Comparison of Stability Criteria for Concrete Dams in Different Approximate Methods Based on Finite Element Analysis

AbstractDifferent regulations for the design of concrete dams suggest various criteria for stability control of dams. Some of these criteria, which are conservative, lead to the over-design of dam sections. By using the finite element method, which is considered more accurate than many, this research is intended to determine the accuracy of approximate methods and compare them with each other. Since, according to the regulations, the length of an established crack within the interface between the dam and its foundation is considered a stability indicator to calculate overturning and sliding, the same index has been used here. To give a practical example, using the approximate methods of the U.S. Army Corps of Engineers, U.S. Bureau of Reclamation, and U.S. Federal Energy Regulatory Commission regulations for gravity dams, the stability control and safety factors are calculated in all three. Then, the same example is analyzed on the basis of finite element analytical software such as ANSYS as well as the uplift pressure distribution of regulations, and the safety factors are determined and compared with those calculated by other methods. It is important to note that none of the above regulations refers to the elastic properties of foundation materials in the calculation of base stress distribution and safety factors. Accordingly, for different kinds of foundation materials, the stresses of the base are calculated in the same way, and the types of materials have no effect on the safety factors related to stability. This poses a serious problem in all the above regulations, but this problem does not exist in the finite element method. This research demonstrates the necessity of the finite element method for analyzing gravity dams, even in their initial design phase

Pediatric intracranial dural arteriovenous fistulas: age-related differences in clinical features, angioarchitecture, and treatment outcomes.

OBJECTIVE Intracranial dural arteriovenous fistulas (DAVFs) are rare in children. This study sought to better characterize DAVF presentation, angioarchitecture, and treatment outcomes. METHODS Children with intracranial DAVFs between 1986 and 2013 were retrospectively identified from the neurointerventional database at the authors' institution. Demographics, clinical presentation, lesion angioarchitecture, treatment approaches, angiographic outcomes, and clinical outcomes were assessed. RESULTS DAVFs constituted 5.7% (22/423) of pediatric intracranial arteriovenous shunting lesions. Twelve boys and 10 girls presented between 1 day and 18 years of age; boys presented at a median of 1.3 years and girls presented at a median of 4.9 years. Four of 8 patients ≤ 1 year of age presented with congestive heart failure compared with 0/14 patients > 1 year of age (p = 0.01). Five of 8 patients ≤ 1 year old presented with respiratory distress compared with 0/14 patients > 1 year old (p = 0.0021). Ten of 14 patients > 1 year old presented with focal neurological deficits compared with 0/8 patients ≤ 1 year old (p = 0.0017). At initial angiography, 16 patients harbored a single intracranial DAVF and 6 patients had 2-6 DAVFs. Eight patients (38%) experienced DAVF obliteration by the end of treatment. Good clinical outcome (modified Rankin Scale score 0-2) was documented in 77% of patients > 1 year old at presentation compared with 57% of patients ≤ 1 year old at presentation. Six patients (27%) died. CONCLUSIONS Young children with DAVFs presented predominantly with cardiopulmonary symptoms, while older children presented with focal neurological deficits. Compared with other pediatric vascular shunts, DAVFs had lower rates of angiographic obliteration and poorer clinical outcomes

Computer Aided Constructions of Cages (Logic, Algebraic system, Language and Related Areas in Computer Science)

A k-regular graph of girth g and minimal order is called a (k, g)-cage. The orders of cages are determined for only few sets of parameter pairs (k, g), and the general problem of determining these orders and constructing at least one (k, g)-cage for each pair of parameters is called the Cage Problem. The voltage lift construction is among the most widely used constructions of small (k, g)-graphs, with the orders of the constructed graphs depending on the choice of a base graph, a voltage group, and a specific voltage assignment. Successful application of the voltage lift construction therefore often requires significant computer aided experimentation with the three fundamental ingredients. We survey some known results concerning the voltage lift construction, and discuss ways to decrease the orders of the smallest known (k, g)-graphs for some specific parameter pairs (k, g)

Sustainable design pattern language for CSUN's student housing

The purpose of this graduate project was to achieve a more comprehensive sustainable student housing design by taking into consideration both Humane and Green design principles. The approach was based on Christopher Alexander's design methodology of "Pattern Language". This thesis project presents a Pattern Language framework for creating a more sustainable setting for student housing development. CSUN's student housing has been selected for this study. Observations and interviews with management and students who live in the apartments took place in order to determine most common problems of CSUN's student housings. A series of Humane and Green patterns were developed to address the problems and needs. This process led to suggested solutions and conclusions with a conceptual design proposal in the form of patterns. The proposed Pattern Language was then evaluated by students and two design experts in Pattern Language. The conclusion was that the proposed Pattern Language and design recommendations provide a responsive and humane student housing setting for CSUN's students.Includes bibliographical references (pages 71-75)California State University, Northridge. Department of Family and Consumer Sciences