Seismic Response and Stability Analysis of Single Hinged Articulated Tower

Study of dynamic stability phenomenon in transient systems has always created interest amongst the researchers because of its inherent non-linearities. Offshore structures subjected to wave, earthquake or wind loads or a combination of these loads show non-linear transient behaviour. As oceanic waves are better modelled as stochastic process, there is a need to investigate the stochastic stability of flexible offshore structures as well. Present study has been carried out to determine seismic response of Single Hinged Articulated Tower (SHAT) under different categories of wave loads and earthquake followed by its dynamic stability analysis. Different phases of wave/earthquake loading on SHAT have been explored to investigate dynamic instabilities existing during each phase. Two dimensional phase plots have been used to identify phases of dynamic instability existing within the responses of SHAT under various conditions of loading.

Dynamic performance of cable-stayed bridge tower with multi-stage pendulum mass damper under wind excitations——I:Theory

In this paper, wind-induced vibration control of a single column tower of a cable-stayed bridge with a multi- stage pendulum mass damper （MSPMD） is investigated. Special attention is given to overcoming space limitations for installing the control device in the tower and the effect of varying natural frequency of the towers during construction. First, the finite element model of the bridge during its construction and the basic equation of motion of the MSPMD are introduced. The equation of motion of the bridge with the MSPMD under along-wind excitation is then established. Finally, a numerical simulation and parametric study are conducted to assess the effectiveness of the control system for reducing the wind-induced vibration of the bridge towers during construction. The numerical simulation results show that the MSPMD is practical and effective for reducing the along-wind response of the single column tower, can be installed in a small area of the tower, and complies with the time-variant characteristics of the bridge during its entire construction stage.

Dynamic performance of cable-stayed bridge tower with multi-stage pendulum mass damper under wind excitations—Ⅱ: Experiment

The possibility of using a multi-stage pendulum mass damper （MSPMD） to control wind-induced vibration of a single column tower of a cable-stayed bridge during construction was studied theoretically in part I of this work. In this paper, the performance of the MSPMD for reducing bridge tower vibration is studied experimentally. A MSPMD model and a tower model of the bridge with geometry scaling of 1：100 were designed and manufactured. Calibration of the MSPMD model with different wire lengths is conducted to verify the analytical model of the damper. A series of tests for the uncontrolled freestanding tower, tower with cables, and tower with MSPMD model are then performed under harmonic and white noise excitations. The experimental results show that the responses of the tower model significantly decrease with the installation of the MSPMD model, which demonstrates the effectiveness of the M SPMD to mitigate the vibration of the bridge tower.

Shake table experimental study of cable-stayed bridges with two different design strategies of H-shaped towers

As one of the main load-carrying components of cable-stayed bridges,bridge towers are typically required to remain elastic even when subjected to severe ground motions with a 2%-3%probability of exceedance in 50 years.To fulfill this special requirement imposed by current seismic design codes,reinforcement ratios in the bridge towers have to be kept significantly higher than if limited ductility behavior of the tower is allowed.In addition,since the foundation capacity is closely related to the moment and shear capacities of the bridge tower,a large increase in bridge construction cost for elastically designed cable-stayed bridge is inevitable.To further investigate the possibility of limited ductility bridge tower design strategies,a new 1/20-scale cable-stayed bridge model with H-shaped bridge towers designed according to strong strut-weak tower column design was tested.The shake table experimental results are compared with a previous strong tower column-weak strut designed full bridge model.A comparison of the results show that ductility design with plastic hinges located on tower columns,i.e.,strong strut-weak tower column design,is another effective seismic design strategy that results in only small residual displacement at the top of the tower column,even under very severe earthquake excitations.

密度峰值聚类在塔机损伤诊断中的应用研究

建立塔机有限元模型,获取塔机完好状态和各损伤工况的各采集点的动态位移。提出了两种模型建立方法,基于悬臂梁的双输入单输出模型和基于时域数据的动态双输入单输出模型,对基于时域数据的双输入单输出模型首先利用最小二乘法计算参数初值,进一步利用粒子群优化方法进行参数优化,提高了模型精度。以完好工况的塔机数据为基础,建立基于悬臂梁的双输入单输出模型和基于时域数据的双输入单输出模型,计算参数,建立损伤识别模型,用待检状态的位移数值拟合模型,用两种模型计算出的残差方差做损伤因子,利用密度峰值聚类方法对损伤因子进行分析,实现了对塔机的损伤判定和损伤位置的确定。这种基于密度峰值聚类的诊断方法可对塔机微小损伤进行智能诊断和位置确定,该方法只需要塔机完好状态的数据和待检状态的数据即可自动诊断,解决了塔机损伤识别中损伤数据难以获取,因而无法实现智能训练和诊断的问题。

