A method for calculating strand tension in the anchor span of a suspension bridge considering the rotation of a splay saddle

This paper reports a method for strand tension in anchor spans considering rotation.A kind of co-moved coordinate system,a saddle local coordinate system,was set up.This system implemented the rotation of the splay saddle through the rotation of the coordinate system,and all calculations proceeded in this coordinate system.Considering the rotation of the anchoring surface by the rotation of the local coordinate system of the anchoring surface,the anchorage point coordinates of strands were transformed to the local sadle coordinate system.There was a two-layer iteration adopted in the calculation.In the inner iteration,the cable force at the end of the vertical bend was taken as the variable,and the ordinate of the anchorage point was taken as the target value.In the outer iteration,the vertical tangential angle at the end of the vertical bend was taken as the variable,and the ordinate of the anchorage point was taken as the target value.The method carried out the rotation of the splay saddle and anchor surface and was simple,convenient and without approximation.The effect of rotation was considered precisely;it showed stability during the process of two-layer iteration,powerful adaptation and higher efficiency and had been successfully applied in the construction control of the Wufengshan Yangtze River Bridge,the world's first kilometer-level combined highway and railway suspension bridge.

Elastic Dynamic Stability of Big-Span Power Transmission Tower Subjected to Seismic Excitations

By combining the time-history response analysis and the eigenvalue buckling analysis, this paper developed a computational procedure to study the elastic dynamic stability of a transmission tower by APDL language in ANSYS. The influences of different input directions of seismic excitations and damping ratio on the elastic dynamic stability of tower were discussed. The following conclusions were obtained： （ 1 ） Longitudinal direction of the transmission lines is the worst input direction of seismic excitation for the transmission tower. （2） Dead load has no significant effect on the critical load and the occurrence time of buckling. （3） Vertical input of seismic excitations has no great effect on the dynamic stability of the transmission tower. （4） Damping effect has an influence on the dynamic stability of the transmission tower; however, the inherent characteristics of dynamic buckling is not changed.

Improved methods for decreasing stresses of concrete slab of large-span through tied-arch composite bridge

Mechanical behavior of concrete slab of large-span through tied-arch composite bridge was investigated by finite element analysis (FEA). Improved methods to decrease concrete stresses were discussed based on comparisons of different deck schemes, construction sequences and measures, and ratios of reinforcement. The results show that the mechanical behavior of concrete slab gets worse with the increase of composite regions between steel beams and concrete slab. The deck scheme with the minimum composite region is recommended on condition that both strength and stiffness of the bridge meet design demands under service loads. Adopting in-situ-place construction method, concrete is suggested to be cast after removing the full-supported frameworks under the bridge. Thus, the axial tensile force of concrete slab caused by the first stage dead load is eliminated. Preloading the bridge before concrete casting and removing the load after the concrete reaching its design strength, the stresses of concrete slab caused by the second stage dead load and live load are further reduced or even eliminated. At last, with a high ratio of reinforcement more than 3%, the concrete stresses decrease obviously.

双柱悬索拉线塔风致倒塌易损性分析

作为风敏感结构,双柱悬索拉线塔在强风荷载作用下易遭受不同程度的损伤甚至发生倒塌破坏,因此,有必要对其进行风灾易损性分析。为此,本文提出一种双柱悬索拉线塔风致倒塌易损性分析方法。首先,考虑结构参数的不确定性,基于拉丁超立方抽样建立双柱悬索拉线塔不确定性模型,完成所有样本模型的非线性静力推覆分析;然后,利用B-R准则和对数正态分布函数拟合得到双柱悬索拉线塔倒塌易损性曲线;最后,研究风向角和拉线初张力对结构倒塌易损性曲线的影响。研究结果表明:相较于确定性倒塌分析,不确定性倒塌分析能够更好地评估双柱悬索拉线塔的抗风承载能力;风向角对双柱悬索拉线塔的倒塌易损性影响较大,结构的最不利风向角为45°,当基本风速小于56.5 m/s时,结构在任一风向角下的倒塌概率都很小;拉线初张力对结构倒塌临界风速无影响,但对立柱顶点位移易损性曲线影响较大;增大拉线初张力,左右侧立柱的顶点位移易损性曲线均向左移动,且其对背风侧立柱的影响更大。

大跨度斜拉桥索塔侧壁锚固区受力性能分析

以大跨度斜拉桥主塔索塔锚固区为研究对象,采用Midas FEA NX软件建立索塔锚固区实体有限元模型,并对索塔锚固区空间应力进行分析。结果表明:1)主塔在挂索前后、运营阶段及断索工况下,塔壁横桥向、纵桥向应力均为压应力,预应力配束较为安全合理;2)长索锚固齿块的正上方区域锚后牵拉效应较为突出,设计过程中应加强该区域的配筋,限制其开裂。

