Keeping the trusses to manageable pieces
meant each one was delivered to site in at
least 11 sections. The erection process had to
be carefully planned with close tower crane
co-ordination required to erect the trusses.
Individual elements were held in place with
one tower crane, while another section was
craned in and connected before each truss
To reduce crane lifts and the risk of
additional bolting at height, the flange splice
plates were profiled with rounded ends and
bolted on prior to transit. This allowed them
to be swung round to complete the splice
connection at high level. The web splice
plates were then bolted on to alternate sides
to complete the jigsaw.
Prior to delivery, each of the trusses was
trial erected at Severfield’s fabrication yard to
ensure they could be fully assembled on site.
“This process also gave the client the
opportunity to see the completed trusses,”
says Mr Kercel. “It was also interesting for
them to observe the assembled steelwork
and the large splices as some will be left
exposed in the completed scheme.”
One Crown Place is due to complete in
Substantial forces in the steel trusses at One
Crown Place demand commensurate design
and detailing of the splice connections –
many of which can be seen in the accompanying
photographs. The splices have been detailed with
preloaded assemblies to ensure that the joints do
not slip – essential in trusses of this nature where
there are many splices and slip would have led to
significantly increased deflection.
The splices are detailed with cover plates on the
inside and outside of the flanges to accommodate
the large forces (and bending moments, since the
truss was analysed with continuity at the nodes).
A common assumption is to distribute axial force
in proportion to the cross section of the member,
so a UC flange typically carries around 40% of the
The splices at One Crown Place were designed
as bearing splices – direct transfer of compressive
forces between the members. BS EN 1993-1-8
specifies minimum requirements for the
splice components in clause 188.8.131.52 (13) and
(14) – the choice for a bearing splice is highly
recommended. The same clause specifies that the
web connection must carry a proportion of the
bending moment, even if it had been assumed
that moment was carried entirely by the flanges.
This requirement tends to lead to larger web
connections than previous UK practice.
When multiple bolts are required in the
direction of the force, clause 3.8 requires a
reduction factor to be applied reflecting the nonuniform
distribution of force between bolts. A
joint is described as ‘long’ if the distance between
end fasteners exceeds 15d (bolt diameter). This
should be checked each side of a splice joint.
As can be seen in the photographs, the
mating surfaces (called ‘faying’ surfaces) of the
splices were left unpainted – vital if a reasonable
coefficient of friction is to be achieved. Good
practice is to agree the value of the slip coefficient
to be assumed before starting connection
design, and secondly to agree if the connection
is category B or C – non-slip at SLS or ULS
respectively. If category B connections are
designed, the slip resistance is verified at SLS, but
the bolt shear and bolt bearing are both verified
at ULS to ensure that resistance at ULS is sufficient.
Category B is a reasonable design choice as
the applied loads should never exceed SLS –
something has gone badly wrong if this happens.
At One Crown Place, HRC bolts (commonly
known as ‘tension control bolts’) were used.
Preload in the bolt is achieved when the splined
end of the bolt shank shears off as the nut is
tightened. Tightening torque is applied by contrarotating
sockets within the electric shear wrench.
This type of preloaded assembly is widely used in
Non-slip splice joints David Brown of the SCI
comments on the trusses’ design
The overall project includes
a number of retained
elements including a pub
and a Georgian façade