e-mosty December 2018 e-mosty December 2018 | Page 11

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A harp arrangement of stay is used to give uniform
stay sizes which rationalises the types of saddles
and anchorage details. The stay cables are
replaceable and, to the detail, filled with foam at
discrete locations to prevent the vibration of the
HDPE duct against the strands.
Unusually I developed asymmetric prestress within
the towers to counter the torsion in the deck and
cater for a range of stress states in construction
and in the permanent condition.
The crossbeams at the towers carry significant
structural forces and cope with different deck
geometries at each pier. The dramatic curve and
detail of deck connection with the beam offers
needed stiffness whilst minimizing the visual
impact and gives interest and clarity when viewed
from underneath.
The cross beams are
prestressed to cope with erection and permanent
loads and are designed to be robust enough to be
used as bases for tower cranes to minimise the
size of crane required.
Prestressed earth anchors tie the pilecaps into the
bed rock to provide a sufficiently-robust
foundation under seismic loads.
In an environment where economic factors often
produce uninspiring structures with brutal short
spans and simply supported precast beams on
bearings or in-situ concrete box girders – the Wadi
Abdoun Bridge is unique. I utilised my experience
in design and engineering to give efficient and
economical construction. I believe that the bridge
stands as a landmark of quality and excellence for
Jordan’s capital city.
Balanced cantilever erection over the arterial road at
the base of the valley give safe construction over a
busy live road using bespoke gantries.
3. CLARITY OF THE STRUCTURAL FORMS
I believe that the forms of structural elements
adopted for any particular project are integral with
and inseparable from the concept design. The
development of the type of bridge deck, supporting
pier, rationalisation of long span structures,
precasting for achieving quality, economy and
durability and construction technology are then all
considered at the concept stage.
4. SIMPLICITY IN CONSTRUCTION
The construction method often dictates the
economics of the structure, but with the emergence
of the privatisation of infrastructure projects some of
the criteria hitherto ignored are assuming greater
importance. In particular, the construction time
should be as short as possible, quality should be
guaranteed and above all the structures should be
constructed with simplicity and minimal risk.
In arriving at the total cost of the project, the material
cost must be considered together with the time
required for construction. Thus the material cost of
structures taken alone is not of overriding significance
now that market forces have also placed the engineer
in a managerial role to conceive and deliver a
complete project on time and on budget.
2. NEED FOR KNOWLEDGE ON SITE & CARE
The buildability of the structure was an important
consideration in the concept, especially given the
limited local experience with this structure type. The
bridge is also a complex structure to construct, with
large cantilevers deforming in three dimensions and
to be accounted for with the deck and tower
precamber.
Further complexities include super elevation and the
effect of staged stay stressing on a curved deck. I
personally guided the contractor through these issues
adding value above and beyond the contractual
requirements to enable the project to be completed
successfully.
4/2018
Figure 5: Night view with stay lighting