Experimental and analytical studies on the vibration serviceability of long-span prestressed concrete floor

An extensive experimental and theoretical research study was undertaken to study the vibration serviceability of a long-span prestressed concrete floor system to be used in the lounge of a major airport.Specifically,jumping impact tests were carried out to obtain the floor’s modal parameters,followed by an analysis of the distribution of peak accelerations.Running tests were also performed to capture the acceleration responses.The prestressed concrete floor was found to have a low fundamental natural frequency（≈8.86 Hz）corresponding to the average modal damping ratio of≈2.17%.A coefficients plate with simply-supported edges.The calculated analytical results（natural frequencies and root-mean-square acceleration）agree well with the experimental ones.The analytical approach is thus validated.

Effects of Vibration Technology and Polyvinyl Acetate Emulsion on Microstructure and Properties of Expanded Polystyrene Lightweight Concrete

To prevent expanded polystyrene （EPS） beads from rising up to the surface in the molding process of EPS lightweight concrete, vibration with pressure was applied and the polyvinyl acetate （PVA） emulsion was adopted to improve its mechanical properties. The mechanical properties, thermal properties and durability of EPS lightweight concrete were tested. The microstruetures of EPS lightweight concrete were observed by scanning electron microscope （SEM）. Vibration with pressure reduces the number of small cracks. The 180 d compressive strength and flexural strength increase obviously as a large amount of PVA was added. The mixed amount of PVA has no obvious influence on the thermal performance when it is not more than 10% of the cement. Vibration with pressure and surface modification of EPS beads by PVA improve the combination of EPS beads with cement stone and the mechanical properties of EPS lightweight concrete.

Vibration sensitive admixture for roller compacted concrete

In order to further speed up the construction progress,shorten the rolling time and reduce the rolling times of roller compacted concrete after analyzing work of construction progress improvement measures of roller compacted concrete,research on vibration sensitive admixture is carried out and satisfactory results are acquired.The new type vibration sensitive admixture was used in the project of Jinghong hydropower station in Yunnan Province,China.The engineering experimental results show that various indexes have been verified.Meanwhile,the compactness of roller compacted concrete is improved under the same rolling times,the rolling times and the duration time can be reduced under the same compactness requirement in construction practice.

THE MEASUREMENT AND STUDY OF BLASTING VIBRATION AFFECTING IN SITU CAST CONCRETE LINING OF VERTICAL SHAFT

Vertical shaft is main form of drivage in deep mineral depoist. They also serve as the entrance into and the exit from the underground mine. The main problems in shaft and tunnel engineering is to solve the contradiction between drivage and lining. The measurement of blasting vibration affecting concrete lining strength of vertical shaft is carried out in experiment and theory in this paper.

Detecting Damage in Reinforced Concrete Beams Using Vibrational Characteristics

This paper evaluates two methods of diagnosing damage, Natural frequency and Stiffness-Frequency change-Based damage detection method in reinforced concrete beams under load using vibration characteristics such as natural frequency and mode shape. The research uses finite element method with crack damage instead of deleting or reducing the bearing capacity of the element like in previous studies. First, a theory of the damage diagnosis method based on the change of natural frequency and mode shape is presented. Next, the simulation results of reinforced concrete beams using ANSYS will be compared with the experiment. Particularly, the investigated damage cases are cracks in reinforced concrete beams under loads. Finally, we will evaluate the accuracy of the damage diagnosis methods and suggest the location of the vibration data and specify the failure threshold of the methods.

Dynamic finite element model updating of prestressed concrete continuous box-girder bridge

The dynamic finite element model （FEM） of a prestressed concrete continuous box-girder bridge, called the Tongyang Canal Bridge, is built and updated based on the results of ambient vibration testing （AVT） using a real-coded accelerating genetic algorithm （RAGA）. The objective functions are defined based on natural frequency and modal assurance criterion （MAC） metrics to evaluate the updated FEM. Two objective functions are defined to fully account for the relative errors and standard deviations of the natural frequencies and MAC between the AVT results and the updated FEM predictions. The dynamically updated FEM of the bridge can better represent its structural dynamics and serve as a baseline in long-term health monitoring, condition assessment and damage identification over the service life of the bridge .

