Mozambique, located on the east coast of southern Africa with a coastline of 2800 km, is rich in natural resources and is rated as the 4th fastest growing economy in Africa. Part of the
Mozambique's National Development Master Plan is to improve the transportation network between the capital city Maputo and the south of the country. To achieve this aim, a bridge is being constructed across the Maputo Bay as a connection to South Africa. After its completion in 2018, it will be the longest suspension bridge in Africa with a main span of 680 m and a total length of 1225 m.
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Africa's largest
supension bridge
Mozambique, located on the east coast of southern Africa with
a coastline of 2800 km (fig. 2), is rich in natural resources and is
rated as the 4th fastest growing economy in Africa. Part of the
Mozambique's National Development Master Plan is to
improve the transportation network between the capital city
Maputo and the south of the country. To achieve this aim,
a bridge is being constructed across the Maputo Bay as a
connection to South Africa. After its completion in 2018, it will
be the longest suspension bridge in Africa with a main span of
680 m and a total length of 1225 m. Construction of the Maputo-Katembe Bridge (photo 1 and fig. 3)
started late 2014 with a total project value, including the southern
link roads, of approx. US$ 700 million. Design and execution is
being carried out by China Road & Bridge Corporation (CRBC)
and is based on FIDIC's Silver book EPC contract. German
consultant GAUFF Engineering is responsible for quality supervi-
sion as well as design verification according to the Eurocode.
Concept of the bridges
The bridge consists of reinforced concrete approach viaducts on
the North and South banks of the crossing, which connect to the
main span, a suspension bridge constructed of steel box girder
sections, with two large subsoil gravity anchor blocks that are
filled with sand and concrete. The bridge will carry four traffic
lanes, two in each direction, with a design speed of 80 km/h.
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Africa?s largest supension bridge 3 2017
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The North and South Approach bridges are being constructed
using two different design and construction methods influ-
enced by the local urban development. In the north, located in
the middle of a very congested central business district and
harbour, the approach bridge will be a balanced cantilever
853 m long construction rising up towards the main pylon.
The main distances between the piers are 119 m. The Southern
Approach Bridge, situated in a totally rural area without any
obstructions, will be built using prefabricated post-tensioned
T-beams to form its total length of 1234 m (photo 4 and 5).
The approach bridges connect on either side to a single-span
double-hinged suspension bridge with a centre span of 680 m,
supported by hangers attached to two cables, which are draped
over the main cable saddles of the towers and connected to the
anchor blocks on each side of the river. Side spans are 260 m
and 285 m long.
The bridge concept was designed according to Chinese stand-
ards with the overall design verified against Eurocode specifi-
cations and specifications according to the South Africa Trans-
port and Communications Commission (SATCC). Especially
for the pile foundation changes in the amount of reinforcement
were required considering considering the requirements by the
different codes.
Each gravity anchorage is made up of the foundation,
splay-saddle buttress, and anchorage chambers. Some of these
chambers are empty, and some are filled with concrete and
sand requiring a specific density, all adding to the total weight
of the structure. Each shaft has an external diameter of approx-imately 50 m, a wall thickness of 1.20 m and a wall panel depth
of up to 56 m. The deepest anchorage structure was the one on
the south side of the crossing; with 37 m it is believed to be one
of the world deepest constructed during the last years. Figure 6
gives the structural detail of the shaft and photo 7 shows the
final construction stage for the completion of the anchorage
block inside of the shaft. Photo 8 illustrates the completion of
Africa's largest
supension
bridge
Jörn Seitz
GAUFF GmbH & Co. Engineering KG,
Nuremberg (Germany)
Dean Gary Swanepoel
GAUFF GmbH & Co. Engineering KG,
Maputo (Mozambique)
B. Pengyu
China Road and Bridge Corporation
(CRBC), Bejing (China) 1 Maputo construction site: North Approach Bridge with
two of the eight piers for the free cantilever bridge that
will lead over the anchor block
credits photos: GAUFF Engineering2 Map of Mozambique
3 Visualisation of the finished Maputo Katembe Bridge
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Africa?s largest supension bridge 3 2017
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IP + 25.900
QZK17 5000
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150
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using the Crosshole Sonic Logging (CSL) testing method by an
independent third party after 28 days. Concrete cubes were
manufactured even for 365-day compressive strength tests.
Pylon, cables and steel box girders
The main structure of the tower is formed of rectangular
hollow box sections, with a length of 7.00 m and a width of
5.00 m. The wall thickness of the upper tower is 1.00 m, and
this increases to 1.20 m towards the bottom, resulting in a total
thickness of 1.80 m at the base. The final height of the tower on
the north, Maputo side, will be 135 m and on the south,
Katembe side, just one meter higher (fig. 10 and photo 11).
Prefabricated parallel wire strands will be used for the main
cables, which are made up of 91 galvanised high-strength steel
wires, 5 mm in diameter with a nominal tensile strength of
the massive concrete construction built on the shaft to hold the
main cables.
