Noise reduction mechanism of high-speed railway box-girder bridges installed with MTMDs on top plate

The issue of low-frequency structural noise radiated from high-speed railway(HSR) box-girder bridges(BGBs) is a significant challenge worldwide. Although it is known that vibrations in BGBs caused by moving trains can be reduced by installing multiple tuned mass dampers(MTMDs) on the top plate, there is limited research on the noise reduction achieved by this method. This study aims to investigate the noise reduction mechanism of BGBs installed with MTMDs on the top plate. A sound radiation prediction model for the BGB installed with MTMDs is developed, based on the vehicle–track–bridge coupled dynamics and acoustics boundary element method. After being verified by field tested results, the prediction model is employed to study the reduction of vibration and noise of BGBs caused by the MTMDs. It is found that installing MTMDs on top plate can significantly affect the vibration distribution and sound radiation law of BGBs. However, its impact on the sound radiation caused by vibrations dominated by the global modes of BGBs is minimal. The noise reduction achieved by MTMDs is mainly through changing the acoustic radiation contributions of each plate of the bridge. In the lower frequency range, the noise reduction of BGB caused by MTMDs can be more effective if the installation of MTMDs can modify the vibration frequency and distribution of the BGB to avoid the influence of small vibrations and disperse the sound radiation from each plate.

Analysis of free vibration characteristic of steel-concrete composite box-girder considering shear lag and slip

Based on Hamilton principle,the governing differential equations and the corresponding boundary conditions of steel-concrete composite box girder with consideration of the shear lag effect meeting self equilibrated stress,shear deformation,slip,as well as rotational inertia were induced.Therefore,natural frequency equations were obtained for the boundary types,such as simple support,cantilever,continuous girder and fixed support at two ends.The ANSYS finite element solutions were compared with the analytical solutions by calculation examples and the validity of the proposed approach was verified,which also shows the correctness of longitudinal warping displacement functions.Some meaningful conclusions for engineering design were obtained.The decrease extent of each order natural frequency of the steel-concrete composite box-girder is great under action of the shear lag effect.The shear-lag effect of steel-concrete composite box girder increases when frequency order rises,and increases while span-width ratio decreases.The proposed approach provides theoretical basis for further research of free vibration characteristics of steel-concrete composite box-girder.

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 .

Free Vibration Analysis of RC Box-Girder Bridges Using FEM

The free vibration analysis of simply supported box-girder bridges is carried out using the finite element method.The fundamental frequency is determined in straight,skew,curved and skew-curved box-girder bridges.It is important to analyse the combined effect of skewness and curvature because skew-curved box-girder bridge behaviour cannot be predicted by simply adding the individual effects of skewness and curvature.At first,an existing model is considered to validate the present approach.A convergence study is carried out to decide the mesh size in the finite element method.An exhaustive parametric study is conducted to determine the fundamental frequency of box-girder bridges with varying skew angle,curve angle,span,span-depth ratio and cell number.The skew angle is varied from 0°to 60°,curve angle is varied from 0°to 60°,span is changed from 25 to 50 m,span-depth ratio is varied from 10 to 16,and single cell&double cell are used in the present study.A total of 420 bridge models are used for parametric study in the investigation.Mode shapes of the skew-curved bridge are also presented.The fundamental frequency of the skew-curved box-girder bridge is found to be more than the straight bridge,so,the skew-curved box-girder bridge is preferable.The present study may be useful in the design of box-girder bridges.

Simulation of Temperature Field in Original Segment of Concrete Box-Girder Bridge

Temperature field and its variation with time are necessary for analyzing the thermo-mechanical performance of mass concrete structures at their early ages. This paper carries out a temperature field simulation analysis for an original segment of a real box girder bridge with the finite element software ANSYS. Two representative exothermic rate models are used to describe the heat- releasing process caused by the cement hydration in concrete. The exothermic rate model that conforms to reality more closely is recognized by comparing the simulation results with the data gathered from the optical fiber temperature sensors pre-embedded in the original segment. The air temperature and wind velocity that constitute thermal boundary conditions are determined in the light of the local meteorological department and correlative research achievements of recent years. Moreover, the consideration for the steel formwork acting as a barrier to heat loss is also proved to be beneficial to improve the simulation effect.

