A Study of the Behavior of Shell Footings using Finite Element Analysis

In this research, the conical shell foundation is investigated. The two components of the interacting system; the soil and the shell foundation, are modelled using the finite element method. In this study, 15-node isoparametric triangular axisymmetric elements with two degrees of freedom at each node are used to model the shell and soil. The soil-structure interaction between the footing and the supporting medium are modelled using interface elements. Comparison between the results obtained by the present analysis and those obtained by other investigations are made. The present analysis shows satisfactory results when compared with those obtained by other studies with largest percentage difference of 14% in the value of the ultimate load. Parametric studies have been carried out to investigate the effect of some important parameters on the behaviour of shell foundations. Three parameters are considered which are: semi-vertical angle, footing embedment and edge beam

NUMERICAL ANALYSIS OF THIN BEAMS RESTING ON NONLINEAR ELASTIC FOUNDATIONS

The finite difference method is used for solving the basic differential equation for the elastic deformation of a thin beam supported on a nonlinear elastic foundation. A tangent approach is used to determine the modulus of subgrade reaction after constructing a second degree equation for load-deflection diagram. Results of plate loading test of soil obtained in Iraq were used in the analysis. An iterative approach is used for solving the nonlinear problem until the convergence of the solution. The method of analysis, as programmed for a computer solution, considers the continuous elastic, nonlinear foundation to be active only when the beam is pressing against the foundation. Two examples of with simply supported beams are presented to illustrate the application of the method of analysis

ANALYSIS OF TIMOSHENKO BEAM RESTING ON NONLINEAR COMPRESSIONAL AND FRICTIONAL WINKLER FOUNDATION

ABSTRACT This paper deals with linear elastic behavior of deep beams resting on linear and nonlinear Winkler type elastic foundations with both compress ional and tangential resistances. The basic or governing equations of beams on nonlinear elastic Winkler foundation are solved by finite difference method. The finite element method in Cartesian coordinates is formulated using two dimensional plane stress isoparametric finite elements to model the deep beam and elastic springs to model the foundation. Two computer programs coded in fortran_77 for the analysis of beams on nonlinear elastic foundations are developed. Comparisons between the two methods and other studies are performed to check the accuracy of the solutions. Good agreement was found between the solutions with percentage difference of 3%. Several important parameters are incorporated in the analysis, namely, the vertical subgrade reaction, horizontal subgrade reaction and beam depth to trace their effects on deflections, bending moments and shear forces

Free Vibration of Simply Supported Beam on Elastic Foundations

Fourier series and finite element analysis are utilized to obtain the solution of simply supported beams resting on elastic foundations with different loadings in order to arrive at a free vibration. The equation of the free vibration of beam on elastic foundation is derived and solved. Good agreement has been obtained between the results of the present study Fourier and finite element analysis and other previous solutions. The effect of modulus of subgrade reaction, axial tension force (foundation modulus) and beam depth on the behavior is studied

Hollow Core Slabs on Winkler Foundation

This research dealt with the linear elastic behavior of hollow core slabs resting on a linear Winkler type foundation. A finite difference method was used to model the slabs as wide beams and the foundation as elastic springs. The finite element method was also used to model the problem using ABAQUS 6.10 software program. A comparison between the method proposed in this paper and methods from previous studies was made to check the accuracy of the solutions. Several important parameters were incorporated in the analysis, viz. the hollow core size and shape, subgrade reaction and slab depth, to trace their effects on deflections, bending moments and shear forces. A computer program coded in Fortran was developed for the analysis of hollow core slabs on an elastic foundation. It was found that the maximum difference in deflection between the present study and the exact solution was 3% for the finite difference and 7% for the finite element method

Finite Element Analysis of Thick Orthotropic Square Plates on Elastic Foundations

This paper deals with the linear elastic behavior of thick orthotropic square plates on Winkler type elastic foundations with both compressional and tangential resistances. The finite element method with different isoparametric thick plate and brick elements are used to solve problems, which were previously solved by the finite difference method. Good agreement is found between the different methods with percentage difference about 1%

Association of vitamin D status in the pathogenesis of chronic obstructive pulmonary disease

