Renewal Design of Pedestrian Bridges from the Perspective of Environmental Behaviors

With the continuous deepening of urbanization,the focus of urban construction has shifted to internal renewal,and the phenomenon of decreased vitality caused by the spatial limitations of pedestrian bridges with a single transportation function as the main focus has gradually emerged.Based on this,environmental behavior theory is used to seek the convergence point between the material space and behavioral activities of pedestrian bridges to solve this dilemma.In this paper,the pedestrian bridge of Southwest Hospital of Army Medical University is taken as an example.Starting from the three types of spaces of pedestrian bridges,through behavior observation,interview research,and data analysis,the correlation between the material space of pedestrian bridges and the behavioral characteristics of the population is analyzed,stimulating the spatial vitality of pedestrian bridges,and providing reference for the sustainable development,construction,and renovation of pedestrian bridges.

Dynamic Characteristics Evaluation of Innovative UHPC Pedestrian Cable Stayed Bridge

KICT (Korea Institute of Construction Technology) is conducting a project called “SUPER BRIDGE 200—Development of Low Cost and Long Life Hybrid Cable Stayed Bridge”. This project aims to reduce the construction and main- tenance costs of long-span bridges by 20% and double their lifetime through the exploitation of ultra-high performance concrete (UHPC). This paper presents the design and construction of the first pedestrian cable stayed bridge using UHPC developed by KICT. UHPC, compared to conventional concrete, has not only high compressive and tensile strengths but also high ductility. The UHPC developed at KICT is a steel fiber-reinforced cement compound presenting design compressive strength larger than 180 MPa and design tensile strength exceeding 10 MPa with water-to-binder ratio below 0.24 and admixing of 2 volume percentage of steel fiber. To show the applicability of UHPC to structures, a pedestrian cable stayed bridge (Super Bridge I) exploiting the characteristics of the developed UHPC has been planned, designed and erected at KICT. The dimension of UHPC deck is 2.7 m × 7 m as a precast segment with a typical thickness of deck of only 7 cm. However, harmful crack was observed in the deck at the time of the fabrication of the deck segments. Accordingly, new fabrication method was conceived and applied to prevent cracking of the UHPC slender deck. Four UHPC deck segments were fabricated successfully without any crack. After construction, the dynamic characteristics (natural frequencies and mode shapes) were evaluated through vibration tests since several users felt excess vibration. A vertical tuned mass damper (TMD) was proposed and installed on the parapet of the bridge. The TMD reduces the acceleration by about 30% from 0.0316 g to 0.0244 g when two pedestrians are crossing the bridge.

Proposing a New Model of Hangers in Pedestrian Suspension Bridges to Solve Hangers Slackness Problem

The hangers of suspension bridges can be placed in two forms: vertical or inclined form. Inclined hangers are more liable to fatigue. Vertical hangers are subjected to greater fluctuations of stress resulting from bridge wind loads. To improve aerodynamic stability, inclined hangers can be used instead of vertical ones. Some inclined hangers show considerable signs of distress and some of them show slackness due to their location against loads. In this paper a pedestrian suspension bridge with vertical hangers has been studied as a case study. Then, the same bridge has been studied with inclined hangers. To reduce internal forces, fatigue and slackness in hangers, horizontal cables have been added to inclined hangers. This modification is proposed by the present authors. The added horizontal cables transfer the tensile load from overstressed hangers to adjacent slacked hangers. Three different hanger patterns have been analyzed under nonlinear static analysis for symmetrical and nonsymmetrical live load plus dead load. Results showed that the modified hanger system had been improved considerably in comparison with vertical or inclined hangers and wherever that there is no improvement some solutions have been proposed.

Vibration Measurement of Pedestrian Bridge Using Double Magnetic Suspension Vibrator Based on Wavelet Analysis

Aiming at the problem of pedestrian bridge vibration measurement,a vibration measurement system of pedestrian bridge with dual magnetic suspension vibrator structure was designed according to absolute vibration measurement principle. The relationship between the magnetic repulsion force of vibrator and its displacement was obtained by the experimental method and the least square fitting method. The vibration equations of two magnetic suspension vibrators were deduced respectively,and the measurement sensitivity of the system was deduced. The amplitude-frequency characteristic of the system was studied. A simulation model of vibrator measurement system with double magnetic suspension vibrator was established. The analysis shows that the sensitivity of the vibration measurement system with double magnetic suspension vibrator is higher than that with single magnetic suspension vibrator. The four vibration waveforms were measured,that is,no one passes through a pedestrian bridge,there are cars running under the pedestrian bridge,single pedestrian passes through the pedestrian bridge and multiple pedestrians pass through the pedestrian bridge. The multi-scale one-dimensional wavelet decomposition function was used to analyze the vibration signals. The vibration characteristics were obtained using one dimension wavelet decomposition function under four different conditions. Finally,the vibration waveforms of four cases were reconstructed. The measured results show that the vibration measurement system of pedestrian bridge with double magnetic suspension vibrator structure has high measurement sensitivity. The design has a certain value to monitor a pedestrian bridge.

