136
X2
Category 2: Civil Structures
The footbridge is composed of three different structural
materials. The main bearing structure and secondary
bearing structure are designed as glue-laminated timber
beams. Connecting members, anchoring seats and
stability bracings are designed with structural steel. The
complete supporting structure with foundations and pilots
are designed as massive concrete structures.
Architectural design
The architectural design is based on a smooth curved
structure with a natural look to fit in a natural environment.
Terrain at each end will be raised to prevent the flooding
of the cycling track and pedestrian walkway. Both end
foundation blocks will be partially filled with earth to form
a new embankment raised to a new flood protection
height. The main span is divided into three smaller spans
with two middle support pillars. These pillars will be
placed beyond the main river stream on dry river bed. The
bridge structure is designed as a U-type channel with two
large main beams connected with smaller cross beams
at the bottom and longitudinal secondary beams for
attaching walking boards.
Design of the structure and technical data
Timber bearing structure
Two main beams are used to bridge across all three
spans. The cross-section dimensions of these beams are
24 x 160 cm. The middle span beams are curved beams
because of the curved bridge design. Span sections are
connected together with steel plates and a large number
of bolts to assure a rigid connection. Hinge connections
are used to attach the beams to concrete supports and
steel sockets will be used because of the large height of
the cross-sections, in order to gain stability and prevent
overturning.
The main beams are connected with smaller cross-beam
dimensions of 20 x 22 cm and are placed approximately
every 5.0 m. The connections of these beams are rigid.
This is achieved with the usage of steel plates and a large
number of bolts in each connection. These beams also
provide stability that counters overturning. Secondary
beams with dimensions of 16 x 16 cm are then placed
on top of the cross beams at an 83 - 84 cm distance
to ensure the bearing of the final walking surface. The
secondary beams are attached with hinge connections.
All the beams are made as glue-laminated beams with
Gl28h grade quality.
Steel elements of the structure
Besides the steel plates for all the connections and
anchoring seats, steel bracing diagonals were used
to achieve the global stability of the structure. These
diagonal bracings are placed in intersections of cross
beams and main beams and are attached through steel
plates on the socket connections of the cross beams. All
the diagonals have a strain link to gain the correct tension
of the elements. Some diagonal bracing elements must
be anchored to concrete supports to assure the global
stability of the structure.
Concrete foundations and pillars
Both end foundation blocks are designed as concrete
U-wall element blocks on strip foundations. The walls
of the foundation blocks are 50 - 60 cm thick. On each
front wall there are two raised concrete seats for the
timber beams of the main bearing structure. Both rebar
and mesh reinforcement were used for the adequate
reinforcement of cross-sections. The middle pillars are
slightly different, being made as walls with two inclined
arms. Each inclined arm has a seat for the main timber
beam on top. The walls of the middle pillars are anchored
to a massive concrete girder on two pilots, which are
drilled 5 - 6 m deep in bedrock.
Software and calculation model
Scia Engineer 2012 was chosen for the complete
3D-Modeling and for the calculation because there were
three different structural materials in interaction. Some
calculations were also “handmade”, such as for the
timber section design because of complex vertical and
horizontal frequencies that had to be calculated to prevent
uncomfortable vibrations.
The concrete design and reinforcement was carried
out in cooperation with another engineering bureau
with Nemetschek Allplan software. Some details for
connections were also “handmade” and transferred into
the computer design.
Software: Allplan Engineering, Scia Engineer
Wooden Footbridge with a Cycling Track Across the River “Sava” - Bohinjska Bistrica, Slovenia
