城市桥梁地震反应中防碰撞措施分析

在地震过程中城市桥梁上部相邻结构的碰撞,不仅使结构受损,甚至发生倒塌,这是地震工程研究领域一个关键而又难以解决的问题。给出各国规范对于落梁防止装置的规定,通过对工程实践中常采用的防碰撞措施进行分析,改进了常用的拉杆装置、落梁防止装置的设计方法,给出了简化的计算方法,可以更好的应用到工程实践中。     

大跨屋盖结构的竖向MTMD减震控制

建立了屋盖结构竖向MTMD的振动控制方程,根据屋盖结构振型密集的动力特性提出了三种MTMD设计思路。结合某工程实例讨论了屋盖结构MTMD的设计步骤和减震效果,结果表明MTMD对不同的地震波都有一定程度的减震效果,表现出良好的鲁棒性,响应峰值降低10%～40%;地震波对MTMD控制效果影响较大,应根据场地条件和结构特点选择合适的地震波进行分析。     

非规则梁桥伸缩缝处的碰撞对地震反应的影响

针对非规则梁桥在地震作用下伸缩缝处的碰撞现象,在建立考虑双边碰撞效应的简化动力分析模型的基础上,采用非线性地震反应时程分析方法,研究了纵向地震作用下非规则梁桥伸缩缝处的碰撞效应,并分析比较了双边碰撞与单边碰撞对桥梁结构位移的影响,研究结果对同类型的非规则梁桥的抗震设计具有一定的参考价值。     

Analytical expressions for preliminary design of dissipative bracing systems in steel frames

In this paper a direct displacement-based design (DDBD) method for seismic design of steel frames equipped with dissipative braces is proposed. Attention is focused on concentric braced steel frames with pinned beam-to-column joints in which the bracing system (with viscoelastic or elastoplastic dissipative devices) is the main seismic resistant component. The proposed design method uses an equivalent continuous model where flexural deformability and shear deformability are related respectively to columns and diagonals of the bracing system. In this way, analytical expressions of the required flexural and shear stiffness distributions are obtained. These expressions are quite simple and can be conveniently used in preliminary design of dissipative diagonal braces and columns. Examples are shown for steel frames with dissipative braces based on elastomeric dampers (viscoelastic devices) and steel frames with buckling-restrained braces (elastoplastic devices). Results of time history analyses are illustrated and discussed in order to evaluate the effectiveness of the proposed DDBD procedure.     

高墩桥地震碰撞效应初步研究

针对我国西部山区典型的高墩桥,建立了某桥的纤维单元模型;在各伸缩缝处梁间设置多个间隙单元模拟碰撞,采用非线性时程反应分析方法对模型进行运算,通过比较和分析计算结果,探讨了该高墩桥在不同地震波输入下的碰撞反应以及碰撞对结构的影响。分析结果表明,地震波的频谱特性与结构各部分的固有频率是影响结构碰撞反应的重要因素,碰撞在某种程度上对部分结构是有利的。     

地震作用下西部地区连续梁桥的落梁研究

以西部地区某连续梁桥为例,分析了E1,E2两个设计水准地震作用下连梁装置的抗震性能。研究发现,通过在连续梁梁端设置连梁装置,可以显著降低梁端相对位移,有效减小结构关键截面的地震内力,建议在高烈度区采用连梁装置,以提高连续梁桥的抗震性能。     

Seismic rehabilitation of historical masonry buildings

Masonry buildings frequently present unsatisfactory behavior under seismic activity, due to the poor resistance of the masonry walls to tensile stresses and to the presence of flexible wooden floors. This paper presents a comparative study of the performance of different seismic retrofitting techniques, implemented in a model of an existing masonry building. The first part of the study considers the testing of different methodologies to strengthen the building floors, to enable them to behave as stiff diaphragms. In the second stage, the seismic protection of the building is studied with these different solutions: insertion of concrete walls, the use of a base isolation solution, and the implementation of viscous dampers. A particular analysis is made on the use of viscous dampers since it improves the seismic behavior with little interference.     

