Small Strain Finite Element Analyses Research Articles

Large-Deformation Numerical Modeling of Short-Term Compression and Uplift Capacity of Offshore Shallow Foundations

AbstractLarge-deformation finite-element analysis has been used to model the undrained response of skirted shallow foundations in uplift and compression. Large-deformation effects involve changes in embedment ratio and operative local soil shear strength with increasing foundation displacement—either in tension or compression. Centrifuge model testing has shown that these changes in geometry affect the mobilized bearing capacity and the kinematic mechanisms governing failure in undrained uplift and compression. Small-strain finite-element analysis cannot by definition capture the effects of changing foundation embedment ratio and variation in local soil strength with foundation displacement. In this paper, load-displacement relationships, ultimate capacities, and kinematic mechanisms governing failure from large-deformation finite-element analyses are compared with centrifuge model test results for circular skirted foundations with a range of embedment between 10 and 50% of the foundation diameter. The re...

Consolidation beneath Circular Skirted Foundations

The effect of foundation embedment on consolidation has not been considered previously in a systematic manner, although this is of particular interest for offshore foundations, where embedment is provided by skirts that enclose a compressible soil plug. For skirted foundations, critical uncertainties include what to assume in terms of the degree of drainage at skirt tip level, and the relative time scales of consolidation within the soil plug and beneath the foundation. In this paper, results from small strain finite-element analyses are used to quantify the immediate and time-dependent response of circular skirted foundations to uniaxial vertical loading. Foundations with frictionless and fully rough skirt-soil interfaces with varying ratio of embedment depth to foundation diameter are considered and the responses compared with those for surface foundations. The findings show that both skirt-soil interface roughness and embedment ratio have a significant effect on the consolidation response.

Three-Dimensional Large Deformation Finite-Element Analysis of Plate Anchors in Uniform Clay

Three-dimensional large deformation finite-element (FE) analyses were performed to investigate plate anchor capacity during vertical pullout. The remeshing and interpolation technique with small strain approach was expanded from two-dimensional to three-dimensional conditions and coupled with the FE software, ABAQUS. A modified recovery of equilibrium in patches technique was developed to map stresses after each remeshing. Continuous pullout of rectangular plate anchors was simulated and the large deformation results for strip, circular, and rectangular anchors were compared with model test data, small strain FE results, and plastic limit solutions. Interface conditions of no breakaway (bonded) and immediate breakaway (no tension) were considered at the anchor base. The effects of anchor roughness, aspect ratio, soil properties, and soil overburden pressure were investigated. It was found that the anchor roughness had minimal effect on anchor performance. For square and circular deep anchors under immediate breakaway conditions, the maximum uplift capacity increased with soil elastic modulus, which suggests that lower bound limit analysis and small strain FE analysis may overestimate the capacity. The soil beneath the anchor base separates from the anchor at a certain embedment depth near the mudline, once tensile stresses were generated. The ratio of separation depth to anchor width was found to increase linearly with the ratio of soil undrained shear strength to the product of soil effective unit weight and anchor width and was independent of the initial anchor embedment depth.

An operator‐split ALE model for large deformation analysis of geomaterials

AbstractAnalysis of large deformation of geomaterials subjected to time‐varying load poses a very difficult problem for the geotechnical profession. Conventional finite element schemes using the updated Lagrangian formulation may suffer from serious numerical difficulties when the deformation of geomaterials is significantly large such that the discretized elements are severely distorted. In this paper, an operator‐split arbitrary Lagrangian–Eulerian (ALE) finite element model is proposed for large deformation analysis of a soil mass subjected to either static or dynamic loading, where the soil is modelled as a saturated porous material with solid–fluid coupling and strong material non‐linearity. Each time step of the operator‐split ALE algorithm consists of a Lagrangian step and an Eulerian step. In the Lagrangian step, the equilibrium equation and continuity equation of the saturated soil are solved by the updated Lagrangian method. In the Eulerian step, mesh smoothing is performed for the deformed body and the state variables obtained in the updated Lagrangian step are then transferred to the new mesh system. The accuracy and efficiency of the proposed ALE method are verified by comparison of its results with the results produced by an analytical solution for one‐dimensional finite elastic consolidation of a soil column and with the results from the small strain finite element analysis and the updated Lagrangian analysis. Its performance is further illustrated by simulation of a complex problem involving the transient response of an embankment subjected to earthquake loading. Copyright © 2007 John Wiley & Sons, Ltd.

Analysis of Plane Stress Ductile Fracture Propagation by Simulating Necking

Fracture experiments at room temperature on full-scale specimens fabricated from relatively thin plates of HSLA-80 and EH-36 ship steel consistently show the development of the plastic limit load on the net section and ductility greater than times yield strain, despite large fatigue cracks. A limit-load analysis can accurately predict the load at any point in the deformation if the crack length is known. Predicting crack extension using a constant crack-opening angle is a simple and reasonably accurate approach. The difficulty is in predicting the onset of extension after the development of strain localization. A simple approach using conventional small-strain finite-element analysis and a special “necking” stress–strain curve that is calibrated from conventional tensile test data is proposed. This approach gives very good predictions of the onset and propagation of ductile tears, including the spread of plasticity to the gross section.

On Higher-Order Crack-Tip Fields in Creeping Solids

In view of the near-tip constraint effect imposed by the geometry and loading configuration, a creep fracture analysis based on C* only is generally not sufficient. This paper presents a formulation of higher-order crack-tip fields in steady power-law creeping solids which can be derived from an asymptotic development of near-tip fields analogous to that of Sharma and Aravas and Yang et al. for elastoplastic bodies. The higher-order fields are controlled by a parameter named A2*, similar as in elastoplasticity, and a second loading parameter, σ∞. By means of the scaling properties for power-law materials, it is shown that A2* for a flat test specimen is independent of the loading level. Finally, we carry out small-strain finite element analyses of creep in single-edge notched tension, centered crack panel under tension, and single-edge notched bending specimens in order to determine the corresponding values of A2* for mode I cracks under plane-strain conditions. [S0021-8936(00)01202-2]