Cyclic tests on large‐scale models of existing bridge piers with rectangular hollow cross‐section

Cyclic tests on two large‐scale models of existing bridge piers with rectangular hollow cross‐section were performed in the ELSA laboratory. The prototype structure is an existing reinforced concrete highway bridge constructed in Austria in 1975. The piers presented several seismic deficiencies and consequently they showed poor hysteretic behaviour and limited deformation capacity as well as undesirable failure modes that do not comply with the requirements of modern codes for seismic‐resistant structures. Experimental data are compared to numerical and empirical predictions. Copyright © 2003 John Wiley & Sons, Ltd.     

A mixed finite element method for Hele-Shaw cell equations

A new numerical method to solve the system of equations describing two phase flow in a Hele-Shaw cell is presented. It combines a mixed finite element method, the method of subtraction of the singularity and a front tracking grid in a single computational strategy. This choice of discretization techniques is well motivated by the difficulties present in the system of equations and the physics of the problem. The new method was tested against analytical solutions and also by solving the Saffman–Taylor viscous fingering problem for finite and infinite mobility ratios. In both cases convergence under mesh refinement is achieved for the fingers developed from an initial sinusoidal interface. Finger splitting is observed for low values of the surface tension and high mobility ratio. Different explanations, based in our results, are provided for this phenomenon. This revised version was published online in July 2006 with corrections to the Cover Date.     

松江河电厂小山水电站导流洞出口边坡稳定性分析

小山水电站导流洞出口边坡其地质结构为下部中侏罗世安山岩（αＪ２），其上覆盖了第三纪末第四纪初的玄武岩（βＮ～Ｑ），两者间为不整合接触，不整合面夹有０．１～０．６ｍ厚的粘土状及碎石粘土状夹层，产状倾向河床，倾角±２５°。在上覆玄武岩层中见有高倾角的宽张裂隙带，与不整合面一起构成松动岩体，不整合面为底滑面。通过边界条件的分析和稳定计算，松动岩体的抗滑系数Ｋ＝３．１０２，边坡是稳定的。在施工过程中采取了相应的安全保护措施，导流洞出口提前２８ｍ进洞，节约挖方量６００００ｍ３，提前了工期。经三年多的施工到运行，边坡无异常变化，表明该项优化设计是可行的。     

大跨度切眼锚网锚索支护研究

全煤大跨度切眼传统的支护方式是钢棚支护,为解决无轨胶轮车直接进入工作面,提高工作面设备安装效率,课题组进行锚网锚索支护试验与研究。该项目的试验成功,为矿井高产高效创造了条件。     

Dynamic performance of twin curved cable‐stayed bridges

The dynamic behaviour of two curved cable‐stayed bridges, recently constructed in northern Italy, has been investigated by full‐scale testing and theoretical models. Two different excitation techniques were employed in the dynamic tests: traffic‐induced ambient vibrations and free vibrations. Since the modal behaviour identified from the two types of test are very well correlated and a greater number of normal modes was detected during ambient vibration tests, the validity of the ambient vibration survey is assessed in view of future monitoring. For both bridges, 11 vibration modes were identified in the frequency range of 0ndash;10Hz, being a one‐to‐one correspondence between the observed modes of the two bridges. Successively, the information obtained from the field tests was used to validate and improve 3D finite elements so that the dynamic performance of the two systems were assessed and compared based on both the experimental results and the updated theoretical models. Copyright © 2003 John Wiley & Sons, Ltd.     

Seismic response of a cable‐stayed bridge deck under multi‐component non‐stationary random ground motion

A Markov method of analysis is presented for obtaining the seismic response of cable‐stayed bridges to non‐stationary random ground motion. A uniformly modulated non‐stationary model of the random ground motion is assumed which is specified by the evolutionary r.m.s. ground acceleration. Both vertical and horizontal components of the motion are considered to act simultaneously at the bridge supports. The analysis duly takes into account the angle of incidence of the earthquake, the spatial correlation of ground motion and the quasi‐static excitation. A cable‐stayed bridge is analysed under a set of parametric variations in order to study the non‐stationary response of the bridge. The results of the numerical study indicate that (i) frequency domain spectral analysis with peak r.m.s. acceleration as input could provide more r.m.s. response than the peak r.m.s. response obtained by the non‐stationary analysis; (ii) the longitudinal component of the ground motion significantly influences the vertical vibration of the bridge; and (iii) the angle of incidence of the earthquake has considerable influence on the deck response. Copyright © 2003 John Wiley & Sons, Ltd.     

