大吨位基桩抗压载荷试验中的锚桩预应力保护技术

竖轴向承载力是桩基础设计的重要参数,现场静载试验是目前确定桩基承载力的主要手段之一。本文依托黄陵—延安段高速公路洛河特大桥试桩工程,通过对原有工程桩施加预应力,形成了以工程桩为锚桩的锚拔体系。加载过程中试桩应力、锚桩应力及桩顶位移测试,结果表明,结合预应力技术,以工程桩作为锚桩构成桩基础静载试验的锚拔体系是可行的,同时提出了施加预应力大小的原则、方法以及确保后期曾作为锚桩的工程桩有足够承载能力应采取的必要措施。     

岩质边坡稳定性及预应力锚固分析现状

本文首先对目前常用的各类边坡稳定性分析方法的主要特点进行了评述,包括定性方法类的历史分析法、工程地质类比法、图解法、专家系统法,定量分析方法类的确定性模型法,如极限平衡法,应力应变分析法;非确定性模型法,如可靠性分析法、灰色系统理论法及模糊综合评判法等;及两类方法结合而成的随机有限元法。其次,对预应力锚固边坡的设计及稳定性分析作了阐述。     

Mode interaction in triple-bay prestressed stayed columns

Prestressed stayed columns are an innovative type of structural system where the compressive load-carrying capacity can be enhanced through prestressed external cable stays. A nonlinear analytical model for prestressed stayed columns with multiple crossarm systems along the column length, based on the Rayleigh–Ritz method, is presented that captures modal interactions for perfect geometries explicitly for the first time. It is demonstrated that the theoretical compressive strength enhancements under certain configurations can only be obtained at the expense of triggering a sequence of destabilizing bifurcations. This can give rise to dangerously unstable interactive post-buckling behaviour including so-called ‘mode jumping’ and ‘snaking’ phenomena. Parametric spaces where the system is most susceptible to the modal interactions are identified and it is for those configurations that the system is likely to be highly sensitive to initial imperfections. The model is validated using a nonlinear finite element model formulated within the commercial code ABAQUS and excellent comparisons are obtained.     

Optimal Design of Prestressed Laminate/Ceramic Plate Assemblies

It is well known that the dynamic compressive strength of ceramics is enhanced by confining compressive stress. The paper shows how a biaxial in-plane compressive stress can be induced in a ceramic layer by encapsulation in a fiber-prestressed composite laminate. Optimal prestress distribution in individual plies of the laminate is found, together with the resulting residual stresses. Large compressive stress, 600–1000MPa can be supported in an alumina layer by aramid/epoxy or carbon/epoxy laminates of the same total thickness as the ceramic. Stress relaxation due to either temperature changes or matrix creep is found to be of minor significance. Examples present results for specific material systems and laminate layups. Sommario. E'ben noto che la resistenza dinamica dei materiali ceramici viene migliorata dal confinamento degli sforzi di compressione. Questo lavoro mostra come uno stato piano di compressione biassiale possa essere indotto in uno strato di materiale ceramico imprigionandolo in un laminato composito con fibre presollecitate. Viene determinata la distribuzione ottimale delle presollecitazioni nei singoli strati del laminato, nonché l'entità degli sforzi residui risultanti. Compressioni elevate, dell'ordine di 600–1000Mpa, possono essere indotte in uno strato di allumina da laminati epossidici rinforzati con fibre aramidiche o carboniche dello stesso spessore. Il rilassamento degli sforzi dovuto a cambiamenti di temperatura o al comportamento viscoso della matrice risulta avere importanza limitata. Gli esempi forniscono risultati relativi a specifici materiali e orientamenti dei laminati.     

用外加电压控制摩擦力的机理与技术

用外加电压控制金属摩擦学磨损是摩擦领域很有发展前景的新技术之一，能够有效地降低干摩擦下金属间的摩擦与磨损，但国内外有关的研究报道却还少见．因此，利用特制的球－盘式摩擦磨损试验机，对几种配对金属的摩擦自生电势和摩擦力进行了测量，揭示了摩擦自生电势与摩擦力的相关性，并且考察了外加电压对金属间摩擦力的影响，发现在外加电压与摩擦自生电势相抵消时的摩擦系数最低，比无外加电压时的摩擦系数低１２％～２６％     

Transverse vibrations of prestressed continuous beams on rigid supports under the action of moving bodies

The main objective of the paper is to investigate the dynamic response of the prestressed beams on rigid supports to moving concentrated loads. The governing equation of the transverse vibration of a prestressed continuous beam under the ununiformly distributed load is analytically formulated, taking into account the effect of the prestressing. The forced transverse vibration of the beam under the action of a large number of moving bodies has been investigated by using the method of substructures. In addition, the reaction forces at every rigid supports can be determined from the obtained differential equations. A comparison between the numerical results for the prestressed and the non-prestressed beam is presented to show the influence of the prestressing and the moving velocity of the bodies on the dynamic response of the beam. The calculating results are also examined and validated by experimental measurements at a large ferroconcrete bridge in Vietnam.