桥梁刚度变化对高速铁路独塔斜拉桥车⁃桥耦合振动的影响分析

以高速铁路独塔斜拉桥为研究对象,建立车-轨-桥耦合系统的空间多体动力学分析模型,开展高速铁路斜拉桥的车-轨-桥耦合振动的仿真分析。通过改变材料弹性模量的方式调整桥塔和主梁刚度,研究桥梁刚度变化对桥梁车-桥-耦合振动的影响规律。研究结果表明,随着桥塔刚度的增大,主梁跨中竖向和塔顶纵向位移响应逐渐减小,其峰值减幅分别为7.57%和10%;随着主梁刚度的减小,主梁跨中竖向位移和塔顶纵向位移峰值呈逐渐递增趋势,主梁刚度变化对车体竖向加速度和Sperling竖向舒适度指标影响相对较大;相比于桥塔刚度的变化,主梁刚度变化对车-桥振动响应的影响更大;整体上,列车运行的安全性和平稳性指标满足规范要求。

独塔非对称钢-混混合梁斜拉桥抗震性能研究

【目的】研究独塔非对称钢-混混合梁斜拉桥的抗震性能,并探明非对称结构地震响应的差异。【方法】以长沙香炉洲大桥西汊航道桥为依托,采用MidasCivil软件建立非对称钢-混混合梁斜拉桥全桥有限元模型,分别采用反应谱法和非线性时程分析法对其进行地震响应分析,并重点研究了结构非对称性对斜拉桥辅助墩、过渡墩及其桩基抗震性能的影响。【结果】独塔非对称钢-混混合梁斜拉桥的动力特性和地震响应规律呈现出明显的非对称性,非对称布置的两过渡墩和两辅助墩在地震作用下的内力响应存在较大差异,结构的非对称性对横向地震更加敏感,在抗震设计时应予以重视;除两过渡墩桩基外,长沙香炉洲大桥按照静力计算设计的结构尺寸及配筋形式均能满足各工况地震作用下的抗震性能目标;塔身、墩身在横向+竖向地震作用下的安全储备均大于纵向+竖向地震的,桩基在横向+竖向地震作用下的安全储备几乎都小于纵向+竖向地震的;受结构非对称性的影响,边跨的27#过渡墩桩基总是先于主跨的31#过渡墩桩基发生破坏;在横向地震作用下,受群桩承台影响横向各排桩基地震轴力有较大差异。【结论】从经济性和抗震合理性角度出发,应对独塔非对称钢-混混合梁斜拉桥进行差异化的抗震设计,研究成果可为非对称斜拉桥及其他非对称桥梁结构的抗震设计提供有益参考。

考虑不确定性斜拉桥参数的重要性与易损性分析

许多结构参数对桥梁数值模型的计算结果产生影响,结构的恒载、阻尼以及相关材料特性等参数涉及的不确定性被称为建模不确定性。研究表明建模不确定性的存在使得结构易损性曲线的偏差程度达到70%,因此在地震易损性分析中考虑不确定性很有必要。文章采用一种基于随机森林(random forest,RF)模型的概率地震需求模型(probabilistic seismic demand model,PSDM)易损性计算方法,分析桥梁构件的材料特性、荷载条件和构件几何特性等不确定因素对桥梁易损性的影响,并从中筛选出重要的不确定性参数。借助随机森林模型的学习与预测功能对结构易损性曲线进行预测。

单塔塔顶循环丙烷回收工艺特性与能耗评价

为改善现场DHX丙烷回收流程产品收率低、能耗高的缺陷,将原重接触塔和脱乙烷塔合并为单塔,将塔分为吸收段和分馏段,从中引出侧线实现总能耗降低和热集成度的提高,形成SCORE丙烷回收流程。通过单因素模拟实验,分析了脱乙烷塔塔压、侧线抽出液相流量、塔顶回流比、原料气分流比对丙烷收率和总能耗的影响,考察了不同气质组成对工艺的适应性,并对换热网络进行改进。流程改进后,工艺总能耗从28172 kW降至25476 kW,能耗降幅9.56%,节能效果显著。

