Assessment of Numerical Models for Live Load Distribution in a Road Slab Bridge

This paper presents comparison of numerical models used in an analysis of a road bridge deck. The models were adapted for computing the live load distribution coefficients in composite concrete bridge deck. The load distribution method was chosen for assessment of the usability of different numerical model in slab bridge deck analysis. The goal of the study is to determine a simplest but still accurate numerical model to estimate live load effects on composite slab bridge. In the analysis, the well-established grillage approach was adapted for representation of the bridge deck as a basic model as well as more sophisticated three-dimensional models which was supposed to better represent the real behavior of the deck under concentrated wheel loads. The bridge deck was effectively modeled using beam and shell elements. The grillage method compares well with the finite-element method. This finding is allowed to establish simplification in numerical modeling of slab bridge decks for live load effect computations.

Numerical Approach for the Live Load Distribution in Road Bridges

The numerical method for computing the live load distribution coefficients in bridge decks is presented. The grillage analogy for representation of bridge decks is adopted in determining the general behavior under traffic loads. The principles of Maxwell＇s reciprocal theorem are developed in computing live load distribution coefficients and their influence lines. The presented method uses the approach developed in traditional methods of transversal live load distribution but bridge decks are modeled more realistic with the help of well-established grillage analogy. Simple numerical programs for grillage analysis can be used and no special software is needed. While computing the distribution coefficients for a bridge deck the rest of the analysis can be performed with habitual procedures of structural mechanics.

Optimization of Dead Load State in Earth-Anchored Cable-Stayed Bridges

In order to determine the reasonable completed dead load state in earth-anchored cable-stayed bridges,a practical method is proposed. The method is based on the rigidly supported continuous beam method and the feasible zone method,emphasizing on the mutual effect between the self-anchored structural parts and the earth-anchored ones. Three cable-stayed bridge models are designed with the main spans of 1 400 m,including a partially earth-anchored cable-stayed bridge,a cable-stayed-suspension bridge and a fully selfanchored cable-stayed bridge,in which the C50 concrete and Q345 steel are adopted. The partially earthanchored cable-stayed bridge and the cable-stayed-suspension bridge secure lower compressive force in the girder than the fully self-anchored cable-stayed bridge by 25 percent at least. The same is for the material consumption of the whole bridge. Furthermore,the anchor volume is more than 20% lower in the partially earthanchored cable-stayed bridge than that in the cable-stayed-suspension bridge. Consequently,the practical span of cable-stayed bridges can be accordingly extended.

Technical Analysis of Highway Bridge Static Load Test

Highway bridges are an important part of the transportation industry and can promote social economic construction and development.In actual operation,highway bridges are often damaged due to overload and natural factors,which tend to affect the safety and shorten the service life of these bridges.Assessing the overall state and performance of highway bridges is therefore a key element.Static load test,which is a type of sustainable detection experiment,has many advantages,including low cost,high efficiency,and high accuracy.In this paper,the bridge structure is analyzed through the application of theoretical calculations and relevant comparisons,so as to judge the operating state of the bridge.

Dynamic effect of heavy-haul train on seismic response of railway cable-stayed bridge

This paper focuses on understanding and evaluating the dynamic effect of the heavy-haul train system on the seismic performance of a long-span railway bridge. A systematic study on the effect of heavy-haul trains on bridge seismic response has been conducted, considering the influence of vehicle modeling strategies and dynamic characteristics of the seismic waves. For this purpose, the performance of a long-span cable-stayed railway bridge is assessed with stationary trains atop it, where the heavy-haul vehicles are modeled in two different ways: the multi-rigid body model with suspension system and additional mass model. Comparison of the bridge response in the presence or absence of the train system has been conducted, and the vehicle loading situation, which includes full-load and no-load, is also discussed. The result shows that during the earthquake, the peak moment of the main girder and peak stress of stay cables increase by 80% and by 40% in the presence of fully loaded heavy-haul trains, respectively. At the same time, a considerable decrease appears in the peak acceleration of the main girder. This proves the existence of the damping effect of the heavy-haul train system, and this effect is more obvious for the fully loaded vehicles. Finally, this paper proposes an efficient vehicle modeling method with 2 degrees of freedom(DOF) for simplifying the treatment of the train system in bridge seismic checking.

