Soil-structure interaction (SSI) analysis is generally a required step in the calculation of seismic demands in nuclear structures, and is currently performed using linear methods in the frequency ...domain. Such methods should result in accurate predictions of response for low-intensity shaking, but their adequacy for extreme shaking that results in highly nonlinear soil, structure or foundation response is unproven. Nonlinear (time-domain) SSI analysis can be employed for these cases, but is rarely performed due to a lack of experience on the part of analysts, engineers and regulators. A nonlinear, time-domain SSI analysis procedure using a commercial finite-element code is described in the paper. It is benchmarked against the frequency-domain code, SASSI, for linear SSI analysis and low intensity earthquake shaking. Nonlinear analysis using the time-domain finite-element code, LS-DYNA, is described and results are compared with those from equivalent-linear analysis in SASSI for high intensity shaking. The equivalent-linear and nonlinear responses are significantly different. For intense shaking, the nonlinear effects, including gapping, sliding and uplift, are greatest in the immediate vicinity of the soil-structure boundary, and these cannot be captured using equivalent-linear techniques.
•Described a method of performing time-domain nonlinear SSI analysis.•Benchmarked this method against the established frequency-domain code, SASSI.•Performed fully nonlinear SSI analyses of two buildings using LS-DYNA.•Compared LS-DYNA results to those calculated using SASSI.•Observed significant differences for cases with highly nonlinear behavior.
Offshore wind turbines (OWTs) have emerged as one of the most sustainable and renewable sources of energy. The size of OWTs has been increasing, which creates more challenges in the design of ...foundations due to the potential higher‐mode effects involved in the dynamic soil‐structure interaction (DSSI) response. Several foundation modeling techniques are available for calculating the OWT fundamental frequency; however, their capability to predict the higher modes by considering real geometric configurations is unclear. The main aim of this study is to perform a rigorous modal analysis of the NREL 5MW reference OWT to investigate the higher mode effects using the 3D finite element method. A detailed parametric analysis is also performed to study the effects of soil inhomogeneity, initial soil modulus, and the monopile dimensions (diameter, thickness, and embedded pile depth) on higher modes' natural frequencies and effective mass participation ratios. The study shows that dynamic soil‐structure interaction has a significant role in modal response and the simplified foundation models are not accurate enough. Given the significant contribution from higher modes, they should not be simply ignored in the OWT design, particularly in earthquake‐prone zones.
Summary
The problem of the through‐soil coupling of structures has puzzled the researchers in the field for a long while, especially regarding the varied performance of identical, adjacent buildings ...in earthquakes. The phenomenon of structure‐soil‐structure interaction (SSSI) that has often been overlooked is recently being recognized: The possible effects in urban regions are yet to be thoroughly quantified. In this respect, the goal of this work was to rigorously investigate the interacting effects of adjacent buildings in a two‐dimensional setting. Detailed finite element models of 5‐, 15‐, and 30‐story structures, realistically designed, were used in forming building clusters on the viscoelastic half‐space. Perfectly matched layers were used to properly define the half‐space boundaries. The interaction of the structure and the soil medium because of the presence of spatially varying ground motion on the boundary of excavated region was considered. The effects of the foundation material and the distance between adjacent buildings on the structural behavior of the neighboring buildings were investigated using drift ratios and base shear quantities as the engineering demand parameters of interest. The effects of SSSI, first investigated in the frequency domain, was then quantified in the time domain using suites of appropriate ground motions in accordance with the soil conditions, and the results were compared with the counterpart SSI solution of a single building. The results showed that, for identical low‐rise structures, the effects of SSSI were negligible. Yet, neglecting SSSI for neighboring closely spaced high‐rise structures or building clusters with a large stiffness contrast was shown to lead to a considerable underestimation of the true seismic demands even compared with solutions obtained using the rigid base assumption.
This study aims to investigate the role of arbuscular mycorrhizal (AM) symbiosis in reducing N loss from paddy fields, using two rice lines: a mycorrhiza-defective rice line (non-mycorrhizal) and its ...mycorrhizal progenitor. Two rice lines were grown in the presence of an AM fungal isolate. In this study, N loss of runoff, leaching, N.sub.2O emission, and NH.sub.3 volatilization were measured, and in addition, N uptake of rice, soil aggregates, and plant available N concentration of soil. The results obtained suggest that N loss via runoff, leaching, NH.sub.3 volatilization, and N.sub.2O emission of mycorrhizal rice was 11%, 8%, 6%, and 1%, lower than that of non-mycorrhizal rice, respectively. Meanwhile, mycorrhizal rice has higher biomass and plant N uptake. Our study shows that the AM symbiosis contributes to the sustainability of rice production by reducing N loss, enhancing soil aggregation and increasing plant N uptake.
