Prototype of no-projected and Sandglass-shaped Bolt with High- Strength and Durability for Efficient Steel Structures Maintenance

High-strength frictional bolted joints in civil engineering structures are corroded due to the thin coating thickness at the corners of the bolts and the nuts. A sandglass-shaped bolt composed of a countersunk head bolt and countersunk sleeve nut is being developed to secure the constant coating thickness and prevent corrosion. As its thread diameter is smaller than the usual one by the mechanism, an ultra-high-strength material must be applied to require the same fastening capacity as conventional bolts while considering stress concentration related to hydrogen embrittlement. This paper proposes a novel thread shape for the prototype of the sandglass-shaped bolt, whose stress concentration factor can be reduced by more than 30% current standard thread in Japan, focused on the magnitude of stress concentration. Moreover, FE analysis reveals the general fastening performance by comparing with or without the proposed thread.

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