Development of the applicability of simplified Henry’s method for skewed multicell box-girder bridges under traffic loading conditions

Concrete precast multicell box-girder(MCB) bridges combine aesthetics with torsional stiffness perfectly.Previous analytical studies indicate that currently available specifications are unable to consider the effect of the twisting moment(torsional moment) on bridge actions.In straight bridges the effect of torsion is negligible and the transverse reinforced design is governed by other requirements.However,in the case of skewed bridges the effect of the twisting moment should be considered.Therefore,an in-depth study was performed on 90 concrete MCB bridges with skew angles ranging from 0° to 60°.For each girder the bridge actions were determined under the American Association of State Highway and Transportation Officials(AASHTO) live load conditions.The analytical results show that torsional stiffness and live load positions greatly affected the bridges' responses.In addition,based on a statistical analysis of the obtained results,several skew correction factors are proposed to improve the precision of the simplified Henry's method,which is widely used by bridge engineers to predict bridge actions.The relationship between the bending moment and secondary moments was also investigated and it was concluded that all secondary actions increase with an increase in skewness.

Evolution of suspension bridge structural systems,design theories,and shape-finding methods:A literature survey

Modern suspension bridges exhibit a trend of lighter structures,more diversified structural forms,and longer spans,the latter already exceeding two kilometers.Bridge performance under dead and live loads depends on their structural and main cable systems,while cablesupported bridges especially rely on the design analysis and construction control of the main cable.This literary survey systematically analyzes the research progress and state-ofthe-art status quo in the structural systems and design theories of suspension bridges,focusing on the structural systems,main cable shape analyses,live load effect analyses,and emerging lucrative research directions.More than 100 reliable references have been surveyed.(1)Multi-span or multi-main cable schemes appeal to increasing attention,which may become a better choice in terms of structural systems in scenarios with extremely long spans and heavy loads.The cable layouts,such as spatial main cables and hybrid cable-stayed suspension systems have also become feasible approaches for enhancing structural stiffness.(2)The shape-finding analysis during the construction phase is more complex and has more essential factors than that of the completed bridge state.Refined theories combining analytical methods and finite element methods are more suitable for the shape-finding analysis of complex cable systems than any single theory of the two,especially for novel cable systems.(3)The live load effect analysis methods based on traditional deflection theory or modified/improved deflection theories still have wide applications,but the refined theory of treating hangers as discrete members is also constantly developing,which is expected to provide new ideas for more complex structural analysis under the different types of live loads and their distribution forms.

钢筋混凝土拱桥加固施工次序方案及效果评价

为研究钢筋混凝土拱桥最优的加固施工次序,以一座在役4跨箱形拱桥的加固方案为背景,设计了3组针对性的加固方案,并对不同拆除加固施工次序下的主拱圈力学性能进行了分析;采用恒载应力变化率(αD)和荷载效应变化率(αN)评价了施工中拱圈的应力变化规律及加固后原拱圈的荷载效应。研究结果表明:拱上结构的拆建次序对加固后主拱圈的力学性能影响较小,但对加固过程中主拱圈的受力状态影响较大;拱顶对称拆除时αD<0,结构处于“卸载”状态,有利于拱桥施工中的受力;αN随着拱上结构恒载减小而增大,且增速减缓,故加固层材料利用率也随拱上结构恒载减小而增大,且增幅变缓;αN越大,则加固效果越好。

Vision-based survey method for extraordinary loads on buildings

The statistical modeling of extraordinary loads on buildings has been stagnant for decades due to the laborious and error-prone nature of existing survey methods,such as questionnaires and verbal inquiries.This study proposes a new vision-based survey method for collecting extraordinary load data by automatically analyzing surveillance videos.For this purpose,a crowd head tracking framework is developed that integrates crowd head detection and reidentification models based on convolutional neural networks to obtain head trajectories of the crowd in the survey area.The crowd head trajectories are then analyzed to extract crowd quantity and velocities,which are the essential factors for extraordinary loads.For survey areas with frequent crowd movements during temporary events,the equivalent dynamic load factor can be further estimated using crowd velocity to consider dynamic effects.A crowd quantity investigation experiment and a crowd walking experiment are conducted to validate the proposed survey method.The experimental results prove that the proposed survey method is effective and accurate in collecting load data and reasonable in considering dynamic effects during extraordinary events.The proposed survey method is easy to deploy and has the potential to collect substantial and reliable extraordinary load data for determining design load on buildings.