Resilience-incorporated seismic risk assessment of precast concrete frames with“dry”connections

A resilience-incorporated risk assessment framework is proposed and demonstrated in this study to manifest the advantageous seismic resilience of precast concrete frame(PCF)structures with“dry”connections in terms of their low damage and rapid recovery.The framework integrates various uncertainties in the seismic hazard,fragility,capacity,demand,loss functions,and post-earthquake recovery.In this study,the PCF structures are distinguished from ordinary reinforced concrete frame(RCF)structures by characterizing multiple limit states for the PCF based on its unique damage mechanisms.Accordingly,probabilistic story-wise pushover analyses are performed to yield story-wise capacities for the predefined limit states.In the seismic resilience analysis,a step-wise recovery model is proposed to idealize the functionality recovery process,with separate considerations of the repair and non-repair events.The recovery model leverages the economic loss and downtime to delineate the stochastic post-earthquake recovery curves for the resilience loss estimation.As such,contingencies in the probabilistic post-earthquake repairs are incorporated and the empirical judgments on the recovery parameters are largely circumvented.The proposed framework is demonstrated through a comparative study between two“dry”connected PCFs and one RCF designed as alternative structural systems for a prototype building.The results from the risk quantification indicate that the PCFs show reduced loss hazards and lower expected losses relative to the RCF.Particularly,the PCF equipped with energy dissipation devices at the“dry”connections largely reduces the expected economic loss,downtime,and resilience loss by 29%,56%,and 60%,respectively,compared to the RCF.

附加H型钢三段肋预应力预制底板抗弯性能研究

研究附加H型钢的三段肋预应力预制底板(HRP底板)的抗弯性能,为工程设计应用提供参考。应用ABAQUS有限元分析软件对比HRP底板、钢筋桁架预制底板及带通长肋钢筋桁架预制底板的抗弯性能,探讨HRP底板的免支撑施工可行性及适用跨度,分析不同因素对其抗弯性能的影响。HRP底板承载力较其他两者提高32%~143%,抵抗变形能力提高17%~39%,可实现跨度为6.6~7.5 m的跨中免支撑施工要求;增加型钢长度、预应力筋直径,其抗弯性能提高了30%~98%;增大型钢惯性矩、预应力,减小螺栓间距,其承载力和抵抗变形能力提高了6%~30%;改变桁架上弦筋、桁架下弦筋、预应力、钢筋桁架榀数、预制肋长度、预制肋混凝土强度等级对其抗弯性能影响小于10%。HRP底板具有工程可行性,可满足跨度达7.5 m时的免支撑施工要求,型钢长度、预应力筋直径是影响其抗弯性能的主要因素。

预制混凝土构件钢筋浆锚对接连接受拉性能

为改善预制混凝土构件钢筋连接工艺及性能,提出一种预制混凝土构件钢筋浆锚对接连接技术。针对该新型钢筋连接的传力可靠性问题,开展了考虑钢筋直径、混凝土强度和浆锚长度变化的接头单向拉伸试验。试验结果表明,钢筋浆锚对接连接接头受拉性能由钢筋浆锚长度与帮条钢筋承载力共同控制,与混凝土强度无明显关系,表现为帮条钢筋配置相同的条件下,12 mm、14 mm直径连接钢筋试件分别在0.5l a(受拉钢筋基本锚固长度)、0.6l a钢筋浆锚长度条件下实现钢筋拉断,16 mm直径连接钢筋试件在0.6l a钢筋浆锚长度条件下发生帮条钢筋拉断。结合数据分析,建议12~16 mm直径连接钢筋浆锚长度按0.6l a控制,帮条钢筋与连接钢筋牌号相同的前提下,12~14 mm直径连接钢筋的帮条钢筋按4 C 8设计,16 mm直径连接钢筋的帮条钢筋应按6 C 8设计。同时,试验中钢筋镦头构造可保证钢筋充分锚固,其具体尺寸可用于指导钢筋加工;螺旋筋对接头受拉性能影响不明显,可参照本次试验参数进行设计。

装配式局部活性粉末混凝土梁柱节点恢复力模型

为了验证所提出的装配式局部活性粉末混凝土框架梁柱节点的抗震性能,对4个足尺节点进行了低周反复荷载试验,在试验的基础之上,针对节点的连接特点,提出了强度和变形计算方法,构建了平顶的三折线骨架曲线理论模型.通过理论计算得到试验滞回曲线各阶段曲线刚度值,并拟合得到试件在低周往复荷载作用下各级加载、卸载刚度与加载位移角的关系,进而根据滞回规则建立恢复力模型.计算结果表明:通过理论计算所建立的三折线骨架曲线和滞回曲线与试验结果均吻合较好,能够较好地反映该类连接节点在各阶段的受力特点,为弹塑性分析和抗震设计提供理论依据.

