Optimum Design of Cable-Stayed Bridges

Owing to their excellent structural characteristics, aesthetic appearance, low maintenance cost, and efficient use of structural materials, cable-stayed bridges have gained much popularity in recent decades. Stay cables of a cable stayed bridge are post-tensioned to counteract the effect of the bridge dead load. The solution for an optimum distribution of post-tensioning cable forces is considered one of the most important and difficult tasks in the design of cable-stayed bridges. A novel approach that utilizes the finite element method, B-spline curves, and real coded genetic algorithm to determine the global optimum post-tensioning cable forces is developed. The effect of geometric nonlinearity on the determination of the post-tensioning cable forces is assessed. The study is further extended to develop the first surrogate polynomial functions that can be used to evaluate the post-tensioning cable forces in semi-fan cable stayed bridges. The developed post tensioning functions are then used to investigate the optimal geometric configurations, which lead to the most uniform distribution of the post-tensioning cable forces. Details of an optimization code developed in-house specifically to optimize the design of composite cable-stayed bridges with semi-fan cable arrangement are then reported. The optimization design code integrates a finite element model, the real coded genetic algorithm, the post tensioning polynomial functions, and the design provisions provided by the Canadian Highway Bridge Design Code. An extensive parametric study is then conducted using this optimization code to develop a database for the optimum design of semi-fan cable stayed bridges. The database covers bridge lengths ranging from 250 m to 700 m. It describes the variations of the optimum design parameters, such as the main span length,height of the pylon, number of stay cables, and cross-sectional dimensions with the total length of the bridge

Geochemistry of fluid inclusions in the Vazante zinc deposit, Minas Gerais, Brazil

The Vazante deposit in Minas Gerais, southeast-central Brazil is the world’s largest known occurrence of hypogene non-sulfide zinc (HNSZ) mineralization, originally consisting of about 28.5 million tonnes of ore at an average grade of 18% zinc. The zinc mineralization consists mainly of willemite with lesser, broadly coeval sphalerite and is hosted by sheared Proterozoic slaty dolomites. The Vazante deposit lies at the southern end of the 120 km long Vazante-Unaí trend, the largest district of Zn-Pb mineralization in Brazil, which consists of both hypogene non-sulfide and sulfide deposits. All of the Vazante-Unaí mineralization lies within the Brasília fold belt in the western part of the Bambuí foreland basin and is thought to be a product of fluids mobilized by the 630-610 Ma Brasiliano orogeny. Little is known about the nature of the fluids that form HNSZ deposits beyond fluid inclusion bulk salinities and homogenization temperatures. The present study of the Vazante deposit is the first to measure the elemental composition of potential mineralizing fluids in a HNSZ deposit, and was carried out using LA-ICP-MS and microthermometry. The analyses were all performed on fluid inclusions hosted by sphalerite, as no primary fluid inclusions were identified in willemite. Most of the primary fluid inclusions in sphalerite were found to contain aqueous liquid and vapor in highly variable proportions. Some primary fluid inclusions (~20%) consist entirely of aqueous liquid. Most secondary fluid inclusions were found to consist of a single aqueous liquid phase with about 10% consisting of aqueous liquid + vapor. A few fluid inclusions were observed to contain rhombohedral crystals, which are interpreted to be accidental carbonate mineral inclusions rather than daughter minerals based on their inconsistent occurrence within fluid inclusion assemblages, variable sizes in proportion to their host fluid inclusion sizes, and the abundance of carbonate mineral inclusions in the sphalerite matrix. Microthermometry was performed only on the liquid-vapor primary fluid inclusions and yielded highly variable homogenization temperatures ranging between 47 and 352° C. This high degree of variability is interpreted to be a product either of the deformation and low grade metamorphism that affected the Vazante-Unaí trend during the Brasiliano orogeny, or of necking down during cooling. Salinities were also found to be highly variable, ranging from 0.9 to 22 equivalent weight percent NaCl, and are interpreted to reflect mixing of a saline fluid with a dilute fluid. No correlation between salinity and homogenization temperature was observed. LA-ICP-MS analyses were preformed after the microthermometry analyses to determine the elemental compositions of the fluid inclusions. Absolute elemental concentrations varied widely in keeping with the wide range of fluid inclusion salinities, but the atomic ratios of elements with respect to Na were relatively constant as a function of salinity, consistent with the pattern expected from the dilution of a saline fluid. Average atomic ratios were K/Na = 0.36, Mg/Na = 0.078, Ca/Na = 0.12, and Sr/Na = 0.001. Ba was consistently detected in the fluid inclusions at concentrations of 10’s to 100’s of ppm. Pb was quantifiable in about 14% of the fluid inclusions in concentrations of 100’s to 1000’s of ppm. Vazante fluid inclusion compositions obtained from the present study were compared to Morro Agudo fluid inclusion compositions obtained from previous studies. Vazante and Morro Agudo fluid inclusions were found to have similar K/Na and Ba/Na ratios but Vazante fluid inclusions were found to have significantly lower Mg/Na, Ca/Na, and Sr/Na ratios and to be overall more dilute. Also, none of the Morro Agudo fluid inclusions contained any detectable Pb. Thus, the Vazante and Morro Agudo deposits and their corresponding different styles of mineralization appear to have been formed by different fluids. The compositions of Vazante fluid inclusions were also compared to the compositions of fluid inclusions in Mississippi Valley-type (MVT) deposits in the central United States and in the Irish deposits. Vazante fluid inclusions were found to have higher Ba/Na, K/Na, and Mg/Na but lower Ca/Na and Sr/Na atomic ratios than Ozark MVT fluid inclusions. Vazante fluid inclusions were also found to be distinct from Irish fluid inclusions, having higher Ca/Na, K/Na, and Mg/Na ratios but lower Ba/Na and Sr/Na ratios than Irish fluid inclusions. The fluid inclusion microthermometry and LA-ICP-MS data suggest that the Vazante mineralization formed as a result of dilution of a brine. Willemite and sphalerite solubility are identically sensitive to salinity, but willemite solubility decreases more strongly than sphalerite solubility with respect to pH increase. If the diluting fluid had a higher pH than the brine, then the higher fraction of dilute fluid present in Vazante fluid inclusions compared to Morro Agudo fluid inclusions may mean that the pH of the ore fluid mixture at Vazante was higher than at Morro Agudo, which would favor willemite precipitation and explain its predominance at Vazante. This hypothesis was tested using reaction path modeling, in which potential end member ore fluids were extracted from the fluid inclusion data and allowed to mix. The results confirmed that willemite precipitation should predominate over sphalerite when a cool, dilute, basic, oxidizing fluid mixes with a hotter, saline, acidic, reducing fluid, and produce an overall ore mineral assemblage that resembles what is observed in the field

