Modular buildings are gaining popularity as an affordable and sustainable solution. This design and delivery method has been adopted by Netherlands-based hotel operator citizenM, who have brought their steel-framed modular hotels to New York and Los Angeles.

Polcom Group, specialist off-site modular manufacturers, were appointed to build 228 modular units for the hotel. They identified that they would need to modify their normal production and assembly process to meet US building practices and standards.

Due to time constraints the traditional method of connecting units together on-site by drilling and bolting was not chosen, whilst hot welding risked damaging the critical waterproof membrane that protects each module.

Design Solution – Special steel structural shear plates were designed and added to the steel enclosures of the modules during production so that they could be connected to each other with Lindapter Hollo-Bolts during on-site assembly.


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Hollo-Bolt was specified for its high strength capacity and ability to be installed from one side of the Structural Hollow Section (SHS). Each module was wrapped in a protective air and water barrier, pressurised to keep windows in place and shipped on a private vessel from Poland to Seattle in the US.

Installation – Mortenson Construction were the appointed main contractor for the construction of this seven-storey, 264-room hotel. Each 18,144kg modular unit was lifted by crane and carefully stacked on top of each other.

Hexagonal head and countersunk Hollo-Bolts were then used to connect through the structural shear plates to the SHS of each module.

Installation was quick and easy. Each bolt was inserted into pre-drilled holes and tightened with a torque wrench to the recommended tightening torque to provide the necessary clamping force.

Result – Hollo-Bolts provided a weld free connection that was quick and easy to install without damaging the waterproof membranes.

This allowed the client to improve their modular construction method, which provided many advantages over traditional methods, including shorter constructions schedules, consistent quality control and reduced disruption on-site.


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