Seismic performance of benchmark highway bridge installed with piezoelectric friction dampers

Dynamic response of the benchmark highway bridge installed with semi-active piezoelectric friction dampers (PFDs) is investigated under six bidirectional earthquake ground motions. PFD utilises the response of the structure to develop control actions by adjusting frictional damping characteristics of the system. Conventional friction dampers abruptly fluctuate between stick-slip states. On the other hand, PFDs change the friction force continuously and smoothly. The study is based on the simplified lumped mass finite-element model of the 91/5 highway bridge, located in Southern California. The parameters affecting the performance of PFDs are gain factors, coefficient of friction and the preload on damper. Exhaustive studies are carried out to determine the most optimum values of these parameters. Eight dampers are installed at each deck-end and abutment junction (phase I). Additional four dampers are installed at the centre (phase II), at the junction of bent beam and piers of the bridge. In each case, the response of the bridge is compared with the corresponding uncontrolled case and that controlled by the alternate sample semi-active control strategy, using magnetorheological (MR) dampers. It is concluded that with the installation of PFDs, the seismic response of the bridge under near-fault motions can be controlled significantly. The PFDs are quite effective in reducing the peak response quantities of the bridge to a level comparable to or superior to that of the MR dampers.     

Seismic performance of isolated curved steel viaducts equipped with deck unseating prevention cable restrainers

This paper presents an in-depth analysis to evaluate the efficiency of using cable restrainers connecting isolated and non-isolated spans for preventing unseating of curved steel viaducts. For this purpose, the overall three-dimensional non-linear bridge response is examined in detail under the action of strong earthquake ground motions. The expected seismic vulnerability of bridge structures with curved deck geometries has been demonstrated, providing a refined estimation of seismic demands on most critical bridge components. The advantage of using a precise three-dimensional model has revealed the concentration of large seismic forces on specific steel bearing supports and cable restrainer units that greatly increase their failure possibility. Moreover, the unbalanced distribution of pounding forces found across the expansion joint is able to cause local damage to colliding girders and transmit high impact forces to bearing supports. In general, restrainers perform effectively to minimize the possibility of deck unseating and reduce the pounding forces at the expansion joint. Special attention should be paid to the non-linear bridge dynamic response in order to avoid failure of restrainers and ensure the adequate proportioning of the cables according to the characteristics of isolation bearings.     

地震作用下横向碰撞对连续梁桥地震反应的影响

地震作用下,结构的碰撞问题被认为是影响结构地震反应和结构抗震性能的一个重要因素,碰撞是一种非常复杂的非线性问题,其影响因素很多.采用非线性时程地震反应分析方法,探讨了横向地震作用下梁体与抗震挡块间的碰撞对连续梁桥地震反应的影响,结果表明:梁体与抗震挡块间的碰撞不仅产生很大的撞击力.还会导致桥墩的地震需求增大,对结构抗震不利.通过参数分析表明接触单元刚度、初始间隙以及墩高等参数对碰撞效应有很大影响.     

双柱式简支-桥面连续梁桥横向地震碰撞和防撞措施分析

地震作用下,结构的碰撞问题是影响结构地震反应和抗震性能的一个重要因素。本文针对简支-桥面连续梁桥在横桥向地震作用下主梁与抗震挡块间的碰撞行为,建立了考虑支座非线性、墩柱弹塑性以及桩土相互作用的碰撞模型。在此基础上分析了主梁与抗震挡块间的碰撞效应,探讨了减轻碰撞的措施和方法,并比较了两种措施的防撞效果。结果表明:主梁与抗震挡块间的碰撞不仅产生巨大的碰撞力,还会增大桥墩的地震需求,对结构抗震不利;在抗震挡块内侧安装橡胶缓冲垫和采用铅芯橡胶支座均能减小碰撞力、墩顶底的剪力和塑性转角,但后者的防撞效果更好。     