Cross correlations between nominal load and resistance terms in limit state functions for geotechnical soil–structure interaction problems can be expected. A closed-form solution for the reliability ...index for a simple linear limit state function is used to examine the influence of nominal load and resistance correlations on computed margins of safety. The formulation also includes the contribution of the underlying accuracy of the load and resistance equations (method bias) and bias dependencies with the magnitude of nominal load and resistance values assumed in the limit state design function. Sensitivity analyses and example problems for the external sliding limit state for a cantilever wall and the pullout limit state for internal stability of reinforced soil walls with different soil reinforcement types are presented. Ignoring nominal correlations where they exist is shown to underestimate the reliability index in some cases and to overestimate the reliability index in other cases. In the example problems, these differences are shown to exceed one order of magnitude in terms of probability of failure, but in the sensitivity analyses using a wider range of input parameter values, the differences can be several orders of magnitude.
Tuned Mass Dampers (TMDs) can represent an attracting solution to mitigate vibrations of a structure under seismic excitation, but their effectiveness can be considerably altered by the dynamic ...interaction with the foundation soil. The available design criteria for TMDs do not account for these effects and can therefore lead to a non‐optimised structural performance. In this paper an investigation on the dynamic interaction of the TMD with the whole soil‐structure system is presented, with the objective of highlighting the system parameters governing the response and the effectiveness of the device as seismic protection. An interpretative model of the soil‐structure‐TMD system expressed in a rigorous non‐dimensional form is proposed, and an extensive global sensitivity analysis on its performance under harmonic loading is carried out. The identification of the typical performance regions shows that the seismic effectiveness of a TMD is mainly controlled by a limited number of parameters describing the structural behaviour and the soil‐structure interaction, such as the structure‐to‐soil relative stiffness and those governing foundation rocking. The non‐dimensional system parameters leading to either a favourable or detrimental effect on the TMD performance due to soil‐structure interaction are also identified, and two design methodologies proposed in the literature are critically assessed in light of the framework proposed.
Soil structure interaction (SSI) may affect significantly the seismic vulnerability of structures with several mechanisms that depend on the mutual effects of soil properties and structural ...characteristics. A probabilistic-based approach is here applied to evaluate the effects of SSI on the fragility assessment of two selected benchmark buildings: a Reinforced Concrete with Infill Masonry Walls (RCIMW) and a Reinforced Concrete (RC). Analytical fragility curves were developed by performing non-linear 3D numerical simulations with Opensees that implements hysteretic materials and advanced plasticity models for representing non-linear soil conditions and structural configurations. The effects of soil deformability and structural flexibility on the non-linear response of the system (soil-foundation-structure) were assessed and discussed by referring to four limit states (slight, moderate, extensive and collapse) with respect to the maximum inter storey drifts.
•Soil structure interaction.•Analytical fragility curves.•3D Numerical simulations.•Opensees.•Non-linearity.
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.
The dynamic through-soil interaction between underground station and nearby pile supported structure on viscous–elastic soil layer, under vertically incident S wave, is numerically studied. To this ...end, a commercial software for finite element analysis, ANSYS, has been further developed and enhanced for calculation in frequency domain, in which damping of hysteretic type can be considered for both the soil and the structures, so that structure–soil–structure interaction (SSSI) can be investigated making use of a direct methodology. The influence of arrangement of structures, shaking direction of seismic wave, distances between structures, shear wave velocity, damping of soil, burial depth and number of spans of underground structure on SSSI, in terms of horizontal acceleration magnification factor of ground structure, is addressed. For ground structure, different lengths of pile, stiffnesses, styles, and numbers of storeys and structures are considered. Maximum acceleration responses are also presented for 12 seismic inputs. Arrangement and shaking direction are two of the most important factors. The system response can be either amplified or attenuated according to the distance between adjacent buildings, which has been related to dynamic properties of the overall system. Those neighboring low-slung buildings around underground structure are heavily affected.
•We reviewed studies about interaction of ground structure and underground structure.•ANSYS has been further developed and enhanced for damping of hysteretic type.•We discussed the influence of subway station on the neighboring ground structure.•We examined the influence parameter of the dynamic interaction.
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