Part of the development included the design and installation of an internal, one storey high spiral staircase. Engineers considered different options for connecting steel treads to a large hollow steel centre post. The time required to weld all the treads was estimated at three days, however to meet a challenging construction timescale, a faster solution was needed to reduce installation time and provide the necessary structural strength.

The engineer decided to specify the Hollo-Bolt by Lindapter, an expansion bolt that requires access to only one side of a Structural Hollow Section (SHS), and offers a faster alternative to on-site welding.

The connection design incorporated four Hollo-Bolts per tread to achieve the required shear resistance and safe working load. Hollo-Bolt was also chosen due to its range of independent technical accreditations, which include the CE mark, TÜV and ICC-ES Seismic approvals.

Holes in the structural centre post and end plates of each tread were pre-drilled off-site by the steelwork fabricator and then delivered to site.

Hexagonal head, size M10 Hollo-Bolts with a zinc plated finish were used to connect through the end plates to the centre post. Installation was quick and easy as each bolt is simply inserted into the pre-drilled holes and tightened with a torque wrench to the recommended tightening torque to provide the necessary clamping force.

Hollo-Bolts provided a drilling and weld free connection on-site that was quick and easy to install. Installation of the treads was completed in just two and a half hours rather than the estimated three days for welding. This allowed the contractor to stay on schedule and avoid any costly delays.

• Fast, cost saving installation from one side
• Suitable for square, rectangular and circular hollow sections
• High resistance to shear and tension
• Unique high clamping force design
• CE Mark, TÜV and ICC-ES Seismic approvals