生产阶段PC构件碳排放计算与预测

为了进一步探究生产阶段预制混凝土(Precast Concrete,PC)构件碳排放及影响因素,并简化其计算过程,利用过程清单分析法建立生产阶段PC构件碳排放计算公式,立足于实际生产对叠合板、预应力叠合板等5种PC构件在生产阶段的碳排放进行计算与对比分析,进而建立相关数据集。基于6个PC构件的基本特征建立了6种不同的机器学习模型,通过评价指标对模型性能进行全面比较。研究结果显示:5种构件的碳排放量主要来自建材生产,其中叠合板的单位体积碳排放量最高;各机器学习模型可以较好地预测PC构件生产阶段碳排放,其中极端梯度提升模型(eXtreme Gradient Boosting,XGBoost)表现最佳,在测试集上的R^(2)为0.966。研究结果可为PC构件设计与生产制定低碳策略提供一定的理论参考,并为预测PC构件生产阶段碳排放提供一种较为简便的方法。

Experimental validation of horizontal joints in an innovative totally precast shear wall system

To investigate the feasibility and seismic performance of the horizontal joints in an innovative precast shear wall system, two test walls were fabricated, and the monotonic and cyclic loading tests were performed on the two test walls, respectively. Then, the lateral load-top displacement curves, load beating capacity, ductility, lateral stiffness, strains of steel bars, strain distribution on the connecting steel frame （CSF）, and relative slippages between the CSF and embedded limbic steel frame （ELSF） were discussed in detail. The test results show that the load bearing capacity and ductility of the test wall are both favorable with a displacement ductility factor of more than 3.7. The normal and shear stresses in the CSF except for the compression end are far smaller than the yield stresses throughout the test procedure. Certain slippages of about 1.13 mm occurs between the CSF and ELSF on the compression side of the test wall, while almost no slippages occurs on the tension side. The seismic performance of the test wall is favorable and the new-type scheme of the horizontal joints is both feasible and reliable.

螺栓钢板连接预制混凝土轴压性能及承载力计算公式

预制混凝土墙板结合夹心保温技术可大幅提升墙体的保温隔热性,提高建造速度和节能效率。本文设计了螺栓钢板拼接预制混凝土夹心墙板试件,开展试件的轴向压力荷载试验,研究其轴压性能,提出了考虑螺栓钢板拼接影响下的墙板轴心受压极限承载力计算公式。试验结果表明:夹心墙板破坏模式主要为螺栓钢板节点上方以及墙趾两端混凝土的压溃,混凝土面板与夹心保温层在墙体底部轻微分层,墙体侧面出现较大竖向裂缝。将试件的试验轴向荷载承载力与本文提出的公式及现有的公式进行了对比,结果表明:国内现有公式计算值与试验值的差值百分比为5%,国外现有计算公式与试验值的差值百分比为45.7%~77.2%,然而本文提出的公式与试验值差值百分比仅为0.4%。国外现有的公式非常保守,本文提出的公式能够准确预测此种螺栓连接墙板的轴向承载力。在试验研究基础上,考虑了长细比、墙体厚度、连接件布置、混凝土边肋等参数,进一步建立有限元模型验证本文提出的公式。分析结果表明:数值模型的计算结果与本文提出的计算公式误差在–8.05%~2.65%之内,国内现有公式和国外现有公式与计算值误差分别在–2.25%~8.58%和41.61%~78.41%范围内,本文公式预测结果较为准确。最后,分析了各个参数对螺栓钢板拼接预制混凝土夹心墙板轴向承载能力的影响,发现墙板的配筋率对极限承载力无明显影响;合理布置GFRP连接件、设置竖向混凝土肋、减小墙板长细比和增加混凝土板厚度可以提高墙体承载性能。