Comprehensive Optimal Control on Seismic Response of a Single-Tower Self-Anchored Suspension Bridge

Earthquake may cause severe damage to all kinds of bridge such as the falling down of the girder; therefore,effective measures should be employed to control the seismic displacement. In this paper,the method of comprehensive optimal control,com-bined with analytic hierarchy process,is employed to investigate the seismic response control of the Nanjing Jiangxinzhou Bridge,which is a single-tower self-anchored suspension bridge （SSSB）. Also,3-dimensional nonlinear seismic response analyses are con-ducted. Three types of practical connection measures for seismic response control of SSSB are investigated,and the optimal pa-rameters of the connection devices are achieved by this method. Results show that both the elastic connection devices and the damp-ers with rational parameters can reduce the seismic displacement of the bridge effectively,but the elastic connection devices will in-crease the seismic force of the tower. When all factors are consid-ered,the optimal measure is by using the elastic connection devices and the dampers together. These results can provide references for seismic response control of SSSBs.

平臂式塔式起重机自振周期计算方法研究

塔式起重机的自振周期是其基本属性,关乎风振动力系数的选取,影响风载荷及其对塔身偏移的计算。文章以永茂5513型塔帽式和中天6513型平头式塔式起重机为例,简化塔身的刚度简化,将塔式起重机简化为单自由度模型,推导了自振周期简化公式,对比分析了现场测试和有限元模拟结果,验证了该公式的可行性,并引入考虑塔机质量分布影响的修正系数,修正了其简化公式。结果表明:塔式起重机自振周期简化公式计算结果与现场实测自振周期吻合较好,在粗略计算塔式起重机自振周期时可以使用该简化计算公式。根据有限元模拟结果,给出了塔式起重机自振周期简化公式的修正公式,并给出了塔帽式、平头式塔式两种起重机修正系数的推荐值及线性内插公式。

跨铁路独塔斜拉桥索塔平转施工技术与监测研究

某跨铁路独塔斜拉桥索塔高85 m,左右塔柱内倾81.22°,采用翻模+平面转体法施工,逆时针转体93°,转体质量约18 500 t。因此,针对该桥塔因转体质量大、重心高所带来的水平转体施工安全问题,开展了独塔斜拉桥索塔平转施工技术分析、实桥跟踪测试,得到了称重、配重、姿态监测与调整等技术要点。得出的主要结论包括:沿桥塔下横梁与0号梁段上对称平衡配重50 t,可降低桥塔重心;平转过程受不平衡力矩和偏心距的影响较为敏感,桥塔称重与配重误差需严格控制;索塔姿态调整前移出配重,并通过临时支墩锁定索塔姿态;转体前、后垂直度应尽量保持一致。

中波斜拉线弱定向天线的应用

为保证中波发射对特定区域的覆盖效果,多采用定向天线达成目标,本项目对特定频点发射天线采用了单塔斜拉线弱定向技术以增强对主方向的覆盖。经历计算机仿真计算、模型试验验证和安装实施过程,最后经过对覆盖区域场强的实测,达到了设计指标,实现了所需的功能,保证了覆盖效果满足使用需求。

独塔斜拉-自锚式协作体系悬索桥合理约束体系研究

为研究独塔斜拉-自锚式协作体系悬索桥合理约束体系,以主跨2×350 m的济南绕城高速二环线北环段工程黄河特大桥主桥为背景,采用BNLAS软件建立主桥空间有限元模型,对比不同纵向、竖向约束体系方案下结构的荷载响应、自振特性,分析不同塔梁约束体系对独塔斜拉-自锚式协作体系悬索桥静、动力性能的影响。结果表明:塔梁处竖向双排支座有效约束了塔梁之间的相对转动自由度,使塔梁协调受力,相较于传统的全飘浮体系和竖向单排支座体系,竖向双排支座体系提供了更大的整体结构刚度;设置纵向约束能显著增强独塔斜拉-自锚式协作体系悬索桥结构纵向刚度,建议在纵向上设置固定约束;相较于传统塔梁墩固结体系,竖向双排支座体系对主梁提供了更强的转动约束,且塔梁间约束在构造上处理简单。该桥桥塔处设置竖向双排支座并设置纵向固定限位装置。