Reinforcement and numerical analysis on the corbel of a halfthrough arch bridge

Corbels support the crossbeams of half-through arch bridges. They are prone to cracking easily due to their characteristics and complicated loading conditions. Based on a practical diagnosis of a bridge crossbeam, we bonded steel plates onto bridge corbels to strengthen them. We carried out a numerical analysis on the effectiveness of the reinforcement by using the commercial sof^are ANSYS. The numerical analysis shows that the stresses near the section break increased slightly, but the variation amplitude was small and all the stresses were within an allowable range. The loading test indicates that it is feasible to strengthen the corbel with vertical bonded steel plates. Therefore, the reinforcement is effective and economical. This reinforcement method is suitable for this type of corbel and can be applied in similar cases.

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.

曲线钢桁桥人致振动舒适性评价现场试验研究

大跨曲线钢桁梁人行桥竖向、横向和扭转振型耦合强,人致振动舒适度评价和减振控制难度大。以湖南省长沙市浏阳河一主跨为120 m的曲线双层桥面三跨连续钢桁梁桥—汉桥为工程背景,通过理论分析和人群激励现场动力试验,识别桥梁固有模态参数,评价人致振动舒适性,优化设计调谐质量阻尼器(Tuned Mass Damper,TMD)并评价TMD的减振效果。研究表明:因桥梁第一阶竖弯模态和第一阶扭转模态的阻尼比仅为0.23%和0.3%,人致振动加速度不满足舒适性要求;采用竖向TMD进行竖弯模态和扭转模态的减振控制,减振后的桥梁满足舒适性要求。

槽形钢箱梁涡振性能及抑振措施试验研究

为提高槽形钢箱梁桥的抗风性能,对槽形钢箱梁的涡振性能及抑振措施进行试验研究。以某人行景观桥槽形钢箱梁为背景,通过主梁节段模型风洞试验,研究+3°、0°、-3°风攻角下均匀流与紊流风场中槽形钢箱梁的涡振性能,分析交替封闭栏杆、将栏杆楔形扶手改为圆形扶手、提高阻尼比等措施的抑振效果。结果表明:原槽形钢箱梁断面涡振性能不满足规范要求,均匀流风场中,3个风攻角下均出现了超限的竖弯涡振,+3°和-3°风攻角下出现了不同程度的扭转涡振,最不利风攻角为-3°;紊流风场中,最不利风攻角下原断面竖弯涡振振幅降低了23%,未见明显扭转涡振;楔形扶手栏杆交替封闭使结构竖弯涡振振幅增大,主梁涡振性能降低;单独改变栏杆扶手形状为圆形对主梁涡振性能影响不大,在此基础上交替封闭栏杆能够有效抑制主梁涡振;提高结构阻尼比能有效抑制主梁涡振,阻尼比为7‰时,主梁竖弯涡振振幅可降至规范限值的一半左右。

超越分隔与连接——两座乡镇步行桥设计探讨

桥的本意在于连接两处,它改变了地方的空间结构和人们行动的轨迹。桥作为一种存在物成为建成环境一部分,它所处的位置和形态成为有意味的新景观。桥作为人们相遇的空间节点,它可以超越基本的功能,成为地方的公共空间。文章从齐美尔讨论“桥与门”的关系开始,借用齐美尔论述桥的三个差异功能“分者相连”“意图付诸实施”和“直观可见”来讲述重庆石柱县中益乡场镇上两座新步行桥(小河桥和大河桥)的形成过程,探讨它们成为场镇上人们日常生活的一部分和重要的公共空间背后的设计理念。

某景区柔性人行悬索桥静载试验研究

为测试某人行悬索桥的承载能力是否达到要求,文中结合静载试验与有限元模拟软件,研究在不同测试工况下主梁控制截面的应力、应变和挠度值与主缆挠度值,将实测结果与计算结果进行比对。研究结果表明,主梁各控制截面及主缆的实测挠度小于模拟值,挠度校验系数合理,测试截面的实测应力正常,应力校验系数在0.75~0.90之间,桥塔的纵向变位较小,抽样检测的吊杆拉力增量与计算增量基本吻合,此桥受力状态正常,其结构强度、刚度均符合规范要求。研究成果可为同类型桥梁的安全评估提供参考。