三面围合的人字结构——北京N公寓结构设计

基于某大跨斜连体三塔结构项目,采用多软件对比小震弹性分析、时程分析以及大震动力弹塑性分析方法,对其进行了斜连体传力路径分析、斜连体超限高层结构计算分析、斜连体防连续倒塌验算、斜连体与塔楼连接薄弱部位关键节点有限元分析。分析结果表明,斜连体传力路径可靠,斜连体及与塔楼连接关键传力节点在大震下不屈服,整体结构满足大震下的变形和承载力要求。故本项目结构布置合理,结构体系安全可靠。

Parameter effects on the dynamic characteristics of a super-long-span triple-tower suspension bridge

A 3D finite element model for the Taizhou Yangtze River Bridge,the first triple-tower long-span suspension bridge in China,is established based on the nonlinear finite element software ABAQUS,and the dynamic characteristics of the bridge are analyzed using the LANCZOS eigenvalue solution method. The study focuses on the effects of the vertical,lateral and torsional stiffness of the steel box girder,the rigid central buckle and the elastic restraints connecting the towers and the steel box girder on the dynamic characteristics of the triple-tower suspension bridge. Our results show that,in general,the dynamic characteristics of the triple-tower suspension bridge are similar to those of two-tower suspension bridges. The vertical,lateral and torsional stiffness of the steel box girder have different effects on the dynamic characteristics of triple-tower suspension bridges. The elastic re-straints have a more significant effect on the dynamic characteristics than the central buckle,and decreasing the stiffness of the elastic restraints results in the appearance of a longitudinal floating vibration mode of the bridge. Also,rigid central buckles have a greater influence on the dynamic characteristics of triple-tower suspension bridges than on those of two-tower suspension bridges. The results obtained could serve as a valuable numerical reference for analyzing and designing super-long-span triple-tower suspension bridges.

特大跨径拱桥系杆张拉优化技术分析

为提高威海石家河公园大桥这一特大跨径拱桥的结构稳定性,保障拱桥建筑施工质量,研究特大跨径拱桥系杆张拉优化技术分析。威海石家河公园大桥共采用34根吊杆,其中中拱14根吊杆,边拱20根吊杆,考虑系杆张拉顺序对质量的影响,设计2种张拉方案,方案1为先张拉两边吊杆、后张拉中间吊杆;方案2为先张拉中间吊杆、后张拉两边吊杆。采用有限元模拟2种张拉方案在施工时所产生的应力、位移变化,从而选取最佳方案。模拟分析可知:采用方案1张拉时主梁所承受应力更大,且主梁、中拱、边拱的位移明显较大,而采用方案2张拉时,可避免主梁出现严重失稳问题,还可保持较小的拱肋位移;同时方案2稳定安全系数较高,在成桥阶段方案2最大吊杆拉应力为433.0 MPa,处于1860钢绞线的安全承载范围内。可见采用先张拉中间吊杆、后张拉两边吊杆方式可有效实现系杆张拉优化。

型钢拱架日光温室结构稳定性能及参数分析

型钢拱架日光温室结构的主要受力构件长细比大,暴雪等极端灾害天气下易引发结构失稳灾变。针对此问题,该研究利用弹塑性力学理论和非线性有限单元法,建立型钢拱架日光温室结构精细化有限元模型,开展雪荷载下日光温室稳定性能分析;通过对型钢截面类型(平椭圆形截面、箱形截面和几字形截面)、温室跨度(8、10和12 m)、雪荷载分布形态(分布厚度非均匀和分布区域不对称)等参数下日光温室失稳全过程分析,分别确定日光温室稳定承载力,揭示雪荷载分布对日光温室稳定承载力的量化影响;结合日光温室的荷载系数-位移全过程曲线和不同加载时刻点的变形图、应力图、轴力图与弯矩图,从直观现象和内在本质两个层面深入探明日光温室的静力失稳机理。分析结果表明:在保证不发生平面外整体失稳的前提下,当型钢截面面积和翼缘宽度相同时,相较于箱形截面型钢、几字形截面型钢,采用平椭圆形截面型钢拱架的日光温室稳定承载力分别提高了19.2%和44.2%;跨度对日光温室稳定承载力的影响较大,与8 m跨度相比,10、12 m跨度的日光温室的荷载系数分别下降了27.1%和57.9%;相较于均匀分布雪荷载,在非均匀分布雪荷载下日光温室的稳定承载力最大下降63.8%;相较于不设置拉杆和撑杆的情况,单独设置拉杆的日光温室稳定承载力最大可提高9.0%,单独设置撑杆的日光温室稳定承载力最大可提高66.8%。该研究得出的结果和给出的建议可为型钢拱架日光温室结构抗雪设计、稳定性研究和防灾分析提供技术指导和理论参考。

