progress in Light-weight High Entropy Alloys

High entropy alloys(HEAs)possess good mechanical properties and a wide range of industrial applications.In this paper,phase formation prediction theory,microstructure,properties and preparation methods of light-weight HEAs(LWHEAs)were reviewed.The problems and challenges faced by LWHEAs development were analyzed.The results showed that many aspects are still weak and require investigation for future advanced alloys,such as clarification of the role of entropy in phase formation and properties of HEAs,improved definition and different generations division of HEAs,close-packed hexagonal(HCP)phase structure prediction and corresponding alloy design and fabrication.Finally,some suggestions were presented in this paper including in-depth research on formation mechanism of multi-component alloy phase and strengthening of large-scale HEA preparation methods via technology compounding and 3D printing technology.Also,there is a need for more research on the in-situ preparation of HEA coatings and films,as well as developing LWHEAs with superior strength and elevated temperature resistance or ultra-low temperature resistance to meet the requirements of future engineering applications.

Preparation of Light-weight Spinel Refractories by Foaming-gel Process

Light-weight magnesium -aluminate spinel materi- als were prepared by foaming-gel process with polyalumi- nium chloride （PAC） as gel. Effect of solid loading in initial slurry on microstructure, porosity, pore size distri- bution, thermal conductivity and mechanical properties was investigated. The results show that the bulk density of the light-weight magnesium -aluminate spinel mate- rials is in the range of O. 7 1.2 g cm-3 ; pore size distribution curves show single-peak characteristics and the mean pore size is in the range of 30. 83 - 61.37 μm ; with the increase of solid loading, the linear shrinkage of the green body during firing and the permanent change in dimensions on heating at l 600 ℃ for 3 h de- crease, but the bulk density increases, the mechanical properties increase obviously; the maximum compressive strength and bending strength reach 35. 25 MPa and 9. 92 MPa, respectively, while the bulk density is 1. 16 g · cm ; and the thermal conductivity at 1 000 ℃ tea- ches 0. 371 W · m-1 . K-1 while the bulk density is O. 7 -3 g · cm

Investigation on microstructures and properties of semi-solid Al_(80)Mg_(5)Li_(5)Zn_(5)Cu_(5)light-weight high-entropy alloy during isothermal heat treatment process

The Al_(80)Mg_(5)Li_(5)Zn_(5)Cu_(5)light-weight high-entropy alloy with globular microstructure was fabricated by isothermal heat treatment.The effects of isothermal temperatures and holding times on the semi-solid microstructure evolution were investigated.The results indicate that,with increase of the isothermal temperature,the average grain size increases and the spheroidization time shortens.With prolongation of holding time,the shape factor increases firstly and then decreases,and the average grain size decreases at first and then increases when the isothermal temperature is below 520°C,however it increases gradually at 540℃.The optimal semi-solid microstructure is obtained at 520℃ for 30 min,whose shape factor and average grain size are 0.90 and 56.4μm,respectively.Compared with as-cast Al_(80)Mg_(5)Li_(5)Zn_(5)Cu_(5) light-weight high-entropy alloy,the compressive strength and plasticity of semi-solid Al_(80)Mg_(5)Li_(5)Zn_(5)Cu_(5) light-weight high-entropy alloy are increased by 36%and 108%,respectively.The formation of semi-solid microstructures includes three stages:melting separation,spheroidization,and coarsening growth.The sluggish diffusion effect of Al_(80)Mg_(5)Li_(5)Zn_(5)Cu_(5) light-weight high-entropy alloy leads to a low coarsening rate,resulting in slow grain growth.

Principles and Chief Technologies in Developing Light-weighted Worsted Fabrics

More and more light-weighted fabrics are being required by the market, especially for the worsted manufacture.In the past, such fabrics are produced mainly through changing the structure of woven goods or by using finer yarns. But these possibilities are very limited. In this paper, new devices are discussed: (1) on the yarn level- to use single yarns instead of conventional doubled ones, to decrease number of fibers in yarn cross sections beth during spinning and after finishing; (2) on the fiber level - to use finer fibers in blends with wool and modification of the wool fibers; (3) on the macromolecule level - to stretch the macromolecules in alpha keratin, to get super fine wool fibers.

