Each accommodation unit of InnoCell is a MiC module formed by structural steel sections with corner boxes along the perimeters and secondary beams at the top and bottom planes to support the floor slab and ceiling. The floor of each module is formed with 100mm concrete and the walls along the long sides are formed with corrugated sheets. Each module was fabricated in a factory with all MEP provisions, interior finishes and furniture installed before being transported to the site for installation.

As the physical separation between the MiC modules results in discontinuity of the floor slabs between them, we studied the stiffness, deformation and stress of the individual slabs, as well as the stiffness of the framing layout formed by the interconnection between modules, and how the lateral forces are transferred to the cores. The central communal areas formed by in-situ RC flat slabs tie all MiC modules together to form a compact floor diaphragm capable to transfer the loads back to the cores.

We have a number of innovative design features for InnoCell, including the use of preloaded bolts (or high friction grip bolts), which play a vital role in the transmission of lateral forces across MiC modules to the in-situ concrete cores at each floor. We also derived a method to check the design of the composite wall based on a Vierendeel truss approach, as there is no design guide being available to evaluate the shear/web buckling of the thin wall panel acting as the beam web.

In structural design, fire protection to the structure is an indispensable consideration. Apart from applying cementitious spray and intumescent paint to the steelworks and providing adequate cover to the concrete elements, the MiC modules at InnoCell encounter a unique circumstance of having a physical separation between modules. The project team explored a cost-effective solution to form independent cavity barriers between modules with fire stop sealants. A fire test was conducted to simulate formation of a typical joint between modules in order to justify the amount of sealant required to be applied.

Apart from prefabricated modules with 13.2% of the outside surface works made from recycled materials, the overall design of the project also promotes energy efficiency and sustainability.

InnoCell’s layout effectively reduces building energy consumption by lowering the demand for air conditioning. Ventilation is enhanced by locating windows in opposite directions and perpendicular to each other. Furthermore, the axis of the building is oriented with an angle of 45° to prevailing wind direction. We took these sustainability features into consideration when doing the structural layout and detail designs.

InnoCell also takes advantage of the proximity and relatively low-cost manufacturing in Pearl River Delta of China to promote MiC application. With off-site construction, MiC method significantly improves discharged water quality on site through reducing suspended solid by 50% and lowering chemical oxygen demand by 80%. Also over 5% mitigation of construction noise level was observed.

Compared to traditional in-situ construction, MiC shortened the overall construction programme by 40%, reduced construction wastage on site as well as achieved better quality with cost-effectiveness and in a safe site environment. 

The engineering designs of InnoCell demonstrate the feasibility and sustainability of adopting MiC as a new construction form for certain types of projects, and WSP has shown leadership in harnessing this technology in Hong Kong. It was named a winner of Grand Award at the HKIE Structural Excellence Award 2022 and Hong Kong Green Building Award 2021.