Piling and diaphragm walls for the anchorage shafts
As there was no comparable project in Mozambique for the
design of the bridge foundation piles, the design was based on
the findings of a geotechnical investigation, which started two
years ahead of the actual construction work. Pile construction
for the towers and foreshore bridge piers began in tandem with
the anchorage excavation. Before pile production could begin,
their bearing capacity was verified using static test loads. Based
on this all 331 piles were optimised in diameter and length.
A total of 283 piles were constructed for the approach bridges,
each with a diameter of 1.50 m and an average depth of 50 m,
and 48 piles were installed for the towers, 24 at each tower, and
each with a diameter of 2.20 m and length of 110 m at the
south tower and 95 m at the north.
The excavation for the piling followed the international
reverse-circulation-drilling method. The quality and integrity
of the concrete in all piles was verified over their total length
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5
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Africa?s largest supension bridge 3 2017
4 Pylon M2 (south) and piers of the approach bridge
5 Second of 34 piers of the Southern Approach Bridge
(December 2016)
6 Cross section of southern shaft with charateristic soil layers
7 Construction stage of the southern anchor block
8 Massive concrete construction of the northern anchor block
1670 MPa, resulting in an outside diameter of 509 mm and a
total strand length of 1317 m. The main cables are connected
on each side of the bay into the gravity anchorage blocks
(photo 9 and 12). The cables are specially protected against
corrosion in a permanent airtight system.
For the hangers, galvanised high strength steel wires will be
used. The transverse distance between the main cables hangers
is 21.90 m and the standard distance between the hangers along
the bridges main span orientation is 12 m, with the length of
hangers ranging from 73 m at the towers to 3 m at midspan.
The steel box girders are being manufactured in Nantong near
Shanghai in China and will be delivered to Maputo by ship by
manufacturer ZPMC.
Special concrete
One of the unusual aspects of the concrete on this project was
the addition of up to 40% fly ash. This not only offers immediate
cost savings but also long term benefits. The fly ash is produced
in and delivered from South Africa and gives the concrete an
extremely high durability, a fact which was confirmed by the
University of Cape Town's Concrete Materials & Structural
Integrity Unit which performed Durability Indexes testing on
the samples cored from the bottom slab of the anchorage. The
tests performed were the OPI- oxygen permeability, WSI-Water
sorptivity Index and the CCI-chloride conductivity index. The
results obtained were confirmed as the best test results ever
obtained from a site concrete. High workability was of vital
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8
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4.200
pylon prole
12 m
A-A 5 m 7 m
0.000 B-B
8 m
133.0 m
8 m
5 m 133 m
7 m
47.0 m 70.1 m5 m3.5 m
pylon elevation
5 m
17.4 m
5 m
136.376
2 m
6 m
2 m
6 m
9 Installation of the steel construc-
tions for the anchorage of the
main cables (north side)
10 Details of the pylon
11 Construction of southern Pylon
M2 (January 2017)
12 Construction of the southern
anchor block
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Africa?s largest supension bridge 3 2017
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importance to the project during the casting of the anchorage
base slabs and pumping the concrete up to heights of 140 m.
Laboratory testing confirmed that the concrete was still workable
up to 16 hours after the initial mixing. This is directly related to
the high quantity of fly ash and a retarder from China specifically
formulated for this project. Concrete cube crushing strengths
at 28 and 90 days have confirmed a remarkable strength gain.
C40 concrete had results of 51.9 MPa and 69.5 MPa at 28 and
90 days respectively.
Producing sustainable concrete and most importantly a
sustainable project is particularly important to CRBC and the
client. Achieving a balance of social, environmental and
economical factors is part of the contractor's quality manage-
ment system which was developed by GAUFF Engineering
following the 'Triple Bottom Line' concept from the United
Nations' Bruntland Report. Through this CRBC aspires to
produce a sustainable structure as a whole and to promote
sustainability across the board. Reduction of its carbon foot-
print by reducing CO
2 emissions is part of the company's
mix-design philosophy and is achieved through the use of fly
ash as an extender; it has resulted in dramatically lowering the
cementitious CO
2 emissions of the concrete from an estimated
352.5 kg CO
2/t to 229.5 kg CO 2/t, a reduction of 35%.
Summary
For this project, CRBC and GAUFF together with the client
have developed a comprehensive quality management monitor -
ing system, which covers all aspects of construction in Maputo
and also the extensive production of the complex steel compo-
nents being manufactured in China.
The calculations using Chinese standards and their verification
against Eurocodes were completed in June 2016, alongside the
production of piles and diaphragm walls. In the coming 18
months the construction work will focus on steel fabrication
for the suspension bridge, erection of the main cables, lifting
of the 57 steel box girder segments, and the respective quality
monitoring of the production in China.
At the same time the construction of the highly demanding
balanced cantilever post tensioned North Approach Bridge
will commence (photo 1) as well the installation of the
T-beams for the Southern Approach Bridge. Handover of the
new bridge to the Mozambique Nation is scheduled to take
place early 2018.
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Africa?s largest supension bridge 3 2017
Reacties
J Haasjes - SWINN 19 juni 2017 08:17
bedoelen jullie een suspension bridge? https://en.wikipedia.org/wiki/Suspension_bridge