130
X2
Category 2: Civil Structures
Description of Structure
The structure of the passage/arcade consists of a
U-shaped tunnel covered with two double-track railway
bridges with a platform in between. The U-shaped
tunnel (floor, walls and columns) is made of reinforced
concrete. The railway bridges and the platform are
constructed from pre-stressed concrete. In order to
reduce the height of the construction (top of rail - bottom
of deck), the railway bridges are constructed as trough
bridges. A further reduction of the height is obtained
by reducing the thickness of the ballast bed (with
authorisation from ProRail). The platform between the
two double-track trough bridges is constructed as a
double T-deck. Although an integral construction was
briefly investigated and seemed possible, the client
preferred a more proven method of construction.
Therefore, it was decided to keep the superstructure
separated from the substructure by the use of
elastomeric/spherical bearings.
Method of Construction
In order to reduce the number and duration of the
‘out-of-operation’ periods for the rail tracks, the following
considerations were made:
• Use of natural foundation instead of pile foundation;
• Pre-construction of the complete structure at the site
north of Tilburg Central Station (the former Nedtrain
facility).
The use of a natural foundation results in differential
settlements between the supports. These differential
settlements do not fulfil the requirements of the client
(ProRail) and result in too high stresses in the girders of
the trough bridges and also in tension forces at the end
supports of the trough bridges and platform.
In order to meet the requirements regarding the
differential settlements and stresses, jacking of the
bridges and platform is necessary immediately after
positioning of the structure and a second time (1 year
after positioning). For the end supports, spherical uplift
load bearings are used.
By pre-constructing the entire structure, the hindrance
to the rail traffic is reduced to a minimum. For the
positioning of the structure in its final position, several
options have been considered. The definitive design
and the tender specification are based upon the method
of ‘tunnel pressing in an open construction pit’.
Structural Model in Scia Engineer
The entire structure, the U-shaped tunnel, the two
double-track trough bridges and the platform are
modelled in Scia Engineer using Plate and Shell
elements. The girders of the trough bridges are defined
as subregions, with a different thickness, within the
main slab. The girders of the double T-deck (platform)
are modelled by using a standard ribbed plate element.
Working with one overall model instead of several
separate models for the individual structures, it is
necessary to make sure that interaction between the
different structures and structures with the subsoil is
implemented correctly in the calculations.
Modelling of the natural foundation is done by using
an individual surface support on the bottom slab of the
U-shaped tunnel. The subgrade reaction modulus (C1z
parameter) is determined by Plaxis calculations. With
Scia Engineer an analysis is performed to determine the
sensitivity of the structure for the range of the subgrade
reaction modulus. It is concluded that the lower limit
for the modulus is critical for all the main structural
elements.
Using an overall model means that the bearings
between the trough bridges/platform and the wall of
the tunnel have to be modelled with beam elements
because the use of spring elements between structural
elements is not possible. The beam elements that
represent the bearings were rigidly connected to the
wall elements. The connection to the superstructure
is modelled as a joint. Because the stiffness of the
bearings in all three directions is different, a study is
performed to determine the size, length and modulus of
elasticity of the beam elements so they would represent
the stiffness of the bearings in all directions.
The use of Scia Engineer made it possible to design this
complex structure within the requirement specifications
of the client.
New Passage / Arcade at Tilburg Railway Station - Tilburg, The Netherlands
Software: Scia Engineer
