Structural pounding between adjacent buildings subjected to strong ground motions. Part I: The effect of different structures arrangement

The effect of different structures configurations on the collision between adjacent planar RC building frames subjected to strong earthquakes is examined in this paper. Two 5‐storey and two 8‐storey frames, regular or with setbacks, are combined together to produce nine different pairs of adjacent RC structures. These pairs of buildings are subjected to six strong ground motions that are absolutely compatible with the design process. Various parameters are investigated such as maximum displacements, permanent displacements, members' ductility and internal forces and interstorey drift ratios. It is concluded that the effect of collision of adjacent frames seems to be unfavourable for most of the cases and, therefore, the structural pounding phenomenon is rather detrimental than beneficial. Copyright © 2013 John Wiley & Sons, Ltd.     

Gravity potential at the Major Vertical Datum as primary geodetic constant

Summary On the basis of the fundamental relations of the Molodensky's Earth's figure theory (1945), admitting the inequality of the gravity potentials at the Major Vertical Datum W₀ and on the surface of the reference level ellipsoid U₀, and taken into account that potential W₀ enters into equations directly, it is recomended, W₀ should be adopted as a primary geodetic constant. Parameters of the best fitting ellipsoid are not needed for the solution of geodetic problems and for the investigation of the Earth's gravity field. The reason for requiring the reference and actual fields be close is only that the boundary-value problem can be solved in the linear approximation. Dedicated to the Memory of M.S. Molodensky Contribution to the I.A.G. Special Commission SC3 Fundamental Constants (SCFC).     

错位转换层位置对高层建筑竖向构件受力性能影响的研究

作为一种新型转换层结构——错位转换层结构,其竖向位置的移动对高层结构在水平地震作用下竖向构件受力性能有何影响目前尚未见文献报道。采用有限元程序对高层带错位转换层结构进行了水平地震作用下的时程反应和反应谱分析．分析了上部转换层和下部转换层相对位置保持不变的情况下．整体改变错位转换层位置对结构地震作用、剪力及竖向构件内力的影响。分析研究发现。错位转换层整体位置的竖向移动对结构整体剪力、上部转换层下承托墙肢内力、上部转换层框支剪力墙内力影响不大．但对落地剪力墙、上部转换层下框支柱和下部转换层梁托柱内力有较大影响。     

Dynamic analysis of large 3-D underground structures by the bem

An up to date literature survey on the dynamics of underground structures is presented briefly. The dynamic response of large three-dimensional underground structures to external or internal dynamic forces or to seismic waves is numerically determined by the frequency domain boundary element method. This method is used to model both the structure and the soil medium, which are assumed to behave as linear elastic or viscoelastic bodies. The full-space dynamic fundamental solution is employed in the formulation and this requires a free soil surface discretization, confined to a finite portion around the area of interest, in addition to soil—structure interface and free structural surface discretizations. The dynamic disturbances can have a harmonic or a transient time variation. The transient case is treated with the aid of numerical Laplace transforms with respect to time. Various numerical examples involving lined cavities and long lined tunnels buried in the full- or the half-space subjected to harmonic or transient external forces or seismic waves are presented to illustrate the method and demonstrate its advantages.     

转动弹簧宏模型模拟剪力墙受力性能

本文将剪力墙结构根据精度需要划分成若干6节点矩形单元,每个单元由2根斜置正交弹簧及联结的上下水平刚性横杆组成,2根斜置弹簧方向分别与外力作用下的主拉、压应力方向一致。本文引入单元位移场线性假定及斜压场理论计算弹簧内力,根据变形协调条件由单元结点位移计算弹簧变形,由弹簧刚度及倾角推导了该宏模型单元刚度矩阵,迭代计算使结构内力及位移逼近真值。算例分析表明,该模型能较好地反映剪力墙的受力性能。     

用椭圆衰减关系模型计算任意场点烈度及地震动参数的数值方法

用椭圆衰减关系计算地震动或地震烈度,比较经典的做法是建立极坐标系,采用极坐标方程的方法.给出了一种在直角坐标系中即可求解的用椭圆衰减关系计算地震动或地震烈度的数值计算方法.另外,地震动椭圆衰减关系,应满足一定的模型要求,才能更客观地反映实际的地震动衰减物理过程.本算法的附加功能能够鉴别非标准的椭圆衰减关系.     