基于随机行走模型的人致振动舒适度研究

为研究人群密度对人行桥结构的振动影响,首先,建立了双向随机行走模型,推导了随机荷载作用下结构振动响应解析解;然后,对比分析了人群密度对结构振动响应的影响规律;最后,通过研究行人实感时程与总时程之间的相关关系,定义了舒适度放大系数,以荆州市某人行天桥为例,进行振动舒适度评价,验证了双向随机行走模型及舒适度放大系数的适用性。结果表明:人行桥结构加速度响应随人群密度增大呈现出先增大后减小的规律;行人实感时程与总时程具有显著的相关性,根据舒适度放大系数可建立对应关系;舒适度放大系数随着振动响应峰值的增大而减小,随着人群密度的增大而增大;该类结果对人行桥振动舒适度定量计算具有参考借鉴意义。

异型单肋双索面人行钢拱桥吊杆张拉方案研究

为实现异型人行拱桥梁施工各阶段合理受力状态,需探索合理的吊杆张拉方案。以云溪桥-异型单肋双索面人行钢拱桥为研究对象,根据桥梁自身特点确定出吊杆张拉方案的合理性原则和多种吊杆张拉方案,建立桥梁有限元模型进行桥梁施工阶段分析,采用正装迭代法得到各施工阶段的吊杆张拉控制力,探讨多种吊杆张拉方案对桥梁主要构件施工阶段受力及变形的影响。结果表明:从拱肋受力与变形角度来看,从两边拱脚向中间拱顶顺序张拉吊杆方案对桥梁结构更有利;初始张拉双根吊杆措施更适合从中间拱顶向两边拱脚顺序张拉吊杆;同时张拉内外侧吊杆比先张拉外侧吊杆后张拉内侧吊杆更有利于拱肋、主梁受力与变形;双批次先外侧后内侧张拉吊杆使主要受力构件应力及变形峰值更小、变化过渡更为平缓,优于单批次内外侧同时张拉吊杆方案。桥梁内侧吊杆设计索力较小,不宜分批次张拉,外侧吊杆设计索力稍大,可进行二批次吊杆张拉。

基于随机行走模型的行人实感振动响应分析

针对人群荷载随机性对行人振动感知的影响,研究随机行走模型中行人感知振动响应动态变化规律.首先,基于随机人群行走模型,建立了考虑行人实感的竖向振动响应分析方法 .然后,对比分析不同随机行走模型下行人实感最大振动响应、出现时刻以及位置区间上的变化规律.最后,通过研究行人实感最大振动响应与结构跨中峰值加速度之间的相关关系,定义振动响应折减系数和变异系数,提出行人实感最大振动响应的近似计算方法 .研究结果表明:有序排列模型(Ordered Arrangement Model,OAM)、随机到达模型(Stochastic Arrival Model,SAM)、随机分布模型(Stochastic Distribution Mode, SDM)、动态平衡模型(Dynamic Equilibrium Model, DEM)4种人群行走模型下,行人实感的最大加速度响应服从近似的正态分布,OAM的值域范围大于其他3类模型;最大响应出现位置以及出现时刻取决于行人的行走方式,随人群密度增长无明显变化;OAM与SAM分布规律相同,出现时刻主要集中在总时程内的中间段,而SDM与DEM分布相对均匀;行人实感的最大响应计算值与实际值最大误差不超过5%.

肇庆市民乐人行天桥设计研究

文中依托肇庆市民乐人行天桥实体工程,基于“以人为本”的设计原则,详细介绍了该天桥主梁、坡道、梯道以及基础相关的设计方案,阐述了人行天桥设计要点,为类似实体工程提供一定参考,对设计高质量天桥工程具有十分重要的意义。

人行悬索桥结构参数对舒适度的影响研究

以人行悬索桥为研究对象,根据我国行人的步行特性,用影响线原理将同步调行人荷载分别以集中力的方式单独施加在结构最不利位置,进行人致振动响应分析,最终求得最大振动响应,并且对主缆吊索间距、加劲梁布置形式以及抗风缆分张角度的改变,给人行悬索桥舒适度带来的影响进行了探究。结果表明:结构的舒适度会随着行人数量或步频的增大而变差,因此要严格控制桥上的行人数量和步频,保证结构的舒适度;基于背景工程,以舒适度为选型标准,最终确定出吊索间距应选择3.0 m或6.0 m,加劲梁应选择“三根纵梁+全部斜撑”的布置形式,抗风缆分张角度在30°、45°或60°中选择为宜。

