 Composite
constructions are currently growing in importance, since robustness, maintenance
and suitability for testing are taking on a greater role in bridge building
for economic reasons. In conventional construction methods for composite-
construction bridges, the loads of concrete formwork and construction
concrete are only connected to the steel girders. Only the subsequently
applied loads of the bridge deck and traffic act on the composite section.
During the construction phase, the behaviour of the steel girders is unstable,
due to low horizontal rigidity; this instability must be compensated by
integrating reinforcing braces. These reinforcements are time-consuming,
expensive and obstruct traffic below during assembly.
As a solution to these disadvantages in conventional
composite construction, SSF has developed a type of composite girder that
can be almost completely prefabricated in the factory. These have an upper
boom which acts as an economical cross section under compression, as a
shell element for the bridge floor slab and as a horizontal stabilising
element. Construction and tilting braces are no longer needed for concreting
the in-situ concrete plate. The amount of construction steel required
is reduced considerably, since this is determined by the amount needed
in construction and not the amount contained in the bridge structure.
In this combination, the demands of modern construction methods are met
with particular success, due to the well-planned and economic use of steel
and concrete materials.
The VFT® construction method is equally suitable
for continuous girder systems and framework constructions. Simple connection
rod links in the support area allow the girders to be coupled in the construction
phase, in order to achieve a continuous effect. After the installation
and reinforcing stages, the in-site concrete plate can be laid continuously
and therefore more economically.
|
Steel girder, concrete upper boom not yet added.
|
|
|
|
VFT® girder at the prefabricated part works.
|
|
|
|
Oberhartmansreuth viaduct, installation of VFT®
girders, bridge deck constructed later with formwork carriages.
|
|
 |
|
Completed double-span bridge over the motorway.
|
|
|
Characteristics of the VFT® construction method
- The high quality of the finished structure keeps
maintenance costs low, due to the strong design with easily accessible
steel girders and a monolithic in-situ concrete plate.
- Extensive prefabrication of the girders reduces
the amount of work on the building site, so that construction deployment
is very economical with efficient construction times.
- The VFT® girders can also be used in areas other
than the conventional uses of prestressed concrete girders: in single-span
and continuous systems, in frames and viaducts.
- The low weight of the VFT® girders combined
with high flexural strength opens up new dimensions in the span length
of prefabricated bridges and allows the construction of slender and attractive
structures.
- The concrete flanges that form the upper boom make
buckling braces in the steel girders unnecessary, considerably reduce
the amount of steel used in construction, since the composite material
is mounted in advance, and increase the tilt resistance, i.e. no assembly
braces are needed.
Longitudinal cross-section -single-span girder bridge over railway, span
about 50 m
Regular cross-section with 5 VFT® girders
|
