Situated at the heart of art and design district Victoria Dockside, the new bustling cultural-retail destination K11 MUSEA, is a collaborative design effort by 100 Creative Powers that features local and international artists, architects and designers.
Presented by K11 Group as Hong Kong’s Silicon Valley of Culture, K11 MUSEA is a blend of cutting-edge design fused with art and culture, creating an immersive experience to inspire the next generation. It is only fitting then that the innovation in both the architecture and the engineering of the building reflected this and its prime Victoria Harbour waterfront location. The new glass, tubular facade of K11 MUSEA, designed by Facade Engineer Eckersley O’Callaghan, in conjunction with SO-IL Architects and specialist Contractor seele, is an inspiring, totally unique and ground-breaking facade. It has pushed new boundaries in its fabrication, installation and the advancement of the closed cavity facade system (CCF). After years-long testing and development, the façade is now unveiled to a wealth of critical acclaim.
K11 MUSEA – the facade
SO-IL aimed to create a transparent, sculptural, frameless glass facade which plays with the arrays of reflection and light. The result was a facade comprising over 300 9m high, 900mm diameter glass tubes wrapping around the whole perimeter of the mall on the sixth and seventh floors of K11 MUSEA.
But the challenge was to translate the vision into reality taking into account typhoon wind loading, high humidity, the height of glass required and the tight radius to which the glass had to be bent to create the cylinders. To put this into context, typical wind loads in the UK may range from 0.8kPa to 1kPa, but in Hong Kong, typical pressures on the facade are in the order of 2.5kPa up to 5.1kPa around the openings.
Two types of panels are used to form the glazed envelope – half tubes, leading to a single glazed wall with a difference in internal and external appearance and full tubes, which are made by connecting two half tubes to form closed tubes.
Developing the glass tubes
Creating the glass tubes to a radius of 450mm with the required strength was the first challenge. To do so, Eckersley O’Callaghan first investigated whether it was possible to use a gravity drawn process to shape the glass into 900mm diameter cylinders using borosilicate tubes. A limitation of tubes are able to be produced, meaning that the team then had to conduct a series of tests to splice a full tube together using 3m and 1.5m sections to create a 9m long laminated full tube.
Lamination tests were conducted with a Sentry Glass interlayer at Sedak and with a poured resin interlayer at Schott’s in-house laboratory. However, due to the dimensional tolerances of the tubes due to their vertical gravity, drawing process was significantly larger than what is common in the curving of flat glass, initial lamination tests were not successful. The pressure of the autoclave led to stress concentrations in the glass because the radius of the two layers did not match precisely enough. Another limitation was a maximum radius of 400mm and hence the team diverted to a more traditional approach starting with flat glass.
It was then decided to create the tubes as two half tubes so that the glass could be bent into shape and then joined together.
Automated curving ovens were then used to mould the glass while simultaneously toughening it as it quenched. This process can only form a radius down to approximately 1000mm, so this method was ruled out.
The alternative to this was to use gravity bending to slump the heated flat sheets of glass over a mould. Rather than rapidly cooling to achieve a pre-stress, the slow annealing process to release any stress that has been induced in the process, was carried out by CRICURSA in Barcelona.
“With this technique for bending glass, to get the quality right when you’re slumping it over the mould, you have to make sure the thickness of the glass is uniform throughout and the surface of the glass is not distorted as it happens,” says Eckersley O’Callaghan Facade Director Damian Rogan.
“It’s a very specialist thing and that is why we engaged the CRICURSA early on in the design process to perfect the method to do this.”
Despite having to use the annealed glass, the inherent stiffness which came with the change in geometry from flat to curved was sufficient to require only two 12mm-thick-plies of glass laminated together to span the 9m height. As a comparison, a flat glass would have required approximately 10 layers of 10mm glass, to achieve a similar performance over the span of 9m.
The thinness of the glass also increased its transparency with the thicker build up having an increased light absorption. The curvature results in an increase in light transmission of 20%. But this was not the only benefit of the thinness of the glass.
“The colour plays a very important role in the perception of transparency,” says Eckersley O’Callaghan Associate Director Lisa Rammig. “The smaller the perceivable tint in the material, the clearer the glass appears.
“Even on a glass tube with a reduced iron content as used in this installation, a tint is existent, which becomes more visible when more layers of glass are stacked and laminated together.”