栏杆对景区人行悬索桥主梁涡振性能影响研究

为研究桥面栏杆对主梁涡振性能的影响,以国内某座宽跨比为0.0284的景区人行悬索桥为工程背景,采用CFD数值模拟方法分别对有栏杆、无栏杆主梁的涡振响应特性进行分析计算,并针对桥面栏杆的栏杆形式、不同透风率对主梁涡振特性的影响规律进行分析总结。在此基础上,从涡脱演化形式、风压系数分布揭示其对主梁涡振性能的影响机理。研究结果表明,设置栏杆后,主梁的最大涡振幅值达到无栏杆主梁的2.2倍;增大栏杆弧度会引起主梁涡振幅值增大,但增大栏杆透风率可以有效降低主梁涡振幅值;相较于无栏杆,有栏杆主梁上表面形成的漩涡尺度更大、数量更多,平均风压系数和脉动风压系数曲线均出现较大波动,这种较大波动在一定程度上说明了设置栏杆后主梁涡振幅值增大的原因。

W形人行天桥人致振动舒适度与减振研究

为解决W形人行天桥在极端人群荷载作用下的人桥共振问题,以西南地区某实际工程为例,基于数值模拟的方法进行极端人群荷载下的动力舒适度分析,并对其减振方案进行研究。研究结果表明:当人行天桥竖向一阶自振频率为3.04 Hz时,W形人行天桥存在人桥共振隐患;通过计算,0.2、0.5、1.0、1.5、4.6 P/m^(2)五种人群荷载工况下主梁峰值加速度为0.96 m/s^(2),舒适度指标为中等,未达到最优的舒适性等级。在振幅最大位置处设置质量比为1%的调谐质量阻尼器(TMD)后,主梁峰值加速度降为0.10 m/s^(2),减振率为89.6%,人行天桥满足最优的舒适度等级。研究成果可为同类异形人行天桥人致振动舒适度评价与减振设计提供技术参考。

抗风缆布置形式对悬索桥人致振动影响分析

为研究人行悬索桥使用过程中抗风缆拉索不同布置形式对人行悬索桥自振特性及人致振动的影响,以某人行玻璃悬索桥为实例,采用Midas Civil软件建立抗风缆拉索设置形式为平行直拉式、交叉斜拉式、非交叉斜拉式和不设置抗风缆的有限元模型,先单独计算改变抗风缆拉索布置形式悬索桥的自振特性参数,再计算人行简谐波荷载作用下抗风缆拉索布置形式对人行桥主梁竖向及横向加速度的影响,参考德国人行桥设计指南EN03对人行桥舒适度进行评价。结果表明,设置抗风缆能提高结构的自振频率,增加结构的整体刚度;在人行简谐波荷载作用下,相比其他3个模型,增设交叉斜拉式拉索的抗风缆能有效减小主梁竖向及横向最大加速度,对人行悬索桥的人致振动舒适度的改善效果最明显。

人行桥人致横向振动及横向锁定分析

为了研究人群荷载下人行桥的人致振动特性,采用Duhamel积分求解了行人上下桥过程中简支梁桥的人致横向振动理论解,分析了横向锁定条件和临界人数。结果表明:与原地踏步相比,行人上下桥过程中,桥梁横向振动响应增大;频率比为1.0时,跨中横向加速度最大,产生横向锁定的同步临界人数最少;随着桥上总人数增加,跨中横向加速度最大值线性增加,但超过临界人数后由于同步概率的增加使增长幅度提高;在临界人数附近桥梁发生横向锁定,行人舒适性接近“较差”等级下限值。

大跨度人行斜拉桥人致振动荷载模式研究

随着城市综合交通的快速发展,人行天桥跨度大幅度增大,已建成多个大跨度人行天桥。然而,大跨度人行天桥自振频率较低,普遍存在舒适度设计难题。人行天桥的舒适度设计一般采用与振型一致的固定动力荷载,但固定动力荷载引起的桥梁加速度响应与移动人群引起的加速度响应存在明显区别,因此通过实际人群移动探寻移动荷载对人行天桥加速度响应的规律。依托某大跨度人行斜拉桥实际工程,建立该桥的动力分析模型,并基于实桥测试结果验证模型有效性。基于校核的数值模型,对比规范建议满载与移动满载异同,并且分析不同长度、步幅的人行荷载对人行斜拉桥振动响应的影响规律。结果表明,规范建议满载与移动满载的区别体现在非卓越频率人行荷载作用下主梁加速度峰值大小及分布;人群长度为主跨跨径的0.3倍时,梁上加速度峰值可达到满载的80%,是设计实桥试验的最佳人群长度,与欧洲规范建议人数相比,人工成本降低65.8%。