结合消阻护筒的试验桩桩侧摩阻力和桩端阻力试验研究

石家庄地铁人民广场站试桩采用静载试验方案加载测试,设计要求除进行承载力测试外,还需确定桩侧各土层的分层极限侧摩阻力和桩端土的端阻力,以及桩侧摩阻力和桩端阻力占单桩极限承载力和承载力特征值的比例。利用消阻双护筒消除无效土层的侧摩阻力,通过桩身应力观测,利用弹性力学公式推算桩身轴力、桩侧摩阻力及端阻力的分布及变化规律,为设计提供依据。结果表明:1)双护筒消阻装置可直接消除无效土层段的侧摩阻力,使试验桩真实反映工程桩的实际承载力、侧摩阻力、端阻力及沉降值;2)达到极限承载力时,桩侧总阻力占比65%~66%,桩端总阻力占比34%~35%;达到承载力特征值时,桩侧总阻力占比76%~80%,桩端总阻力占比20%~24%;试桩承载力类型均为端承摩擦桩;3)局部范围内土层桩侧摩阻力表现为应力和位移的软化特征;4)桩端持力层主要为卵石层,对承载力的贡献平均占比约30%。     

The influence of suspension components friction on race car vertical dynamics

This work analyses the effect of friction in suspension components on a race car vertical dynamics. It is a matter of fact that race cars aim at maximising their performance, focusing the attention mostly on aerodynamics and suspension tuning: suspension vertical and rolling stiffness and damping are parameters to be taken into account for an optimal setup. Furthermore, friction in suspension components must not be ignored. After a test session carried out with a F4 on a Four Poster rig, friction was detected on the front suspension. The real data gathered allow the validation of an analytical model with friction, confirming that its influence is relevant for low frequency values closed to the car pitch natural frequency. Finally, some setup proposals are presented to describe what should be done on actual race cars in order to correct vehicle behaviour when friction occurs.     

Tire–road friction coefficient estimation based on the resonance frequency of in-wheel motor drive system

In this paper, a resonance frequency-based tire–road friction coefficient (TRFC) estimation method is proposed by considering the dynamics performance of the in-wheel motor drive system under small slip ratio conditions. A frequency response function (FRF) is deduced for the drive system that is composed of a dynamic tire model and a simplified motor model. A linear relationship between the squared system resonance frequency and the TFRC is described with the FRF. Furthermore, the resonance frequency is identified by the Auto-Regressive eXogenous model using the information of the motor torque and the wheel speed, and the TRFC is estimated thereafter by a recursive least squares filter with the identified resonance frequency. Finally, the effectiveness of the proposed approach is demonstrated through simulations and experimental tests on different road surfaces.     

桩基承载力自平衡试验法在济宁运河桥中的应用

该文介绍了桩基自平衡试验法在济宁市太白楼西路运河大桥工程中的应用。概述了自平衡法的基本原理、测试方法及过程,并对测试数据进行了整理和分析。应用结果表明,试验可靠,测试取得较好的工程效果。     

桥梁桩基设计中若干问题的探讨

该文结合设计实践,参考相关规范及文献,针对现行公路桥梁地基与基础设计规范中关于桩基承载力设计计算的几个问题进行了初步探讨。     

Experimental study on the interlayer friction and wear mechanism between armor wires of umbilicals

Friction and wear behavior between armor wire layers of umbilical plays an important role in its mechanical properties, in particular its fatigue life. The present paper addresses friction tests to investigate the interlayer sliding friction and wear mechanism of armor wires in an umbilical. A series of friction tests were carried out to study the evolution of coefficient of friction (COF) and wear between armor wire layers. The results show that the COF increases with increasing number of reciprocating sliding cycles in dry friction condition. A dual stable trend was found in the evolution process of interlayer friction and wear of armor wires. A friction model was proposed to describe this trend by dividing the evolution process into three stages: the initial stable stage, the transition stage, and the latter stable stage. The mechanism of the dual stable trend was revealed, which was mainly caused by wear process of nylon fiber tape, and effected by dry/wet wear condition and wear coefficient. The effect of the contact condition, sliding amplitude and number of nylon fiber tape on COF was studied. The COF of the latter stable stage increases with increasing sliding amplitude and number of layers of nylon fiber tape. The finding in this paper provides a valuable approach for a more accurate fatigue life prediction of an umbilical.     

摩擦楔块几何尺寸对货车转向架性能的影响

分析了俄罗斯18-100型三大件货车转向架摩擦楔块结构的特点,指出改变摩擦楔块形状可以改进转向架的性能.     

港口工程混凝土结构界面糙率试验模拟

通过两个典型案例,对港口工程中影响混凝土结构抗滑稳定性的界面糙率模拟问题进行讨论,阐述波浪模型试验中对结构物界面糙率进行准确模拟的必要性,并提供了对预制和现浇混凝土结构底部糙率的试验室模拟技术,为相关工程设计和模型试验提供参考。     

考虑土体非线性固结沉降的复合地基桩侧负摩阻力研究

基于Davis一维非线性固结理论,求得桩周土体固结沉降随时间和深度变化的计算公式;结合桩-土双曲线荷载传递模型,建立复合地基中桩体平衡方程的矩阵表达式,通过将矩阵方程组联立迭代求解,得到复合地基中桩侧摩阻力、桩身轴力及中性点位置.通过针对某工程实例的对比分析,验证了本文中所建理论计算方法的可靠性;继而探讨了地基土固结度、桩周土体初始体积压缩系数、桩端土体压缩模量及桩-土应力比对桩侧负摩阻力和中性点位置的影响.研究结果表明:所建立的考虑土体非线性固结沉降的桩侧负摩阻力计算模型可以有效、准确地反映复合地基中基桩负摩阻力和中性点位置随地基土固结时间的变化规律;桩周土体初始体积压缩系数对桩侧摩阻力影响显著,桩端土体压缩模量对中性点位置影响显著;桩身下拽力、中性点深度随着桩-土应力比的增大而减小.     

某越野车双向自增力中央驻车制动器的匹配

双向自增力鼓式制动器因其效能因数高,在越野车和轻型卡车上作为中央驻车制动器应用较多。就双向自增力中央制动器在开发过程中的几项设计要点进行了详述,解析了自增力鼓式驻车制动器效能因数的计算方法,并通过理论计算和试验对比,验证了方法的准确性。同时,分析了摩擦系数的选择方法,对制动间隙的设计和控制进行了研究。