Evolution of nonlocal damage in steel under cyclic straining

For high dynamic excitation, e.g. by earthquakes, the vibrations of steel structures lead to inelastic material behavior. Hystereses, developing under cyclic loading, are responsible for the dissipation of energy. Additionally, stress concentration at small defects results in the nucleation and the growth of microvoids which is referred to as damage, here especially as ultra low cycle fatigue. The material damage influences the stiffness of a structure and its response to dynamic excitation. With increasing load the voids can coalesce and form a macrocrack which destroys the structural integrity and peril the overall safety. A material model is proposed which describes the evolution and distribution of inelastic strains and isotropic ductile damage for mild construction steel by means of a set of internal variables. Viscoplasticity as well as isotropic and kinematic hardening are taken into account. The evolution of isotropic hardening is related to the growth of a strain memory surface which accounts for the strain amplitude history of the material. Under tension isotropic ductile damage develops for significant inelastic strains [1]. The material model is implemented in the frameworks of the finite element method with displacement based ansatz functions. The equation of motion is solved with the Newmark method. To overcome the phenomenon of vanishing dissipation energy in case of mesh refinement due to strain localization a nonlocal extension in the form of an implicit gradient formulation is applied. The presented model is used to analyse 3D structures subjected to seismic excitation

Strain Limits for Concrete Filled Steel Tubes in AASHTO Seismic Provisions

INE/AUTC 13.1

The Effect of Load History on Reinforced Concrete Bridge Column Behavior

INE/AUTC 12.1

Seismic Performance of Steel Pipe Pile to Cap Beam Moment Resisting Connections

INE/AUTC 13.0

Imaging of a fluid injection process using geophysical data - A didactic example

In many subsurface industrial applications, fluids are injected into or withdrawn from a geologic formation. It is of practical interest to quantify precisely where, when, and by how much the injected fluid alters the state of the subsurface. Routine geophysical monitoring of such processes attempts to image the way that geophysical properties, such as seismic velocities or electrical conductivity, change through time and space and to then make qualitative inferences as to where the injected fluid has migrated. The more rigorous formulation of the time-lapse geophysical inverse problem forecasts how the subsurface evolves during the course of a fluid-injection application. Using time-lapse geophysical signals as the data to be matched, the model unknowns to be estimated are the multiphysics forward-modeling parameters controlling the fluid-injection process. Properly reproducing the geophysical signature of the flow process, subsequent simulations can predict the fluid migration and alteration in the subsurface. The dynamic nature of fluid-injection processes renders imaging problems more complex than conventional geophysical imaging for static targets. This work intents to clarify the related hydrogeophysical parameter estimation concepts

Internet conferencing tools for deaf and hard of hearing users

This research study investigates Internet chat visual tools in communications used by Deaf and hard of hearing users and how the users interact with the chat tools expressing their visual language to convey the best message they can in general. A number of Internet chat tools consisting of visual emoticons have been established and implemented for online communications. These tools are generalized for public use. In this study, the research includes the current IM model, along with my recent studies, which use Deaf/hard of hearing for this project. An analysis of the results and prototype of this study on Internet Chat tools for Deaf and hard of hearing users is included. The majority of the Deaf and hard of hearing users prefer an animated library of smiley faces