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.

Vibration reduction analysis of new barriers in large model experiment

A large model box was developed in our experiment to study the vibration reduction effect.Five hydraulic highperformance actuators are arranged in the upper part of the model box.There is a time difference between adjacent actuators,which can simulate the train induced vibration.To reduce vibration a composite barrier is designed;the barrier consists of a honeycomb concrete canvas and PE polymer water bags.The concrete canvas can be mixed with water to produce a hydration reaction to form a structure with a certain hardness.By simulating different train speeds and loads,vertical vibration velocity,and acceleration before and after the barrier are compared and analyzed.The experimental results show that the new barrier can achieve a good vibration reduction effect.When the simulated train speed increases,the damping effect of the barrier is improved.At a speed of 180 km/h,an amplitude of 1.5 m after the barrier is found to be 48.6%lower than that before the barrier.Velocity decreases by 24.2%at 36 km/h and by 38.1%at 108 km/h.

大体积混凝土板微振动控制能力的测试与分析

精密大科学设施具有十分严格的微振动控制要求。为研究某大型精密设施内大体积混凝土底板对微振动的控制效果并为类似项目建设提供参考,在该设施建设现场进行了冲击激励、跑车激励和环境激励下的测试。通过对实测速度时程数据的处理,得出测点1~100 Hz内1 s的位移有效值。分析结果表明,在环境激励下,该设施中试验大厅底板表面的微振动水平能够达到控制要求;在冲击激励下,试验大厅底板表面微振动信号主要分布在5~30 Hz的频带内;场地内的车辆开动会对场地的微振动水平产生明显的影响;环境激励下,整个建设场地的微振动水平基本一致。研究结果对该精密大科学装置及类似工程的防微振设计具有重要的理论及参考价值。

大跨度钢-混结合梁悬索桥涡激振动控制指标体系研究

为保证已建桥梁发生涡激振动后桥梁结构的安全以及桥上行车和行人安全,提出综合考虑人员舒适性、结构受力和停车线形三方面的大跨度钢-混结合梁悬索桥涡激振动控制指标体系。该体系包含9项指标,分别为驾乘人员舒适度、驾乘人员晕动症、行人舒适度(狄克曼指标)、加劲梁强度、加劲梁应力、加劲梁挠度、桥面纵坡、竖曲线半径和停车视距。以武汉鹦鹉洲长江大桥为背景,分别计算了“限速”和“封桥”2个交通管制措施下9项指标对应的涡激振动振幅限值。在此基础上,将9项指标对应的涡激振动振幅限值的最小值作为涡激振动限值建议取值。结果表明:当该桥发生低阶竖弯涡激振动(VS1、VAS1)时,涡激振动的控制因素为加劲梁挠度指标;当大桥发生VAS2模态的竖弯涡激振动时,涡激振动由驾乘人员晕动症指标和行人舒适度指标共同控制;当大桥发生高阶竖弯涡激振动(VAS3、VAS4)时,涡激振动由行人舒适度指标控制。涡激振动控制指标体系及限值标准的计算框架可适用于不同桥型涡激振动限值的计算。

桥梁动力效应对粗骨料UHPC的影响

为解决粗骨料超高性能混凝土(UHPC)在桥梁工程可能遭受的桥梁动力效应问题,通过小型振动台进行模拟桥梁振动,以振动幅度和频率为振动参数,研究了桥梁振动对粗骨料UHPC的力学性能、超声波波速及粗骨料沉降系数的影响规律.试验结果表明:1 mm的振动幅度可以有效改善孔结构,对粗骨料UHPC的力学性能和超声波波速具有促进作用;当振动幅度大于1 mm时振动会引入内部缺陷,并且粗骨料离析程度增大,刚性骨架被破坏,抗压强度、弹性模量和超声波波速降低;当振动频率增大时,能够有效改善钢纤维与基体的黏结性能,增强粗骨料UHPC的弯曲韧性;在实际粗骨料UHPC用于桥梁施工过程中应注意控制桥梁振动幅度,不应超过3 mm。