钢桥疲劳研究关键技术分析

针对当今大跨度钢桥的建设和既有钢桥的使用状况进行分析,结合工程建设和运营管理中涉及疲劳的重点研究领域作了阐述,对钢桥疲劳研究成果的应用作了归纳,并展望了钢桥疲劳研究的前景。     

相邻结构碰撞研究进展

地震引起的相邻结构碰撞会导致结构局部破坏或倒塌,造成人员伤亡和财产损失。文章将相邻结构碰撞模型分为经典碰撞模型、接触单元法碰撞力模型和有限元碰撞模型,并对研究现状分别进行介绍,梳理相邻结构设计参数对结构碰撞响应的影响,归纳最小防震缝宽度对相邻结构的影响及缝宽的计算方法,总结相邻结构防止碰撞的研究,分析相邻结构碰撞研究中存在的问题,提出今后应研究的方向。     

大跨度双塔悬索桥在地震动行波激励下的响应规律研究

本文以一座主跨850m的大跨双塔悬索桥为工程背景,采用时程分析法研究了行波效应大跨双塔悬索桥地震响应的影响。通过建立三维有限元分析模型,在分析了大跨度双塔地锚式悬索桥动力特性及一致激励下地震响应规律的基础上,进一步探讨了行波效应对大跨双塔地锚式悬索桥地震响应的影响规律。分析结果表明:地震波纵向行波作用下,主塔的地震响应随着视波速的减小而先减小后增大;主梁的竖向振动则较一致激励下显著增大;主缆及吊索轴力则受地震动行波效应的影响不大。     

东日本大地震后的日本公路桥梁抗震设计

为了解决高烈度条件下公路桥梁的抗震设计问题,参考与借鉴日本的工程实践经验,对日本规范的发展变迁进行研究。就日本规范中地震水平设计加速度与我国规范进行对比,发现日本罕遇地震作用强度明显高于我国,上世纪90年代以来,日本主要是针对罕遇地震的设计做了一系列改进,日本规范在罕遇地震时坚硬场地土上采用更大的设计加速度,这使弹塑性动力学分析成为罕遇地震条件下进行抗震设计所采用的最主要分析计算手段。希望通过本文唤起对罕遇地震设计的进一步重视。     

桥梁中抗震限位装置设计方法的研究

为防止桥梁上部结构在地震中发生落梁破坏,通常在伸缩缝处安装限位装置。在调查影响伸缩缝处相邻梁体相对位移因素的基础上,根据线性化模型提出一种限位装置设计方法。该方法既考虑了相邻桥跨不同向振动的动力特性,又考虑了相邻梁体间碰撞对相对位移的影响。运用替代结构法考虑墩柱的弹塑性,使用考虑碰撞效应的相对位移反应谱考虑碰撞对相对位移的影响。通过参数研究对提出的限位装置设计方法的可靠性进行验证,并通过与已有的限位装置设计方法相比,评估了所提出的限位装置设计方法的限位效果。与已有的设计方法相比,本文提出的限位装置设计方法与非线性时程分析结果的相关性更好。     

某双塔斜拉桥抗震性能研究

以某大跨双塔斜拉桥为例,建立了主桥和引桥一体的动力模型,通过反应谱和非线性时程方法,分析了其地震响应,研究表明该桥满足抗震性能目标,纵向设置粘滞阻尼器后能显著的减少纵向地震反应内力。     

刚架拱桥大小节点的安全性分析

本文根据刚架拱桥结构的受力特性和构件本身存在的缺陷,通过取出MIDAS/Civil建立的全桥模型计算出来的大、小节点处的最不利内力组合,施加于ANSYS模型中,对刚架拱桥大小节点处的破坏进行安全分析,计算分析发现大、小节点在该内力作用下上缘均出现了较大的应力,分析结果为大小节点的加固提供参考。     

芜湖长江大桥钢梁整体节点的制造

介绍了芜湖长江大桥概况,整体节点弦杆构造、制造技术难点、制造工艺要点及措施．