Investigation on Mechanical Properties of 302 L Stainless Steel Sheets under constant amplitude loading

 في هذه الدراسة تمت دراسة الخواص الميكانيكية مثل مقاومة الكلال وظاهرة نمو شق الكلال لصفائح الفولاذ المقاوم للصدأ 302 (S.SL بأسماك مختلفة (0.05 ملم، 0.1 مم و1.5 ملم). وأجريت التجارب العملية بالإضافة الى تقدير حياة الكلال باستخدام نموذج ووكر. تم إعداد العينات وفقا لمعيار المواصفات الامريكية العالمية E647-08. وأظهرت النتائج أن عينات الفولاذ بسمك 0.05 ملم أظهرت مقاومة الشد أعلى ولكن ليونة محدودة مع عدم وجود دليل واضح على مقاومة الخضوع بالمقارنة مع العينات الفولاذية الأخرى بأسماك 0.1 ملم و1.5 ملم.In this study, the mechanical properties i.e., fatigue strength and fatigue crack growth (FCG) behaviour of 302 L stainless steel (S.S.) sheets with different thicknesses (0.05 mm, 0.1 mm and 1.5 mm) were investigated. The experimental investigation as well as fatigue life predication by using Walker model were performed. The FCG specimens were prepared according to the ASTM E647-08 standard. The results showed that S.S. sheet with 0.05 mm thickness exhibited higher tensile strength but limited ductility with no clear evidence of yielding as compared to 0.1 mm and 1.5 mm thickness

Experimental Analysis of Fatigue Crack Path for Strained Functionally Graded Materials

This paper experimentally discusses crack paths in strained Functionally graded materials under constant loading conditions and vibration fatigue. The objective is to synthesize the body of knowledge on the stability of FGM. The article presents the development, production, and characterization of multi-Al (aluminum), Ni (nickel), and Titanium alloys. FGM it was successfully modified using the powder metallurgical technique. Five-layer FGM samples frequently utilize (Al, Ni), on one end and (Al-Ni-Ti) on the first. FGM sample mechanical characteristics have been investigated using wear and Fatigue testing. The Al/Ni/Titanium FGM compact specimen approaches the yield stress and ultimate stress values, which is regarded as a significant improvement in mechanical qualities with less weight. The test findings are for a constant amplitude load fully reversed with zero mean stress. The stress life approach examined three samples' fatigue characteristics and natural frequency under random vibration

