波浪力对深水桥墩结构在地震和冰荷载作用下的响应影响分析

考虑到波浪力对深水桥墩地震响应和冰振响应的影响,本文基于非线性Morision方程,同时考虑附加质量效应和流固耦合效应,通过建立深水桥墩结构有限元分析模型及动力平衡方程,对深水桥墩结构进行了波浪、冰荷载、地震3种环境激励荷载单独作用下,以及不同组合形式共同作用下的数值分析;进而对计算结果进行了比较,探讨了动水压力对深水桥墩结构响应的影响程度,可为今后深水桥墩抗震以及抗冰设计提供一定的借鉴和参考。     

处于海洋环境的桩柱在瑞利波作用下的响应

本文以一海洋深水环境桩柱为例,考虑到海洋地基为两相饱和土介质,基于Biot两相饱和多孔介质理论,通过数值算例分析了饱和介质中瑞利波加速度、位移分布规律并与单相弹性介质地基条件下进行了对比,结果表明,瑞利波主要作用于地表附近且振动幅度随深度衰减很快,饱和地基下的瑞利波影响深度要大于单相弹性地基,在瑞利波地震作用下,考虑两相饱和介质下的桩柱位移响应大于单相弹性介质地基。并且由于桩柱处海洋深水环境,本文对环境水体对桩柱振动响应的影响进行了研究,结果表明,流固耦合效应可明显降低桩柱运动响应,在海洋深水环境地震响应分析时,有必要考虑饱和地基以及流固耦合效应对桩柱运动响应的影响。     

地震与水平环境荷载下风电单桩基础动力响应分析

为探究复杂环境荷载和地震共同作用下饱和场地中单桩基础的动力响应,文中采用有限差分整体时程数值分析方法,对饱和砂土场地中海上风电单桩基础在水平环境荷载与地震荷载联合作用下的动力响应进行了非线性分析。通过与离心机试验结果对比,验证了所建立的数值分析模型的合理性与有效性。基于数值计算结果,对地震单独作用和水平环境荷载-地震联合作用2种工况下海上风电单桩基础的动力响应规律差异进行探讨,并进一步分析了上部结构质量、埋深等对联合荷载作用下单桩基础动力响应的影响。研究结果表明,在海上风电单桩基础结构设计中应考虑水平环境荷载与地震联合作用的影响,且应将桩的埋深作为重要设计参数加以考虑,而结构质量对联合荷载作用下海上风电单桩基础结构体系响应的影响较小。     

考虑流固耦合的水中结构物地震反应方法

基于运动控制体的雷诺输运定理,采用任意拉格朗日-欧拉描述推导控制流体运动的Navier-Stokes方程;提出考虑流固耦合效应的水中结构物地震反应计算方法,并以水中垂直板的地震反应为例,阐明流固耦合体系的求解方法.分析地震动频率和水深对场地土-结构-流水构成的流固耦合系统动力反应的影响,结果表明:采用不可压缩流算法的Navier-Stokes方程能够合理模拟流场的位形变化,并保证流固耦合计算的收敛;考虑流固耦合作用使得结构地震反应幅值明显增大,并使频谱特性发生改变;水深对流固耦合效应的影响较大,并具有明显的非线性特征.     

地震-列车移动荷载耦合作用下高铁路基振动特性研究

基于轨道结构-路基-地基动力相互作用理论,建立考虑地震-列车移动荷载耦合输入的轨道结构-路基-地基动力学模型,研究高速铁路路基及轨道在耦合荷载作用下的振动响应问题。通过编制DLOAD子程序并与ABAQUS有限元计算程序联立,实现地震荷载与列车移动荷载耦合作用的施加,以高速铁路桩承式路基及自由式路基为研究对象,对地震-列车移动荷载耦合作用下两种路基系统的动力响应进行数值计算并比较两者的振动响应差异。结果表明,耦合荷载对桩承式路基动力响应影响显著,该荷载作用下桩承式路基会发生共振现象,使得桩承式路基中轨道和路基振动位移幅值均大于自由式路基的振动位移幅值;桩承式路基不会影响路基系统的振动频率,但会改变路基系统的振动大小,桩承式路基中轨道X方向加速度、路肩边及路基坡脚处的竖向加速度分别减小6.2%、50%、28.6%。     

