156
EUROPA
New metallic structures:
the lantern and the
atrium’s façade
The study of the project has required special
attention taken into account the size and
complexity of the metallic structures , not
only due to their height (12 storeys), but
also due to their reach, whether it be the
atrium, the trusses and the Vierendeel wall
that straddle the metro tunnel or the lantern
whose largest floor exceeds 30 metres.
The technical inspector must constantly
have an overall vision of the project in order
to draw the parties’ attention to sensitive
points and to anticipate certain scenarios,
notably with respect to the interface
between the various sections or building
trades whose coordination is first and fore-
most a general contractor’s task.
Therefore, in their bilateral contacts with
each of the contributors specific to a
section, the various members of the inspec-
tion team (each a specialist in their area of
expertise) endeavoured to complete the
information in possession of a subcontractor
by matching it up with the actual situation
and their on-site experience.
For the metal frameworks in particular,
one of the major challenges was the study
and impact of the assembly method and
phasing on the initial overall proportioning
of the various structures (lantern, atrium,
Vierendeel wall).
The management and coordination of the
interfaces also led to numerous exchanges
on assembly tolerances, soundness and
alignment, to be respected for these tall
structures and made up from the succes-
sive stacking, floor by floor, of the various
factory-built prefab components.
The execution of the lantern’s metal frame-
work required follow-up in the factory for
their manufacture and their assembly for
testing purposes, as well as on-site inspec-
tion of the completion of the anchoring to
the building shell and the assembly by bolts
and welding. The atrium and Vierendeel
wall structures are therefore totally welded,
both in the factory for the production of the
modules and on-site for their connection.
The choice of thermal insulating protection
in the event of fire, by intumescent paint,
flocking or rigid protection, was made for
each structure, not only based on fire resist-
ance requirements and critical temperatures,
but also on architectural requirements, de-
pending on whether the structure is visible
or not.
The fire resistance requirement Rf 2h has
also required in-depth reflection whereby
plausible scenarios were defined for each of
the structures or sub-structures.
The lantern structure is fully protected by
flocking with the distinctive feature for the
beams of the underpinned floors of the
large conference rooms on floors R5, R7
and R9, whose level of protection is higher,
i.e., protection is supposed to limit heating
to 200 °C instead of 540 °C as for other
components, whilst the tie beams on the
other hand are not protected. This additional
requirement is aimed at limiting the thermal
expansion of these long beams and there-
fore the impact on the ring-shaped posts
and beams.
For the latter, it nonetheless proved to be
necessary to design the assemblies similar to
fusible alloys, in order to allow them to adjust
to the forced distortions resulting from the
expansion of the beams under the influence
of a fire in a room, without, however, be-
coming the centre of normal stress they are
unable to withstand. These beams are in fact
always at ambient temperature since they are
located in another compartment, outside the
rooms that are subject to fire. The operation
of these fusible alloys is based on a potential
shift from a specific amount of stress at the
assembly level.
To conclude, the mullions on the lantern
façade are protected with intumescent paint.
The shell
The history of the
Résidence Palace
is
marked by upheavals. Iconic during its
construction in the 1920s, the building was
extended in 1960 in the style specific to that
era and, since then seems to have settled
into peaceful everyday life, when architects,
engineers and construction workers brought
it out of its torpor, disrupting its shell,
amending its architecture, thus projecting it
into the 21st century .
The preserved structure is insulated in order
to guarantee better thermal comfort, to
limit losses and to fall within the scope of a
responsible approach to the environment.
The original façades having been preserved,
insulation was applied inside and to avoid
any concerns linked to the spreading of
fumes, a new material regulating ambient
humidity was used.
The implementation of this material proved
to be tricky, as it is in fact important to
create an insulation plan without inter-
ruption in order to prevent condensation
to appear in the masonry or in the joints
between materials. SECO’s experience in
the hygrothermal behaviour of the shells
of buildings enabled to support the project
team in its initial choice whilst allowing for
efficient quality control (points of attention
as to execution, highlighting of non-
compliance or faults).
The project team’s desire to use a species
of sustainable wood, and a wood protec-
tion treatment for the new window frames,
respectful of environmental requirements,
was approved in collaboration with the
company designated for their manufacture
and installation.
Special care was also taken with the old
wing’s air tightness. These renovations to
the existing structure will allow for optimal
indoor hygrothermal comfort whilst signifi-
cantly lowering power consumption in the
building.
The new double skin façade that closes the
rectangle created by the old wing and the
new structure represents in more than one
respect an almost Herculean exploit, and in
any case, a technical one. The steel structure
that covers this double façade is the one
that forms a bridge overhanging the metro
railway tunnel.
GLASS ELLIPSES
