Browsing by Author "Salimi, Yadollah"

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Kaivosteollisuuden teräsbetonisen tornimaisen reaktorin rakenteellinen optimointi
(2013) Salimi, Yadollah
School of Engineering | Master's thesis
The aim of the studied tower-like reactor is to utilize poor ores by improving hydrometallurgical processes. The reactor is about 70 meters high and it consists of three parts; lower tank, shaft and upper tank. The main aim of this thesis is to optimize the structures of the lower tank under hydrostatic and temperature loads. Also the axisymmetric shaft of the reactor with free and fixed bottom and the joint between the shaft and lower tank are studied. The greatest load challenge is hydrostatic pressure and temperature load in the lower tank. The literature part is a review over the calculations of axisymmetric shells. The structural optimization of the shaft is defined and also studied as a reinforced and a pre-stressed structure. The shape of the lower tank is defined as well as its structural optimization is carried out. The lower tank is divided into two parts: lower part and upper part. An axisymmetric pre-stressed method is applied on upper part. The joint is strengthened with a box-shaped concrete structure against hydrostatic pressure. The joint is also studied both as composite and steel structure. The analysis was carried out with Abaqus software, According to heat transfer calculations the internal mineral wool in the shaft should be at least 100 mm thick in order to keep the temperature of the concrete layer within the acceptable range (<=+65 °C). The concrete layer of the shaft with a fixed bottom will be exposed to high tensions if the temperature of the structure is -20 °C. Tensions caused by temperature load could be reduced with different structural solutions in both parts of the lower tank. Based on the study the optimized structure in the lower part is: 50 mm reinforced plastic, 25 mm mineral wool, 125 mm polyurethane, concrete layer and 100 mm polyurethane and in the upper part: 50 mm reinforced plastic, 150 mm mineral wool, 700 mm pre-stressed concrete layer and 100 mm polyurethane. The internal and external insulations are necessary to keep the temperature of the concrete layer within the acceptable range. The tension in the upper part may be nullified by the applied pre-stressing method, Hydrostatic pressure is the largest load loading the joint and the stresses caused by it cannot be reduced efficiently with strengthening. Only a small portion of the steel could be utilized if the joint is designed as a composite structure of steel and concrete. If the load in the joint area is carried out by a steel structure its thickness should be at least 150 mm. However, in future a more exact study should be made for the joint area and for the distribution of temperatures around structural discontinuities. Also the interaction between the material layers of the structures, constructability and implementation of pre-stressing should be paid attention to.