NSC 25
May 18
the very long spans needed for the sports
hall and auditorium.”
The auditorium’s roof is formed by a
series of long rafters, spliced together at
mid-point to create an overall 46m clear
span. They were transported to site in
23m-long pieces using Walter Watson’s own
fleet of extendable rear steer trailers.
Two 60t-capacity mobile cranes were
used to lifted the 7.5t rafters into position,
with each crane lifting a single beam.
The rafters were then connected to the
stanchions at eaves level before being
connected at the apex haunch. One crane
would remain connected to the portal rafter,
while the other crane lifted the purlins and
tie beams into position. This stabilised the
portal before the second crane released its
load.
At two locations within the main
auditorium roof, the 43m-long rafters are
supported off a carrier beam spanning two
bays to leave a large clear opening for a
skylight.
“Additional lateral bracing had to be
designed and fitted at these two locations to
stabilise the carrier beams in the absence of
any first-floor slab to prevent spreading of
the portal and dipping of the apex,” explains
Walter Watson General Manager Structural
Division Trevor Irvine.
The auditorium has been designed as
a portal frame and it is propped at the
surrounding first floor of the building to
negate any deflection.
Some added flexibility has been designed
into the auditorium so that it can be doubled
in size to create a larger 3,200-capacity
venue. At present the auditorium’s seating
rakers are arranged in a quarter circle
configuration around a stage, but by
removing one perimeter wall further
steelwork can be bolted to the frame to form
a larger half circle auditorium around an
enlarged stage.
“A steel-framed structure was always
the preferred design for this building for a
number of reasons, with its flexibility and
ease of adding an extension a prime mover,”
says RPS Project Engineer John Ellis.
Covering the auditorium’s roof is a
seven-layer insulated cladding, which has
been specified to prevent any noise from
escaping from within the venue to keep the
neighbours happy.
Surrounding the auditorium on three
sides is the building’s first floor. This upper
level contains the structure’s other large
column-free space; a double-height sports
hall.
Forming the sports hall is a series of
trusses that required a tandem lift erection
procedure to install them. The trusses
measure 18m-long × 2m-deep and they
were brought to site as complete sections on
extendable trailers and then erected using
two mobile cranes.
The two-level element of the building
has been designed as a braced frame with
bracings located within the exterior walls.
In order to avoid windows and doors,
wind portals (goal posts) with no diagonal
members have been used.
A spokesman for the Church said: “Green
Pastures Church believes in Ballymena and
is committed to supporting local companies,
local jobs and the local economy.”
Green Pastures hopes to have its first
service in the building in late 2019.
Religion
The large open-plan
first floor sports hall
The auditorium can be
enlarged in the future
How the completed
facility will look
/Leisure_buildings#Ability_to_span_long_distances
/Fabrication#Handling_and_transportation
/Construction#Mobile_cranes
/Portal_frames#Plan_bracing
/Portal_frames
/Leisure_buildings#Flexibility_and_adaptability
/Building_envelopes
/Trusses
/Braced_frames