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Exoskeletons in buildings The Brunel Building adopts an exoskeleton.
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July/Aug 18
retrofitted with an orange aluminium
shroud that sits outside of the cladding,
providing another stand-out feature.
Forming the floors of the building, the
Fabsec cellular beams support precast
panels, all of which have been installed by
Severfield along with the steelwork. They
have a highly architectural polished finish
to their undersides as this part will be left
exposed in the final scheme, while on top,
a concrete topping is applied to form the
floor.
Prior to the topping being applied the
panels would ordinarily need to be propped
as they would not be stable. However, on
this scheme, most of the temporary props
have been dispensed with as the panels have
a steel torsional restraint which provides
rigidity during the temporary state.
The restraint is a steel beam fixed to the
underside of each panel, which is removed
once the floor has been cast. Either end of
the panel has a steel plate that connects to
the adjoining panel, and these are cast-in
and hidden from view once the floor is
complete.
Severfield’s programme involved erecting
three floors of steelwork before using the
same tower cranes to install the concrete
floor panels, by lifting them carefully down
through the steel members.
The site’s two tower cranes are positioned
in voids either side of the main central
core and the two outer cores. These areas,
which measure up to 8m-wide, will be
infilled by Severfield during a return visit
once the cranes are no longer needed and
dismantled.
“Coordination has been key to the
success of this project,” explains Laing
O’Rourke Project Manager Craig Stokes.
“Severfield has had to work closely with our
offsite precast panel production to install
the steel restraints prior to them being
delivered to site.”
Steelwork starts at ground level and
is founded on a concrete substructure
encompassing a two-level basement. This
has been formed by a combination of raft
foundations, a secant wall up to 25m-deep
and a concrete capping beam.
“The secant wall and the raft have to
work in conjunction as in one corner of
the building the proximity of the Bakerloo
Underground Line meant no deep piles
could be installed,” explains Mr Peet.
The Brunel Building is due to be
completed during 2019.
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Exoskeletons are present in various creatures to support and protect the
animal’s body. Examples are such insects as grasshoppers and crustaceans
such as the lobster. Humans have an endoskeleton as do most buildings.
Exceptions are described by Kathleen Villaluz1 and include the Centre Pompidou
(Paris) and the Hotel Arts (Barcelona). Placing the structure of the building
externally allows large open spaces in the interior and using it to resist lateral loads
maximises the lever-arm in the structure and therefore minimises the uplift forces
due to overturning. A penalty is paid for this in the necessary penetrations through
the building façade to allow the connections of the horizontal structure to the
exoskeleton. Other building forms which employ the structure at the perimeter to
resist lateral loads are the framed tube pioneered by Fazlur Khan in the 1960s (eg
the Willis Tower, Chicago) and the braced tube (eg 30 St Mary Axe – colloquially,
the Gherkin). In these buildings, although the lateral load resisting structure is
on the perimeter, allowing the same generous open spaces in the interior, it is
enclosed within the façade.
Another example of a building with an exoskeleton in London is Bush Lane
House by Arup Associates in which the external diamond lattice structure transfers
vertical loads to the main vertical columns and shares in resisting the lateral loads
on the building in one of the orthogonal directions. A particular feature of the
external structure in Bush Lane House is that the external bracing is of stainless
steel and is water filled to provide fire protection. The external structure therefore
has several different functions.
The exoskeleton of the Brunel Building is an architectural feature which
supports vertical loads but does not resist lateral loads, thus not fully exploiting
the available structure. The lateral stability of the building is provided by three
substantial concrete cores. The absence of stiffeners in the connection details
between the less-steeply inclined elements and the steeper ones in the exposed
frame confirms that the forces in the former elements are not significant.
1 https://interestingengineering.com/
top-7-exoskeleton-structures-around-the-world
Richard Henderson of the SCI discusses the structure.
Orange shrouds
cover the connections
between the skeleton
and the internal beams
/Facades_and_interfaces
/Service_integration#Composite_beams_with_web_openings
/Construction#Temporary_works
/Steel_construction_products#Flat_products_-_plates
/Construction#Steel_erection
/Construction#Tower_cranes
/Concept_design#Concrete_or_steel_cores
/Floor_systems#Precast_units
/Facades_and_interfaces
/Visually_expressed_structural_forms
/Steel_construction_products#Stainless_steel_products
/Steel_construction_products#Stainless_steel_products
/Fire_protecting_structural_steelwork
/Concept_design#Structural_options_for_stability
/Concept_design#Concrete_or_steel_cores
/top-7-exoskeleton-structures-around-the-world
/top-7-exoskeleton-structures-around-the-world