The Best Width of Wood Specimen for Zero-span Tension Test

In recent years, the zero-span tension technique of paper and pulp-making industry was applied to wood industry for indirectly testing the longitudinal tensile strength of tracheids. In this paper, this technique was used to test the longitudinal tension strength of tracheids for Chinese fir specimens with different widths. The results showed that average tension strength was 357.39 MPa. The order of average tension strength of tracheids was: 3 mm > 12 mm > 6 mm > 9 mm > 7.5 mm. But, earlywood samples frequently contained a little latewood and sample-making was difficult when the width of specimen was bigger, both the testing and the putting of samples were difficult when the width of specimen was smaller. Therefore, the width of 6 mm was chosen as the best width of specimen of Chinese fir.

基于调研数据的部分斜拉桥设计关键参数研究

针对部分斜拉桥设计关键参数缺少足够规范指导的问题,通过对国内外的部分斜拉桥进行设计主要参数调研统计,并与现有相关规范、科研成果进行对比研究,讨论了部分斜拉桥各型结构体系适用性、拉索布置形式,总结给出拉索倾角和间距、边主跨比、塔跨比、索梁刚度比和无索区长度等重要设计参数取值范围。结果表明,拉索倾角一般为11°~35°,主梁上拉索间距一般采用3.5 m~8 m,塔上的拉索间距一般采用0.5 m~1.2 m;3跨布置时,边主跨比一般集中在0.41~0.70,塔跨比宜采用1/3~1/13,索梁刚度比宜小于30;主跨跨中无索区长度与跨径之比宜取0.06~0.21。

海岛大跨越输电塔线体系风振响应及动力失稳分析

跨海输电塔线体系具有铁塔高、跨度大、风速大、恢复困难等特点,是岛屿电网的关键薄弱位置,尤其受台风等灾害天气影响严重,为进一步认识跨海输电塔线体系的风振响应特点和强风作用下的铁塔风致失稳特征,以温州洞头某线路典型跨海段(耐—直—直—耐)线路为研究对象,采用ABAQUS软件建立该跨海段两塔三线有限元分析模型。首先分析导线、裸塔及塔线体系的动力特性参数,然后开展不同风向角下的风振响应分析及位移风振系数计算,最后,采用增量动力分析方法(incrementaldynamicanalysis,IDA)模拟强风作用下考虑塔线耦合效应的铁塔非线性倒塌过程。研究表明:大跨越导线、地线对输电塔在不同风向角下的风振响应影响存在差异,0°风向角下,大跨越导线、地线增大体系的阻尼,降低风振响应;90°风向角下,大跨越导线、地线在横向风作用下产生较大面外位移,增大塔线体系的风振响应;强风作用下,输电塔斜材相较于主材更容易发生动力失稳,引起结构内力重分布,使得塔身中上部受力集中,最终导致输电塔发生渐进式倒塌。

某全民健身中心大跨度预应力钢筋混凝土跨层桁架结构分析与设计

为了实现某全民健身中心局部多层的无柱大空间,结构设计采用了在二层设置大跨度预应力梁和在三层、四层设置大跨度预应力钢筋混凝土跨层桁架的方案。采用SAP2000软件对比了跨层桁架中预应力筋一次性全部张拉施工和分层浇筑、分批张拉施工下杆件的内力情况,结果表明后者的桁架下弦杆件的最终拉力较小,符合设计要求。通过各施工阶段下桁架杆件的内力变化情况,确定了预应力筋的布置及数量。最后,介绍了本工程预应力杆件的设计和采取的针对性设计措施,说明了施工阶段的监测情况。通过以上分析及设计,验证了预应力钢筋混凝土跨层桁架结构的可行性,较好地实现了建筑功能。

三塔四跨悬索桥施工阶段颤振性能研究

为了解双主跨悬索桥加劲梁吊装期间颤振稳定性,以跨度为(230+800+800+348)m三塔四跨悬索桥为背景,分析该桥加劲梁吊装期间的颤振性能。建立该桥不同吊装阶段三维有限元模型,分析竖弯、扭转模态特性,采用理想平板颤振临界风速理论公式计算桥梁不同吊装阶段及各模态组合下的颤振临界风速,以确定最不利吊装阶段及模态组合;基于此,设计节段模型风洞试验测试原断面及上桥面中央增设竖向稳定板断面桥梁颤振临界风速。结果表明:三塔四跨悬索桥施工阶段的模态特性复杂,颤振分析时模态组合需考虑两主跨间的振动关系;该桥吊装率为8.5%和19.8%时,颤振临界状态由以北侧主跨振动为主的扭弯模态组合确定,吊装率≥29.3%时,颤振临界状态由以南侧主跨振动为主的扭弯模态组合确定,最不利吊装率为40.8%;该桥加劲梁原断面的颤振性能较差,在上桥面中央增设竖向稳定板可以有效提升桥梁的颤振临界风速。

