HDG Magazine Issue 1 2018

HOT DIP GALVANIZING
01 | 2018
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use of prefabrication and barged delivery to site
strengthening of the existing Victorian masonry viaduct and station
roof
use of overwater ground investigation to inform the pier design
tailored working methods in and around the three operational railway
lines
FE analysis of the soil structure interaction for the pile design
use of bespoke lifting equipment.
Technical excellence
Many of the innovative solutions for the project lie unseen below the
new building. This includes the foundations and galvanized steel that
form the ground floor concourse.
The foundations comprise two concrete piers supported on 24,900 mm
diameter piles socketed into bedrock below the river bed. Over water
ground investigation proved essential to confirm the depth to rock; its
highly fractured nature led to a change in piling methodology prior to
construction. Advanced soil structure interaction, verified by finite element
analysis, was undertaken together with consideration of flexural
rigidity of the composite pile sections.
The piers support a concourse deck formed from a grillage of 600 mm
deep steel beams, which support the superstructure, transferring column
loads to the new piers. Fifty percent of the concourse is constructed
below the existing viaduct and above the river. Up-stand trusses
supporting the new floor and escalator pit span through one of the
barrel vaults, transferring load to new foundations outboard.
The new super-structure, comprising a curved steel diagrid frame,
exposed internally, is partially supported by a Victorian masonry
viaduct and the existing station roof.
A complex assessment of these structures was undertaken to determine
capacity, including measurement of strain under existing rail load
using innovative video gauging. Strengthening of the existing quadripartite
ribs involved the erection of 7.5 tonne steel arches within the
confined space of the viaduct, anchored to the existing piers with 1 m
long embedded bolts.
Hot dip galvanizing
Hot dip galvanizing was chosen as the method of corrosion protection
to all steelwork located above the River Aire forming the ground floor
concourse, as well as the bridges linking the concourse to the river
banks. In order to achieve the required performance the specification
included grit blasting the steel prior to galvanizing in order to achieve
a thicker coating and hence additional protection. It was felt that galvanizing
offered benefits over a painted finish in terms of life to first
maintenance and the overall durability afforded to steelwork located in
such a harsh environment.
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