Ultra-thin and light-weight spoof surface plasmon polariton coupler achieved by broadside coupled split ring resonators

Low profile and light weight are very important for practical applications of a spoof surface plasmon polariton（SSPP）coupler, especially at low frequencies. In this paper, we propose and design an ultra-thin, light-weight SSPP coupler based on broadside coupled split ring resonators（BC-SRRs）. The size of BC-SRR can be far less than λ/100 and can extremely well control the reflective phases within a subwavelength thickness. Due to the broadside capacitive coupling, the electrical size of BC-SRR is dramatically reduced to guarantee the ultra-thin thickness of the SSPP coupler. The weight of the SSPP coupler is reduced by a low occupation ratio of BC-SRR in the unit cell volume. As an example, a C-band SSPP coupler composed of phase gradient BC-SRRs is designed, fabricated, and measured. Due to the ultra-small size and low occupation ratio of BC-SRRs, the thickness of the coupler is λ/12 and the surface density is only 0.98 kg/m^2. Both simulation and experiment results verify that the coupler can achieve high-efficiency SPP coupling at 5.27 GHz under normal incidence.

Prickle of Light-Weight Worsted Woven Wool Fabrics

Using the forearm test, the prickle of 26 commercially available light-weight worsted woven wool fabrics and 7 other fiber fabrics were studied under (24±1)℃ temperature and (65±5)% RH conditions. The surface fiber diameter of part of the wool fabrics was measured using a microscope. It was found that most of the light-weight worsted woven wool fabrics gave a prickle sensation under the above conditions. The prickle sensation was significantly correlated with the mean fiber diameter of the surface hairiness. It was also found that the prickle of the light-weight worsted woven wool fabrics was significantly correlated with the number of surface fibers which were coarser than 26 μm diameter.

Effect of Commercial Synthappret BAP Treatment on the Tailorability of Light-Weight Worsted Wool Fabrics

By means of measurement with the FAST instruments, the effect of commercial Synthappret BAP treatment on the tailorability of light-weight wool worsted fabrics has been investigated. It was found that the commercial Synthappret BAP treatment unproved the tailorability of the light-weight wool fabrics mainly by increasing the bending stiffness of the light-weight wool fabrics.

A Study of Thermal Response and Flow Field Coupling Simulation around Hayabusa Capsule Loaded with Light-Weight Ablator

The numerical simulation of flow field around Hayabusa capsule loaded with light-weight ablator thermal response coupled with pyrolysis gas flow inside the ablator was carried out. In addition, the radiation from high temperature gas around the capsule was coupled with flow field. Hayabusa capsule reentered the atmosphere about 12 km/sec in velocity and Mach number about 30. During such an atmospheric entry, space vehicle is exposed to very savior aerodynamic heating due to convection and radiation. In this study, Hayabusa capsule was treated as a typical model of the atmospheric entry spacecraft. The light-weight ablator had porous structure, and permeability was an important parameter to analyze flow inside ablator. In this study, permeability was a variable parameter dependent on density of ablator. It is found that the effect of permeability of light-weight ablator was important with this analysis.

Effects of Spherical Light-weight Aggregates Additions on Workability and Mechanical Properties of Al_2O_3-SiO_2 System Castables

In order to clarify the effect of spherical light-weight aggregates addition on properties of A12 07 - Si02 system castables, adopting ATO mullite traditional light-weight aggregates and ATO mullite spherical light-weight aggre- gates, bauxite homogenization powder, microsilica , cal- cium aluminate cement as main raw materials, light- weight Al2 03 - SiO2 system castables were prepared by replacing conventional light-weight aggregate with spherical light-weight aggregates. The effects of spheri- cal light-weight aggregates addition on workability, me- chanical properties of castables after heated at different temperatures were researched; the microstructure of the aggregates was analyzed by SEM. The result shows that the introduction of spherical light-weight aggregates can significantly improve the flowability and reduce the water addition of the castables. Water demand of the castable is reduced from 18% with the conventional light-weight aggregates to 14% with spherical light-weight aggre- gates. In addition, light-weight castables prepared by spherical aggregates can keep the same workability with- in a wider range of water addition. Therefore, spherical aggregates are user-friendly. The introduction of spheri- cal light-weight aggregates is favorable to packing densi- ty and mechanical properties of castables, such as cold crushing strength, cold modulus of rupture, hot modulus of rupture at 1 200℃.