地基中混凝土排桩主动隔振研究

为了探究地基中设置混凝土排桩后,排桩的各参数变化对近场主动隔振的影响规律,在有限元软件中建立与试验场地一致的三维有限元模型,通过计算与分析验证了有限元计算结果的有效性;参考TB 10621—2014《高速铁路设计规范》建立了足尺寸的有限元模型,分析在列车荷载作用下排桩的各参数变化对隔振效果的具体影响规律。研究结果表明:桩长参数对隔振效果影响较为明显,随着参数增大,隔振效果越理想,当桩长参数为10.5以后,继续增加比值,隔振效果提升不显著;随着桩间距参数越大,隔振效果越不理想,较小的桩间距可获得理想的隔振效果;埋深参数对隔振效果影响显著,参数越大,隔振效果越不理想,当参数为3.5时,隔振效果已很不理想,较浅埋深能获得较理想的隔振效果。

针片状骨料含量对沥青混凝土骨料级配的影响研究

为研究针片状骨料含量对沥青混凝土骨料级配的影响,本文采用逐级填充法,选用骨架稳定性为衡量骨架级配优劣的唯一指标,考虑针片状含量为0%、20%、25%、30%、35%,利用垂直振动压实仪成型试件。结合加州承载比(CBR)值、骨架密度与空隙率综合评价骨架稳定性,以此确定各组粗骨料级配。采用合成级配的设计方法,将粗细集料进行全粒径骨料级配设计。结果表明,随着针片状骨料含量的增加,全粒径骨料骨架稳定性呈现先增后减的趋势,其中针片状骨料含量为30%的骨架稳定性最优,针片状骨料含量35%的稳定性最劣。

燃气爆炸荷载作用下钢筋混凝土板抗爆性能数值模拟

为了研究不同燃气爆炸荷载下混凝土板的动态响应特点,本文通过已有文献中的钢筋混凝土板抗爆试验,利用LS-DYNA有限元软件建立数值模型并验证其可靠性。然后,在混凝土板面施加不同峰值的简化三角燃气荷载,研究混凝土板在燃气荷载作用下的位移、速度、加速度等。结果表明:试验用钢筋混凝土板的最大位移和振动都出现在板跨中位置,且随着荷载峰值的增大而增大;当荷载峰值超过20 kPa时,随着作用在混凝土板上荷载量值的增加,结构的刚度受到削弱,在受迫振动阶段结构振动加速度的特性会发生变化,出现高频振荡;高频振荡开始时间随着燃气爆炸荷载峰值的提高而提前;当荷载结束后,混凝土板进入自由振动阶段,板的振动周期受残余刚度的影响,随着荷载峰值的提高而增大。

轨道交通下层状地基中混凝土排桩隔振效果研究

为了研究在轨道交通荷载作用下混凝土排桩的隔振效果,特建立“车轮-轨道-地基”耦合模型,通过轨道竖向不平顺功率谱建立不平顺轨道并模拟列车在其表面行驶过程,根据控制变量法研究在混凝土排桩几何参数变化的情况下对混凝土排桩隔振效果的影响,通过本文的研究结果表明:混凝土排桩具有一定的隔振效果,随着各个参数的变化其隔振效果也会发生改变;桩长的增加,地基表面和地基深处隔振效果增强;随着埋置深度和桩间距的增加,混凝土排桩的隔振效果均下降,布置混凝土排桩埋深越浅隔振效果越好,布置混凝土排桩越紧密隔振效果越好。在土层的分界面上会出现振动加强的效果,在实际施工中应注意土体分层面带来的影响。

