Dammam Bridge: a strategic project in Saudi Arabia
Dammam, the capital of the Eastern Province
and the fifth most populated city in Saudi Arabia with 4.1 million inhabitants,
is experiencing high levels of industrial and population growth. Standing
on the shores of the Persian Gulf, Dammam boasts a strategic vantage point
between the Emirate of Bahrain to the south, the industrial city of Jubail
to the north and the road leading to Riyadh in the west. This dynamic city
is home to the country's oil industry.
In an effort to support its development,
the local authorities launched a wide-ranging programme to improve the
road infrastructures between Dammam and Khobar, the twin cities adjoining
Such improvements included the construction
of the Dammam Bridge, a seafront flyover located at the intersection between
the Coastal Road and the Port Road, an area that was constantly gridlocked
due to train traffic from the port.
The structure and its design
The structure comprises four parallel viaducts
that are designed to ensure that the two central decks shoulder the main
traffic coming in both directions from the Coastal Road (North & South
Major Bridges) and that the two adjacent ramps provide access to the Port
There were plans to create three lanes
for each bridge, except for the South ramp, which only has two. The deck
width is consequently 12.610 m and 10.360 m respectively. The deck
features a constant height of 3.0 m along its entire length. 17 segments
make up each span, typically measuring 55 m. Span segments are 3.22 m long.
Pier segments are 3.32 m long. The structure's vertical profile reaches
a longitudinal slope of 4% on the central decks and up to 6% on the access
ramps. From a plan perspective, the structure is relatively straight, since
it offers a minimum radius of curvature of 1,700 m. The layout of the piers
follows the railway line, meaning that the span lengths are highly variable
from 16.40 m to 55 m.
The access ramps to the viaduct were created
from backfill using Reinforced Earth®, thereby minimising their footprint
and offering an elegant architectural motif with their panel facings.
The structure was designed by consulting
firm Saudi Consolidated Engineering Company (Khatib & Alami), which
focused on a solution with precast segments and prestressed concrete. The
spans were fitted with expansion joints at each pier and replaceable external
prestressing. Pot bearings created the interface between the superstructure
and the piers.
The general contractor chosen by the Dammam
Port Authority to build the bridge was Saudi firm Al Yamama Company for
Trading & Contracting (Al Yamama Co.).
An array of bespoke services
Freyssinet was involved in the project
as a superstructure specialist, from precasting the segments through to
installing and prestressing the spans. The scope and type of services were
tailored to the context and expectations of Al Yamama & Co., which
was looking for a bespoke service.
Freyssinet dispatched a team of experts
to design and organise the segment precasting area. Four precasting units
were also designed, manufactured and shipped to Saudi Arabia for assembly
and commissioning. The process of adjusting the formwork (using a proprietary
geometric design control program) and the concreting operations were supervised
by the same employees.
In addition to precasting, Freyssinet was
also involved in fitting the spans. A launching gantry was modified and
made available for the Dammam project. The gantry had previously been used
on the Prai River Bridge in Malaysia and therefore required a complete
inspection to ensure that it was appropriately scaled to the Dammam Bridge,
while new components had to be designed and manufactured to meet the project's
specifications. This construction technique was used for the very first
time in Saudi Arabia on this particular project and proved to be indispensable,
since traffic along the railway and the Port Road could not be cut off
during construction. Freyssinet oversaw the heavy lifting and equipment
commissioning operations, as well as installation of the prestressing.
The precasting plant
The segment precasting plant was organised
into three areas: the reinforcement cage preparation area, the concreting
area and the precast segment storage area.
The first area was specifically dedicated
to cutting, bending and assembling the reinforcement bars into moulds matching
the exact geometric dimensions of each type of segment, which enabled the
teams to create the reinforcement cages. This area featured two tower cranes,
which hoisted the batches of reinforcements that been delivered by road.
A 20-ton forklift truck was also used to move the fully-assembled reinforcement
cages to the concreting area.
The concreting area comprised a space for
delivering the concrete and reinforcement cages, a space for the four precasting
units and a space for finishing the segments. This area featured a rail-mounted
175-ton gantry crane with a 25 m span above the four precasting units.
Given that the weight of the pier segments (151 tons) was considerably
higher than the other segments (68 tons for the deviators), it was thought
advisable to create a permanent storage area for the pier segments beneath
the gantry crane.
The storage area continued on from the
concreting area and offered a storage capacity of 102 segments. This area
also contained a buffer stock of segments to supply the continuous work
zone. An 80-ton gantry crane with a 36 m span was used to move the segments
and especially load them onto the trucks.
Precasting units for segments with a
The precasting method used for this project
was the so-called "match-casting" principle. This technique involves
using the previously cast segment as a "casting mould", so that
the faces of two adjacent segments always form a precision fit.
This method requires specific formwork
– precasting units – which can be used to prefabricate the bridge deck
segment-by-segment by following the imposed horizontal and vertical alignment.
714 segments constitute the project's 48
spans as follows:
standard segments with a fixed length of 3.22 m
deviator segments for deviating the external prestressing tendons
middle segments with a variable length from 1.1 m to 4.0 m
To precast as many segments as possible
in the same unit and to avoid the time-consuming process of moving freshly-stripped
segments from one unit to another, precasting units were made according
to a standardised design:
specific unit for precasting the pier segments
so-called "versatile" units for precasting standard, deviator
and middle segments
Removable and modular components were designed
for the versatile units in order to quickly convert them for each type
of segment. This organisation saved considerable time at the height of
production, since it concentrated each unit on precasting a span from end-to-end
(except for the pier segments, which were cast in a specific unit).
