Flexible spacer system for hot desert climate

Heinsberg, May 2020. CRICURSA Cristales Curvados, SA and Super Spacer® have been a proven
team in the production of curved XXL insulating glass units for iconic buildings with unique glass
facades for some time now. Especially for energy-efficiency reasons, the warm edge spacer
system was also used for the 5,500 square metre glass facade of the Qatar National Library in
Doha, which was completed in 2018.

Rob Nijsse, Professor of Structural Analysis and former partner of the Dutch engineering company
ABT Arnhem, and ABT structural consultant Ronald Wenting were both involved in a leading
capacity in the structural design for the first congenial collaboration of Rem Koolhaas and
CRICURSA: the Casa da Música concert hall in Porto, the wave-shaped glass facades of which
have become something of a trademark of star architect Rem Koolhaas and his Rotterdam office
OMA architects over the last 15 years.

In their article “Designing and constructing corrugated glass facades” Rob Njisse and Roland
Wenting write: “If the desired corrugated form can be folded from a sheet of paper, then the glass
industry will also be able to produce it. ” Indeed, the static benefits of a facade designed as a
wave are obvious. In the same way as a sheet of paper that has been folded to form an
accordion, it possesses much more rigidity than flat paper. But one should not interpret this quote
as nonchalantly as it first sounds. This is because the two structural engineers know from their
own experience that there are only a handful of glass bending shops in the world capable of
producing curved XXL glass panes in the required qualities, with the necessary tight radii and
minimal tolerances.

The planning team also broke new ground with its solution involving the construction of the glass
facade as a load-bearing, bracing element. In the case of Porto, Rem Koolhaas had the vision of
glass facades without steel and where possible without disruptive pillars, beams, steel cables or
frames. A considerable challenge, which was ultimately met by CRICURSA, one of the world’s best
renowned manufacturers of curved glass. Curved XXL glass panes arranged in close proximity to
each other in a wave-like design, which stabilise each other and thus jointly bear the loads acting
upon them, made it possible to dispense with vertical frames.

Rem Koolhaas also opted for a corrugated glass facade for the recently completed Qatar National
Library building for the new Education City in Doha. This time the glass panes are designed in an
omega shape, inspired by the notion of drying paper sheets. In a manner resembling the corners
of a box being folded up, the glass facades form the shape of a diamond. They filter out the
glaring sunlight and illuminate the library with as much diffuse, glare-free daylight as possible. The
light is reflected down into the room via a white aluminium ceiling.

You do not enter the 138-metre long library from the side, but instead access the centre of a
single triangular room under the supported corner of the building and you are immediately
surrounded by three terraces with marble bookshelves. The Qatar National Library houses more
than one million books and 500,000 digital editions across an area of some 42,000 square metres.
A mezzanine floor with reading tables, media rooms, study rooms and a large auditorium is
accommodated on a self-supporting bridge that spans almost the entire room. OMA architects
Rotterdam has come across a particularly spectacular solution for the accommodation of the
Heritage Collection, which comprises particularly valuable scriptures and manuscripts on Arab-
Islamic civilisation and is presented in the form of a permanent exhibition: a 6-metre deep room
with a glass ceiling covered with beige travertine, reminiscent of an excavation labyrinth, was
embedded into the ground. The message is clear: Books are treasures that are worth raising in the
public’s consciousness.

In the Qatar National Library, the absence of metallic elements in the glass facade additionally has
a decisive climatic benefit: there are no potential thermal bridges that conduct heat into the
interior of the building and which could weaken the insulating effect of the gas layer and warm
edge in the curved double glazing. “Qatar is one of the regions most markedly affected by the rise
in average temperatures caused by climate change”, explains CRICURSA’s Marketing Director Joan
Tarrus. “Outdoors, temperatures exceed 40 degrees centigrade in the summer, the temperature
inside the library should be a pleasant 20 degrees. The energy-related and thus production-related
challenges placed upon the facade glazing were thus enormous, especially in view of the fact we
did not want to plan for mechanical shading under any circumstances.”
The arrangement of the curved glazing ensures the facade is self-supporting and exceptionally
resistant to wind loads. “Antoni Gaudí made use of the same principle when he inserted the
famous Catenarian arches,” according to Joan Tarrus. Compared to a flat glass surface with an
identical pane thickness, the corrugated shape enables much higher loads to be transferred both
out of the plane of the glass – the load-bearing capacity increases by 1,000 % here according to
Rob Nijsse and Roland Weining – and also in-plane of the glass. In Doha the steel bases between
the glass elements were connected with interior columns to provide the construction with even
more stability.

Joan Tarrus continues: “When we started analysing OMA’s architects new challenge, undulating
DGU facade, the new there was only on way: slumping technique. Despite the technical challenges
we knew we were going to face due to the extreme climate conditions in Doha, curved annealed
glass was the only possible approach to provide an integral solution (geometry, coatings, ceramic
frit, dimensions) corrugating the glass to 550 mm radius, providing us with greater freedom in the
design process”
(Picture caption) The curved glass panes in the Qatar National Library have a radius of 550 mm.
The glass panes that are up to 5.50 metres high, laminated and curved, are designed as double
glazed insulating glass units. A low-e coating, and a solar control coating, filter and reflect
sunlight. A grey grid of 3 mm metallic dots with a precise 6 mm spacing between them was burnt
into them in order to reduce radiation transmission even further; it represents a technological
masterpiece due to these tight radii and the immense sizes involved.

Warm Edge indispensable in desert climes

CRICURSA chose the Super Spacer® TriSeal™ Flex product as its warm edge spacer. The product
developed by Edgetech/Quanex especially for curved glazing is, based on the experiences of
CRICURSA, ideally suited for the extreme climate loads in the desert.

“In this climate region, the use of a warm edge for double glazing is indispensable in order to
optimise the energy efficiency of a building,” explains Joachim Stoss, Managing Director of
Edgetech Europe GmbH and Vice President International Sales at Quanex. The constant transition
between hot sunlight, shade and cooler night temperatures leads to the permanent movement of
the glass, and consequently, to considerable mechanical stress on the edge seal. “Flexible spacers
such as Super Spacer hermetically seal the space between the panes for many years. Due to the
properties of the structural foam the spacer system absorbs the pumping motions of the panes
and prevents wear of the primary seal”, explains Joachim Stoss.



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