基于振动传递率函数的水泥混凝土铺面脱空识别方法

为提高水泥混凝土铺面脱空识别的准确性和便捷性,提出一种基于振动传递率函数的板底脱空识别方法。首先,建立了九块板全尺寸铺面结构三维有限元模型,获取冲击荷载作用下铺面板的多点加速度响应;其次,在2个振动传递方向上,分别计算相邻2个测点间的振动传递率函数,分析特定频段内传递率函数的差异,并提出传递率损伤指标(transmissibility-damage indicator,TDI)及其矩阵表达式;最后,计算分析11种不同脱空形式、程度下TDI矩阵的差异,并分析测点布设方式、信号噪声水平对TDI矩阵的影响。结果表明:该脱空判定指标能较好识别定位板角和板边局部脱空。所得TDI矩阵在板角脱空的2个传递方向均十分显著,在板边脱空的垂直脱空边方向较为显著;对于板中脱空,2个传递方向上的TDI矩阵均无法有效识别。板中脱空的分布与TDI矩阵的分布一致性较差;对于多区域脱空,其计算得到的TDI矩阵与单区域脱空类似,对于板角和板边局部脱空均能有效识别;测点布设越密,TDI矩阵的分布与脱空分布的一致性越高。然而,该识别方法对噪声水平较为敏感,噪声水平越高,识别精度越低,需要较高精度的传感器或设备予以支撑。

主动激励声波在后张法混凝土传播机理可视化及影响研究

当激振器作为主动激励信号时,不同的激励频率和激励幅值的声波在后张法混凝土结构内的传播机理及影响因素对实际工程提供主动激励信号波形参数选取及声发射传感器布置方式具有重要意义。该文利用COMSOL数值模拟方法可视化了激振器激励声波在后张法混凝土梁内的传播机理,提出了激振器主动激励信号波形参数确定的方法。结果表明:数值模拟方法可视化了激振器激励声波在后张法混凝土结构内的传播路径;构建了不同激励频率和激励幅值声波在后张法混凝土结构内衰减模型,可作为稳定的主动激励信号波形参数选取和声发射传感器布置方式的理论基础,当激励幅值相同,激励频率为10 kHz时,激励声波在后张法混凝土结构内衰减系数最小,实际工程中为保证信噪比,较大的激励幅值更有优势。

地铁诱发的砖混结构环境振动及传递规律研究

为解决地铁运行引起的邻近砖混结构环境振动问题,以某7层砖混结构为研究对象,实测隧道内、室外地面、结构楼板的振动响应,分析振动沿“隧道-地面-结构”的传递规律,并由此提出建筑物内环境振动超标可能的原因:隧道埋深浅、建筑与隧道距离近且处于同个土层使得土体对振动的衰减效果较差;结构部分楼板共振导致振动响应超过评价规定的室外地面和室内首层。进一步建立该砖混结构的有限元模型,采用实测柱底竖向加速度作为荷载,并对比实测楼板响应验证模型的准确性。模拟计算结果证实中间层及顶层楼板的放大效应,并通过分析获得了楼层数量、层高、板厚、墙厚参数对振动响应空间分布的影响。研究成果对砖混结构的环境振动评价具有一定参考价值。

高速铁路简支钢-混结合箱梁振动特性研究

对一高速铁路32 m简支钢-混结合箱梁进行锤击试验,分析其振动特性。建立轨道-桥梁垂向耦合有限元模型,利用谐响应分析计算轨道-桥梁系统各板件的速度导纳,与试验结果进行对比,验证模型的有效性后分析振动在梁上的传递特性。采用虚拟激励法得到行车条件下的轮轨力,作用于有限元模型上,讨论钢-混顶板的混凝土厚度、扣件刚度等对钢-混结合箱梁振动的影响。为钢-混结合梁振动的进一步研究提供参考。

±800kV与500kV混压大跨越钢管混凝土塔等效风荷载分析

大跨越钢管混凝土塔相比于普通钢管塔存在质量、刚度突变的特点。为探究钢管混凝土塔和钢管塔在风荷载作用下的响应规律及设计风荷载的取值,该文以实际工程为例,通过有限元模拟分析了两种塔型的动力特性和风振响应,并将等效静力风荷载与规范结果进行比较。结果表明:钢管混凝土塔的刚度明显高于钢管塔,且前几阶频率相对密集,振型间相互耦合明显;按规范等效风荷载的结构响应大于时程分析响应极值;按规范计算的钢管混凝土塔风振系数在灌入混凝土顶部附近存在突变;钢管混凝土塔顶部位移、加速度响应明显小于钢管塔,且钢管混凝土塔的脉动响应下降更为明显。