Outer strength

Designed by Zaha Hadid Architects, the new Morpheus hotel in Macau features what the practice believes to be the world’s first freeform, high-rise exoskeleton structure.

Located in the City of Dreams casino resort in Cotai on the southern Chinese island, this striking design contrasts with resort architecture that takes inspiration from famous faraway places – there are already Venetian and Parisian-themed hotels on the island, the latter complete with its own Eiffel Tower. But it was important that the 42-storey Morpheus had its own architectural identity, says project director Viviana Muscettola, and the assertive exoskeleton certainly provides that.

‘The client’s goal was to create something unique and specific to Macau,’ she says, adding that ZHA built its own parametric 3D tools and scripts to realise the exoskeleton structural axis and exo-cladding surfaces. Engineer BuroHappold also made parametric tools to analyse and design the structure.

Conceptually, the architects envisaged the 780-bed hotel as a 160m-high extrusion of the 52m by 99m site footprint, rather than splitting it into more customary tower and podium components (although Morpheus connects to the adjacent City of Dreams podium). Designed as two linked towers, each with their own cores and vertical circulation, this building nonetheless appears as one fluid element that has been ‘carved’ to form three irregular voids through the building linking the north and south facades, which are mirror images of each other. Inspired by China’s tradition of jade carving, these ‘urban windows’ maximise daylight and views out either way from the centre of the tower while creating a distinctive overall design both inside and out. The lower floors contain a spectacular 40m high atrium. Both of the bridges across the central voids contain restaurants, bars and guest lounge areas with the swooping external structure visible all around. On the top is a swimming pool, created where the exoskeleton folds down over the top of the building to form a sheltered sunken terrace.

The decision to employ an exoskeleton for the building envelope to realise both structural integrity and sculptural form was ­taken very early on, according to BuroHappold Engineering associate director Tim Kelly.

‘An exoskeleton was absolutely the right and efficient structural response to create that form,’ he says. ‘It’s doing a structural job. Clearly it takes the vertical load from gravity but because of its triangulation, it also resists lateral loads such as earthquakes and typhoon winds.’

For ZHA, its use was a continuation of the practice’s ongoing research into the integration of form and structure into one envelope. Along with Morpheus’s reinforced concrete cores, this aluminium-clad exoskeleton forms a dual stability system. It is connected to the internal floor and beam structure via stub connections penetrating the curtain wall. The exoskeleton stands 1.3m proud of a 43,388m2 glass facade, freeing up the interior from the constraints of columns and supporting walls and providing additional screening from the sun. In addition, where visible, the external lattice lends an expressive quality to the interior spaces.

For the exoskeleton concept, the design team created a bespoke Grasshopper script to take the geometric model into structural analysis, testing thousands of iterations of its geometry against performance requirements and constraints including potential movement and settlement to determine the optimum member design and arrangement.

This was an immense task; the exoskeleton has 1200 exo nodes and 1300 bolted steel connections along the members. The exoskeleton can be divided into three main area types: the zones of rectangles on the flat sides of the building; the single curved areas at the four corners, and the double-curved freeform area of triangular openings and glazing around the central voids – the most complex and making up 21% of the grid. While the diagrid is denser and more intricate towards the base of the tower, it is more dispersed with lighter members at the top.

The structure followed a number of core rules – all nodes were horizontally aligned to the floor edge beam; all stubs were horizontal and perpendicular to the glazing reference surface; and all members were planar and single-curved. Connections were bolted unless in the freeform area, when they were welded.

Due to the extreme complexity, BuroHappold rather than the steel fabricators designed exoskeleton steel connections, described by the design team as ‘the most analytically and geometrically challenging’ large-scale steelwork connections ever built. These, and their associated plates, had to be contained within the cladding zone defined by ZHA. This feat was achieved using Rhinoceros and Grasshopper tools with various analysis software.

All steel was produced locally by a ship building company and fireproofed with epoxy intumescent paint. Once installed, the exoskeleton was clad in 57,000m2 off-white aluminium panels, designed to absorb the difference between the axis of the structural members and the glazing. While the front and back of the cladding is parallel to the glazing, the other two sides follow the axis of the structure. Lighting is integrated.

The facade consists of 24,577 panels, typically of Saint Gobain Coolite ST136 solar control, high performance glass, but in a variety of types including flat, single and double curved, and single and double glazed, according to their positioning. Aluminium frames were used for the flat and facetted areas with steel in the freeform areas to give more slender profiles and cleaner connections. In this particularly complex area, the triangular facets were isolated from the exoskeleton to avoid imposing stress on the glazing and formed into large composite panels each weighing up to 20 tonnes.

Morpheus has been a tour-de-force of co-ordination, not only through the parametric design phase but through construction, which involved four different facade contractors and complex co-ordination of sequencing and temporary structures.

Muscettola hopes that Morpheus demonstrates new possibilities for architectural form: ‘We hope it’ll make the construction industry aware of possibilities that 10, even five years ago, weren’t even thought of.’