Nested Friction Bolt Structure for Higher Pull-Out Resistance

The patent applies the nesting principle by placing an inner tube inside the outer friction bolt tube. The inner tube is inserted into the outer tube such that the outer diameter of the inner tube is substantially the same as or slightly larger than the inner diameter of the outer tube, creating a nested configuration. This nested structure allows both tubes to expand radially together when forced into the bore, generating increased friction forces that prevent slipping while maintaining the simplicity and cost-effectiveness of the friction bolt design.

The patent applies the extraction principle by removing the complex grout sock component and replacing it with a simpler inner tube structure. Instead of using pre-filled grout socks that require curing and complicated installation, the invention uses a bare inner tube that is simply inserted into the outer tube and then forced into the bore together. This extracts the unnecessary complexity while maintaining the essential function of increasing pull-out strength through radial expansion and friction.

The patent applies the local quality principle by specifying that the inner tube's outer diameter should be substantially the same as or slightly larger than the outer tube's inner diameter at the contact region. This creates a localized interference fit that generates sufficient friction for pull-out resistance without requiring extremely tight tolerances along the entire length of both tubes. The aligned longitudinal splits allow both tubes to expand radially together, creating the necessary contact pressure locally where needed while maintaining manufacturing feasibility.