Influence of Steel and Carbon Fiber Reinforcement Bars on Seismic Performance of Precast Segmental Bridge Columns

为了得到快速施工和利用新材料的预制节段桥墩设计方法，研究了部分钢筋替换为碳纤维筋时预制节段桥墩的水平承载力和破坏等级．首先通过与拟静力试验结果的比较证明了仿真分析的正确性，然后研究了部分普通钢筋替换为碳纤维筋，对拟静力循环荷载和地震地面运动分别作用时预制节段桥墩响应的影响．结果表明：碳纤维筋能提高桥墩水平承载力，增大有效刚度，降低等效粘滞阻尼比和滞回能量耗散．地震时程计算表明：部分普通钢筋替换为碳纤维筋时，使得预制节段桥墩在较强烈地震底面运动下不倒塌．利用绝对能量法分析了桥墩在地震地面运动下的能量吸收和耗散情况，并主要研究了4种桥墩试件在3种不同地震地面运动作用下的输入能量和滞回能量耗散，结果是随着桥墩输入地震能量的增大滞回能量耗散增长缓慢．

螺栓连接装配式墙板结构连接节点本构模型及体系建模方法

螺栓连接装配式墙板结构体系具有建造快速、施工便捷、连接可靠、可拆卸和可修复等优势,适合低多层乡村住宅建筑,近年来工程应用逐渐增多。该体系预制墙板之间采用离散的干式螺栓连接,受力时接缝处产生滑移变形,与传统的现浇剪力墙结构或湿法连接的剪力墙结构存在本质区别,为了分析结构体系的整体性,建立适合该结构体系的“非等同现浇”的抗震设计方法具有重要意义。本文结合已进行的螺栓连接节点轴向拉伸试验和剪切试验,提出螺栓连接节点拉伸和剪切的本构模型。在此基础上,将单个螺栓连接节点简化为3个平动自由度(x、y、z)的非线性弹簧,模拟连接节点的力学行为,建立简化计算模型。借助螺栓连接预制墙板的拟静力试验结果验证了螺栓连接节点简化模型的有效性,显示可用于分析结构体系的抗震性能。基于节点简化模型,依托Midas Gen软件,提出了螺栓连接装配式墙板结构体系的建模方法。以实际工程为例,建立了该结构的设计模型,并进行在小震、中震作用下的弹性分析及大震作用下的弹塑性时程分析。结果表明:在各地震工况下,螺栓连接装配式墙板结构体系侧向位移较小,层间位移角分别小于弹性位移角限值的1/1200和弹塑性层间位移角限值的1/120,符合规范要求,螺栓连接节点承载力满足抗震需求,墙板角部混凝土没有被压溃,说明螺栓连接装配式墙板结构体系抗震性能优越。研究成果可为螺栓连接装配式墙板结构体系的工程建设提供设计依据,为该新型结构体系的推广奠定理论基础。

强震区装配式和现浇地铁车站结构地震响应对比研究

以往的地下结构抗震研究大多是针对现浇结构开展的,而装配式结构由独立的预制构件拼装而成,从根本上区别于传统整体现浇结构,已有研究得到的认识对其适用性尚不明确,这极大地限制了装配式地下结构在强震区的推广与应用。该文以实际工程为背景,开展了全装配式和同型现浇车站结构的三维非线性有限元时程分析,对比了结构在八度区设防、罕遇和极罕遇地震下的变形、内力和损伤等响应。结果表明:装配式和现浇车站结构整体的地震变形差异不大,但柔性装配式车站结构榫槽节点可产生张开变形。设防和罕遇地震下,节点张开有利于结构减震,装配式车站结构的损伤小于现浇结构;而在极罕遇地震下,节点张开变大,榫槽、榫头和构件边缘的部分区域损伤集中,装配式和现浇结构地震响应产生了较大差异,但因应变幅值有限且损伤范围较小,此时全装配式与现浇车站结构整体的损伤程度基本相当。