地震荷载下考虑管内有压流体的PCCP耦合动力分析

PCCP（预应力钢筒混凝土管）因其优良性能被广泛应用于我国水利水电及市政给排水等生命线工程的建设中。现有研究多为静力分析,少有学者对PCCP管内流体的动力相互作用开展研究。本文利用ABAQUS对PCCP结构及其管内流体在地震荷载下的双向流固耦合作用进行分析,开展了考虑流固耦合与未耦合条件下管道各个结构层的动力响应。进一步计算了考虑内水压力、地震荷载大小和管内水流速度等条件变化对管道受力变形特性的影响。结果表明:流固耦合模型能更加真实地还原和模拟在役PCCP的工作状态;内水压力显著影响管道的受力状态,PCCP结构随着输水压力的增大逐步由受压状态向受拉过渡,且受拉区域和拉应力峰值逐渐增大;管内水流速对应力场影响很微弱。     

波浪地震联合作用下砂质海床沉管隧道动力响应分析

对于埋置于海床表层的沉管隧道,波浪作用是不容忽视的常遇海洋环境因素。不同于陆域地下结构,海底沉管隧道地震反应分析和安全评价应考虑波浪的联合作用。基于Biot完全耦合的动力有效应力分析方法,对波浪与地震联合作用下砂质海床-隧道之间的动力相互作用特性进行研究。研究结果表明,相较仅有地震作用,波浪荷载加速了沉管隧道周围海床地震残余超孔压的增长和渐进液化进程,增大了沉管隧道上浮量;波浪与地震联合作用对应的β谱谱值更大,且卓越反应周期向长周期偏移;波浪对海床地震动的影响深度有限,仅对海床地表以下15 m范围内的地震动有放大效应。忽略波浪环境作用对砂质海床场地设计地震动参数的影响,对于沉管隧道抗震设计是偏于不安全的。     

考虑流-固耦合梁式矩形渡槽横向地震响应研究

根据豪斯纳尔（Housner）理论, 建立了考虑槽内水体与渡槽槽身流-固耦合的横向地震响应计算模型,分析了槽身断面深宽比变化对渡槽结构抗震的影响,并对某大型渡槽进行了多工况地震时程响应计算. 结果表明,在地震波作用下,渡槽槽内大质量水体对渡槽的横向地震响应有较大的影响, 但水体的晃荡作用有明显的TLD效应. 若将水体视为刚体, 质量全部附加到槽体上,将严重地夸大水的地震惯性力作用,且在渡槽槽身断面选择时应考虑深宽比对墩身地震响应的影响, 以减小地震力.      

LNG储罐桩基础隔震长周期地震作用效应分析

为了研究在长周期地震动作用下桩基础-隔震层的相互作用对16×104m3LNG储罐地震响应的影响,本文利用有限元分析软件ADINA进行数值仿真分析,考虑流体的微可压缩性,储液采用FCBI流体单元,输入峰值为0.2g的El Centro位移波和Tcu068位移波,对不考虑桩土不隔震、隔震和考虑桩土不隔震、隔震4种工况储罐的地震响应进行分析。结果表明:采用隔震措施后可以有效降低长短周期地震动作用下储罐的地震响应,但是短周期地震动作用下的隔震效果更为明显,长周期地震动会引起较大的晃动波高。此外,非隔震情况下考虑桩土效应后,地震响应峰值会有所降低,隔震时考虑桩土效应会加大地震响应峰值,由此说明非隔震时不考虑桩土效应的设计方法偏于保守,隔震时考虑桩土效应是安全的设计方法。     

近地空中爆炸作用下钢框架结构冲击响应

采用多物质欧拉与拉格朗日耦合算法,对框架结构和混凝土地面采用Lagrange单元、空气和炸药采用多物质ALE单元,建立流固耦合有限元模型,对一个五层的钢框架结构在近地爆炸作用下冲击压力波的传播过程、结构冲击响应和变形以及破坏过程进行了数值模拟.数值模拟分析结果表明,拉格朗日-欧拉耦合算法较好地模拟了爆炸冲击波在介质中的传播和作用在结构上的爆炸荷载效应.在爆炸近区,空气爆炸冲击波的衰减速率快;爆炸产生强烈的冲击波首先使钢框架结构正面的柱和梁柱节点区产生很大的塑性变形,钢框架柱在发生爆炸的瞬间失去承载能力,最终导致建筑物整体倒塌.考虑结构变形和流体荷载间的相互影响可以较真实地模拟结构在爆炸荷载作用下的连续倒塌过程,为研究结构在爆炸荷载作用下的连续倒塌提供了有效手段.     

