Soil–structure interaction in resonant railway bridges

This paper explores dynamic soil–bridge interaction in high speed railway lines. The analysis was conducted using a general and fully three-dimensional multi-body finite element–boundary element model formulated in the time domain to predict vibrations caused by trains passing over the bridge. The vehicle was modelled as a multi-body system, the track and the bridge were modelled using finite elements and the soil was considered as a half-space by the boundary element method. The dynamic response of bridges to vehicle passage is usually studied using moving force and moving mass models. However, the multi-body system allows to consider the quasi-static and dynamic excitation mechanisms. Soil–structure interaction was taken into account by coupling finite elements and boundary elements. The paper presents the results obtained for a simply supported short span bridge in a resonant regime under different soil stiffness conditions.     

Ottoman archives and the assessment of the seismicity of Greece 1456–1833

This article examines the contribution of Ottoman sources of historical information for the study of the seismicity of Greece, in particular of Athens during the period of the Ottoman domination, a period during which relatively few original Greek sources of data are available. An annotated list of a number of case histories of earthquakes in Greece from Ottoman sources is presented translating only a summary of the information for those who want to access the whole document. They contain not only a valuable record of earthquakes, but also, for the earthquake historian, a wealth of information about locations where earthquakes were not felt. The article discusses the effects of earthquakes, of the 1826–7 siege on the Acropolis its purpose being to provide information with such annotation as would facilitate its use by engineering seismologists with additional macroseismic data that could supplement the rather meagre information.     

Equivalent linear substructure approximation of soil–foundation–structure interaction: model presentation and validation

An equivalent linear substructure approximation of the soil–foundation–structure interaction is proposed in this paper. Based on the inherent linearity of the approach, the solution of the structural and the soil domain is obtained simultaneously, incorporating the effects of the primary and secondary soil nonlinearities. The proposed approximation is established theoretically and then validated against centrifuge benchmark soil–foundation–structure interaction tests. The equivalent linear substructure approximation is proved to simulate efficiently the effects of the nonlinear soil behavior on the soil–foundation–structure system under a strong earthquake ground motion.     

Numerical analyses of fault–foundation interaction

Field evidence from recent earthquakes has shown that structures can be designed to survive major surface dislocations. This paper: (i) Describes three different finite element (FE) methods of analysis, that were developed to simulate dip slip fault rupture propagation through soil and its interaction with foundation–structure systems; (ii) Validates the developed FE methodologies against centrifuge model tests that were conducted at the University of Dundee, Scotland; and (iii) Utilises one of these analysis methods to conduct a short parametric study on the interaction of idealised 2- and 5-story residential structures lying on slab foundations subjected to normal fault rupture. The comparison between numerical and centrifuge model test results shows that reliable predictions can be achieved with reasonably sophisticated constitutive soil models that take account of soil softening after failure. A prerequisite is an adequately refined FE mesh, combined with interface elements with tension cut-off between the soil and the structure. The results of the parametric study reveal that the increase of the surcharge load q of the structure leads to larger fault rupture diversion and “smoothing” of the settlement profile, allowing reduction of its stressing. Soil compliance is shown to be beneficial to the stressing of a structure. For a given soil depth H and imposed dislocation h, the rotation Δθ of the structure is shown to be a function of: (a) its location relative to the fault rupture; (b) the surcharge load q; and (c) soil compliance.     

Soil–pile-bridge structure interaction in liquefying ground using shake table testing

The evaluation of seismic pile response is particularly useful for geotechnical engineers involved in the design of foundations in liquefying site. Shake table testing was performed to study the dynamic interactive behavior of soil–pile foundations in liquefying ground under different shaking frequency and amplitude. The soil profile consisted of a clayey layer over liquefiable sand over clay. The model was tested with a series of El Centro earthquake motions with peak accelerations ranging from 0.15g to 0.50g, and time step from 0.006 to 0.02 s. Representative data, including time histories of accelerations and excess pore pressure ratios that characterize the important aspects of soil–pile interaction in liquefying ground are presented. The shaking frequency has no significant effect on the magnitudes of excess pore pressure ratio, ground and pile accelerations and pile bending moments. Excess pore pressure ratio, ground acceleration and pile acceleration, and pile bending moment largely depend on the shaking amplitude.     

