This paper presents an efficient approach for the modal analysis of coupled soil-structure systems, for which the dynamic response is strongly influenced by the embedment in the soil. The methodology ...is based on a finite element-perfectly matched layer model that allows for the derivation of frequency-independent system matrices and the computation of the modal properties of the coupled system. This is achieved by solving a nonlinear eigenproblem using a Compact Rational Krylov (CoRK) eigensolver. A procedure is developed to sort the computed eigenpairs, filter out the spurious modes of the system which are related to the near-field and truncated far-field soil subdomains and select the physical structural modes of system. The proposed method can be used in the dynamic assessment and structural identification of strongly coupled soil-structure systems such as fully or partially buried structures and allows for the interpretation of experimentally identified modal properties of these systems, especially in the presence of highly damped or closely spaced coupled modes. The applicability and the scalability of the proposed approach for 2D and 3D problems is demonstrated in two case studies.
•A FE-PML model together with a CoRK eigensolver are employed for modal analysis of coupled soil-structure systems.•The concept of the stabilization diagram is used to filter out the spurious modes of system.•A criteria is developed to select the physical structural modes of system.•The measured modal properties of a full-scale bridge-soil system is used to demonstrate the methodology.
Wright fishhook cactus is a small globose cactus endemic to an area of 280,000 ha in south-central Utah and was listed as endangered in October of 1979 by the U.S. Fish and Wildlife Service (USFWS). ...There is a general paucity of information about this species, and no published data on the seed bank for any species in the genus. Our objective with this study was to provide insight into the established seed bank density for this species. We processed 500 soil samples from various locations near individual cacti and potential neighboring nurse plants. We found that the species had a detectable seed bank of a size similar to other members of the Cactaceae family. Seed bank densities were the highest immediately adjacent to, and downslope from, parent plants. Our data indicate that areas within 20 cm of seed-producing cacti contain by far the greatest density of seeds. These areas should be given special consideration in future management plans for this species.
To elucidate whether an irregular topography affects the seismic response of nearby structures, an analytical solution to the dynamic interaction between a symmetric V‐shaped canyon and an adjacent ...building under the incidence of SH waves is proposed by using the wave function expansion method. The dynamic canyon‐soil‐structure interaction is decomposed into two problems of scattering and radiation. The building is idealized as a shear wall supported by a semicircular rigid foundation. The analytical solution can be degenerated theoretically to the canonical model of a shear wall embedded in a half‐space for either a zero depth‐to‐width ratio of the canyon or an infinite canyon‐building distance. Through a numerical comparison with two past exact solutions to the sole shear wall model as well as the sole V‐shaped canyon model, the correctness of the method in this paper is verified. A systematic parametrical analysis in both frequency and time domains is performed. It is found that the seismic response of the building may be amplified when it is on the wave‐facing side of the canyon. The degree of amplification is closely related to the size and depth‐to‐width ratio of canyon, the wave velocity of half‐space, and the incident angle and frequency content of seismic waves. The potential adverse effects of the V‐shaped canyon on the ground motion input of adjacent buildings should be considered in the seismic design.
The performance of pipelines subjected to permanent strike–slip fault movement is investigated by combining detailed numerical simulations and closed-form solutions. First a closed-form solution for ...the force–displacement relationship of a buried pipeline subjected to tension is presented for pipelines of finite and infinite lengths. Subsequently the solution is used in the form of nonlinear springs at the two ends of the pipeline in a refined finite element model, allowing an efficient nonlinear analysis of the pipe–soil system at large strike–slip fault movements. The analysis accounts for large strains, inelastic material behavior of the pipeline and the surrounding soil, as well as contact and friction conditions on the soil–pipe interface. The numerical models consider infinite and finite length of the pipeline corresponding to various angles β between the pipeline axis and the normal to the fault plane. Using the proposed closed-form nonlinear force–displacement relationship for buried pipelines of finite and infinite length, axial strains are in excellent agreement with results obtained from detailed finite element models that employ beam elements and distributed springs along the pipeline length. Appropriate performance criteria of the steel pipeline are adopted and monitored throughout the analysis. It is shown that the end conditions of the pipeline have a significant influence on pipeline performance. For a strike–slip fault normal to the pipeline axis, local buckling occurs at relatively small fault displacements. As the angle between the fault normal and the pipeline axis increases, local buckling can be avoided due to longitudinal stretching, but the pipeline may fail due to excessive axial tensile strains or cross sectional flattening. Finally a simplified analytical model introduced elsewhere, is enhanced to account for end effects and illustrates the formation of local buckling for relative small values of crossing angle.