集中力活载作用下悬索桥变形及内力的解析算法

悬索桥作为一种柔性结构,活载下的响应是长期以来被研究的重点内容。该文针对悬索桥提出了一种集中力活载作用下结构变形及内力的解析计算方法。以已知成桥状态参数和活载参数为基础,首先分析了主缆变形、主梁变形、主缆和主梁的关系、桥塔变形。随后建立了4类控制方程,分别为各段主缆的无应力长度守恒、各根吊杆的力与变形协调、各跨跨径及高差闭合和主梁的受力平衡,从而使得控制方程的总数与基本未知数的总数相等。最后将控制方程合并成一个目标函数,并进行规划求解。找到基本未知量的取值,使得全部控制方程同时成立,进而推导出所有其他参数,并表达出结构变形后的状态。以一座主跨1 080 m的悬索桥作为算例,验证了方法的可行性和有效性。活载作用下变形及内力的结果都具有良好的精度,与有限元的结果相一致。

临时性活荷载的解耦随机模型及调查方法研究

临时性活荷载是建筑楼面活荷载的重要部分,但基于荷载单元的传统模型造成现场调查困难,样本匮乏导致临时性活荷载研究长期停滞不前。对此,研究提出了临时性活荷载的解耦随机模型,将活荷载解耦为数量和幅值两种独立随机变量,既可对不同临时性活荷载事件统一建模,也可对荷载的数量和幅值分别采样统计而大大方便了荷载调查。与解耦随机模型相配合,进一步研究了结合目标检测和多目标跟踪的机器视觉调查方法,利用泛在监控设施实现临时性活荷载的持续性调查。以常见人群聚集型临时性活荷载为例,阐述了机器视觉调查方法的实施过程,并通过实际场景下的调查实验验证了调查方法的有效性。解耦随机模型结合机器视觉调查方法为临时性活荷载大样本的获取以及楼面活荷载设计值的研究提供了可行的新方式。

铁路下承式连续钢桁梁桥静动力性能评估

成昆铁路复线完工后,部分老线区段将并入复线,并开行时速为160 km的动车组。为评估老线中典型桥梁在开行动车组后的服役性能,通过数值仿真及现场静动力荷载试验的方式,对某3×64 m连续钢桁梁桥的静力及动力性能进行检测与评估。研究表明,静力荷载作用下,主桁杆件最大轴向拉、压应力分别为143.1,175.4 MPa,均小于容许应力240 MPa,结构具有足够的强度安全储备。第34、35、36孔挠跨比分别为1/1 756、1/1 940、1/1 732,均小于规范规定的1/1 250,表明该桥具备通行动车组的刚度条件。各工况下活动支座纵向位移最大值为3.195 mm,小于支座纵向位移允许限值,表明各活动支座工作状态良好。动荷载作用下,主梁振型、自振频率与既有检定结果差异不大,且均小于理论计算值。主梁跨中竖向加速度、主梁跨中横向加速度、桥墩横向振幅及活动支座横向变形均满足规范要求,表明该钢桁梁桥主梁、桥墩及支座等主要组成部分的技术指标均满足行车要求。

基于大数据的公路桥梁检测技术及应用方法

在实际的公路桥梁设计与施工中,需要进行大量的检测作业,以确保整体工程质量和运营安全。因此,文章利用大数据对公路桥梁结构进行动力学检测,建立荷载试验模型,采用能量释放法对模型进行求解,以加固公路桥梁的刚性结构,并根据历史数据对模型进行调整,提高公路桥梁荷载的准确性。试验结果表明:利用大数据的公路桥梁检测技术使事故减少了23%,公路桥梁性能优良,满足设计与施工要求。

曲线现浇箱梁非对称恒载对桥梁动静力响应影响的量化研究

为量化研究曲线现浇箱梁非对称恒载对桥梁动静力响应的影响,首先推导了非对称恒载偏心扭矩的计算,然后选取常规跨径16、20、30、40m及平面曲线半径30、50、100、200m,建立12组等高三跨现浇连续箱梁桥为研究样本.基于Python语言建模、MIDAS/Civil软件进行有限元分析,研究考虑非对称恒载扭矩与否两种情况对曲线现浇箱梁桥支座反力、主梁应力和下部结构内力的影响.结果表明,非对称恒载扭矩引起支座反力外大内小、影响显著且边墩反力受影响程度大于中墩;当桥梁平面曲线半径为30m内时,非对称恒载对曲线箱梁桥梁体应力影响显著,半径达100m后可不考虑非对称恒载对梁体应力的影响;非对称恒载对桥墩安全度的影响极为有限,地震作用下桥墩承载力计算可不予考虑.

