连续弯箱梁自行车桥地震响应分析          下载免费PDF全文

施有志  林四新  阮建凑  林树枝 《地震工程学报》2020,42(5):1208-1216

为研究厦门市弯箱梁自行车桥的地震响应规律，采用SAP2000有限元软件建立自行车高架桥三维壳体模型，在考虑多遇地震和罕遇地震水准作用及不同加载方向的基础上，分别采用反应谱分析法和时程分析法进行该桥的动力响应分析。结果表明：自行车桥z方向位移分量最大，且z方向分量极值均发生在曲线分叉段；相对剪力而言，桥墩竖向支反力相对较小；E1和E2地震水准响应情况随时间的变化趋势基本一致，桥梁结构未进入塑形状态，抗震性能良好，安全性指标较高；反应谱法计算得到的响应包络值相对3条不同的地震时程结果的峰值大，在实际桥梁抗震分析过程中需要综合考虑两者的分析结果。文章研究结果对今后自行车桥设计和抗震性能分析具有指导意义，并可为研究者对该类桥的进一步研究提供借鉴。  相似文献   

Soil resistances for laterally loaded rigid piles in multi-layered elastic soil     

Bipin K. Gupta 《Geomechanics and Geoengineering》2020,15(1):10-28

ABSTRACT

Short stubby piles like monopiles and large diameter drilled shafts undergo rigid body translation and rotation when subjected to a lateral force and/or a moment at the head. A method of analysis for these piles embedded in multi-layered elastic soil is developed using the variational principles of mechanics. Using this analysis, the soil resistance against pile movement can be rigorously related to the soil elastic constants, and the pile head displacement and rotation can be quickly calculated. The equilibrium equations for pile and soil displacements are obtained using the principle of virtual work and solved using an iterative algorithm. Pile responses obtained from the analysis match well with those obtained from three-dimensional finite element analyses in which the same inputs of loads, geometry, and material properties are given. Based on the new analysis, fitted equations for soil resistance parameters are developed, which can be used to directly calculate the pile head displacement and rotation without the use of the iterative algorithm. Numerical examples are provided that demonstrate how the method can be used to analyse practical problems.  相似文献   

Risk Analysis of Breakwater Caisson Under Wave Attack Using Load Surface Approximation     

Dong Hyawn KIM 《中国海洋工程》2014,(6):739-748

A new load surface based approach to the reliability analysis of caisson-type breakwater is proposed. Uncertainties of the horizontal and vertical wave loads acting on breakwater are considered by using the so-called load surfaces, which can be estimated as functions of wave height, water level, and so on. Then, the first-order reliability method（FORM） can be applied to determine the probability of failure under the wave action. In this way, the reliability analysis of breakwaters with uncertainties both in wave height and in water level is possible. Moreover, the uncertainty in wave breaking can be taken into account by considering a random variable for wave height ratio which relates the significant wave height to the maximum wave height. The proposed approach is applied numerically to the reliability analysis of caisson breakwater under wave attack that may undergo partial or full wave breaking.  相似文献   

潮致泥沙全沙净输运解析模式     

储鏖  徐怡  陈永平  郁夏琰  王彪 《海洋工程》2020,38(4):61-72

泥沙运动作为水流和底床相互作用的纽带,是河流、河口及海岸工程研究的重要内容。在潮波作用明显的河口、海岸地区,周期性的动力作用下的泥沙运动具有往复和可逆的特征,因此研究这类水域的泥沙的净输运更具有实际的意义。基于泥沙输运和流速呈指数关系假设,建立潮流环境下的泥沙全沙净输运的解析解公式,并对该公式的计算结果和数值计算以及数学模型的结果进行了检验和验证,结果表明本研究提出的公式能较好地反应潮流环境下的泥沙净输运。由此,基于本公式采用潮流分潮调和常数可计算得到全沙净输运,并可以分析各分潮流及其相互作用与泥沙净输运的关系。研究结果显示,在受径流影响较大的半日潮河口,S2、MS4、M2三潮相互作用对全沙净输运的贡献显著高于通常的潮流不对称作用,即M2、M4的相互作用。此外,河口区域径流导致的余流对泥沙净输运的贡献不可忽略,特别是在洪季,大径流量条件下往往导致余流较大,其对泥沙净输运的贡献所占比例较大。  相似文献   