Surface cracks growth for superalloy in a round bar under different loading

The main objective of this paper is to experimentally and numerically detect the surface cracks in the round bar for Ni-Al- 315 steel superalloy and calculate the crack depth which induces the sintering of these alloys. Several factors have contributed to surface defects, such as metallurgical defects and notches. The surface crack orientation can be estimated at the observed crack increase by using displacement. Various crack aspect ratios, a/b, ranging from 0.0 to 1.0, and relative crack depth, a/D, ranging from 0.2 to 0.4, are considered. The superalloy (Ni, Al and 315 steel) has been successfully modified utilizing the powder metallurgical process. The specimens are typically made up of Six layers, starting with (Al, Ni) across one side and ending with (Ni-Al- 315 steel) on another. Transmission electron microscopy (SEM) Instrument analysis has been used to detect the surface cracks and analyze the microstructure of superalloy used in detail using the X-pert analytical program

Synthesis and Spectral Analysis of Some Metal Ions Complexes with Mixed Ligands of Schiff Base and 1, 10-Phenanthroline

The free Schiff base ligand (HL1) is prepared by being mixed with the co-ligand 1, 10-phenanthroline (L2). The product then is reacted with metal ions: (Cr+3, Fe+3, Co+2, Ni+2, Cu+2 and Cd+2) to get new metal ion complexes. The ligand is prepared and its metal ion complexes are characterized by physic-chemical spectroscopic techniques such as: FT-IR, UV-Vis, spectra, mass spectrometer, molar conductivity, magnetic moment, metal content, chloride content and microanalysis (C.H.N) techniques. The results show the formation of the free Schiff base ligand (HL1). The fragments of the prepared free Schiff base ligand are identified by the mass spectrometer technique. All the analysis of ligand and its metal complexes are in good agreement with the theoretical values indicating the purity of Schiff base ligand and the metal complexes. From the above data, the molecular structures for all the metal complexes are proposed to be octahedra

Labor outcome among obese postdate women undergoing labor induction

Background: Maternal obesity and postdate pregnancy are common findings among pregnant women worldwide. We aimed to evaluate the influence of maternal obesity on the outcome of labor induction for postdate pregnant women.Methods: We conducted a prospective observational study to compare 118 obese women (≥30 kg/m2) with 118 non-obese women (<30 kg/m2) undergoing labor induction for postdate pregnancy (≥41 weeks). We induced all participants by a uniform protocol according to the Bishop score. The primary outcome measures were the cesarean delivery (CD) rate and the rate of failed induction. Secondary outcomes included prolonged induction- delivery time, prolonged first and second stage of labor, and rate of instrumental delivery. We performed a multivariate regression model to assess for the relation between obesity and the study outcomes of interest.Results: Cesarean delivery was significantly higher in obese women when compared with non-obese women (25.4% vs. 12.7%, p=0.02). Likewise, failed induction rate was significantly lower among non-obese women (5.1% vs. 14.4%. p=0.026). Obese women had increased odds for CD (adjusted odds ratio: 2.24; 95% confidence-interval: 1.13-4.33), failed induction rate (adjusted OR 2.96; 95% CI: 1.15-8.17), prolonged induction-delivery time (adjusted OR 4.57; 95% CI: 1.42-14.74), prolonged first stage of labor (adjusted OR 3.32; 95% CI: 1.07-9.89), prolonged second stage of labor (adjusted OR 4.21; 95% CI: 1.27-13.62), and rate of instrumental delivery (adjusted OR 2.97; 95% CI: 1.16-8.23).Conclusions: Obesity adds more risk to postdate women undergoing induction of labor. Obesity increases the incidence of CD and failed induction among induced postdate women. Therefore, obstetricians should encourage obese women to reduce weight before getting pregnant, and to comply with the optimal weight gain during pregnancy in attempt to reduce the rates of postdating, CD and failed induction

Validity of Finite Element Method: Analysis of Laminated Composite Decks Plates Subjected to in Plane Loading

To verify the accuracy of the present technique, buckling loads are evaluated and validated with other works available in the literature. Further comparisons were carried out and compared with the results obtained by the ANSYS package and experimental results. The good agreement with available data demonstrates the reliability of the finite element method used