深尾水消力池非完全宽尾墩消能试验研究

为解决下游深尾水工程中常规底流式消力池内由于消能紊动不足引起出池水流二次水跃、冲刷下游天然河床等一系列工程难题,结合物理模型和数值模拟对比研究平尾墩、常规宽尾墩以及非完全宽尾墩下游消力池内流场差异。研究结果表明:非完全宽尾墩利用平尾墩闸室与相邻宽尾墩闸室入池水流横向水位落差和纵向流速梯度,迫使雍高射流入池水流呈弧形横向扩散、碰撞,显著增强剪切紊动,促使消力池上游区域形成由底至表不断发展壮大的立轴旋滚,提升消力池内能量紊动耗散、降低出池水流流速,完全解决常规底流式消力池中易出现的二次水跃、消能不充分等问题。     

Enhancing PIV image and fractal descriptor for velocity and shear stresses propagation around a circular pier

In this study,the fractal dimensions of velocity fluctuations and the Reynolds shear stresses propagation for flow around a circular bridge pier are presented.In the study reported herein,the fractal dimension of velocity fluctuations(u′,v′,w′) and the Reynolds shear stresses(u′v′ and u′w′) of flow around a bridge pier were computed using a Fractal Interpolation Function(FIF) algorithm.The velocity fluctuations of flow along a horizontal plane above the bed were measured using Acoustic Doppler Velocity meter(ADV)and Particle Image Velocimetry(P1V).The PIV is a powerful technique which enables us to attain high resolution spatial and temporal information of turbulent flow using instantaneous time snapshots.In this study,PIV was used for detection of high resolution fractal scaling around a bridge pier.The results showed that the fractal dimension of flow fluctuated significantly in the longitudinal and transverse directions in the vicinity of the pier.It was also found that the fractal dimension of velocity fluctuations and shear stresses increased rapidly at vicinity of pier at downstream whereas it remained approximately unchanged far downstream of the pier.The higher value of fractal dimension was found at a distance equal to one times of the pier diameter in the back of the pier.Furthermore,the average fractal dimension for the streamwise and transverse velocity fluctuations decreased from the centreline to the side wall of the flume.Finally,the results from ADV measurement were consistent with the result from PIV,therefore,the ADV enables to detect turbulent characteristics of flow around a circular bridge pier.     

钢筋混凝土箱型高墩双向拟静力试验研究

随着高墩大跨桥梁的广泛应用,其抗震问题也越来越突出。本文主要考虑轴压比、长细比的影响,进行了6个钢筋混凝土薄壁箱型高墩缩尺模型的双向拟静力试验,以及反复荷载作用下的非线性分析。研究表明：①钢筋混凝土薄壁箱型高墩柱在多维荷载共同作用下,主要发生典型的弯曲破坏,但剪切作用也不容忽视;②墩枉的破坏受到不同方向耦合作用的显著影响,尤其是抗弯刚度小的一侧受到的影响更大,较早就出现开裂,提前进入塑性发展阶段;③非线性有限元计算的滞回曲线、骨架曲线等与试验结果基本吻合;④建立了考虑轴压比、长细比影响的钢筋混凝土薄壁箱型高墩的双向荷载一位移恢复力模型,该模型基本能够反映钢筋混凝土薄壁箱型高墩的抗震性能,可供钢筋混凝土箱型高墩柱及高墩桥梁结构的抗震设计和动力计算参考。     

承台型式对可液化场地桥梁桩-柱墩地震响应影响振动台试验

基于相同土层结构地基条件下,分别采用低承台群桩-独柱墩与高承台群桩-独柱墩结构,完成了两次可液化场地群桩-土-桥梁结构地震反应振动台试验,据此研究了承台型式对桥梁桩-柱墩地震反应的影响。研究表明,与高承台桩相比,可液化场地中低承台桩的抗震性能更优;地震中砂层尚未液化或液化不充分时,低承台更多表现出减弱桩尤其桩上段的加速度反应的作用,相反高承台更多起到放大桩的加速度作用,而高承台桩与低承台桩的峰值应变自下而上更多表现出逐渐增大趋势;即使砂层完全液化时,低承台桩的峰值应变自下而上仍以渐增为主;与低承台桩相比,高承台桩更有助于放大墩顶加速度、位移反应,对结构体系整体稳定性产生了不良影响;虽然低承台桩未出现严重破坏,但砂层中部桩的应变却很大,液化砂土-桩运动相互作用对桩的抗震性能影响不容忽视。     

基于FENAP平台的RC高桥墩破坏过程模拟及分析

为精细模拟钢筋混凝土高桥墩在静力推覆荷载作用下的破坏过程,本文基于钢筋混凝土精细化纤维梁柱单元模型分析平台FENAP,对一实际的西部山区空心截面高桥墩进行了Pushover分析,通过对构件、截面和纤维层次的力-位移关系曲线分析,模拟了桥墩从墩底混凝土开裂、纵筋屈服到受压区混凝土压碎的完整破坏过程。并将FENAP平台与OpenSees计算结果进行对比,结果表明,FE-NAP平台可有效地模拟高墩在静力推覆荷载下的破坏过程和软化行为,具有较高的求解精度。进一步比较了不同轴压比、是否考虑约束混凝土效应及纵筋屈曲效应等因素对分析结果的影响,得出结论,轴压比和约束混凝土效应对高桥墩的破坏过程发展有较大影响,而纵筋屈曲效应影响较小,可忽略不计。     