人行悬索桥的步行参数研究

以九峰山人行悬索桥为观测点,采用视频记录与人工筛选相结合的方法获取了2236个行人样本的实测数据,进而统计得到人行悬索桥上的行人步行参数(步频、步幅和步速)的分布特性和统计值,并给出了人行悬索桥上的步频-步速、步幅-步速和步频-步幅之间的转换关系式,得到以下结论:1)在人行悬索桥上,全部行人的步行参数都服从正态分布,即步频~N(1.726,0.258)Hz、步幅~N(0.596,0.094)m、步速~N(1.013,0.260)m/s,它们的合理性也在某工程实例的应用中得以验证;2)人行悬索桥上的行人步行参数的均值(标准差)要小于(大于)其他行走环境所统计得到的行人步行参数的均值(标准差);3)中国人的步频和步幅的均值(标准差)都小于(大于)西方人的步频和步幅的均值(标准差).因此,在设计我国的人行悬索桥时,不能直接采用其他人种和行走环境的行人步行参数的统计值,而应采用适合于人行悬索桥的步行参数.

吊索断裂对人行悬索桥冲击效应的影响研究

人行悬索桥吊索断裂不但会使局部桥面坍塌,还会由于剩余构件应力重分布程度过大而引发吊索连续断裂。采用数值模拟方法对单根吊索断裂和相邻2根吊索断裂后人行悬索桥的动力响应进行分析,并通过静力重分布系数SRF、动力重分布系数DRF、振荡系数OF和动力放大系数DAF对冲击效应进行综合评估。结果表明,单根吊索瞬断后同侧相邻吊索及断索区域纵梁的静、动力重分布程度明显,但对主缆及对侧吊索产生影响较小;同侧相邻2根吊索断裂比对侧断裂对剩余吊索和断索区主梁的影响更大;除边吊索和跨中吊索外,其他剩余吊索的SRF均在50%左右,DRF均在100%左右;接近跨中区域剩余吊索的DAF均为2.0左右,但边吊索的DAF较跨中区域增大25%左右,DAF采用2.0对于边吊索偏于不安全。单根吊索断裂后其下方相应位置处纵梁弯矩的DAF值均在1.20~1.40之间。

环境行为学视角下的步行桥坡度的宜步性要素与优化策略研究

步行桥作为当今城市滨水景观的重要连接纽带已在各个地区被广泛建设。其是城市重要的步行载体,其自身的宜步性水平具有重要的价值,而其中以坡度为代表的舒适性设计对其影响最为显著。在环境行为学视角下,步行桥坡度设计应当兼顾心理感知层面与生理感知层面的平衡,其对于步行桥宜步性程度具有重要价值。基于帕累托最优的多目标优化策略,可将心理与生理层面的综合优化分别转译为针对平直区段长度与大坡度爬升阶段长度的优化。通过运用参数化的手段,将桥体坡度拆解为逐点坡度,提出了实现最高宜步性水平的优化路径与方法。

TMD对人行桥疲劳寿命的影响研究

针对人群运动导致人行结构振动过大而日益突出的疲劳破坏问题,可供参考的研究成果甚少。本文以钢-玻璃人行桥为试验平台开展关于安装TMD前后人致人行桥疲劳性能的研究,采用APS400电子激振器激励模拟人行荷载,通过长期应变监测数据,分析得出了该结构下的疲劳应力谱以及日平均损伤度,进而预估其疲劳寿命。结果表明:安装TMD后,结构1/2处的加速度峰值由0.15 m/s²减少到0.084 m/s²,减振率达44.0%;位移峰值由2.98 mm减少到0.92 mm,减振率达69.1%;应变幅值由40με减少到13με,减振率达67.5%。结构跨中处等效应力幅值最大,疲劳寿命最短,为74年;安装TMD后,结构跨中处疲劳寿命为2880年,延长近39倍,其他测点处依次延长了3.95倍、7.41倍。

中、下承式索支承人行桥动力特性的对比分析

为了研究中承式人行索桥的动力特性与弯扭耦合特征,以某下承式人行索桥为蓝本,在相同设计条件下变化桥面高度,构造了中承式人行索桥模型,采用Midas/Civil软件建立有限元模型,通过自振特性分析并定义弯扭耦合系数,从动力特性的角度对中、下承式人行索桥进行对比分析,并对中承式索桥桥面位置和抗风缆参数对其动力性能的影响进行了研究。结果表明,同等设计条件下,两种桥型均存在横向弯扭振型耦合,中承式耦合程度更大。撑杆高度增大会使扭转主振型延后,频率增大,但各阶竖弯频率和一阶横弯主振型频率减小。随抗风缆矢跨比的增大,结构竖弯和扭转频率略有减小,对称横弯频率增大,反对称横弯频率减小。随抗风缆倾角的增大,结构竖弯、扭转和高阶横弯频率增大,但会降低结构横弯基频。抗风缆矢跨比和倾角的增大均使中承式索桥振型的弯扭耦合程度增强。