Torsionally coupled dynamic performance analysis of asymmetric offshore platforms subjected to wave and earthquake loadings

The dynamic equations of motion of asymmetric offshore platforms under three different environmental conditions:seismic action,wave action and their combination are established in this paper. In establishing these motion equations,three typical eccentricity types including mass eccentricity,rigidity eccentricity and their combination were considered,as are eccentricities that occur un-idirectionally and bi-directionally. The effects of the eccentricity type,the dynamic characteristics and the environmental conditions on the torsional coupling response of platforms are investigated and compared. An effort has also been made to analyze the inffluence of accidental eccentricity on asymmetric platforms with different eccentricity in two horizontally orthogonal directions. The results are given in terms of non-dimensional parameters,accounting for the uncoupled torsional to lateral frequency ratio. Numerical results reveal that the eccentricity type has a great inffluence on the torsionally coupled response under different environmental conditions. Therefore,it is necessary to consider the combination of earthquake and wave action in the seismic response analysis of some offshore platforms.     

Winkler model for dynamic response of composite caisson–piles foundations: Seismic response

A simplified method with a dynamic Winkler model to study the seismic response of composite caisson–piles foundations (CCPF¹) is developed. Firstly, with the dynamic Winkler model, the kinematic response of the CCPF subjected to vertically propagating seismic S-wave is analyzed by coupling the responses of caisson part and pile part. Secondly, a simplified model for the foundation–structure system is created with the structure simplified as a lumped mass connected to the foundation with an elastic column, and through the Fast Fourier Transformation (FFT) this model is enabled to solve transient seismic problems. Thirdly, the proposed method for the seismic response of CCPF-structure systems is verified by comparison against 3D dynamic finite element simulation, in which the Domain Reduction Method (DRM²) is utilized. Lastly, the mechanism and significance of adding piles in improving the earthquake resistance of the foundation and structure is analyzed through an example with different soil conditions. Discovered in this study is that adding piles under the caisson is an efficient way to increase seismic resistant capability of the soil–foundation–structure system, and the main mechanism of that is the elimination of the pseudo-resonance.     

考虑波流影响的深水群桩基础桥墩地震反应分析

用基于ABAQUS软件为平台的平行计算技术,对考虑波流影响的地基土-群桩-桥墩体系进行三维非线性地震反应数值模拟,土体和墩台以八节点等参单元离散,桩以梁单元离散,采用土体黏塑性记忆型嵌套面本构模型描述土的动力特性,采用动力塑性损伤模型描述混凝土的动力特性;基于Morison公式,采用Stokes五阶波浪理论描述表面波流,波浪力以分布力的形式施加于桥墩之上,分析了考虑和不考虑波流作用时不同地震动作用下群桩基础桥墩的地震反应特性,结果表明:波流作用对桩体加速度反应的影响很小,但对桩体相对位移和弯矩的影响显著,波流作用使桩体弯矩和顺流向的相对位移增大、逆流向的相对位移减小,其影响幅度随流速的增大而增大,波流作用与输入地震动特性密切相关。考虑波流作用对深水大型桥梁群桩基础桥墩地震反应的影响是有必要的。     

基坑桩地震冲击下的受力分析模型仿真

当前利用改进动力Winkler模型分析基坑桩地震冲击下的受力情况,不能预防应力波的反射作用,导致其分析结果具有不全面、准确性低的缺点。本论述提出有限元数值模拟的基坑桩地震冲击下的受力分析模型,通过基坑桩小应变模型描述不同应力状态下基坑桩模量的变化,采用有限元数值模拟方法结合基坑桩小应变模型对基坑桩有限元模型进行塑造。在约束基坑桩有限元模型边界条件时,模型选择黏性阻尼器的吸收边界,使模型边界上的应力波不会遭到折射,避免运算结果出现误差。利用Newmark方法对基坑桩有限元模型进行动力时程分析,实现基坑桩在不同应力状态下的受力分析。实验结果证明:所提模型能够有效、准确的对地震冲击下的基坑应力分布、基坑桩身弯曲度、变形位移以及桩体水平位移差值对比等进行全面的分析。     

