Exposed structure and services integration Richard Henderson of the SCI
Working around the building’s one
centrally-positioned core in a clockwise
manner, the steelwork was erected two
floors at a time. The flooring planks were
installed behind the steel programme and
temporarily propped until the concrete
topping had been cast and cured.
Once the topping was cured the props
were dismantled, to be reused elsewhere
on the job, while MEWPs were then able
to use the recently formed floor to erect
the next two levels of steelwork.
It was a complex erection programme
because of the bespoke nature of the steel
“It was completed ahead of schedule and
the fact that the team did a trial erection
before starting on site, using four columns,
four beams and six precast planks, to show
the client how it would look was a great
help and prevented any problems,” adds
One of the site’s tower cranes is
positioned outside of the project footprint
along Howland Street, but the other three
are all within the new steel frame. Once
the scheme is nearing completion and the
cranes are removed, the gaps they leave
behind in the frame will become atria that
allow natural light to penetrate into the
building’s inner areas.
The 80 Charlotte Street development is
due to complete in early 2020.
80 Charlotte Street has a simple beam
and stick steel frame with lateral
stability provided by concrete
cores. The simplicity of the steelwork belies
the effort that has been put into maintaining
a 450mm high structural zone at floor levels to
make the most of the available storey height
of 3.335m and to comply with British Council
for Offices guidance. Prestressed precast
planks 100mm thick with fair faced soffits are
supported on shelf plates welded to the webs
of 450mm deep primary beams. A 50mm
concrete topping completes the concrete floor.
The primary beams stand down by 300mm so
that the upper third is embedded in the floor
slab. These beams are provided with holes in
the webs for reinforcement to pass through for
tying and anchorage. Columns are tied together
for robustness in the direction perpendicular
to the primary beams by 150mm deep tie
beams within the depth of the slab such that
only the bottom flange is visible from below.
The zone immediately below the slab between
the primary beams is therefore uninterrupted
by structure and the horizontal runs of heavy
building services from the core are uninhibited.
In certain areas, the orientation of the precast
planks changes so that some beams support
planks on one side only. These beams have
been designed to carry the planks on their top
flange and are 300mm deep to maintain the
same level to the underside of the structure
throughout the floorplate. The webs of these
beams and of primary beams which cross the
runs of services have been perforated where
necessary to maintain the same zone for
The steelwork is to be left exposed when
complete and the detailing of the connections
is simple and unfussy. Flush end plates have
discusses the solution adopted.
been adopted with toe plates in certain places.
Some tie beams have also been provided with
horizontal triangular fillets in the connection of
their bottom flanges as an architectural feature.
Fire protection requirements for beams which
pass through compartment walls and for beams
with top flanges at floor level were optimised
using computational heat transfer modelling.
The structure has a 90 minute fire resistance
period and is provided with intumescent paint
pigmented with a dark grey colour to add to the
industrial feel of the space.
Once the steel was
erected it was all
repainted to get
to suit the exposed