Density,stress, and gravity anomalies in the interiors of the earth and mars and the probable geodynamical implications: Comparative analysis

The formulas that allow, within the quadratic approximation, for the contribution of the anomalous masses, distributed along the height relative to the reference ellipsoid, in the Stokes parameters are derived. It is shown that the contribution of the quadratic terms is largest and commensurate, by the order of magnitude, with the linear contribution if the anomalous masses have a dipole distribution along the height. The quadratic contribution is particularly significant for Mars, where the span of relative variations in the surface topography is by an order of magnitude larger than in the Earth. The problem is solved and the method is developed for finding the depths of compensation for the topographical harmonics of different order and degree. The most probable levels of compensation for topographic irregularities are determined by the analysis of the distribution histograms for the depths of compensation. The maps of lateral distributions of the compensating masses at the selected levels are calculated. It is shown that the observed anomalous structures generate the anomalies in the internal gravity field, which may serve as a cause for the convective motion in the mantle and core of the planet. Besides, the probable nonisostatic vertical stresses in the crust and mantle of the Earth and Mars are calculated.     

Seismic performance of cylindrical latticed-intersected-three-dimensional-beam-system reticulated mega-structure with single-layer latticed-intersected-cylindrical-shell substructures

This paper is focused on the research of seismic performance of cylindrical latticed-intersected-three-dimensional-beam-system (LITDBS) reticulated mega-structure with single-layer latticed-intersected-cylindrical-shell (LICS) substructures by time history method accounting for geometrical nonlinearity. The distribution laws of the dynamic internal forces and those of the ratios of the dynamic to static internal forces of members in this innovative structure are first studied. The behaviors of the structure under different multi-component seismic actions are analyzed, and the reasonable components of the seismic action that should be considered in design are thus obtained. Then taking the maximum dynamic internal force of the structure as the index, a series of parametric analyses are carried out, and the suitable values of several key form parameters are recommended. Additionally, the results by the response spectrum method with those by the time history method are compared, which indicates that the former is not on the safe side. Therefore, the mode-superposition response spectrum method can only be used to do preliminary seismic design of this kind of structure, and the results must be checked by the time history method at the end.     

粘弹性拉张型地震破裂过程的解析解

本文应用包括地壳破裂发震过程中具有激发及衰减的非线性Rayleigh阻尼,用Voigt粘弹性模型表示地壳,它能更全面地反映地壳介质分子之间的内摩擦造成的粘滞性阻尼,在数学方法上,用解非线性问题解析法的摄动理论结合动坐标的富氏级数,把问题的非线性控制方程组化为各阶线性化的控制方程组后,再简化为标准的Mathieu方程构成的耦连方程组,再用WKBJ方法,给出其在稳定区域的近似解,从而得出了问题的解析解。     

海洋重力勘探中的完全布格校正

海洋重力测量由于海底地形的复杂性,需要在简单布格校正的基础上加入海底地形校正,从而使理论地球模型更好的符合实际的地球椭球体.本文总结了完全布格校正的理论,从空间域和频率域的角度对中间层和地形校正的方法作了介绍,并引入了一种综合的方法且将之运用到了实际的工作中,并取得了很好的效果.     

Seismic passive resistance with vertical seepage and surcharge

Present paper focuses on the computation of the seismic passive earth pressure acting on a vertical rigid retaining wall by a soil mass subjected to vertical steady-state seepage and a uniform surcharge load. Based on the basic assumptions of Coulomb's theory and a pseudo-static method of analysis, a general solution for the passive earth pressure containing two coefficients is presented. In the solution, many parameters, such as unit weight of saturated soil, soil effective internal friction angle, soil/wall friction angle, water/soil unit weight ratio, surcharge intensity coefficient, horizontal and vertical seismic acceleration coefficients, Poisson's ratio of soil mass, hydraulic gradient, and coefficients of pore water pressure, are considered. The effects of hydraulic gradient and seismic forces on passive earth pressure coefficient and passive earth pressure distribution are investigated. The results indicate that passive earth pressure increases with increasing hydraulic gradient for downward water flow case, but decreases for upward water flow case, and that the presence of seismic forces induces a reduction in passive earth pressure.     