钢管混凝土吊杆拱桥检测评估及加固改造探讨

文中以贵州省普通国省干线公路桥梁定期检查服务QLDJ-01标段钢管混凝土吊杆拱桥为例,对该桥的检测评估及加固改造方案进行分析;针对病害情况,提出更换吊杆、增设加劲纵梁、主拱圈灌浆、拱座加固、混凝土构件缺陷修复等加固改造方案,以提高桥梁结构安全性。

宁波地区双桥静探法估算单桩承载力的应用

预制桩被大量地应用于宁波软土地区,且在工民建项目中有应用越来越多的趋势。结合宁波中心城区工程实例,对比分析根据JGJ 94—2008建筑桩基技术规范双桥静力触探法和经验参数法所估算预制桩单桩竖向极限承载力标准值的差异,并与静载检测成果作对比分析,进而对规范公式进行适当修正,初步得出适用于该工程的经验公式,为宁波地区运用双桥静力触探试验方法准确计算单桩竖向承载力标准值、优化桩基设计方案提供借鉴意义。

变截面连续箱梁承载能力检验方法

文章以某变截面连续箱梁桥为例,通过动静载试验,模拟桥梁在设计荷载作用下,承载能力是否满足设计要求。试验结果表明:该桥在动静载试验作用下处于弹性工作状态,未表现出明显的塑性变形,试验桥跨结构刚度及整体受力性能满足原设计要求,整体承载力满足原设计荷载等级“城市-A级”标准,符合设计荷载要求。

常泰长江大桥主航道桥桥塔横向偏位及其控制方案研究

常泰长江大桥主航道桥为(142+490+1176+490+142)m公铁两用双层桥面斜拉桥,下层桥面采用上游侧布置两线城际铁路、下游侧布置4车道一级公路的非对称布置,造成大桥横桥向恒载非对称。为研究该桥桥塔在横桥向非对称恒载下的横向偏位以及控制方法,采用MIDAS Civil软件建立主桥桁架有限元模型,分析了不对称恒载对桥塔的作用模式、桥塔横向偏位成因,研究增设体外预应力索和塔上锚点偏移2种桥塔横向偏位控制方案的可行性。结果表明:上塔柱可简化成悬臂梁受力模式,桥塔横向偏位主要受空间斜拉索的横桥向分力和竖向分力控制,横桥向分力起主要控制作用;增设体外预应力索可有效控制桥塔的横向偏位,可操作性强;通过偏移锚点能够改善桥塔的横向偏位情况,但需要综合考虑主梁和桥塔的线形和内力,且可移动的距离受限,综合考虑该桥最终采用设置体外预应力索方案。

公铁平层斜拉桥超宽幅钢箱梁节段模型试验及活载作用效应研究

为研究公铁平层斜拉桥超宽幅钢箱梁受力特性和活载作用效应,以宜宾临港长江大桥宽度为63.9 m的超宽幅钢箱梁节段为研究对象,设计制作相似比为1∶10的全截面缩尺模型开展静载模型试验,并进行有限元计算分析,分别研究恒载状态、公路车辆荷载作用、铁路列车荷载作用及不同活载组合作用下超宽幅箱梁受力特性,纵、横向正应力分布情况及梁体变形特征。结果表明,该桥超宽幅钢箱梁横向弯曲受力行为显著,梁体在活载作用下表现为挑担式支撑梁力学特性和变形特征,其中梁体中箱在铁路列车荷载作用下表现为正弯矩简支梁受力特性,梁体两侧边箱在公路车辆荷载及人群非机动车辆荷载作用下表现为负弯矩悬臂梁受力特性,梁体横截面设计合理,活载作用机理明确,中、边箱结构传力清晰。研究成果为超宽幅钢箱梁的设计和施工提供了重要的参考和设计依据,并为类似桥梁设计提供指导。

在役梁拱组合体系景观桥梁荷载试验分析

为了研究在役梁拱组合体系景观桥梁的承载能力,选取主拱跨中、腹孔主梁跨中和拱肋根部三个截面进行测试,基于三种不同工况进行试验。通过静载试验测得桥梁结构的微应变和挠度,通过脉动试验分析桥梁的振动特性。试验结果表明:桥梁结构的强度、刚度和整体刚度都满足使用要求。试验分析结果可作为桥梁状况评价的依据,也为同类桥梁荷载试验在测试截面选取、测点布设、加载试验、脉动试验等方面提供参考。