Simulation of soil–foundation–structure interaction of Hualien large-scale seismic test using dynamic centrifuge test

Understanding the soil–structure interaction (SSI) mechanism is crucial in the seismic design of nuclear power plant (NPP) containment systems. Although the numerical analysis method is generally used in seismic design, there is a need for experimental verification for the reliable estimation of SSI behavior. In this study a dynamic centrifuge test was performed to simulate the SSI behavior of a Hualien large-scale seismic test (LSST) during the Chi-Chi earthquake. To simulate the soil profile and dynamic soil properties of the Hualien site, a series of resonant column (RC) tests was performed to determine the model soil preparation conditions, such as the compaction density and the ratio of soil–gravel contents. The variations in the shear wave velocity (V_S) profiles of the sand, gravel, and backfill layers in the model were estimated using the RC test results. During the centrifuge test, the V_S profiles of the model were evaluated using in-flight bender element tests and compared with the in-situ V_S profile at Hualien. The containment building model was modeled using aluminum and the proper scaling laws. A series of dynamic centrifuge tests was performed with a 1/50 scale model using the base motion recorded during the Chi-Chi-earthquake. In the soil layer and foundation level, the centrifuge test results were similar to the LSST data in both the time and frequency domains, but there were differences in the structure owing to the complex structural response as well as the material damping difference between the concrete in the prototype and aluminum in the model. In addition, as the input base motion amplitude was increased to a maximum value of 0.4g (prototype scale), the responses of the soil and containment model were measured. This study shows the potential of utilizing dynamic centrifuge tests as an experimental modeling tool for site specific SSI analyses of soil–foundation–NPP containment system.     

Centrifuge modelling of normal fault–foundation interaction

Earthquake fault ruptures may emerge at the ground surface causing large differential movements. When fault ruptures emerge at or adjacent to the position of existing foundations, significant damage can be caused. However, the study of recent faulting events revealed that in some circumstances the fault-rupture emergence is deflected by the presence of buildings leaving the buildings intact. A centrifuge modelling study has been conducted to investigate how normal faults interact with strip foundations which run parallel to the strike direction. The study confirms that fault rupture may be deviated by the presence of the foundation so that the foundation is protected from the most serious differential movements. However, whilst the fault propagates to the soil surface the foundation has to withstand initial movements before the final fault rupture emergence mechanism is activated. The centrifuge results suggest that it is the bearing pressure of the foundation which causes the deviation of the fault rather than the kinematic restraint of the foundation. The interaction between the earthquake fault and the shallow foundation depends on the foundation bearing pressure, foundation width, soil depth and position of the fault relative to the foundation and these aspects should be considered in design. Results from the tests are used to validate a series of finite element analyses as reported in an accompanying paper.     

Centrifuge modelling of reverse fault–foundation interaction

The propagation of reverse faults through soil to the ground surface has been observed to cause damage to surface infrastructure. However, the interaction between a fault propagating through a sand layer and a shallow foundation can be beneficial for heavily loaded foundations by causing deviation of the fault away from the foundation. This was studied in a series of centrifuge model tests in which reverse faults of dip angle 60° (at bedrock level) were initiated through a sand layer, close to shallow foundations. The tests revealed subtle interaction between the fault and the shallow foundation so that the foundation and soil response depend on the foundation loading, position, breadth and flexibility. Heavily loaded rigid foundations appeared best able to deviate fault rupture away from the foundation but this deviation could be associated with significant foundation rotations. However, a lightly loaded foundation was unable to deviate a reverse fault and the fault emerged beneath the foundation. This led to gapping beneath the foundation as well as significant rotations and may cause severe structural distress. As well as providing insight into the mechanisms of behaviour, the data from the tests is used to validate finite element analyses in a separate article.     

Soil–structure interaction effects on seismic inelastic analysis of 3-D tunnels

This paper investigates the importance of seismic soil–structure interaction in three-dimensional lined tunnels, assuming inelastic material behaviour for both the concrete liner and the soft rock type of soil. The seismic response of the soil–structure system is determined by the finite element method (FEM) in the time domain. Viscous absorbing boundaries are used in conjunction with the discretization of the rock medium. Both the rock medium and the concrete liner are assumed to behave inelastically on the basis of the continuum damage mechanics theory. The seismic waves are assumed to have any arbitrary time variation and direction of propagation. The system is analysed with and without soil–structure interaction in order to assess its importance on the response of the system. Through parametric studies, the influence of the most critical parameters affecting the structural response is determined and critically discussed.     