•We develop a closed-form solution for the force–displacement relationship of a buried pipe.•We implement this solution within a FE model for simulating end effects.•We analyze buried pipelines crossing a horizontal fault in terms of appropriate performance criteria.•We examine in particular longitudinal stretching effects on pipe deformation.•We present an analytical model that illustrates efficiently the deformation of a pipeline crossing a horizontal fault.
This paper presents an analytical method for calculating the dynamic impedance of pile groups comprising an arbitrary number of cylindrical piles connected with a rigid cap. The solution allows ...consideration of ground waves due to pile vibration that propagate along both the horizontal and vertical planes, as well as the effect of the actual pile section geometry on the reaction from the surrounding soil. For that, we introduce a dynamic pile–soil–pile interaction factor that is defined on the basis of soil reaction developing on receiver piles, instead of the classical displacement-based interaction factor used in past studies. Despite the fact that the solution is applicable to problems where low-to-moderate soil strains are expected to develop, it poses as an attractive, efficient alternative to numerical methods for the analysis of very large pile groups.
The seismic performance of integral abutment bridges (IABs) is affected by the interaction with the surrounding soil, and specifically by the development of interaction forces in the ...embankment‐abutment and soil‐piles systems. In principle, these effects could be evaluated by means of highly demanding numerical computations that, however, can be carried out only for detailed studies of specific cases. By contrast, a low‐demanding analysis method is needed for a design‐oriented assessment of the longitudinal seismic performance of IABs. To this purpose, the present paper describes a design technique in which the frequency‐ and amplitude‐dependency of the soil‐structure interaction is modelled in a simplified manner. Specifically, the method consists of a time‐domain analysis of a simplified soil‐bridge model, in which soil‐structure interaction is simulated by means of distributed nonlinear springs connecting a free‐field ground response analysis model to the structural system. The results of this simplified method are validated against the results of advanced numerical analyses, considering different seismic scenarios. In its present state of development, the proposed simplified nonlinear model can be used for an efficient evaluation of the longitudinal response of straight IABs and can constitute a starting point for a prospective generalisation to three‐dimensional response.
Model testing in laboratory, as an effective alternative to field measurement, provides valuable data to understand railway׳s dynamic behaviors under train moving loads. This paper presents ...comprehensive experimental results on track vibration and soil response of a ballastless high-speed railway from a full-scale model testing with simulated train moving loads at various speeds. A portion of a realistic ballastless railway comprising slab track, roadbed, subgrade, and subsoil was constructed in a larger steel box. A computer-controlled sequential loading system was developed to generate equivalent vertical loadings at the track structure for simulating the dynamic excitations due to train׳s movements. Comparisons with the field measurements show that the proposed model testing can accurately reproduce dynamic behaviors of the track structure and underlying soils under train moving loads. The attenuation characteristics of dynamic soil stresses in a ballastless slab track is found to have distinct differences from that in a ballasted track. The model testing results provide better understanding of the influence of dynamic soil–structure interaction and train speed on the response of track structure and soils.
•Train moving loads were implemented in the model testing of railway infrastructure.•Highest train speed of 360km/h was achieved in the physical model testing.•Roadbed plays a critical role in vibration reduction of ballastless tracks.•Dynamic soil stress differs noticeably between ballastless and ballasted railways.•A new formula on dependency of dynamic soil stress on train speed is proposed.
This paper presents the development, implementation and application of an integrated simulation method for non‐linear soil‐structure interaction (SSI) analysis of nuclear structures. The integrated ...simulation method allows decomposition of the soil‐structure system into three subsystems: the superstructure, the soil‐foundation interface, and the soil domain. Each decomposed subsystem can be modelled independently using a proper finite element analysis program to accurately represent its non‐linear behaviour as per the current guideline for non‐linear SSI analysis of nuclear structures. The integrated simulation method is applicable to both static and dynamic analysis cases. The method was applied to the detailed SSI analysis of a realistic nuclear containment structure. The analysis was benefited by using different analysis tools for the three subsystems to capture both material and geometrical nonlinearities such as sliding and gapping at the soil‐foundation interface. The integrated model was compared with the model based on the fixed‐base assumption. Different results address the importance of non‐linear SSI analysis for seismic performance assessment of nuclear structures.
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