钢管脐带缆扭转平衡设计     

牛学超  祝庆斌  潘盼  邵鹏进  胡明  谢书鸿 《海洋工程》2020,38(6):151-157

钢管脐带缆包含多种螺旋缠绕的功能单元，其在外力载荷下会发生相对运动，而且钢管的刚度较大对扭转平衡有重要影响，因此，相对于普通电缆，钢管脐带缆在扭转平衡设计时更加困难。根据扭转平衡理论公式，采用控制变量法，以第二层铠装钢丝的绞合角度为变量进行扭转平衡设计。首先建立脐带缆缆芯有限元模型，对其施加拉伸载荷，结果显示缆芯出现了扭转，这证明不能将脐带缆缆芯视为一实心圆柱。其次建立不同绞合角度的脐带缆有限元模型，设置各功能单元的材料属性和摩擦系数，分析模型在拉伸载荷下的扭转角度，并将相同拉伸载荷下的扭转角度拟合为直线，从而得到钢管脐带缆在扭转平衡状态时的最优绞合角度。最后，采用试验方法对实物钢管脐带缆进行扭转平衡测试，测试结果显示在拉伸载荷下脐带缆单位长度扭转角度十分微小，这表明缆是扭转平衡的。因此验证了使用的有限元方法在钢管脐带缆扭转平衡设计中的有效性。  相似文献   

级配碎石填料大三轴试验及累积塑性应变预测模型     

杨志浩  岳祖润  冯怀平  叶朝良  马德良 《岩土力学》2020,41(9):2993-3002

级配碎石作为重载铁路基床表层的主要填料，其受列车荷载的影响最大。因此，研究级配碎石在循环荷载作用下的动力行为及累积塑性应变演化特征变得尤为重要。首先，通过制备不同细粒含量的级配碎石填料，开展一系列大型动三轴试验，探究细粒含量、围压及动应力幅值对循环荷载作用下试样累积塑性应变的耦合影响机制。其次，基于塑性安定理论，确定不同应力水平下试样的动力行为，得到考虑围压及细粒含量参数的塑性蠕变状态临界动应力计算模型。最后，结合试验数据，建立考虑应力水平及细粒含量参数的塑性蠕变动力行为累积塑性应变预测模型，并明确各参数的物理意义。其研究成果可为既有重载铁路路基健康状态评估及考虑强度、变形综合控制的路基结构设计提供参考。  相似文献   

Dynamic responses of unsaturated half‐space soil to a moving harmonic rectangular load          下载免费PDF全文

Zheng Lu  Ran Fang  Hailin Yao  Cheng Dong  Shaohua Xian 《国际地质力学数值与分析法杂志》2018,42(9):1057-1077

The problem of the dynamic responses of a semi‐infinite unsaturated poroelastic medium subjected to a moving rectangular load is investigated analytical/numerically. The dynamic governing equations are obtained with consideration of the compressibility of solid grain and pore fluid, inertial coupling, and viscous drag as well as capillary pressure in the unsaturated soil, and they can be easily degraded to the complete Biot's theory. Using the Fourier transform, the general solution for the equations is derived in the transformed domain, and then a corresponding boundary value problem is formulated. By introducing fast Fourier transform algorithm, the unsaturated soil vertical displacements, effective stresses, and pore pressures induced by moving load are computed, and some of the calculated results are compared with those for the degenerated solution of saturated soils and confirmed. The influences of the saturation, the load speed, and excitation frequency on the response of the unsaturated half‐space soil are investigated. The numerical results reveal that the effects of these parameters on the dynamic response of the unsaturated soil are significant.  相似文献   

Response of hybrid isolation system during a shake table experiment of a full‐scale isolated building     

Keri L. Ryan  Taichiro Okazaki  Camila B. Coria  Eiji Sato  Tomohiro Sasaki 《地震工程与结构动力学》2018,47(11):2214-2232

