نشریه مهندسی عمران و محیط زیست دانشگاه تبریز
سال سی و نهم شماره 3 (پیاپی 59، پاییز 1388)

In this study the efficiency of USBF
in biological nitrogen removal for achieving the optimum nitrogen concentration and COD/N ratio according to the maximum system removal efficiency was determined. The synthetic wastewater used in this research was composed of glucose and urea with COD/N ratio of around 10 with nitrogen concentrations of 10, 30, 50, 75, 100 and 150 mg/L and with COD/N ratio of about 6.67, 5 and 4 with nitrogen concentrations of 75, 100 and 125 mg/L. The initial experimental results have shown that by increase in nitrogen concentration with COD/N of 10, the nitrogen removal efficiency was increased in such a way that in concentrations of 10, 30, 50 mg/L after reaching the stable condition, the mean nitrogen removal efficiency was reached to about 89, 91 and 92.2 percent respectively. But as concentration increased to 75, 100, 150 mg/L, the mean nitrogen removal efficiency was decreased to 85.5, 82.4, 76.3 percent respectively. Then, with the COD/N ratio of 4, 5 and 6.67 and increased in concentration to 75, 100 and 125 mg/L, the percent nitrogen removal efficiency reached to 93.3, 87.4 and 82 respectively. Finally, COD and nitrogen concentrationof 500 and 75 mg/L (COD/N ratio of 6.67) were selected as optimum conditions for pilot-scale USBF process.

Tensegrity structures are a family of space structures that mainly consist of two distinct member types: first the members that merely bear compression or bar members, second members that bear only tension or cables. In these structures, cables are used in the place of the tension members, so they are even lighter in weight. These structures need to be pre-stressed to be stable. After being introduced in by these structures are extensively studied statically. However, there are a few researches in the field of dynamic behavior of the tensegrity structures and even less is in the field of seismic behavior. Recent earthquakes around the world revealed that despite preliminary expectations, the space structures are not entirely aseismic structures. In this paper a tensegrity grid structure with various amounts of initial strains is considered and its behavior under threeearthquakes of Northridge 1994, Imperial Valley 1979 and Tabas 1978 are examined. It is shown that the tensegrity grids are sensitive to initial strains and although the initial strain make a tensegrity grid stiffer, but makes it brittle.

Applying gravity loads on unequal spans, or lateral loads usually produce moment transfer between slab and column. The moment increases the shear stress of concrete in the vicinity of columns and reduces the punching capacity of slab. In the cases in which the estimation of unbalanced moment is laborious or when the ductility of slab-column connection is assessed, it is suggested to control the rotational capacity of connection instead of its unbalanced moment capacity. Existing mechanical models, except the Broms [1] model, are not able to predict the rotational capacity of the connections. The mechanical model of Muttoni [2] which was proposed for the estimation of punching capacity of centrically loaded slabs is developed to calculate the rotational capacity of the connection. The effect of eccentricity of loads on the ultimate punching resistance of slabs, and the rotational capacity of slabs with respect to column, is studied numerically performing non-linear finite element analyses using ATENA. Three experimentally tested slab-column connections by Krueger [3, 4] are selected for simulation and verifying the numerical models. The results of the analyses are compared with ACI [5] and EC2 [6] codes predictions and with the mechanical model of Broms [1] and the developed model of Muttoni. The rotational capacities predicted by the developed model are in better agreement with the test or analyses results in comparing with same values calculated by Broms [1] model.

One of the most commonly method of river bank erosion is the use of the spur dikes. Spur dike creates rapid variations in flow, sediment transport, and hydraulic geometry of river. The mechanism of flow and sediment discharge in channel bend is very complicated, when a structure like bridge pier, spur dike, and abutment is constructed in a bend. Most of the previous investigations on the flow behavior and scour around spur dike werecarried out in straight flume. In this paper results of experiments on scour around spur dikes under clear-water condition in a channel bend are presented. In order to estimate the influence of spac and locations of spur dikes on scour hole extensive experiments were conducted in a 90° channel bend. Sand with uniform grain size with amedian size d50 = 1.28 mm was used as the bed materials. Spur dikes were made of Plexiglas with a thickness of 1cm and length of 9 cm fixed to the side of flume. Experiments were performed near threshold condition in straight channel i.e. 0.9

Abstract View Paper Original: Persian