Background: The most important pathogenic mechanisms involved in the development of chronic obstructive pulmonary disease (COPD) are protease–antiprotease imbalance, inflammation, lung remodeling and oxidative stress. Interestingly, lower vitamin D levels have been related to regulation of each of these processes, that is, higher expression of proteases, modulation of inflammation, modulation of extracellular matrix turnover, and increased oxidative stress. Thus, one can speculate that lower vitamin D levels may be linked to increased risk of developing COPD. In some clinical studies, lower levels of vitamin D, measured as plasma 25-hydroxyvitamin D (25(OH)D), have been associated with lower lung function and faster lung function decline, but the results are conflicting. Aim of the study: The aim of this study is to evaluate the evidence of the effect of vitamin D on COPD. Subjects and methods: The present study, included 120 subjects, 80 patients diagnosed as COPD and 40 healthy volunteers (20 smokers and 20 nonsmokers). Plasma 25-OHD was measured by Enzyme Linked Immunosorbent Assay (DiaSorin, Stillwater, Minnesota, USA) in all study participants. Results: The mean concentration of 25-OH-D was significantly higher in the reference groups (smokers and nonsmokers) compared with severe COPD group (p = 0.001, 0.001) respectively. The mean concentration of 25-OH-D was significantly higher in the reference groups (smokers and nonsmokers) compared with moderate COPD group (p = 0.029, 0.049) respectively. The mean concentration of 25-OH-D was not significantly higher in the reference groups (smokers and nonsmokers) compared with the mild COPD group. Conclusion: We observed a novel association of lower plasma 25(OH)D levels with a higher risk of COPD

Role of oxidant–antioxidant imbalance in the pathogenesis of chronic obstructive pulmonary disease

Background: Chronic obstructive pulmonary disease (COPD) is a common respiratory condition involving the airways and characterized by airflow limitation. Antioxidants are substances that may protect cells from the damage caused by unstable molecules known as free radicals. Antioxidants interact with and stabilize free radicals and may prevent some of the damage free radicals might otherwise cause. Under physiological conditions a balance exists between the amount of reactive oxygen species (ROS) produced in normal cellular metabolism and the endogenous antioxidant defense. An imbalance between the antioxidant capacity and the production of reactive oxygen species leads to oxidative stress, which is associated with the pathogenesis of several human diseases. An oxidant/antioxidant imbalance has been proposed as having a key role in the pathogenesis of COPD. The lung is directly exposed to high levels of oxygen, and therefore has to have efficient antioxidant mechanisms. Aim of the study: To examine the role of altered levels of oxidant–antioxidants in disease severity of COPD and correlate it with the degree of airflow obstruction in the Egyptian population. Subjects and methods: Eighty subjects with COPD, 20 healthy smokers, and 20 healthy nonsmokers participated in this study. The investigation included determination of the lung function and the measurements of plasma superoxide dismutase activity (SOD), glutathione content (GSH) reduced form, glutathione peroxidase activity (GSH-Px), catalase activity (CAT), lipid peroxidase (LP), and nitric oxide (NO). Results: The mean concentration of nitric oxide (NO) was significantly higher in the control subjects (smokers and nonsmokers) compared with the COPD group (p = 0.001, 0.0001) respectively. Also the mean concentration of nitric oxide (NO) was significantly higher in control nonsmoker group compared to control smoker group (p = 0.002). The mean concentration of lipid peroxidase (LP) was significantly higher in COPD patients compared with control subjects (smokers and nonsmokers), (p = 0.0001, 0.0001) respectively. The mean concentration of glutathione (GSH) was significantly higher in the control subjects (smokers and nonsmokers) compared with COPD patients (p = 0.001, 0.001) respectively. There is no significant difference in the concentration of glutathione-peroxidase (GSH-Px) in all study participants (COPD patients, control smokers, control nonsmokers). The mean concentration of catalase (CAT) was significantly higher in control nonsmokers, compared to COPD patients and control smokers (p = 0.001, 0.018) respectively. The mean concentration of superoxide dismutase (SOD) was significantly higher in the control subjects (smokers and nonsmokers) compared with COPD patients (p = 0.012, 0.001) respectively. Also the mean concentration of superoxide dismutase (SOD) was significantly higher in control nonsmoker group compared to control smoker group (p = 0.001). Conclusion: These results support the hypothesis that an oxidant–antioxidant imbalance, associated with oxidative stress in COPD patients, plays an important role in the progression of disease severity, also these results revealed the presence of an oxidative presence in smokers and in subjects with COPD and that the imbalance may be important in the pathogenesis of this disease. The use of cigarette increased oxidative stress by causing plasma lipid peroxidation and imbalance in erythrocyte antioxidant. Nitric oxide (NO) metabolism was not increased in patients with chronic obstructive pulmonary disease compared to healthy subjects. It has been reported that GSH plays a major role in pulmonary antioxidant protection