From police station to cultural hub: Transforming a Hong Kong landmark

Adaptive reuse of heritage fabric 

With no record drawings or construction information about the existing buildings, we started by investigating the conditions and strength of the existing structural elements, including historic brickwork, timber, concrete and steel. During investigation works we discovered an unusual type of reinforcement inside reinforced concrete slabs taking the form of three 5mm diameter wires twisted into bundles. 

At the material testing laboratory, samples of these twisted wire reinforcement were demonstrated to have similar tensile strength to modern reinforcing bars. Using first principle approaches combined with statistical analysis of the test data and appropriate design factors, we proved the technical viability of reusing the existing slabs with twisted wire reinforcement to the authorities and avoided extensive recasting of floor slabs in both the Police Headquarters and the Central Magistracy. 

Conservation with sympathetic structural enhancement 

As most of the existing buildings were built by local builders with limited codes and regulations in place at the time of construction, inevitably our engineered approach to the assessment of the existing buildings has led to some requirements for structural enhancement. 

The vast collection of existing building forms and materials resulted in a case- by-case approach by our Hong Kong structural team in collaboration with the London Advance Technology and Research team. 

One of the prison buildings, D Hall, was a significant surviving portion of an original radial prison built in 1860. 

The ground floor in the west wing of the hall was an elegant space featuring a brick vaulted ceiling and arched colonnade. However, our assessment of the arched brick piers showed that they were of limited capacity. In order to avoid internal framing which would ruin the vaulted ceilings, we designed plated steel arches which fit snugly underneath the brick arches to enhance the overall capacity of the perimeter walls. 

New buildings with bespoke façades 

Two new buildings, JC Contemporary and JC Cube, were added to provide space for exhibitions and performing arts. The new blocks rise above the historic boundary walls and create new gathering spaces below, including an outdoor performance space under JC Cube. 

The column-free galleries have been realised using a system of perimeter steel trusses which cantilever from a central reinforced  concrete  core. Two separate ‘boxes’ house up to 7m high gallery floors and a self-standing concrete spiral staircase forms a strong visual element that draws visitors up from the entrance. 

A bespoke cast aluminium brick façade wraps the new buildings. The aluminium bricks were made from 100% recycled alloy wheels and echo the scale of the existing granite wall over which the new buildings emerge.

The interlocking modules of bricks span between vertical members of the perimeter trusses and mock-ups were tested for wind loading and approved by the authorities. 

Innovative foundation solutions 

At the site, bedrock was not encountered for depth over 80m or greater which posed challenges for the end bearing piles. In view of the very deep rockhead level and the proximity to existing heritage buildings, we pioneered the use of shaft-grouted friction H-piles in pre-bored holes as the foundation solution for the new buildings. The adjacent F-Hall, a 2-storey steel frame with brick piers and shallow pad footings, was underpinned by shaft-grouted friction mini-piles.    A 2-stage grouting process was used to enhance skin friction of the pile shaft in the completely decomposed granite stratum. This non-percussive piling method was used to keep any vibrations or disturbance to the existing historic buildings on shallow footings nearby to a minimum. 

The art of lighting   

Our lighting design for Tai Kwun is intrinsically integrated with the architecture and finishes to help interweave together the various forms and spaces.   

For the two new blocks, our lighting design makes full use of the aluminium bricks to express the texture of the façade while providing functional light to these areas. 

On the roof of JC Contemporary, the aluminium façade takes on a further functional form, morphing into a solar shading grid specifically designed for the site to protect the top-floor gallery from direct sunlight. Inside the gallery space, the ceiling is characterised by a stretched diffuse membrane to filter the incoming daylight and create a serene ambient light for the exhibitions within, keeping daylight levels to a controlled range and addressing art conservation concerns. At night, electric lighting above the membrane takes over, maintaining the ceiling glow in place of daylight.  

Managing fire safety   

Using a fire engineering approach, our fire engineers have successfully preserved the historical elements without compromising safety of the buildings.    

In the Police Headquarters and the Central Magistracy, it was not feasible to modify the existing escape staircases to fulfil the prescriptive requirements in terms of staircase and exit widths. We proposed a number of enhancements such as provision of smoke detection. Based on the new occupant loads and enhancements, evacuation analysis was conducted to compare the evacuation time under a code compliant design and the proposed design. This demonstrated that people can leave the building quicker under the proposed design because of the early warning by fire detection and good fire safety management. As such, the original design of escape staircases has been retained.   

In B Hall and E Hall, former prison halls of Victoria Prison, connections between floors were provided by internal circulation staircases. Fixed barriers not less than 450mm measured vertically downwards from the  underside of the ceiling were prescriptively  required around the voids to ensure formation of a hot smoke layer  for active sprinkler protection adjacent to the openings. Due to conservation considerations, neither fixed smoke barriers nor automatic smoke curtains were desirable. 

To overcome the constraint, fast response sprinkler heads were proposed and computational fluid dynamics modelling was conducted to estimate the activation time of these sprinkler heads.