An internal variable approach applied to the dynamic analysis of elastic–plastic structural systems

Discrete elastic–plastic systems subjected to dynamic load conditions are considered and properties related to an implicit time-integration scheme are discussed on the basis of an internal variable formulation. The material models accounted for are quite general: elastic–perfectly plastic and elastic–plastic (subjected to linear or non-linear, kinematic or isotropic hardening). The internal variable approach adopted in the paper leads easily to extremum theorems from which convergence properties of convenient time-integration schemes immediately follow. Next, taking account of the stabilising effect due to inertial and damping forces, it is shown how the above results can be extended to the case of softening (again linear or non-linear, kinematic or isotropic). Finally, some numerical examples are given and an extension to damage models is envisaged.     

Analysis and performance of a predictor‐multicorrector Time Discontinuous Galerkin method in non‐linear elastodynamics

A predictor‐multicorrector implementation of a Time Discontinuous Galerkin method for non‐linear dynamic analysis is described. This implementation is intended to limit the high computational expense typically required by implicit Time Discontinuous Galerkin methods, without degrading their accuracy and stability properties. The algorithm is analysed with reference to conservative Duffing oscillators for which closed‐form solutions are available. Therefore, insight into the accuracy and stability properties of the predictor‐multicorrector algorithm for different approximations of non‐linear internal forces is gained, showing that the properties of the underlying scheme can be substantially retained. Finally, the results of representative numerical simulations relevant to Duffing oscillators and to a stiff spring pendulum discretized with finite elements illustrate the performance of the numerical scheme and confirm the analytical estimates. Copyright © 2002 John Wiley & Sons, Ltd.     

A terrestrial shear pattern?

The concept of the strain ellipsoid is applied to indicate a possible regular shear pattern of earthquake distribution over the Earth's surface. A simple model of the Earth is assumed in the form of a rotating sphere with a plastic interior and a thin, fragile, crust. On this basis rotation of the Earth generates an internal radial pressure at the equator equivalent to 1/300g causing a proportionate distortion of the spherical shell. The system is in dynamic equilibrium with an increase in gravity at the equator. The ellipsoid representing the distortion, has orthogonal principal axes corresponding to the principal strains while radial directions at 54°44 from the poles are unchanged in length and are thus possible axes of shear generating the same distortion. The Alpide region of earthquakes extending from Lisbon to Tokyo and restriction of earthquakes mainly to the broad band between latitudes 55°N or S are in support of the proposed view.Four unique sets of orthogonal shear systems have been identified which form a regular pattern with a definite symmetry with respect to the plane of the ecliptic. This suggests that the hoop stress at the Equator associated with Earth rotation may be triggered off by tidal forces and that earthquake prediction may well be possible. Other implications of this new approach are also discussed.     

Kinematic internal forces in deep foundations with inclined piles

This paper presents a parametric study that looks into the influence of pile rake angle on the kinematic internal forces of deep foundations with inclined piles. Envelopes of maximum kinematic bending moments, shear forces and axial loads are presented along single inclined piles and 2 × 2 symmetrical square pile groups with inclined elements subjected to an earthquake generated by vertically incident shear waves. Inclination angles from 0° to 30° are considered, and three different pile–soil stiffness ratios are studied. These results are obtained through a frequency–domain analysis using a boundary element–finite element code in which the soil is modelled by the boundary element method as a homogeneous, viscoelastic, unbounded region, and the piles are modelled by finite elements as Euler–Bernoulli beams. The rotational kinematic response of the pile foundations is shown to be a key factor on the evolution of the kinematic internal forces along the foundations. Copyright © 2015 John Wiley & Sons, Ltd.     

