Finite element analysis of footwear and ground interaction

Military boots are designed to prevent the soft tissue and skeletal structure of the feet from damage under heavy usage. Good slip-resistant tread patterns of the outer-sole are vital to minimise the risk or severity of slipping under demanding conditions, most likely to result in accidents. However, boot design should also offer the customer flexibility, comfort, and shock absorption, be lightweight and be able to operate regardless of the ground surface texture and various weather conditions. The issue of footwear and ground interaction investigated in this study can be classified as a traditional stability problem. Solutions to these problems are often obtained using the theory of perfect plasticity. Therefore, elastic–perfectly plastic theory was adopted in this study and the Drucker-Prager (DP) material model was chosen to model the soil properties. Literature survey showed that little studies exist on the subject of interaction between foot and soft ground, in particular, using numerical modelling methods. However, there are numerous research works on some relevant domains, such as soil–tillage tool interaction, soil–wheel interaction and soil–structure interaction, etc. A three-dimensional finite-element (FE) analysis of a subsoiler cutting with pressurised air injection was performed by employing a DP harden material model without consideration of friction force by Araya and Gao [1]. Saliba [2] undertook elastic–viscoplastic FE modelling for tire/soil interaction and Mouazen and Nemenyi [3, 4] adopted a DP model for analysing soil–tillage tool interaction

Significance of foundation-soil separation in dynamic soil-structure interaction

THe dynamic response of flexible surface strip-foundations allowed to uplift is numerically obtained for externally applied forces of a transient time variation. The soil medium is represented by an isotropic, homogeneous and linear half-space. The soil is treated by a time domain boundary element method, while the flexible foundation is treated by the finite element method. It was concluded that intermediate relative stiffness leads to moderate deformations when uplift is permitted. Very flexible footings produce higher deformations in unilateral contact compared to bilateral contact, and thus should be considered in their design. Unilateral contact does not significantly increase deformations for stiff footings subjected to concentrated central loading. However, relatively large deformation differences occur when the loading is eccentric, necessitating consideration of uplift in their design

Similitude in soil-structure and soil-soil interaction

Scaling laws are often presented as a criterion that has to be fulfilled. For example: a pile diameter should be larger than 20 times the diameter of the grains to have similitude between the model tip force and the tip force of the corresponding prototype. This paper investigates another approach: What is the mechanism that requires a certain ratio between pile diameter and grain size and can this influence be quantified? If so, it is sometimes possible to calculate the systematic error made and correct the results of model tests. This appeared possible for the influence of the grain size on the pile tip resistance and for the influence of viscous forces in clay. It was not possible when undrained behavior in the model corresponds with drained behavior of the prototype or in situations where flow is important and the solution of Darcy’s equation results in singularities

Fluid - Structure - Soil Interaction of Cylindrical Liquid Storage Tank Subjected to Horizontal Earthquake Loading

Shallow founded tanks are strategic structures used to store a variety of kind of liquids. The fluid develops hydrodynamic effect on solid domain of container during an earthquake. This paper provides the theoretical background for numerical model on seismic response of fluid-structure-soil interaction. The Finite Element Method (FEM) was used for seismic response of shallow founded cylindrical container. The Fluid- Structure-Soil interaction of shallow founded tank was analysed according to theories of I. Limit States - the ultimate limit state (ULS) and II. Limit States - the serviceability limit state (SLS) pursuant to EN 1997-1. Summary of the results: the maximum rotation of foundation is growing with the reduction of the stiffness of the subsoil and the vertical and horizontal bearing capacity depends on the strength properties of the subsoil

Physical characteristics of soil under different cropping and natural system on the plain of jars, Xieng Khouang province, Laos

Conservation agriculture and direct seeding mulch-based cropping (DMC) systems greatly modify plant and soil interaction. Plants commonly provide energy that fuels biological processes and either directly or indirectly creates structure within soils. Under DMC systems 7 large biomass is produced both above and below ground, thereby influencing soil parameters. Different methods can be used to measure soil characteristics, but simple and cheap tools for on-site recording are not common. This study attempts to analyse the physical soil parameters (water-stable aggregate, bulk density and soil permeability) of various ecosystems: savannah grassland, pine forest, ploughed upland rice fields, and improved Brachiaria ruziziensis and Stylosanthes guianensis pasture lands. The results show that these forage species have a clear effect on soil structure: medium soil particles (<0.250mm) are fixed into water-stable aggregates, bulk density decreases, and as a result soil permeability is modified. The continued recording of such data over time will enable evaluation of the iterative and cumulative biological effects (organic content, root density, particle arrangement) of fodder species and cropping systems on soil characteristics. (Résumé d'auteur

Effects of soil-pile-structure interaction on seismic response of moment resisting buildings on soft soil

Dynamic response of structures sitting on soft soils is influenced by the soil properties, and the response is significantly different to the fixed base condition owing to the interaction between the ground and the structure, In order to study this effect, a fifteen storey moment resisting building frame, representing a conventional type of regular mid-rise building frame, resting ,on soil type Ee according to Australian Earthquake action code with the shear wave velocity equal to 150 mls is adopted. The numerical analysis using FLAC2D software is carried out for three different cases, namely: (1) fixed-base structure representing the situation excluding the soil-structure interaction (SSI); (2) structure supported by shallow foundation on soft soil; and (3) structure supported by pile foundation in soft soil. Benchmark earthquakes including the 1995 Kobe, the 1994 Northridge, the 1968 Hachinohe, and the 1940 EI Centro earthquakes are adopted. Results indicate that considering soil-structure interaction in both cases with shallow and pile fouudations is vital, and the conventional desigu procedure excluding soil-structure interaction is not adequate to guarantee the structural safety for the moment resisting buildings resting on the soft soil

A CRITERION FOR CONSIDERING SOIL-STRUCTURE INTERACTION EFFECTS IN SEISMIC DESIGN OF DUCTILE RC-MRFs ACCORDING TO IRANIAN CODES

During the last quarter of the 20th century, the importance of dynamic soil-structure interaction for several structures founded on soft soils was well recognized. If not accounted for in analysis, the accuracy in assessing structural safety in the face of earthquakes cannot be accounted for adequately. For this reason, seismic soil-structure interaction analysis has become a major topic in earthquake engineering. As the Iranian Code of Practice for Seismic Resistant Design of Buildings (Standard No. 2800-05) does not address the soil-structure interaction explicitly, the effects of such interaction on behavior of reinforced concrete buildings with ductile moment-resisting frames, loaded and designed according to the Iranian Building Codes, are studied in this research, using direct soil-structure interaction method. To achieve this objective, four types of structures consisting of 3, 5, 7 and 10 story buildings, which represent the typical buildings in a high risk earthquake prone zone, have been selected in conjunction with three types of soil, representing types II, III and IV, as classified in the Iranian Standard No. 2800-05. Ductile Reinforced Concrete Moment-Resisting Frames, as fixed-base structures, once without soil interaction and the next time considering their soil interaction by direct method are modeled and subjected to different earthquake records. The results of the two cases subjected each to different earthquake records are studied and compared. This Comparison led to a criterion indicate that consideration of soil-structure interaction for seismic design, in buildings higher than three stories on soil type IV (Vs<175 m/s) as well as buildings higher than seven stories on soil type III (175<Vs<375 m/s), is essential

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