井筒对特大跨越输电塔风致响应的影响

采用数值模拟方法研究井筒对特大跨越输电塔风致响应的影响,提出钢管混凝土杆采用钢管杆等代的等效建模方法,采用时域法和频域法研究有无井筒输电塔在顺线路和横线路方向的风致响应,最后将风振系数结果与规范规定值进行比较。研究表明:利用截面刚度等效原则进行钢管混凝土杆等效为钢管杆的方法是可行的;考虑井筒后输电塔的前两阶自振频率降低明显,输电塔的位移和加速度均增大;时域法和频域法的计算结果接近;有井筒输电塔的整体风振系数比无井筒输电塔大11%~15%;风振系数计算结果与《架空输电线路荷载规范》(DL/T 5551—2018)的规定值比较接近。

大跨连续刚构桥三向预应力筋滞后张拉研究

针对大跨预应力连续刚构桥具体施工过程中竖向、横向预应力筋的张拉存在随意性、不规范性的问题,以某特大桥为背景(68 m+120 m+68 m预应力混凝土连续刚构桥),利用MIDAS FEA有限元分析软件,建立2号到6号梁段的实体模型。通过使用生死单元技术实现对不同梁段、荷载、边界条件的激活,以达到模拟不同的施工阶段的目的,研究梁段沿着桥梁纵向的内力变化。经过多方面的对比后,结果表明,滞后一个节段张拉竖向、横向预应力筋可以让梁体的应力更为均匀,受力性能更为优异,因此推荐在施工过程中使用这种张拉工序。

大跨度U形渡槽预应力钢绞线张拉顺序数值模拟及方案比选

为探究大跨度U形渡槽预应力钢绞线张拉过程中拆模时机对渡槽槽身结构受力状态的影响,以国内某大跨度U形预槽为例,考虑温度荷载,基于单弹簧联结单元法模拟预应力钢绞线与混凝土的相互作用,通过数值模拟方法研究预应力钢绞线张拉过程中的拆模时机对渡槽槽身结构应力响应的影响,进而基于渡槽槽身的应力控制标准及预应力钢绞线张拉过程对渡槽预制台座的占用时间,提出了最优的预应力钢绞线张拉方案。结果表明:拆模前施加部分纵向、环向预应力不仅能满足张拉过程中槽身内壁面不出现拉应力的要求,同时能减少对渡槽预制台座的占用时间。

桥梁工程大跨双塔钢混组合梁施工控制技术研究

以某地区的大跨度桥梁工程双塔钢混组合梁结构为例,结合该工程实际情况分析该工程的施工控制难点,并确定施工控制原则后,进行主塔线形控制、主梁应力控制、斜拉索索力控制、钢箱梁合龙控制。对控制效果进行测试后得出:梁顶高程最大控制误差为15.6mm,斜拉索的索力控制偏差结果均在5%以内,满足桥梁工程的施工标准规范。

不同空间相关函数对铁塔风振系数的影响

空间相关函数是描述空间两点脉动风荷载在频域上的相关程度,国内外学者基于实测数据给出了几种不同的空间相关函数,我国规范采用了Shiotani相关函数进行风荷载分析计算,由于其未考虑高度的影响,在计算分析高度不是很高的一般输电线路铁塔时有较强的实用性,但是对于大跨越高塔,有低估脉动风振系数的可能性。本文采用不同脉动相关函数对不同高度铁塔进行分析计算,结果表明,随着高度的增加,与考虑高度影响的相关函数相比,Shiotani计算所得风振系数在塔头段偏低3%~11%,全塔加权值偏低3%~5.5%左右,因此在设计大跨越高塔时,建议适当考虑高度对空间相关系数的影响。

大跨度矮塔斜拉桥关键节点受力性能的仿真分析

宁波中兴大桥跨越甬江,其主桥由于机场航空限高的要求,采用主跨为400 m的大跨度矮塔斜拉桥设计方案。主桥采用V形钢主塔,塔梁固结并通过大型球钢支座支承在主墩上。经分析,索塔锚固区与塔梁固结处是主桥设计的2个关键节点。节点构造设计复杂,需借助3D空间有限元方法对其受力性能进行仿真分析。利用ANSYS软件建立关键节点的3D有限元仿真模型,并与MIDAS整体模型结果进行比较,验证仿真模型的有效性。通过仿真模型,得到不利荷载工况下关键节点空间应力分布的计算结果,为关键节点构造设计提供可靠依据。