A full‐scale 5‐story steel moment frame building was subjected to a series of earthquake excitations using the E‐Defense shake table in August, 2011. For one of the test configurations, the building was seismically isolated by a hybrid system of lead‐rubber bearings and low friction roller bearings known as cross‐linear bearings, and was designed for a very rare 100 000‐year return period earthquake at a Central and Eastern US soil site. The building was subject to 15 trials including sinusoidal input, recorded motions and simulated earthquakes, 2D and 3D input, and a range of intensities including some beyond the design basis level. The experimental program was one of the first system‐level full‐scale validations of seismic isolation and the first known full‐scale experiment of a hybrid isolation system incorporating lead‐rubber and low friction bearings. Stable response of the hybrid isolation system was demonstrated at displacement demands up to 550 mm and shear strain in excess of 200%. Torsional amplifications were within the new factor stipulated by the code provisions. Axial force was observed to transfer from the lead‐rubber bearings to the cross‐linear bearings at large displacements, and the force transfer at large displacements exceeded that predicted by basic calculations. The force transfer occurred primarily because of the flexural rigidity of the base diaphragm and the larger vertical stiffness of the cross‐linear bearings relative to the lead‐rubber bearings.  相似文献   

Transport of moderately sorted gravel at low bed shear stresses: The role of fine sediment infiltration          下载免费PDF全文

Emeline Perret  Céline Berni  Benoît Camenen  Albert Herrero  Kamal El Kadi Abderrezzak 《地球表面变化过程与地形》2018,43(7):1416-1430

A reliable estimation of sediment transport in gravel‐bed streams is important for various practical engineering and biological studies (e.g., channel stability design, bed degradation/aggradation, restoration of spawning habitat). In the present work, we report original laboratory experiments investigating the transport of gravel particles at low bed shear stresses. The laboratory tests were conducted under unsteady flow conditions inducing low bed shear stresses, with detailed monitoring of the bed topography using a laser scanner. Effects of bed surface arrangements were documented by testing loose and packed bed configurations. Effects of fine sediments were examined by testing beds with sand, artificial fine sand or cohesive silt infiltrated in the gravel matrix. Analysis of the experimental data revealed that the transport of gravel particles depends upon the bed arrangement, the bed material properties (e.g., size and shape, consolidation index, permeability) and the concentration of fine sediments within the surface layer of moving grains. This concentration is directly related to the distribution of fine particles within the gravel matrix (i.e., bottom‐up infiltration or bridging) and their transport mode (i.e., bedload or suspended load). Compared to loose beds, the mobility of gravel is reduced for packed beds and for beds clogged from the bottom up with cohesive fine sediments; in both cases, the bed shear stress for gravel entrainment increases by about 12%. On the other hand, the mobility of gravel increases significantly (bed shear stress for particle motion decreasing up to 40%) for beds clogged at the surface by non‐cohesive sand particles. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

A method for uncertainty constraint of catchment discharge and phosphorus load estimates          下载免费PDF全文

Michael J. Hollaway  Keith J. Beven  Clare Mc W. H. Benskin  Adrian L. Collins  Robert Evans  Peter D. Falloon  Kirsty J. Forber  Kevin M. Hiscock  Ron Kahana  Christopher J. A. Macleod  Mary C. Ockenden  Martha L. Villamizar  Catherine Wearing  Paul J. A. Withers  Jian G. Zhou  Nicholas J. Barber  Philip M. Haygarth 《水文研究》2018,32(17):2779-2787

River discharge and nutrient measurements are subject to aleatory and epistemic uncertainties. In this study, we present a novel method for estimating these uncertainties in colocated discharge and phosphorus (P) measurements. The “voting point”‐based method constrains the derived stage‐discharge rating curve both on the fit to available gaugings and to the catchment water balance. This helps reduce the uncertainty beyond the range of available gaugings and during out of bank situations. In the example presented here, for the top 5% of flows, uncertainties are shown to be 139% using a traditional power law fit, compared with 40% when using our updated “voting point” method. Furthermore, the method is extended to in situ and lab analysed nutrient concentration data pairings, with lower uncertainties (81%) shown for high concentrations (top 5%) than when a traditional regression is applied (102%). Overall, for both discharge and nutrient data, the method presented goes some way to accounting for epistemic uncertainties associated with nonstationary physical characteristics of the monitoring site.  相似文献