University of Twente Student Theses


A case study on the temperature differences in a concrete composting bunker

Koopman, E.M.R. (2017) A case study on the temperature differences in a concrete composting bunker.

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Abstract:Concrete structures are exposed to all sorts of environments and need to serve all sorts of functions. Designing a structure which can handle the difficult circumstances is challenging. This bachelor thesis contributes to the research in this field, by using a case study to research the influence of large temperature differences on a concrete construction. PROBLEM STATEMENT AND METHODOLOGY Waste Treatment Technologies (WTT) designs waste treatment systems, which are located all over the world. Their composting systems are placed inside concrete bunkers. During the composting process the temperature becomes 50 ˚C and even 85 ˚C when an error occurs. The concrete thus has to deal with large temperature differences. Temperature differences create a temperature gradient, which is a thermal load to the construction. This creates stresses in the concrete, which can result an uncontrollable appearance of cracks. WTT outsources the designing of the concrete bunkers to (often local) building companies. These building partners don’t know how to deal with the composting environment and the large temperature differences coming with the composting process. As a result they over-design the concrete bunkers, which is expensive, or they under-design, because they don’t how to deal with the unique circumstances, which can result in damage. There is no general bunker template they can base their design on, so WTT encounters differences in the appearance of cracks and in amount of materials used. WTT wants to help the building companies with their design of the concrete bunkers by communicating with them about the building specifications. In the future this may result in a manual or a template they can base their design on. In this bachelor thesis the design of the bunkers is reviewed and the most critical temperature scenarios are identified, after which different optimized solutions have been proposed in order to stop the over- and under-designing. Nine composting bunkers build in the summer of 2017 located in Swisttal, Germany, are used as a case study. The dimensions of this case study are analysed and modelled in the 3D simulation FEM program SCIA Engineer. This program is used to analyse the stresses and forces arising in the nine case study bunkers. The results are used to analyse the influence of the thermal load on the construction, to analyse the calculations made by building company Grotemeier Ingenieure for the case study and to optimize the solutions. RESULTS AND DISCUSSION A general manual and a specific case study manual, given by WTT to the building company, have been analysed and compared, together with the calculation report of the case study in Swisttal made by Grotemeier Ingenieure Bielefeld, Germany). Concluded was that the few guidelines given by WTT are too broad and don’t match with each other. Specific guidelines need to be given, together with an explanation why certain things are required by WTT. The general and specific manual need to be integrated. It is unclear which temperatures need to be used in the calculations. The temperatures used in the calculation report of Swisttal are compared to the temperatures used by this bachelor thesis (taken from NEN-EN 1991-1-5). None of the temperatures matched. Even the temperature inside the composting bunker, given by WTT was different (75 ˚C and 85 ˚C). Some temperatures used by Grotemeier Ingenieure were higher, some were lower. Next, all twenty-seven possible temperature scenarios have been listed. Out of these scenarios the most extreme one is taken to use in further calculations. The influence of this extreme temperature scenario is calculated in SCIA Engineer and expressed in the tensile normal stress. This parameter has been chosen, because concrete can’t handle large tensile forces and cracks can arise due to that. The maximum tensile normal stress found is 12 N/mm2 and this stress is for a major part caused only by the thermal load. Inside the filled bunkers compressive and outside tensile stresses arise, as predicted by the theory. There needs to be an agreement on which temperatures need to be used for these special constructions of WTT. The advice is to take measurements of the real temperatures. WTT could then provide the building companies with all the twenty-seven possible temperature scenarios containing the real temperatures. Out of all these possible scenarios the most important scenario(s), for example the most extreme or the most common, need(s) to be selected and linked to a certain requirement it needs to meet, for example the crack width. It also needs to be given if the(se) scenario(s) need(s) to be calculated in the ULS or SLS and which forces work on the construction. The parameter tensile normal stress has also been used for to optimize the solutions. If the tensile normal stress is larger than the concrete can handle (3.21 N/mm2), the construction is damaged. Using the most extreme temperature scenario, there is found that the maximum tensile normal stress the concrete can handle, is exceeded due to the thermal load. Insulation can be used as a solution for this problem and has been researched further, because it isn’t a solution that needs cracks in the concrete to work (like reinforcement does). Cracks are a risk, because the chemical composting environment can attack the reinforcement, which causes the construction to fail. The insulation thickness is optimized by checking when the remaining tensile normal stresses are lower than 3.21 N/mm2. The optimal thicknesses of three types of insulation (mineral wool, expanded polystyrene, polyurethane foam) have been calculated for the four structural elements in the concrete bunkers (roof, outer wall, floor, inner wall). The calculated thickness of the insulation layers lies between 5 mm and 40 mm, while Grotemeier Ingenieure has used 80 mm of insulation. Grotemeier Ingenieure didn’t give an explanation on why this thickness is used and this confirms the fact that the building companies don’t know how much material they need to lift influence of the thermal load on the construction. So, the two main things that need to be included in the instruction manuals WTT gives to their building partners are: the real temperatures the building companies need to use in their calculations and giving the building companies insight on the type and amount of insulation they need to use. Important to mention is that this bachelor thesis used tensile normal stress to draw conclusions and make calculations, but the bending moments that the thermal load causes aren’t included in the research. This can be further researched in a follow-up study.
Item Type:Essay (Bachelor)
Faculty:ET: Engineering Technology
Subject:56 civil engineering
Programme:Civil Engineering BSc (56952)
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