Behaviour of the Eccentrically Loaded Bolted Joint at Elevated Temperatures
Hämäläinen, Valtteri (2024)
2024
Konetekniikan DI-ohjelma - Master's Programme in Mechanical Engineering
Tekniikan ja luonnontieteiden tiedekunta - Faculty of Engineering and Natural Sciences
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Hyväksymispäivämäärä
2024-10-10
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tuni-202409168738
https://urn.fi/URN:NBN:fi:tuni-202409168738
Tiivistelmä
Boilers in various industries are generally suspended from the support structure with hanger rods. This exposes the furnaces to swaying under horizontal loads, which could be due to either earthquakes or wind. This swaying needs to be controlled with boiler guides between the furnace wall and the support structure. Boiler guides are steel structures made of plates with different thicknesses and connected with welded joints. The boiler guide stops the furnace from swaying and prevents incidents caused by the horizontal movement of the furnace.
The welded connection in the manufacturing process of the guide takes too much time to complete. The entire furnace wall must wait for the guide to be completed, delaying the manufacturing process. Additionally, the welding process applies a significant amount of heat to the components, which can cause bending. Repairing this bending increases the time needed for manufacturing. The research question of this thesis is to determine whether a bolted joint could be used under eccentric seismic load at elevated temperatures to replace the welded connection. If it could be used, must be determined what kind of bolted joint is suitable for this application. Welded connections cannot be replaced entirely, but with bolted joints, the manufacturing can be divided into sub-operations to prevent delays. Literature review is conducted about existing methods for boiler guides, seismic regulations and design principles needed for boiler guide’s bolted joints.
In this thesis, a new boiler guide concept is created to implement bolted joints. The force resistances for the bolts are computed manually according to Eurocodes 3 and 8. The new boiler guide concept is analyzed with non-linear FE-analysis with two load steps, and the loads applied to the individual bolts are determined. To validate the FE-analysis results, analytical calculations are also made and compared to the linear FE-analysis results.
As a result of this thesis, it is found that bolted joints can be used in boiler guides under eccentric seismic loads at elevated temperatures. The joints must be slip-resistant and pretensioned to provide the friction needed to reduce the load applied to the individual bolt. This thesis aimed to design a new concept that could use bolted joints to reduce the length of welding and ensure that the bolts will carry the load. However, during the literature review and research, aspects were found that need to be calculated or improved before implementing the concept in a real project, which did not fit within this scope. These aspects include optimizing the boiler guide to distribute the load over a larger area of the furnace wall and exploring design options to further reduce of welding.
The welded connection in the manufacturing process of the guide takes too much time to complete. The entire furnace wall must wait for the guide to be completed, delaying the manufacturing process. Additionally, the welding process applies a significant amount of heat to the components, which can cause bending. Repairing this bending increases the time needed for manufacturing. The research question of this thesis is to determine whether a bolted joint could be used under eccentric seismic load at elevated temperatures to replace the welded connection. If it could be used, must be determined what kind of bolted joint is suitable for this application. Welded connections cannot be replaced entirely, but with bolted joints, the manufacturing can be divided into sub-operations to prevent delays. Literature review is conducted about existing methods for boiler guides, seismic regulations and design principles needed for boiler guide’s bolted joints.
In this thesis, a new boiler guide concept is created to implement bolted joints. The force resistances for the bolts are computed manually according to Eurocodes 3 and 8. The new boiler guide concept is analyzed with non-linear FE-analysis with two load steps, and the loads applied to the individual bolts are determined. To validate the FE-analysis results, analytical calculations are also made and compared to the linear FE-analysis results.
As a result of this thesis, it is found that bolted joints can be used in boiler guides under eccentric seismic loads at elevated temperatures. The joints must be slip-resistant and pretensioned to provide the friction needed to reduce the load applied to the individual bolt. This thesis aimed to design a new concept that could use bolted joints to reduce the length of welding and ensure that the bolts will carry the load. However, during the literature review and research, aspects were found that need to be calculated or improved before implementing the concept in a real project, which did not fit within this scope. These aspects include optimizing the boiler guide to distribute the load over a larger area of the furnace wall and exploring design options to further reduce of welding.