Centrifuge modelling of raked piles

Inclined piles are prohibited by many codes in seismic areas. Nevertheless the battered effect has not yet been clarified because very few data are available. The present work is a comparison, at reduced scale in the centrifuge, of the response of two simplified pile groups: a 1 × 2 vertical piles and 1 × 2 pile group with one inclined pile. Two configurations are considered: end-bearing and floating pile group, both with pile heads rigidly fixed with a massive cap. First, repeatability tests under horizontal cyclic loading were performed on both floating pile groups. Secondly, repeated horizontal impact tests were performed on both end-bearing pile groups. These impact tests, which highlight the influence of inclined piles on the inertial response of a group, are a first step for the more complex analysis of the performance of such groups under seismic loads where inertial and kinematic interactions are combined. The first part of this work revealed the influence of sand structure around the inclined pile tip on the repeatability of the tests performed on floating pile groups. The second part highlighted differences in the dynamic response between the two end-bearing pile groups through measurements of the pile cap acceleration, the bending moment profile and the axial load in the piles.     

Coupling action of rainfall and vehicle loads impact on the stability of loess slopes based on the iso-water content layer

To clarify the changes in slope stability of loess slopes under the coupling action of rainfall and vehicle loads. Experiments with different water contents under different environmental conditions were carried out indoors, and the relationship function between water content and shear strength parameters was obtained; Secondly, based on Geostudio, an equivalent layered calculation model of water content-strength parameters of loess slope was established, the variation law of soil sample matrix suction with volumetric water content was measured by volumetric pressure plate tester. Finally, by using a combination of finite element analysis of saturated/unsaturated seepage and limit equilibrium analysis of slope stability, the SLOPE/W module in the modeling software GeoStudio is used to calculate and analyze the effects of vehicle loads, rainfall intensity, rainfall duration, and other working conditions on the stability of loess slopes, respectively. The results show that when the lane is in the middle of the slope, the vehicle load parameters have little effect on the uphill stability, but have a greater impact on the downhill; With the increase in rainfall, the change curves of the slope safety coefficient gradually overlap when the vehicle loads are four-axis,five-axis, and six-axis. This shows that when studying the change of slope safety factor under the dual influence of vehicle loads and rainfall, rainfall is the main cause of slope stability; The change rate of slope safety factor increases gradually with the increase of rainfall, and the change trends of the upper, lower and overall parts of the slope are similar.     

桩基础抗震性能的简易评价方法

桩基础的抗震性能可从承载力和变形两方面来评价.承载力可考虑地震时作用于结构上的荷载组合,多采用拟静力法进行分析,不同因素变异的影响可用概率分析或可靠度方法予以考虑.变形分析多为按承载力设计之后的校核,其中地震力和土体参数以及地质条件等因素影响可分别加以评估.本文着重阐明基于一维波动方程和概率分析的桩基抗震性能实用分析方法,并以桥梁桩基础为例进行讨论,其中考虑的关键因素为设计地震加速度、测站记录、基桩尺寸及其配筋率.研究表明,当土层液化可忽略时最大弯矩会发生在桩顶,故增加桩顶延性可有效提升桩基础的抗震性能.     

Flexible support of a pile embedded in unsaturated soil under Rayleigh waves

Under the action of Rayleigh waves, pile head is easy to rotate with a concrete pile cap, and pure fixed-head condition is rarely achieved, which is a common phenomenon for it usually occurs on the precast piles with insufficient anchorage. In addition, the propagation characteristics of Rayleigh wave have been changed significantly due to the existence of capillary pressure and the coupling between phases in unsaturated soil, which significantly affects the pile-soil interaction. In order to study the above problems, a coupled vibration model of unsaturated soil–pile system subjected to Rayleigh waves is established on the basis that the pile cap is equivalent to a rigid mass block. Meanwhile, the soil constitution is simplified to linear-elastic and small deformations are assumed to occur during the vibration phase of soil–pile system. Then, the horizontal dynamic response of a homogeneous free-field unsaturated soil caused by propagating Rayleigh waves is obtained by using operator decomposition theory and variable separation method. The dynamic equilibrium equation of a pile is established by using the dynamic Winkler model and the Timoshenko beam theory, and the analytical solutions of the horizontal displacement, rotation angle, bending moment and shear force of pile body are derived according to the boundary conditions of flexible constraint of pile top. Based on the present solutions, the rationality of the proposed model is verified by comparing with the previous research results. Through parametric study, the influence of rotational stiffness and yield bending moment of pile top on the horizontal dynamic characteristics of Rayleigh waves induced pile is investigated in detailed. The analysis results can be utilized for the seismic design of pile foundation under Rayleigh waves.