“The two layers that are to be laminated, have to be curved together in the same mould to achieve the dimensional precision that was lacking in the initial borosilicate tube splice test. There is then a negotiation between exposure time in the oven to achieve the desired geometrical precision and the quality of the glass surface. Longer exposure to heat can cause visible mould marks on the surface of the glass. CRICURSA did an excellent job at testing and optimising this throughout the manufacturing period”
A Sentry Glass interlayer was used due to its better flow rate in the autoclave which allowed to fill in any tolerances in the girth of the two tubes. As the edges of some of the tubes are exposed, the Sentry Glass interlayer also provides better durability in case of moisture exposure with a lower risk of delamination. Due to the use of annealed glass, the edge quality was very important to avoid breakage due to stress concentrations or thermal stress, so the quality control of the edge polishing was an important procedure. The team then satisfied itself by carrying out a thermal stress analysis that the annealed glass could withstand the temperature differentials which could have caused it to crack under partial sun and shaded conditions.
“Annealed glass is more susceptible to thermal stress and fracture so it’s something we’re always concerned about,” says Rogan. “If sun hits one part, but not another, temperature differentials and stress differentials are set up so that is a common way it can break.
“Because of this we looked at the shading of the site around the perimeter and measured the amount of radiation on the glass. It’s common now, but wasn’t at the time. Because of the geometry and size of the tubes we were concerned that the internal stresses would be more significant than normal. After analysing it, we determined that the stresses would be within the allowable limits.”
To join the tubes together, a special thermally broken extrusion was designed to join the two half tubes to a fully sealed Closed Cavity Facade (CCF) unit. CCFs are typically used to improve acoustic and thermal properties of a typical IGU curtain wall and to allow for dynamic shading in high wind applications like towers. An additional layer of glass in front of the IGU creates a cavity that provides a protected environment for the blinds. In this case the CCF principle was used to avoid condensation in the cavity due to temperature differentials as well as dirt and dust getting into the tubes, which are not accessible.
Within the unit, the tubes are base supported in fitted, circular, polished duplex-stainless steel shoes, and laterally restrained at the top through a similar stainless-steel lid.
With the structural design being done, the next challenge was to overcome the climatic loading and condensation issues for the closed, complete tubes.
Climatic loading and condensation
Traditional double layer facades with typical spaces of 100mm to 300mm have an air volume of 1500l. In comparison, each of the 900mm diameter and 9m long tubes contain around 6000l of air. This proves problematic when this volume is heated, expanding by around 800l.
In a sealed unit, this expansion and contraction can induce very high climatic pressures. Under these applied loads with the glass being curved and therefore stiffer, analysis showed that the tubes would have failed and cracked.
Similarly, the pressures exerted on the silicone joints between the half tubes were causing issues.
The system therefore had to be opened. But in a non-sealed unit, when the air contracts it sucks in humid air and dirt from the surrounding atmosphere leading to contamination and condensation. So a closed cavity facade system (CCF) needed to be employed.
“We needed to depressurise the air volume so it’s an open system,” says seele Head of R&D Martien Teich talking about the process at GPD Finland 2019. “From the top we blow dried, temperate and cleaned air into the air volume. There’s always a slight over pressure in the system to stop outside air being sucked in.”
With the air being dried and temperate, the risk of condensation was minimised. However, with around 6000l of air contained within each tube, it was not clear whether the CCF system would be able to perform having not been used in this way before.
Testing of the system
In order to minimise the energy used by the CCF system, the team carried out a number of tests and numerical analysis to optimise the speed of the airflow needed through tubes to avoid the condensation issues.
“We didn’t want to exchange the air every hour as this would take a lot of energy,” says Teich. “We want to minimise the air flow, the energy consumption and also optimise the machinery which is behind the CCF.
“In general we have an East Facade and a West facade and they are controlled independently by two different systems and you want to minimise any permanent costs.”
In Hong Kong, temperature fluctuations are small and gradual, whereas humidity levels can change rapidly. It was therefore decided to use the internal, conditioned air of the building for the CCF system, since this is humidity and temperature controlled with a high degree of predictability.
Numerical analyses were carried out, modelling the performance of the system over the course of a typical year. From this, the risk of condensation occurring in the tubes was assessed for different air exchange speeds.