广西百色水电站边坡治理工程

文章通过广西右江百色水利枢纽地下发电厂房进水口与尾水洞高边坡的治理，介绍在此工程中具有特殊性的一些施工方法。该工程地质体为弱风化硅质泥岩夹泥化夹层、强风化含洞穴硅质泥岩石、强风化硅质岩及全强风化辉绿岩，地质条件非常复杂，对坡体的稳定极其不利。根据三维有限元的分析计算和国内有关权威专家的调查研究需施工1500kN、1000kN的锚索方能保证坡体的永久稳定。大吨位的锚索需锚固在强风化岩土体上，锚索设计采用能提高锚固力的防腐型压力分散锚索。通过现场锚索基本试验，其锚固力完全能满足工程需要。为保证进水口总体施工的进度，在施工进水口约30m高的垂直壁上的锚索时，笔者采用了通常施工中较少采用的垂直壁悬吊式施工法，满足了水电站的整体施工进度和要求。     

云南个（旧）-冷（墩）公路K22＋336回头湾段边坡治理工程研究

目前，在我国地质灾害防治及道路建设工程中，岩土锚固施工大多采用单一的拉力型锚索工法。一般锚索索体的长效防腐问题没有得到应有的重视。文章对云南省个旧-冷墩公路边坡工程中所采用的压力分散型锚索工法从设计、试验及成功应用等多方面进行了详细介绍。①在一些复杂地形条件下，锚索防护方案有其独特的经济实用性。②在地基承载力较低的软弱地层中，常用的拉力型锚索无法提供防护工程所需的大吨位锚固力。而有多个受力体的压力分散型锚索则因其对锚固段全长范围内地基承载力的充分利用来提供较大吨位的锚固力；③永久锚索防护工程作为一项具有隐蔽性强特点的结构工程，为保证在其报务年限内锚索能够可靠地工作，在设计阶段，锚索体的长效防腐应为不能忽略的主要考虑因素。在该工程中首次应用了新型高强材料——环氧全喷涂无粘结钢绞线作为锚索体的杆材，较好地解决了永久锚固工程中的锚索防腐问题。     

Critical Top Tension for Static Equilibrium Configuration of A Steel Catenary Riser

This paper aims to present the critical top tension for static equilibrium configurations of a steel catenary riser（SCR） by using the finite element method. The critical top tension is the minimum top tension that can maintain the equilibrium of the SCR. If the top tension is smaller than the critical value, the equilibrium of the SCR does not exist. If the top tension is larger than the critical value, there are two possible equilibrium configurations. These two configurations exhibit the nonlinear large displacement. The configuration with the smaller displacement is stable, while the one with larger displacement is unstable. The numerical results show that the increases in the riser＇s vertical distances, horizontal offsets, riser＇s weights, internal flow velocities, and current velocities increase the critical top tensions of the SCR. In addition, the parametric studies are also performed in order to investigate the limit states for the analysis and design of the SCR.     

Micromechanical approach to swelling behavior of capillary-porous media with coupled physics

A detailed multiscale analysis is presented of the swelling phenomenon in unsaturated clay-rich materials in the linear regime through homogenization. Herein, the structural complexity of the material is formulated as a three-scale, triple porosity medium within which microstructural information is transmitted across the various scales, leading ultimately to an enriched stress-deformation relation at the macroscopic scale. As a side note, such derived relationship leads to a tensorial stress partitioning that is reminiscent of a Terzaghi-like effective stress measure. Otherwise, a major result that stands out from previous works is the explicit expression of swelling stress and capillary stress in terms of micromechanical interactions at the very fine scale down to the clay platelet level, along with capillary stress emerging due to interactions between fluid phases at the different scales, including surface tension, pore size, and morphology. More importantly, the swelling stress is correlated with the disjoining forces due to electrochemical effects of charged ions on clay minerals and van der Waals forces at the nanoscale. The resulting analytical expressions also elucidate the role of the various physics in the deformational behavior of clayey material. Finally, the capability of the proposed formulation in capturing salient behaviors of unsaturated expansive clays is illustrated through some numerical examples.