桩土相互作用阻尼系数试验结果与其他结果的对比

当前如何考虑桩土之间的相互作用并将其定量化是限制基桩缺陷定量分析方法准确性的重要因素。低应变条件下将土对桩的作用以粘滞阻尼器考虑,通过桩土相互作用试验测定桩顶速度响应并结合理论分析结果确定桩侧土在不同状态下的桩土相互作用阻尼系数。在现有的一些研究中也有一些其他确定阻尼系数的方法,例如经过动力平衡分析得到桩侧土单位长度阻尼系数的理论表达式,实际测定表达式中各个参数即可确定相应阻尼系数;也有通过多次动静对比试验得到的阻尼系数经验值。由于各个阻尼系数定义并不相同,参考试验时的实际情况确定各个参数,进而将不同定义的阻尼系数转化为同一量纲,分析了不同阻尼系数的差距,发现通过多次动静对比试验得到的Case阻尼系数由于是在大应变情况下得到的,相对桩土相互作用试验得到的阻尼系数有较大差距,应用于低应变分析并不合适。而理论推导得到的阻尼系数相对试验结果虽然并不一致,但是他们之间存在一定的相关性,进而经过拟合分析发现两者之间的比值可以表示为剪切波速的函数。     

Finite Element Modeling of a Fluid Filled Cylindrical Shell with Active Constrained Layer Damping

On the basis of the piezoelectric theory, Mindlin plate theory, viscoelastic theory and ideal fluid equation, the finite element modeling of a fluid-filled cylindrical shell with active constrained layer damping （ACLD） was discussed. Energy methods and Lagrange＇s equation were used to obtain dynamic equations of the cylindrical shell with ACLD treatments, which was modeled as well with the finite element method. The GHM （Golla-Hughes-McTavish） method was applied to model the frequency dependent damping of viscoelastic material. Ideal and incompressible fluid was considered to establish the dynamic equations of the fluid-filled cylindrical shell with ACLD treatments, Numerical results obtained from the finite element analysis were compared with those from an experiment. The comparison shows that the proposed modeling method is accurate and reliable.     

三体船横摇模型试验及其特性分析

三体船在波浪中的横摇特性和优点是三体新船型研发的技术支撑,采用模型试验和理论分析相结合的方法,对三体船横摇运动特性进行探讨。开展三体船静水横摇、正横浪零速波浪横摇模型试验,得出三体船线性、非线性阻尼假设下的横摇阻尼、频率响应和周期。通过横摇响应曲线的分析和对比,得出三体船不同侧体位置下波浪中横摇附加惯量、阻尼和运动响应、周期特性,以及侧体位置对以上各横摇特性影响的规律。研究表明：三体船横摇阻尼远大于常规单体船,而横摇运动幅值响应远小于常规单体船;侧体的横位置对三体船横摇具有显著影响,侧体纵向位置对横摇影响很小。综合考虑运动响应和横摇周期,在不规则波中三体船的横摇比常规单体船缓和得多。     

排水预压法加固某高速公路软基效果的工程实例分析

以某高速公路应用塑料排水板堆载预压法处理深层软基为例,通过监测时加固效果进行分析。结果表明：加固后,土体的十字板剪切强度提高了40％,含水率大为减少;堆载结束后80d内土体固结度达到90％以上,且土体的沉降趋于稳定,加固深度在15m以上,加固效果明显。应用塑料排水板堆载预压法处理深厚层软土,可以加快软土的沉降速率,缩短工期,降低成本,是一种既经济又合理的地基处理方法。     

Dynamics of an ultra-deepwater mooring line with embedded chain segment

A code is developed to study the mooring tensions on a line with an embedded segment considered, based on lumped mass method. The accuracy of this code is validated by published results. The influence of soil-chain interaction on the static and dynamic behaviour of a 1500 m mooring line is studied under two operational situations: shallow embedded taut mooring line and deep embedded semi-taut mooring line. The shallow case has an embedded depth setting as 10 m under seafloor, while the embedded depth is 20 m for deep water. To study the influence of soil on mooring dynamics, three simplified cases without soil force considered are investigated and the results are compared with the dynamics of embedded mooring. These three cases include: i) Case MA has the same spread distance to embedded mooring anchored on seafloor; ii) Case MB is anchored on seafloor and it has the same pretension with embedded mooring; iii) Case MC is anchored to the same point to the embedded mooring but the soil force is not considered. Furthermore, the effects of effective width parameters of tangential and bearing soil resistance on mooring dynamics are also discussed. In this work, three different oscillations are forced on fairlead to study the mooring dynamics, which are low frequency oscillation, hybrid oscillation (low frequency and wave frequency) and wave frequency oscillation.     

