Monotonic Loading (monotonic + loading)

Distribution by Scientific Domains

Selected Abstracts

Cyclic behavior of laterally loaded concrete piles embedded into cohesive soil

Rabin Tuladhar
Abstract Modern seismic design codes stipulate that the response analysis should be conducted by considering the complete structural system including superstructure, foundation, and ground. However, for the development of seismic response analysis method for a complete structural system, it is first imperative to clarify the behavior of the soil and piles during earthquakes. In this study, full-scale monotonic and reversed cyclic lateral loading tests were carried out on concrete piles embedded into the ground. The test piles were hollow, precast, prestressed concrete piles with an outer diameter of 300,mm and a thickness of 60,mm. The test piles were 26,m long. Three-dimensional (3D) finite element analysis was then performed to study the behavior of the experimental specimens analytically. The study revealed that the lateral load-carrying capacity of the piles degrades when subjected to cyclic loading compared with monotonic loading. The effect of the use of an interface element between the soil and pile surface in the analysis was also investigated. With proper consideration of the constitutive models of soil and pile, an interface element between the pile surface and the soil, and the degradation of soil stiffness under cyclic loading, a 3D analysis was found to simulate well the actual behavior of pile and soil. Copyright 2007 John Wiley & Sons, Ltd. [source]

Explicit integration of bounding surface model for the analysis of earthquake soil liquefaction

Konstantinos I. Andrianopoulos
Abstract This paper presents a new plasticity model developed for the simulation of monotonic and cyclic loading of non-cohesive soils and its implementation to the commercial finite-difference code FLAC, using its User-Defined-Model (UDM) capability. The new model incorporates the framework of Critical State Soil Mechanics, while it relies upon bounding surface plasticity with a vanished elastic region to simulate the non-linear soil response. Stress integration of constitutive relations is performed using a recently proposed explicit scheme with automatic error control and substepping, which so far has been employed in the literature only for constitutive models aiming at monotonic loading. The overall accuracy of this scheme is evaluated at element level by simulating cyclic loading along complex stress paths and by using iso-error maps for paths involving change of the Lode angle. The performance of the new constitutive model and its stress integration scheme in complex boundary value problems involving earthquake-induced liquefaction is evaluated, in terms of accuracy and computational cost, via a number of parametric analyses inspired by the successful simulation of the VELACS centrifuge Model Test No. 2 studying the lateral spreading response of a liquefied sand layer. Copyright 2009 John Wiley & Sons, Ltd. [source]

A 2-D constitutive model for cyclic interface behaviour

Giuseppe Mortara
Abstract The paper concerns a 2-D constitutive model for interface behaviour between sand and solid inclusions under cyclic loading. The model is based on the experimental results obtained from laboratory direct shear interface tests conducted under both constant normal load (CNL) and constant normal stiffness (CNS) conditions. The model is formulated in terms of interface stresses and relative velocities and has been derived by extending an elastoplastic isotropic model previously formulated for monotonic loading to stress reversal paths. Such extension consists in adding to the isotropic hardening mechanism a kinematic rotational one defined by an inner conical surface rotating around the origin of the stress space. This allows one to store the memory of the previous stress and relative displacement history giving to the model the capability to analyse the interface behaviour under cyclic loading. After a brief description of the criteria governing the monotonic model, the paper describes in detail the features of the kinematic hardening. Finally, the predictions of the model are compared with the experimental results obtained from CNL and CNS interface tests. Copyright 2002 John Wiley & Sons, Ltd. [source]

Some aspects of the mechanical response of BMI 5250-4 neat resin at 191C: Experiment and modeling,

M. B. Ruggles-Wrenn
Abstract The inelastic deformation behavior of BMI-5250-4 neat resin, a high-temperature polymer, was investigated at 191C. The effects of loading rate on monotonic stress,strain behavior as well as the effect of prior stress rate on creep behavior were explored. Positive nonlinear rate sensitivity was observed in monotonic loading. Creep response was found to be significantly influenced by prior stress rate. Effect of loading history on creep was studied in stepwise creep tests, where specimens were subjected to a constant stress rate loading followed by unloading to zero stress with intermittent creep periods during both loading and unloading. The strain-time behavior was strongly influenced by prior deformation history. Negative creep was observed on the unloading path. In addition, the behavior of the material was characterized in terms of a nonlinear viscoelastic model by means of creep and recovery tests at 191C. The model was employed to predict the response of the material under monotonic loading/unloading and multi-step load histories. 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

Osteon pullout in the equine third metacarpal bone: Effects of ex vivo fatigue

L. P. Hiller
Abstract An important concept in bone mechanics is that osteons influence mechanical properties in several ways, including contributing to toughness and fatigue strength by debonding from the interstitial matrix so as to ,bridge" developing cracks. Observations of ,pulled out, osteons on fracture surfaces are thought to be indicative of such behavior. We tested the hypothesis that osteon pullout varies with mode of loading (fatigue vs. monotonic), cortical region, elastic modulus, and fatigue life. Mid-diaphseal beams from the dorsal, medial, and lateral regions of the equine third metacarpal bone were fractured in four point bending by monotonic loading to failure under deflection control, with or without 105 cycles of previous fatigue loading producing 5000 microstrain (15,20% of the expected failure strain) on the first cycle; or sinusoidal fatigue loading to failure, under load or deflection control, with the initial cycle producing 10,000 microstrain (30,40% of the expected failure strain). Using scanning electron microscopy, percent fracture surface area exhibiting osteon pullout (%OP.Ar) was measured. Monotonically loaded specimens and the compression side of fatigue fracture surfaces exhibited no osteon pullout. In load-controlled fatigue, pullout was present on the tension side of fracture surfaces, was regionally dependent (occurring to a greater amount dorsally), and was correlated negatively with elastic modulus and positively with fatigue life. Regional variation in %OP.Ar was also significant for the pooled (load and deflection controlled) fatigue specimens. %OP.Ar was nearly significantly greater in deflection controlled fatigue specimens than in load-controlled specimens (p < 0.059). The data suggest that tensile fatigue loading of cortical bone eventually introduces damage that results in osteonal debonding and pullout, which is also associated with increased fatigue life via mechanisms that are not yet clear. 2002 Orthopaedic Research Society. Published by Elsevier Science Ltd. All rights reserved. [source]

Effects of loading rate on viscoplastic properties of polymer geosynthetics and its constitutive modeling

Fang-Le Peng
On the basis of the special tensile test results under various loading histories, the rate-dependent behaviors of three polymer geosynthetics due to their viscous properties have been investigated. All the investigated polymer geosynthetics show significant loading rate effects, creep deformation, and stress relaxation. Except for the polyester geogrid showing the combined viscosity, all the investigated polymer geosynthetics exhibit the isotach viscosity. An elasto-viscoplastic constitutive model described in a nonlinear three-component model framework is developed to simulate the rate-dependent behaviors of polymer geosynthetics. The developed constitutive model is verified by comparing its simulated results with the experimental data of polymer geosynthetics presented in this study and those available from the literature. The comparison indicates that the developed model can reasonably interpret the rate-dependent behaviors of polymer geosynthetics under arbitrary loading histories, including the step-changed strain rate loading, creep, and stress relaxation applied during otherwise monotonic loading (ML). POLYM. ENG. SCI., 2010. 2009 Society of Plastics Engineers [source]