独塔双索面斜拉桥荷载试验研究

为准确评估斜拉桥成桥时的承载能力及工作状态,检验桥梁结构是否达到设计及有关规范规定的要求,为桥梁交工验收提供技术依据,以沥桂大桥(独塔双索面预应力混凝土斜拉桥)为研究对象,采用Midas Civil建立了斜拉桥有限元模型,介绍了斜拉桥荷载试验检测的主要测试断面及测试内容,对比分析了主梁应变、挠度、主塔塔顶纵桥向水平位移、索力增量等静力理论计算值与实测数据,并对该桥的自振特性及动力特性等动力荷载试验进行了分析。结果表明:1)该桥各项静载试验参数、校验系数均在规范要求的合理范围内,相对残余均小于20%;2)结构的自振频率、阻尼比及动力响应均处于正常工作状态,该桥整体处于弹性工作状态,受力状态良好,满足设计荷载及有关规范的使用要求。

快换式塔筒过驳吊杠结构设计与工程应用

为了解决风机塔筒过驳工序耗时较长的问题,提高风机整体安装效率,基于ABAQUS有限元软件设计了一种快换式过驳塔筒吊杠,将眼板式吊耳优化为多组圆柱式吊耳,可实现起重船单钩快速水平过驳风机中塔、顶塔。结果表明,相较于传统的双钩合抬方法和使用其他类型吊杠,使用快换式塔筒过驳吊杠可显著降低塔筒过驳用时,工序施工效率整体提升了29.2%。研究成果可为其他大件过驳吊杠的设计与应用提供参考。

论增设转接法兰对通信单管塔结构安全性的影响

铁塔基站平移搬迁工程中,可能存在塔底法兰与预埋成型的地脚螺栓不匹配问题,通过增设转接法兰,解决利旧铁塔无法安装的问题。特选取铁塔公司发布的《低成本铁塔标准图集V2.0》中的0.45风压高度的20 m,25 m,30 m,35 m共计4种高度的单管塔,利用有限元软件3D3S,研究单管塔增设转接法兰后,单管塔自振周期、塔顶位移、塔身最大应力及塔脚倾覆弯矩的增大幅度,为单管塔增设塔脚转接法兰的安全性研究提供一定的参考。

独塔自锚式吊桥的施工与设计优化方案研究

针对独塔自锚式吊桥施工工艺复杂性及设计优化的需求,研究依托某大桥工程,分析了独塔自锚式吊桥的基本构造,针对施工方法展开优化设计。通过对独塔自锚式吊桥进行施工监测,验证了研究提出的优化方案的有效性。结果表明:标高误差最大仅0.012 m,吊索位置上游与下游的误差平均值分别为2.57 mm与3.34 mm,索力值误差均在±3.00%以内。

单管塔塔脚二次浇筑对塔脚构件受力的影响分析

单管塔作为铁塔的一种常见结构,其塔脚法兰板与基础顶面通过螺栓连接。连接形式分为两类,第一类是法兰板与基础顶面无混凝土二次浇筑,第二类则为有混凝土二次浇筑。由于规范中目前没有明确介绍在纯弯矩作用下,这两类连接形式中塔脚构件的受力情况,故运用ABAQUS有限元分析软件对这两种形式进行数值模拟,对比分析塔脚构件的受力情况,并与规范计算值进行对比,结果表明:通过有限元数值模拟的计算结果与按规范计算的结果误差不大,表明有限元数值模拟的分析过程是可靠的;法兰板与基础通过二次浇筑混凝土可以有效增强单管塔基础的整体受力性能。

基于双机一塔循环水系统供暖季单循环水泵应用研究

针对双机一塔循环水系统采暖循环水泵耗电量大问题,提出单循环水泵运行方式,结合供暖机组低压缸零出力运行,定量分析了凝汽器压力报警工况、凝汽器额定压力工况、低压缸零出力运行1台工况,低压缸零出力运行2台工况下循环水流量与循环水泵的匹配性。结果表明,机组负荷<75%时,4种工况均满足单循环水泵运行要求,机组负荷>75%时,凝汽器额定压力工况不满足,需启动双泵运行。通过对单循环水泵运行措施调整,保证了单循环水泵的安全稳定运行,节能效果显著,具有一定推广价值。