高铁预制箱梁桁架式收面装置快速施工技术研究

随着国内工程施工水平的不断发展,高速铁路箱梁预制施工技术及施工组织已基本成熟,宜兴铁路夷陵制梁场通过对制梁工序进行深入研究分析,研究了桁架式收面装置预制箱梁快速施工技术。该技术满足预制箱梁收面要求,所需人工少,与传统收面工艺相比,本收面装置设备轻便,智能化程度高,能实现减员、提高功效、降低劳动强度和施工成本最节约的目的。从施工技术上进行了创新,在宜兴铁路夷陵制梁场得到了推广应用,也给其它类似大中型制梁场提供了有力的技术支持和借鉴。

JC/T 934-2023《预制钢筋混凝土方桩》标准解读

为便于JC/T 934—2023《预制钢筋混凝土方桩》的使用方准确理解标准条款的具体含义,正确贯彻实施标准条款的具体要求和规定,简述了该标准的编制背景、编制目的和意义,解释说明了标准条文的具体内容,并指出了标准实施过程中应注意的事项。

荆荆铁路大型预制梁生产测量技术

新建荆门至荆州铁路为双线高速铁路,时速350km/h,其与襄荆宜铁路、规划建设的荆岳铁路一起,在湖北省中部地区形成一条南北大通道;其中荆荆3标预制简支箱梁538孔,梁场预制场设置制梁台座10个,存梁台座59个,其是荆荆铁路线上的大型预制梁场。为确保梁场能够快速取证并形成规模生产是施工的重难点,经工艺技术研究,并结合现场实践经验提炼总结,采取一系列测量技术措施,尤其是发明了可循环使用的简支梁跨度测量装置,辅助梁体上拱高精测量的稳定装置及顶板厚度、底板厚度测量新方法;通过新型装置及方法助力制梁场在高效快速、高质量、省成本的情况下,保证了预制梁场快速形成流水式规模生产,为全线铺轨工期提供了保障。

Development of a new connection for precast concrete walls subjected to cyclic loading

The Industrialized Building System （IBS） was recently introduced to minimize the time and cost of project construction. Accordingly, ensuring the integration of the connection of precast components in IBS structures is an important factor that ensures stability of buildings subjected to dynamic loads from earthquakes, vehicles, and machineries. However, structural engineers still lack knowledge on the proper connection and detailed joints o fiBS structure construction. Therefore, this study proposes a special precast concrete wall-to-wall connection system for dynamic loads that resists multidirectional imposed loads and reduces vibration effects （PI2014701723）. This system is designed to connect two adjacent precast wall panels by using two steel U-shaped channels （i.e., male and female joints）. During casting, each joint is adapted for incorporation into a respective wall panel after considering the following conditions： one side of the steel channel opens into the thickness face of the panel; a U-shaped rubber is implemented between the two channels to dissipate the vibration effect; and bolts and nuts are used to create an extension between the two U-shaped male and female steel channels. The developed finite element model of the precast wall is subjected to cyclic loads to evaluate the performance of the proposed connection during an imposed dynamic load. Connection performance is then compared with conventional connections based on the energy dissipation, stress, deformation, and concrete damage in the plastic range. The proposed precast connection is capable of exceeding the energy absorption of precast walls subjected to dynamic load, thereby improving its resistance behavior in all principal directions.

Cyclic performance and simplified pushover analyses of precast segmental concrete bridge columns with circular section

In recent years, precast segmental concrete bridge columns became prevalent because of the benefits of accelerated construction, low environmental impact, high quality and low life cycle costs. The lack of a detailed configuration and appropriate design procedure to ensure a comparable performance with monolithic construction has impeded this structural system from being widely used in areas of high seismicity. In this study, precast segmental bridge column cyclic loading tests were conducted to investigate the performance of unbonded post-tensioned segmental bridge columns. One monolithic and two precast segmental columns were tested. The preeast segmental column exhibited minor damage and small residual displacement after the maximum 7% cyclic drift; energy dissipation （ED） can be enhanced byadding ED bars. The experimental results were modeled by a simplified pushover method （SPOM）, as well as a fiber model （FIBM） finite element method. Forty-five cases of columns with different aspect ratios, axial load ratios and ED bar ratios were analyzed with the SPOM and FIBM, respectively. Using these parametric results, a simplified design method was suggested by regressive analysis. Satisfactory correlation was found between the experimental results and the simplified design method for preeast segmental columns with different design parameters.