e-mosty December 2018 e-mosty December 2018 | Page 12

Figures 6 - 8: View of the curving deck (a) from above showing uncluttered deck; (b) from below showing
the structural form of edge boxes with middle T beams; (c) Tower at night
Hence, I feel it is important that an appropriate
construction method must be chosen with this
objective in mind at the concept stage.
Where construction is largely a repetitive process in
viaduct and bridge design, a precast concrete
segmental approach satisfies all of the criteria
deemed necessary to achieve this through
standardisation of the bridge’s main structural
components.
Such an ethos can be employed even on a structure
such as this. I achieved standardisation of edge beam
units using a harp cable system to ensure that the stay
anchorage segments were identical, giving minimum
number of complex or special units.
With the increasing trend to design and build, this
structure is an example of the counter point where by
a good designer considers the whole process of
design and construction that are needed to execute a
project. In doing so, by understanding fabrication,
construction, temporary works, long term
maintenance requirements as well as structural
design, the project can be completed extremely
economically.
The Wadi Abdoun Bridge is the first cable stayed
bridge in Jordan, and multi-spans. It is technically
challenging to build moreover in a country where
contractors are not experienced in such structures.
The design is composed of elements with maximum
repetition. The towers are integral into the deck. This
minimises the need for bearings and long term costs,
but also allows a safe and robust erection method.
I as the designer was on site for long periods during
the construction. This is unusual, but here it directly
helped the contractor to execute the works.
4/2018
My input went much further than my contractual role
in working with the contractor to ensure accurate and
safe work.
5. RATIONALISATION OF THE FORMS AND
FALSEWORK
I introduced rationalisation at the design stage to
minimise the number and types of forms, maximise
their use and as far as possible standardise the
bridge’s components. Forms are invariably lined with
a purpose designed elastic polymer or reinforced
plastic liners which produce an immaculate concrete
finish.
In the case of the Wadi Abdoun Bridge, pier and tower
forms must accommodate a constantly changing
profile which diminishes in cross-section over the full
height of the towers. The variable shaped concrete
sections optimise the stresses in the concrete and
effectively prestress the sections to resist the forces
due to torsion in the deck.
They vary in shape from a modified straight-sided
ellipse at the base 45m below deck level, to a circular
section 26m above the deck at the top. Slenderness is
achieved by the elimination of tower anchors in
favour of a saddle system for the stays and placing
mass where it is required the most.
This variable geometry requires that different
formwork was needed for each 3m lift, but each
formwork section was used four times per pair of
towers, and twelve times in total providing economy
in their use. The formwork is designed in 3m high
sections using an innovative concept in the fabrication
of variable sections.