Dynamic response of structures subjected to pounding and structure–soil–structure interaction

During strong earthquakes, adjacent structures with non-sufficient clear distances collide with each other. In addition to such a pounding, cross interaction of adjacent structures through soil can exchange the vibration energy between buildings and make the problem even more complex. In this paper, effects of both of the mentioned phenomena on the inelastic response of selected steel structures are studied. Number of stories varied between 3 and 12 and different clear distances up to the seismic codes prescribed value are considered. The pounding element is modeled within Opensees. A coupled model of springs and dashpots is utilized for through-the-soil interaction of the adjacent structures, for two types of soft soils. The pounding force, relative displacements of stories, story shears, and plastic hinge rotations are compared for different conditions as the maximum responses averaged between seven consistent earthquakes. As a result, simultaneous effects of pounding and structure–soil–structure interaction are discussed.     

Probabilistic seismic performance and loss assessment of a bridge–foundation–soil system

This paper presents the probabilistic seismic performance and loss assessment of an actual bridge–foundation–soil system, the Fitzgerald Avenue twin bridges in Christchurch, New Zealand. A two-dimensional finite element model of the longitudinal direction of the system is modelled using advanced soil and structural constitutive models. Ground motions at multiple levels of intensity are selected based on the seismic hazard deaggregation at the site. Based on rigorous examination of several deterministic analyses, engineering demand parameters (EDP's), which capture the global and local demand, and consequent damage to the bridge and foundation are determined. A probabilistic seismic loss assessment of the structure considering both direct repair and loss of functionality consequences was performed to holistically assess the seismic risk of the system.It was found that the non-horizontal stratification of the soils, liquefaction, and soil–structure interaction had pronounced effects on the seismic demand distribution of the bridge components, of which the north abutment piles and central pier were critical in the systems seismic performance. The consequences due to loss of functionality of the bridge during repair were significantly larger than the direct repair costs, with over a 2% in 50 year probability of the total loss exceeding twice the book-value of the structure.     

Chemical and isotopic assessment of surface water–shallow groundwater interaction in the arid Grande river basin,North-Central Chile

ABSTRACT

This paper analyses the composition of surface water and shallow groundwater in the Grande River basin, North-Central Chile, using this information to characterize water interactions. Chemical and isotopic data for surface water and groundwater (7 and 6 sampling locations, respectively) were obtained from three sampling campaigns performed in March–April (autumn), August–September (late winter) and December (early summer) 2012. Precipitation samples were also collected. Data was processed using spatial distribution charts, Piper and Stiff diagrams, and multivariate analysis. In general, the results for each method converge on a high degree of connectivity between surface water and shallow groundwater in the study area. Furthermore, approximately a 10% of groundwater contribution to the surface flow discharge was estimated for a particular reach. This multi-method approach was useful for the characterization of surface water–groundwater interactions in the Grande River basin, and may become a suitable and replicable scheme for studies in arid and semi-arid basins facing similar water management challenges.

Editor D. Koutsoyiannis; Associate editor B. Dewals     

Soil–structure interaction analysis of cable-stayed bridges for spatially varying ground motion components

In this study, it is intended to determine the effects of soil–structure interaction (SSI) and spatially varying ground motion on the dynamic characteristics of cable-stayed bridges. For this purpose, ground motion time histories are simulated for spatially varying ground motions, depending on its components of incoherence, wave-passage and site-response effects. The substructure method, which partitions the total soil–structure system into the structural system and the soil system, is used to treat the soil–structure interaction problem. To emphasize the relative importance of the spatial variability effects of earthquake ground motion, bridge responses are determined for the fixed base bridge model, which neglects the soil–structure interaction (no SSI) and for the bridge model including the soil–structure interaction (SSI). This parametric study concerning the relative importance of the soil–structure interaction and spatially varying ground motion shows that these effects should be considered in the dynamic analyses of cable-stayed bridges.     

