Netherlands: high-tech fastening for high-speed track ... - Hilti

Magazine Fall/Winter 2005
Engineering
Page 21
Rheda 2000 slab
concrete sleepers
superstructure
substructure
outer dowels inner dowels outer dowels
interface
With a view to minimizing
the height of construction,
the slab track of the high-speed rail
system under construction in the
Netherlands has an exceptionally
low profile. This led to use of a
concrete slab sandwich design
with the substructure and superstructure
separated by an intermediate
geotextile layer (image 1). In
conventional slab track designs,
transverse and longitudinal forces
are taken up by the walls of the
trough formed by the substructure.
In this particular case, however, the
forces involved were required to
flow between the slabs through a
system of connectors. The Infraspeed
Consortium therefore commissioned
a number of companies
to propose, design and test a system
of connectors suitable for the
task. The solution put forward by
Hilti was subsequently selected for
use in the construction of this
stretch of high-speed track.
High loads in a corrosive
environment
The primary requirement to be fulfilled
by the Infraspeed system –
allowance for longitudinal movement
between the slabs as a result
of deflection, shrinkage or temperature
differences – resulted in a
concept comprising fixed inner
dowels and displaceable outer
dowels. These must be capable of
taking up not only the high dynamic
loads of normal railway operation,
but also the static loads
that may occur in extreme situations
such as derailment. In order
to ensure that loads occurring in
the system do not exceed the permissible
values at any point, a finite
elements program specially
developed by Hilti for applications
Image 1: Hilti slab connection system with inner and outer dowels.
Image 2: Model of numeric simulation.
center track line
in the field of fastening technology
was used to check the distribution
of forces (image 2). Furthermore,
as water is able to seep between the
concrete slabs and, for part of its
length, the track is situated close to
the coast where the atmosphere
contains chloride, consideration
also had to be given to exposure of
the connectors to climatic influences.
This combination of a corrosive
environment and high loads
meant that great care had to be
taken in selecting a suitable corrosion-resistant,
high-strength steel.
Verification
through testing
Loading capacity verification testing
formed a significant part of the
development of the Hilti composite
slab system. The Hilti test engineers
were required to determine
the fatigue strength and expected
deformation of the connectors in
order to provide verification of the
system’s serviceability limit state
and its loading capacity up to failure.
They produced concrete blocks
for the substructure according to
the specification used for the rail
track in the Netherlands. Subsequently,
a Hilti diamond coring machine
was used to drill the holes in
which the concrete dowels were to
be set with Hilti HIT-RE 500 injectable
adhesive mortar. To be on
the safe side, the situation where no
friction is transmitted by the intermediate
geotextile layer was simulated
by laying two sheets of Teflon
foil, each with a thickness of 2 mm,
on the surface of the substructure.
The concrete block of the superstructure
was cast on top of this
(image 3). B35 concrete was used
for this purpose, exactly as specified
for the project in the Netherlands.