Advanced steel brace with multistable hysteretic damping enhanced by a multilayered structure

Water wave impacts on jacket structures would result in heavy impulse loads, which induce strong vibrations because of the low damping characteristics of metallic members. In order to resist the wave-impact and suppress the vibration of structures, a novel steel brace that contains a multilayered multistable (MLMS) column is designed for an adjustable product of sufficient stiffness and high damping. According to finite element simulating, the initial stiffness of the MLMS column was almost same as that of the multistable steel column [1], but the energy dissipation was several times larger than that of this column. To understand the hysteresis mechanism of the MLMS column, we performed a hybrid analysis of multilayer lamination and mixed boundary buckling and noted: the soft layer of the MLMS column conducts the neutral axis and bending stiffness, which controls critical buckling load that decides the highness of the hysteresis loop; the eccentric end caps mediates the loading axis of the MLMS column, which induces in the increment of the postbuckling displacement that broadens the width of the hysteresis loop. So, the displacement-force hysteretic relation of the MLMS column can be effectually adjusted by the appropriate physical parameters of the soft layer and the end caps, which is validated by parameter analysis using FEM. Through FEM simulations, we studied a jacket structure assembled with dissipative braces containing MLMS column, which exhibited a several times increment in the decay rate of impact-induced vibration compared to that of the same jacket platform with existing dissipative columns [1]. This study demonstrated the MLMS column is an effective alternative for obtaining high structural stiffness and high damping in marine engineering.     

轨下新型网孔式弹性垫板力学性能影响研究

为了提高轨道交通轨下弹性垫板的力学性能,使垫板材料的弹性充分发挥,研究一种新型网孔式轨下弹性垫板结构。通过建立网孔式轨下弹性垫板的有限元计算模型,选用Mooney-Rivlin超弹性本构模型模拟橡胶材料特性,在弹性垫板材料参数不变的条件下,通过网孔间距、网孔内接圆直径、板厚和倒角半径等关键参数来调整网孔式弹性垫板的静刚度,分析其对弹性垫板力学性能的影响,并与传统沟槽型弹性垫板进行对比。结果表明:在孔径不变的条件下,网孔间距增大,垫板静刚度近似线性增大,最大应力增大;网孔直径增大,垫板静刚度近似线性减小,最大应力减小。垫板厚度增大,静刚度明显减小,而最大应力小幅减小;网孔结构倒角后弹性垫板的静刚度小幅增加,但最大应力明显减小。相比于静刚度相近的沟槽型弹性垫板,网孔式弹性垫板的最大应力明显减小,可有效提高其耐久性,同时网孔式弹性垫板的静刚度具有可灵活调整的能力,因此,将网孔结构应用于轨下弹性垫板具有可行性。     

胶层厚度不均匀对板式橡胶支座耐久性的影响

根据JT/T4—2004《公路桥梁板式橡胶支座》和JTG D62—2004《公路钢筋混凝土及预应力混凝土桥涵设计规范》的要求,系统地研究、分析了板式橡胶支座胶层厚度大小和胶层厚度不均匀对支座力学性能及耐久性的影响。介绍了支座内部的应力集中现象和内部胶层裂纹萌生的过程及其测试结果。     

车辆悬架最佳阻尼匹配减振器设计

为了使设计减振器对车辆具有最佳减振效果,利用悬架最佳阻尼比,对减振器最佳阻尼系数进行了研究,建立了减振器最佳速度特性数学模型,提出了减振器阀系参数设计优化方法,对设计减振器进行了特性试验和整车振动试验,并与原车载减振器性能进行了对比。计算结果表明:减振器特性试验值与最佳阻尼匹配要求值的最大偏差为9%,而且,在低频范围内,设计减振器的整车振动传递函数幅值明显低于原车载减振器的幅值,有效遏制了簧下质量在13Hz附近的共振,因此,减振器速度特性模型和阀系参数优化设计方法是正确的。     

钢桥面铺装沥青砂胶缓冲层的开发及应用研究

沥青砂胶缓冲层在钢桥面铺装体系中起着重要作用。结合其使用功能及施工性能要求,通过对不同配方改性沥青研究,选定沥青砂胶缓冲层的改性沥青种类。采用贯入度试验方法并结合施工和易性确定其最佳沥青用量,使其能适用于钢桥面铺装。通过试验路施工,认为目前采用人工抹涂的施工方法比较有效。