e-mosty December 2017 MSS and Formwork Travellers | Page 29

The movement of the machine is performed with a
set of 4 winches that are radio controlled - the display
shows the force developed by each winch as well as
other relevant information about the system.
This ensures higher levels of safety during launching
operations. After the first 30m launching the front
nose of the overhead MSS reaches the next free pier.
At this position the supporting frames are
repositioned with the overhead cranes integrated in
the MSS. This feature makes this equipment fully
autonomous with no need for external cranes to
assemble its supports. During these operations two
plane trusses positioned at each end of the main
girder play an essential role in order to guarantee the
stability of the machine. Once the support frames are
repositioned, the MSS is able to perform the final 60m
launching.
As soon as the launching operation is completed, the
entire machine is elevated using hydraulic cylinders,
the formwork tables are closed and the suspension
bars assembled. With these steps finalised, the MSS is
ready to start the construction of a new span.
The construction of the new span starts with the
positioning of preassembled steel reinforcement
cages over the formwork. Once again the overhead
cranes play an essential role, enabling lifting,
transportation and positioning of these heavy loads.
The post-tension steel strands are assembled inside
the ducts that were previously and accurately
positioned inside the steel cages. Before the concrete
operation starts, it is still necessary to assemble the
internal formwork panels that will give the desired
shape to the deck section.
The concrete pouring of the deck is divided in two
stages. In the first stage the bottom slab and webs are
poured creating a U section. In this operation 690m 3
of fresh concrete is poured over the formwork. The
concrete is transported from the concrete plant to the
back of the MSS in concrete mixer trucks. The trucks
deliver the concrete into static pumps that are
responsible for pumping the concrete through
metallic tubes to the concrete distributors. There are
3 distributors strategically placed over the formwork
in order to reach the full length of the deck. During
the concrete pouring operations, the OPS is
continuously monitoring and actively controlling the
structure. According to the load applied to the
structure, the OPS automatically adjusts the tension
of the MSS prestressing cables, which reduces
deflection and minimises tension. Once the 1 st stage
of the concreting operation is finished and the
concrete has hardened, the internal formwork panels
are dismantled and the top slab formwork is put into
position. Then, the top slab reinforcement steel is
assembled and the system is ready for the 2 nd
concrete pouring stage, in which 460m 3 of concrete
are cast. Once this operation is finished the entire
section of the deck is completed.
When the concrete becomes hard enough the post
tensioning cables installed inside the concrete are
tensioned, which gives the necessary strength to the
deck. Once more, during post tensioning the OPS is
monitoring the structure and releasing the tension in
its prestressing cables while the weight of the deck is
being gradually self-sustained.
Post tensioning operation marks the end of the span
construction, meaning that a new cycle is ready to
begin.
The M1-90-S was conceived to achieve construction
cycles (i. e. one span) of 14 days.
The Client: Yuksel Kappa
3. Conclusion
The first application of the OPS system has defined a
new era in the field of bridge construction. Its
innovative technology has enabled reaching new
limits of optimized dimensions, allowing for higher
quality construction with better control and savings
both in time and costs.
References:
PACHECO, Pedro – FONSECA, António: Organic Prestressing.
Journal of Structural Engineering. March 2002. DOI:
10.1061/(ASCE)0733-9445(2002) 128:3(400)
PACHECO, Pedro: Multi-span large decks – the organic
prestressing impact. Taylor & Francis Group, London, 2015.
Pp 103 – 124. ISBN 978-1-138-02757-2
Construction Manuals, drawings and other information
provided by BERD
Acknowledgement:
Professor Pedro Pacheco, CEO BERD
Hugo Coelho, Head of Engineering & Production Department,BERD
André Resende, Project Manager, BERD
Brigitte Rouquet, Marketing Director, BERD
4/2017