Engineering Commons^™

A Theoretical Analysis Of Volatile Contaminant Removal By The Pneumatic Fracturing Process, Yuan Ding

Dissertations

A mathematical model that simulates the process of contaminant removal from a pneumatically induced fracture within a porous medium is presented. It includes: (1) model development; (2) parameter evaluation; (3) statistical sensitivity analysis; and (4) model validation.

Based on the dual porosity approach, a mathematical model for a fractured porous formation is developed for both two dimensional and axial symmetrical cases. This model constitutes a pair of coupled partial differential equations for the porous medium and discrete fracture, respectively. The initial and boundary conditions have been determined based on field considerations of a soil vapor extraction system. By means of …

Shear Strength And Fatigue Crack Propagation In Concrete By Energy Method, Wei Wang

Dissertations

The limit analysis methods have been commonly used to predict the ultimate flexure strength of reinforced concrete members over 50 years. However, current design formulas for shear in structural concrete are mostly empirical. In part one of this dissertation, attempts are made to apply the theory of plasticity to predict the shear strengths of reinforced concrete structures.

The modified Coulomb-Mohr failure criterion is used as the constitutive law of concrete, and the plastic flow is assumed to be associated with this failure criterion. A generalized formulation for energy dissipation in accordance with the failure criterion and associated flow rule is …

A Nondestructive Method For The Determination Of Fracture Energy In Concrete Structures, Been-Jyh Yu

Dissertations

It is generally believed that linear elastic fracture mechanics concepts can not be employed in determining fracture parameters in concrete, and therefore most of the current research effort has focused on applying the principles in yielding fracture mechanics. Despite all these efforts, comparison of results reported by many investigators indicate wide variations in fracture toughness values even for essentially similar materials. The main source of discrepancy in the observed results is the existence of a large process zone at the crack tip. Hence, the amount of energy consumed in advancing the crack will depend on the size of the process …

Composite Beam Analogy Fracture Model (Cbafm) : A Non-Linear Fracture Mechanics Model For Concrete, Mohammed Enamul Haque

Dissertations

The main objective of this dissertation is to develop a simple non-linear fracture mechanics model for the determination of fracture mechanics parameters for concrete, such as fracture process zone length (rp), critical fracture energy release rate (Gic), critical stress intensity factor (KO and fracture energy (GF). The fracture process zone (FPZ) is modeled as a damaged non-elastic cohesive band where the extent of damage due to microcracking varies from no damage at the boundary of FPZ to complete crack surface separation at the notch or macro-crack tip. The proposed method can predict theoretically both the pre-peak and post-peak load versus …

Micromechanics Of Hot Mix Asphalt Material Formulation And Numerical Simulation, Kuo-Neng G. Chang

Dissertations

Hot Mix Asphalt (HMA), a highway and airfield pavement material, is heterogeneous, granular, and composite. It is traditionally modeled as a homogeneous material using continuum mechanics or semi-empirical methods. As a result, the above models either neglect or over-simply component reactions, failing to predict field performance problems resulting from particle segregation. This research presents micromechanical modeling, a novel approach that accounts for the components.

A micromechanical model is developed for HMA by modeling it as an assembly of asphalt cement coated particles. The asphalt cement is modeled as a viscoelastic material. To represent asphalt cement, several viscoelastic elements (i.e. Maxwell, …

Analysis Of Plates And Reinforced Concrete Columns By Cubic B-Spline Function, Gang Wang

Dissertations

Applying spline functions to numerical structural analysis has been more common in recent years. The recent increase use of spline functions is mainly due to their excellent characteristics, such as sectionalized continuity, linear combination, flexibility, and easy use for various boundary conditions. The whole deformed shape of some structures or substructures can be described with one displacement function constructed by a series of spline functions. By doing this, the mesh generation and the huge computer memory space are no longer needed because only one single superelement can be used in the whole process. The choice of spline functions as displacement …