近距离开挖卸荷条件下运营地铁高架桥墩响应研究

上海地铁12号线龙漕路车站基坑下穿运营3号线高架,施工条件受限,需要对位于基坑中间的高架桥墩进行保护以确保3号线运营安全。依托该工程,采用精细化三维数值分析、室内试验和现场实测等方法,对近距离开挖卸荷引起的高架桥墩响应进行研究。监测结果表明：软土地层高架桥墩在近距离开挖卸荷影响下均产生上抬,与数值分析结果吻合;桥墩水平位移总体上朝向卸荷一侧,但发展过程中震荡明显且位移较大,位移终值基本符合数值分析的预估值;近距离卸荷导致桥墩基础桩极限承载力有轻微的损失,但基本不会威胁高架桥的安全;长期沉降表现为半周卸荷条件下上抬可略有恢复,全周卸荷下则不会恢复。     

基础非线性对桥墩地震反应的影响

在桩基础桥墩滞回特性的模型试验基础上,提出了用Clough模型模拟基础(地基)的恢复力特性。桥墩采用Takeda恢复力模型。用强震记录与人工合成地震动作为输入对铁路简支梁桥进行了非线性地震反应分析,讨论了不同地震动输入及不同地震强度时基础非线性对桥梁地震反应的影响。研究结果表明,考虑基础的非线性一般会使墩顶位移增大,而墩底的曲率明显减小,且随着地震动强度的增加,基础的非线性影响更加明显。     

波浪作用对单柱式桥墩地震反应特性的影响

以ABAQUS有限元软件为计算平台,建立了考虑波浪作用影响的单柱式桥墩-桩-土体系非线性地震反应分析二维有限元模型,土体以四节点实体单元离散,采用土体粘塑性记忆型嵌套面本构模型描述土的动力特性;桥墩以及桩以两节点梁单元离散,采用动塑性损伤模型描述混凝土的动力特性;根据Stokes五阶波浪理论,将基于Morison公式计算所得的波浪力以分布力的形式施加于桥墩之上,比较了静水条件下和考虑波浪作用时不同地震动激励下单柱式桥墩结构的地震反应特性,结果表明:波浪作用的影响使桥墩墩身相对墩底的位移反应、桥墩墩底的剪力和弯矩反应有较明显的增大,但对桥墩墩身加速度反应的影响可忽略不计,波浪作用影响的大小与输入地震动特性有关.在单柱式桥墩的抗震设计中考虑波浪作用的影响是必要的。     

Evidence of beneficial role of inclined piles: observations and summary of numerical analyses

The behaviour under seismic loading of inclined piles embedded in two idealized soil profiles, a homogeneous and a non-homogenous “Gibson” soil, is analysed with 3D finite elements. Two structures, modeled as single-degree-of-freedom oscillators, are studied: (1) a tall slender superstructure (H _st = 12 m) whose crucial loading is the overturning moment, and (2) a short structure (H _st = 1 m) whose crucial loading is the shear force. Three simple two-pile group are studied: (a) one comprising a vertical pile and a pile inclined at 25°, (b) one consisting of two piles symmetrically inclined at 25°, and (c) a group of two vertical piles. The influence of key parameters is analysed and non-dimensional diagrams are presented to illustrate the role of raked piles on pile and structure response. It is shown that this role can be beneficial or detrimental depending on a number of factors, including the slenderness of the superstructure and the type of pile-to-cap connection.     

Towards probabilistic seismic performance of vehicle-bridge interaction systems: From stochastic dynamic model to fragility analysis

This paper aims to assess the seismic fragility of vehicle-bridge-interaction (VBI) systems considering the effects of vehicle types, traffic conditions, and road surface qualities. A stochastic nonlinear mechanical model for the earthquake-VBI system is developed, and the fragility functions for the proposed VBI model are derived by considering the relevant probabilistic seismic demand parameters. On the basis of a typical four-span continuous prestressed concrete highway bridge in China, a complete numerical model for the VBI system is built considering multiple uncertainties from bridge and vehicle parameters, as well as the road surface qualities. A total of 120 real ground motion records with different combinations of magnitude-source-to-site distance (M-R) and earthquake intensity characteristics are selected. Meanwhile, 80 scenarios in terms of different combinations of vehicle types, vehicle speeds, and road surface irregularities are defined. In this context, 96,000 nonlinear time-history analyses are performed, and the developed fragility models are applied to the VBI system at both component and system levels. Results indicate that the fragilities of pier drift, bearing shear strain, and the overall VBI system increase with the increase of the vehicle weight or the decrease of the vehicle speed, while the vertical deck displacement is dominated by the vehicle weight. It is also found that the road surface quality has a negligible effect on both component and system fragilities.