Fatigue behaviour of steel connections in potash mine shafts

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When mineral ore bodies are located deep underground, vertical mineshafts are required to access the ore. Large elevators ("skips") are used to transport the ore to the surface, and to transport equipment and personnel between the surface and mine station levels. Skips are hoisted by cables and guided up and down the shaft by means of roller assemblies that travel along vertical steel guides, which are supported laterally at regularly spaced intervals by steel structures ("bunton sets") that are connected to the shaft walls. Skips for recently designed mines weigh as much as 65 tonne, and will travel along the shafts at speeds exceeding 65 km/h. Even a slight misalignment of the guide will cause the skips to bounce from side to side and exert repeated horizontal slamming forces on the supporting steelwork. The steelwork, particularly the bolted connections, must therefore be designed to resist repeated slamming forces without failing for the 50 year design life of the shaft. The proposed research addresses two important design issues related to this problem. First, it is necessary to identify an optimal design for the bolted connections in terms of their configuration and type of bolting technology so that they can withstand a very large number of repeated loads without failing, while not being over-designed. Experimental tests, supplemented by computer modelling, will be conducted on full-scale bolted connections in the laboratory to achieve this objective. Second, the magnitude of the slamming forces must be determined. This will be investigated using sophisticated computer models to calculate the forces as factors such as guide misalignment, skip speed, and stiffness of the steelwork change. This project will allow designers to minimize the quantity of steel and fabrication time, while ensuring adequate levels of safety for the steelwork in mine shafts. It has the potential to provide significant cost savings to mining companies during the construction phase, and provide design engineers with the confidence they require to design safe mine shaft structures. Results are also expected to influence steel design standards related to the resistance of bolted connections subjected to repetitious loading.