The six-storey block sits
adjacent to an existing
The steel deck supports a 14-storey block
and connects to a six-storey steel-framed
accommodation block above, we opted to
design a large steel transfer structure.
“After considering concrete options we
found steelwork provided the most buildable
design. Concrete construction would have
been problematical due to the difficulty of
forming concrete over the Roman wall.”
Measuring approximately 50m × 20m,
the deck is 10m-high and accommodates
two basement levels and a ground floor,
while supporting a 14-storey student
accommodation block above.
Split into two distinct parts, the transfer
structure encompasses two cores that will
serve the accommodation tower, while also
providing the steelwork with some stability.
The northern section, that spans the
Roman remains will accommodate a
three-storey gallery and museum with an
underground public viewing platform, café
and exhibition space.
The southern half of the steel transfer
structure also contains some long spans and
will accommodate a ground floor student
reception area fronting Vine Street, and
two basement levels containing space for
entrepreneurial start-up businesses, and
back-of-house facilities such as bicycle
storage areas and a loading bay.
Prior to the steelwork erection beginning,
main contractor Balfour Beatty had already
encased the Roman remains in order to
prevent any damage during the construction
“We also tweaked the connection design
of the steelwork beams that span the
Roman remains, so all of the bolts could be
tightened from outside of the sensitive area,”
explains Bourne Steel Divisional Manager
To create the column-free space over the
remains, two parallel 17.5m-long girders
have been installed at first floor level.
As they are positioned in the middle of
the transfer structure at the furthest point
from any vehicular access point, there was
a need to redesign these members in order
to limit the size of crane needed to lift them
The girders are consequently formed
from channels, which were spliced together
in-situ, to form a 25t section. There are eight
1,850mm-deep pieces in total; four needed
to complete each girder.
A 500t-capacity mobile crane, which
required a road closure, was needed to install
these large girders. To minimise disruption,
Bourne Steel’s erection programme for the
initial phase was completed in just one
This consisted of nine truckloads of
steelwork, with the heaviest member
being over 22t and measuring 13m-long ×
1.8m-deep with 120mm thick flanges and
45mm thick webs..
“To coordinate nine deliveries over
The overall project also includes a steel-framed
six-storey student accommodation block that
sits adjacent to the transfer structure and has
one weekend was always going to be a
challenge, but we had an excellent team
and successfully installed 180t of steelwork.
We even had time for Balfour Beatty and
our team to sign off the largest plate girder,
which sits encapsulated above the Roman
wall,” adds Mr Davies.
“However, this wasn’t the project’s largest
member, this was a beam that was over
20m-long x 1.25m-deep with 80mm thick
flanges and 50mm thick webs, weighing
27t. This plate girder was installed using a
smaller 250t-capacity crane.”
As well as providing the required long
an entrance on Crosswall.
Joined by a covered walkway, the two steel
structures are both structurally independent, while
the design of the accommodation block has also
been driven by Roman remains.
“The block has been designed to infill an area
between two existing buildings, it also has a
lightweight frame because we could not install piles
as there are further remnants of the Roman wall
beneath its footprint,” explains Robert Bird Group
Engineer Liam Guntrip.
Consequently, to keep the building’s weight to
a minimum, it will be constructed on shallow raft
foundations and will then utilise a steel frame with
lightweight Metsec joists supporting a plywood
Erected around a single stability-giving concrete
core, the steel frame will have a 5m × 5m column
grid pattern. Bourne Steel will begin the erection of
this part of the project in February 2020.