e-mosty December 2018 e-mosty December 2018 | Page 58

Figure 8: Superstructure steel touching down
on western abutment
Figure 7: Superstructure steelwork being lifted
V. SUPERSTRUCTURE
DESIGN FABRICATION AND ERECTION
The superstructure is formed from a steel ladder
bridge deck. Glulaminated timber beams run in the
longitudinal direction supported by the steel cross
beams. The superstructure steelwork was delivered to site in
three sections and bolted together prior to lifting.
Steelwork was lifted from the eastern side using a 350
tonne mobile crane.
The glulaminated beams help reduce the overall
weight and loading of the structure and provide
reliable support for the composite deck planking. A further crane was positioned on the western side to
take some of the load as the steelwork reached halfway.
The balustrades are formed from tapered
glulaminated timber posts, with horizontal stainless-
steel rails and stainless-steel anti-climb infill to
prevent hazards to pedestrians and cyclists from
falling. The smooth mirror-finish stainless steel top rail
is at 1.4m high to restrain cyclists.
The deck steel is erected in a single lift meaning there
are no geometry issues associated with lining up
cantilever construction of a cable stay (this single lift
approach was done for speed and ease of erection).
The primary beams, cross beams, steel outriggers and
the main mast are all governed by the maximum dead
+ live load-case.
The bracing is governed by the transverse seismic
case. For the design of the primary beams an effective
length as 3000mm has been used base on a ‘U-frame’
lateral restraint.
The steelwork was designed as self-supporting (without
the need for stay cables) under its own weight so that a
safe working platform was available for the construction
crew.
Four sets of cables were installed and stressed prior to
installing the additional weight of the decking and
balustrades.
VI. MAST
DESIGN
The superstructure is supported by spiral strand stay-
cables tensioned back to a 22m high inverted Y-shape
steel mast.
The crisp white mast is anchored back to a reinforced
concrete anchorage beam set into the existing ground.
The buckling analysis confirms the first buckling mode of
the mast is in the transverse direction when subjected
to the influence of deadload, live load, and the cable-
stay forces.
4/2018