Freyssinet designed and manufactured the
formwork to strict quality requirements and applicable standards. Dimensional
and geometric inspections were continuously carried out while the metal
structures were being fabricated, as well as complete pre-assembly prior
A distinguishing feature of this trapezoidal
structure is the central web. The web requires a more sophisticated system
than usual with the presence of a two-part internal formwork, which must
be capable of deploying in a confined area during installation and retracting
when stripping away the formwork. Freyssinet overcame all these constraints
thanks to specially-cut panels combined with a series of articulated joints,
hydraulic (or mechanical) jacks and props.
The match-casting method allowed the teams
to precast one standard segment a day. Precasting a pier segment took longer
at three days per segment, since prestressing anchors needed to be fitted
and the bearing sheaves adjusted. Finally, one deviator segment was cast
every two days. Work was organised into day shifts during the winter and
night shifts during the summer to allow the concrete to cure.
Mass production started quickly by using
hydraulic systems to create automated formwork. The goal of producing 20
segments a week was achieved following a learning curve of only a few weeks.
Complete precasting of the structure took 12 months.
A reconditioned launching gantry
The launching gantries used to install
precast segments are generally custom-designed, but they can be reused
after being technically modified.
In the case of the Dammam Bridge, the length
and weight of the spans (1,165 tons with a 55 m span) represented a major
constraint, since they were only just compatible with the so-called "span-by-span"
These baseline data were strikingly similar
to the Sungai Prai viaduct in Malaysia (1,500-ton deck with a 50-metre
span, which was partly erected by the cantilever construction method),
for which Freyssinet had kept the launching gantry. Various modifications
were made to adapt the gantry to the Dammam Bridge.
These modifications included:
extension to the main beams and local reinforcements to satisfy the new
span length of 55 m
creation of a pier bracket
increase in the winch's lifting capacity from 130 to 160 tons
- A reinforcement
to the longitudinal moving system to accommodate the 6% slope
The new design was masterminded by Freyssinet's
teams in Thailand. A risk analysis was incorporated into the design phase
to identify and correct any hazardous situations. The analysis involved
the gantry's designer, manufacturer and user, as well as a safety expert
in order to review all the operations performed by the gantry. Their findings
were factored into the general design and construction methods for the
Assembly and load testing
The launching gantry was initially assembled
on the ground. As many parts as possible were preassembled, so that they
could be hoisted into place by conventional means and thereby minimise
the amount of work at height, which represents a significant risk factor
for operators. The trickiest part of the assembly process involved two
500-ton mobile cranes, which were used to tandem-lift the two 71.52 m long
main beams, one-by-one, onto their supporting structures. Additional parts
were then cantilever-assembled to restore the launching gantry's total
length of 127.35 m. Assembly was completed by installing the wind bracing,
winch, front and rear legs, and finally the segment suspension system.
As with any lifting equipment, a proof
test was carried out before the launching gantry was used for the first
time. This static test was conducted amid special safety conditions and
involved loading the launching gantry 20% beyond its maximum service load,
i.e. with four segments in addition to the 17 segments forming a 55-metre
span. The winch was also tested at 125% of its static capacity and at 110%
of its dynamic capacity before work began on installing the spans.
Installing the spans
The spans were installed during a one-week
cycle (six days worked) as part of a single shift pattern. The cycle began
with the segments, which had been delivered by road, being hoisted and
suspended one-by-one from the launching gantry using hangers. This enabled
the gantry to take its final deflection before starting to assemble the
segments one after the other.
The segments were then assembled with temporary
prestressing after epoxy paste had been applied to the surface of the segment
joints. The span thus created was still suspended from the launching gantry
and had to be "permanently" prestressed in order to become self-supporting.
External prestressing (16 x 27C15 tendons)
was also performed according to a highly specific load transfer sequence
to accommodate any differences in rigidity between the concrete span and
the steel launching gantry and consequently prevent the span from bending
during the operation. Once supported by the piers, the prestressed span
could be disconnected from the launching gantry.
Finally, the gantry was "launched"
to the next span using its main supporting structure, which was fitted
with a wheel track and pushing jacks. Before it reaches the next pier,
the gantry achieves a maximum cantilever deflection of close to one metre.
The front and rear legs offset the deflection and help relocate the main
supporting structure during the launching operation. These operations involve
moving major loads and call for painstaking preparation.
The sequence of events in building the
deck also required complex operations with such an oversize launching gantry.
The gantry had to be slid sideways once it arrived at the end of the structure,
from one span to the next directly adjacent span. Since the decks were
not at the same level, the 1,000-ton gantry had to be jacked up 1.5 m before
sliding and then lowered down after sliding over to the next deck.
Installation was completed in March 2015
after 14.5 months of construction.
A human adventure
The very type of services performed for
this project prompted Freyssinet to form a team with a wide range of complementary
skills spanning pre-casting, geometric control, heavy lifting and prestressing.
Fourteen people were mobilised to prepare
and set up the project as well as carry out the standard operations. This
multicultural team featured people from India, Malaysia, Morocco, Tunisia,
Australia, Canada and France. The project's most tremendous achievement
was not only meeting the technical challenge, but also creating such a
culturally diverse team.
Client: Dammam Port Authority
General contractor: Al Yamama Company
for Trading & Contracting
Engineering firm: Saudi Consolidated
Engineering (Khatib & Alami)
Consultant: AMO & Partners Engineering
Specialised subcontractor: Freyssinet Menard
714 precast segments
4 precasting units
1 launching gantry with a 1,000 ton capacity
1,000 tons of prestressing