Impedance functions for foundations embedded in a layered medium: An integral equation approach

An integral equation technique to calculate the dynamic response of foundations embedded in a layered viscoelastic half-space when subjected to external forces and moments is presented. The technique is based on representing the radiated field as resulting from a set of sources distributed over a surface internal to the actual boundary of the foundation and by imposing the boundary conditions in an integral sense. The resulting non-singular integral equation with symmetric kernel is solved by discretization and reduction to a system of linear algebraic equations. The technique is validated by comparison with previous results for cylindrical foundations with different embedment ratios.     

Vibrations of square and circular foundations with concentric openings on elastic half space

A study on the dynamic characteristics of rigid foundations with special geometries such as square or circular with concentric internal holes, is presented. The foundations are resting on a homogeneous, linear elastic halfspace and are subjected to external forces or seismic wave excitation. Both ‘relaxed’ and ‘non-relaxed’ boundary conditions at the interface between the foundation and the halfspace are considered, and several parametric studies are conducted to assess the influence of either type of boundary conditions upon each of the possible modes of vibration. Results for massive and massless foundations are presented in time and frequency domains for impulsive and harmonic excitations, respectively. A time domain boundary element method (BEM) developed by the authors for the solution of a class of 3-D soil-structure interaction (SSI) problems is used for all the analyses reported in this work. The accuracy and efficiency of the method and the BEM models developed in this work are assessed on the basis of comparison studies with published results.     

大跨度空间网格结构多维多点随机地震反应分析

本文建立了三维正交地震动多点激励下大跨度空间网格结构的随机地震反应分析方法,依据现行抗震设计规范的有关规定,确定了平稳随机地震动功率谱密度的模型参数。数值仿真分析了一柱距80m的正方形平板网架分别在一维地震动或三维地震动的一致激励、行波激励和考虑部分相干效应的随机激励下的地震反应。结果表明:考虑地震动的空间效应会很大程度地改变结构杆件的内力,其中控制杆件的内力增幅达到30%;地震动的行波效应对结构杆件内力的影响比随机地震动的部分相干效应的影响更大;三维地震作用比一维地震作用下结构杆件的内力大。由此得出结论,对于大跨度空间网格结构,必须进行多维多点地震激励下的随机地震反应分析。     

Conversion between solid and beam element solutions of finite element method based on meta-modeling theory: development and application to a ramp tunnel structure

In this study, a new method for conversion of solid finite element solution to beam finite element solution is developed based on the meta-modeling theory which constructs a model consistent with continuum mechanics. The proposed method is rigorous and efficient compared to a typical conversion method which merely computes surface integration of solid element nodal stresses to obtain cross-sectional forces. The meta-modeling theory ensures the rigorousness of proposed method by defining a proper distance between beam element and solid element solutions in a function space of continuum mechanics. Results of numerical verification test that is conducted with a simple cantilever beam are used to find the proper distance function for this conversion. Time history analysis of the main tunnel structure of a real ramp tunnel is considered as a numerical example for the proposed conversion method. It is shown that cross-sectional forces are readily computed for solid element solution of the main tunnel structure when it is converted to a beam element solution using the proposed method. Further, envelopes of resultant forces which are of primary importance for the purpose of design, are developed for a given ground motion at the end.     

ADVANCED METHOD FOR SELF-ADAPTIVE ESTIMATION OF RESIDUAL STATIC CORRECTIONS*

The estimation of residual static corrections is investigated as a linear system. For 1200% coverage shot one way offset weighting functions—or in other words, estimation error operators—are computed. Assuming zero time shift determination errors and zero RNMO it is seen that large residual corrections will distort the effectivity of the estimation. With an iterative procedure which includes the repeated averaging according to depth point, shot point, and geophone point the effectivity of the method becomes more favourable. This can be learnt from the evaluation of estimation error operators computed by recursive formulae. In practice, due to the time shift determination errors, the routine does not give improved results in the desired level. Errors can be reduced with a more reliable time shift determination routine. For detecting and suppressing the unfavourable effect of time shift errors still remaining in the data a self-adaptive method was developed. In this non linear routine the data are evaluated at all three averaging processes according to limit values and weighting factors computed from the data itself. Field examples processed in different ways are presented.