Influence of plasticity on the seismic soil–micropiles–structure interaction

This paper includes an analysis of the influence of soil plasticity on the seismic response of micropiles. Analysis is carried out using a global three-dimensional modeling in the time domain. The soil behavior is described using the non-associated Mohr–Coulomb criterion. Both the micropiles and the superstructure are modeled as three-dimensional beam elements. Proper boundary conditions are used to ensure waves transmission through the lateral boundaries of the soil mass. Analyses are first conducted for harmonic loadings and then for real earthquake records. They show that plasticity could have a significant influence on the seismic response of the soil–micropiles–structure systems. This influence depends on the amplitude of the seismic loading and the dominant frequencies of both the input motion and the soil–piles–structure system.     

Early history of soil–structure interaction

Soil–structure interaction is an interdisciplinary field of endeavor which lies at the intersection of soil and structural mechanics, soil and structural dynamics, earthquake engineering, geophysics and geomechanics, material science, computational and numerical methods, and diverse other technical disciplines. Its origins trace back to the late 19th century, evolved and matured gradually in the ensuing decades and during the first half of the 20th century, and progressed rapidly in the second half stimulated mainly by the needs of the nuclear power and offshore industries, by the debut of powerful computers and simulation tools such as finite elements, and by the needs for improvements in seismic safety. The pages that follow provide a concise review of some of the leading developments that paved the way for the state of the art as it is known today. Inasmuch as static foundation stiffnesses are also widely used in engineering analyses and code formulas for SSI effects, this work includes a brief survey of such static solutions.     

Effects of soil–structure interaction on the dynamic properties and seismic response of piled structures

This paper presents a simple and stable procedure for the estimation of periods and dampings of piled shear buildings taking soil–structure interaction into account. A substructuring methodology that includes the three-dimensional character of the foundations is used. The structure is analyzed as founded on an elastic homogeneous half-space and excited by vertically incident S waves. The strategies proposed in the literature to estimate the period and damping are revised, and a modified strategy is proposed including crossed impedances and all damping terms. Ready-to-use graphs are presented for the estimation of flexible-base period and damping in terms of their fixed-base values and the system configuration. Maximum shear forces together with base displacement and rocking peak response are also provided. It is shown that cross-coupled impedances and kinematic interaction factors need to be taken into account to obtain accurate results for piled buildings.     

Soil–structure interaction for a SDOF oscillator supported by a flexible foundation embedded in a half-space: Closed-form solution for incident plane SH-waves

A closed-form analytical solution is presented for the dynamic response of a SDOF oscillator, supported by a flexible foundation embedded in an elastic half-space, and excited by plane SH waves. The solution is obtained by the wave function expansion method. The solution is verified for the special case of a rigid foundation by comparison with published results. The model is used to investigate the effect of the foundation flexibility on the system response. The results show that the effect is significant for both foundation response and structural relative response. For a system with more flexible foundation, the radiation damping is smaller, the foundation response is larger, especially for obliquely incident waves, while the structural relative response is smaller, and the system frequency shifts towards lower frequencies. This simple model may be helpful to obtain insight into the effects of soil–structure interaction for a slim structure on an extended flexible foundation.     

Use of global ductility for design of structure–foundation systems

This paper investigates the applicability of global ductility in the conventional design procedure of structure–foundation systems under earthquake excitation. For a bilinear elastoplastic model, an equivalent ductility factor for the combined structure and foundation is derived, which can be used in conjunction with the enlarged period and increased damping due to soil–structure interaction (SSI) to determine the design strength. A geometric transformation rule for predicting the ductility demand developed in the structure alone from that experienced by the interacting system is also derived, without the need of computing the rigid-body motion of the foundation. To validate this practical approach for assessing both inelastic strengths as well as ductility demands, a number of numerical results for different system parameters and earthquake excitations are provided. The effects of principal parameters involved are also examined.     

The effect of foundation flexibility variation on system response of dynamic soil–structure interaction: an analytical solution

A closed-form analytical solution is presented for the dynamic response of a SDOF oscillator, supported by a flexible composite foundation embedded in an elastic half-space, and excited by plane SH waves. The solution is obtained by the wave function expansion method. The solution is verified for the two limiting cases of a rigid–flexible composite foundation and a homogeneous flexible foundation by comparison with published results. The model is used to investigate the effect of the foundation flexibility variation on the system response. The results show that the effect is significant for both foundation response and structural relative response. For a system with larger foundation flexibility variation, the peak of the foundation effective input motion is smaller, while the amplitude of structural relative response less changes. When foundation flexibility variation decreases, system frequency will shift to lower frequency, and the shift value is also highly dependent on the foundation flexibility variation.