For high speeds, there was consistently a large difference between cavity and dew point temperature, representing a high factor of safety against condensation. At low speeds, close or coincident cavity and dew point temperature showed a high risk of condensation occurring. At 100-200l/hour it was found that the two temperatures which sufficiently far apart, on a consistent basis, to alleviate any risk of condensation occurring.
“We tested a median value of 120l/hour there you’ll see a more even distribution but there’s not a single count below 5 degrees temperature difference,” explains Teich. “So this gave us the confidence to set the airflow between 200 and 300l/hour with a safety level in the system.”
To create the front entrance, a section of 11 tubes had to be cut and resupported by an S460, 1.4462 grade duplex stainless steel portal frame 80mm thick, 900mm deep and 4.6m tall.
“The portal frame is an engineering feat in itself, it’s a beautiful piece of fabrication” says Eckersley O’Callaghan Senior Associate Franklin Lancaster. “The stainless steel sections are significant in size and not easy to weld. A careful balance had to be struck between the efficiency of the welding so as not to warp the stainless steel and satisfying the building control authority that it was safe.
“It involved a great deal of high end fabrication including annealing the entire assembly to release the stresses in the welds and achieve a precise level of pre-camber.”
Original designs had seen a much thinner top portal frame member, with a steel tube hidden in the floor depth above, spanning between and onto the two full tubes on either side of the frame. Hangers in the form of steel rods placed in the joints between the tubes attached to the top member of the portal frame would have controlled its deflection. However due to building control restrictions in place at the time, this design had to be changed.
To avoid dirt and dust getting into the system, the tubes had to be assembled in a clean room. The curved glass was shipped over from Spain and assembled in a specialist, purpose built facility in Hong Kong. Due to the tight radius of the glass, regular glass suckers could not be used, so a bespoke tool was developed by seele to lift the tubes. With limited access to certain areas of the perimeter, the tubes were lifted into onto a specially designed track system embedded into the shoe fittings at the base. The tubes were then moved around into areas with no or limited access.
With the installation of the tubes now complete, the area is now open to public.
“Rarely does a client have the drive and vision to see a project of this ambitious nature through to the end, but they made it happen,” says Lancaster. “From the first rendering to the completed article they had the faith to realise this beautiful and truly unique facade.”
This article was originally published in IGS Magazines Autumn 2020 Issue: Read the full Magazine here for more thought-leadership from those spearheading the industry
About K11 MUSEA
Hong Kong’s Silicon Valley of Culture, K11 MUSEA, is the latest cultural-retail destination in Victoria Dockside located on the harbourfront of Tsim Sha Tsui. Inspired by ‘A Muse by the Sea’, K11 MUSEA is designed to enrich new consumers’ daily lives through the power of creativity, culture and innovation. A destination 10 years in the making, K11 MUSEA opened its doors in August 2019 to usher in a new era of cultural retail which speaks to the growing consumer demand for immersive consumer experiences in art, culture, nature and commerce.
K11 Group was founded by entrepreneur Adrian Cheng in 2008 with a social mission to incubate creative talent and promote cultural dialogue. In creating K11 MUSEA – K11 Group’s most ambitious project to date – Cheng’s vision is to reinvigorate Hong Kong’s waterfront with 100 Creative Powers and make K11 MUSEA the Silicon Valley of Culture that will inspire global millennials, and facilitate a broader discussion on the interconnectedness of creativity, culture and innovation. By 2025, K11 Group will have gained a footprint of 36 projects (total GFA 2.84 million sqm) in ten cities across Greater China.
History and 100 Creative Powers
K11 MUSEA sits on the site formerly known as Holt’s Wharf, an important go-down in Tsim Sha Tsui that dates back to 1910. The historic logistics hub eventually made Hong Kong one of the busiest ports in the world. Paying tribute to its unique history and its position as the confluence of cultures, K11 MUSEA is committed to incubating the local cultural scene by allowing visitors access to world-class curation of year-round art and cultural programmes. The architecture of K11 MUSEA was led by Kohn Pedersen Fox architecture practice, James Corner Field Operations, and in collaboration with over 100 creatives including Rotterdam-based OMA, Hong Kong-based architecture studio LAAB, AB Concept and a diverse group of artists, craftsmen, designers and more.