148
X2
Category 2: Civil Structures
New Troja Bridge over Vltava River - Prague, Czech Republic
Introduction and description of the bridge
The client, the City of Prague, announced the
architectural competition in 2006. The winning project
was submitted by the Mott MacDonald company
together with the Roman Koucký architectural office.
The construction process for this structure began in the
summer of 2010. The general contractor for the bridge
was Metrostav a.s., while the designer of the steel
structure was Excon a.s. Novák & Partner Ltd. company
was the designer of the incremental launching of the
construction process and the temporary structures used
for the construction process. Under the terms of the
project supervision for the contractor, we also performed
a lot of computational analysis of the structure with
respect to all the construction stages.
The structure of the new Troja Bridge crosses the
Vltava River in a northern part of Prague city centre.
It connects the central part of the city with the city
ring road. The bridge has two spans. The main span,
200.4 m in length, crosses the river, while there is a
side span of 40.4 m in length. The bridge should open
in 2013. The main span is crossed by a steel network
arch, which is extremely flat (the rise/span ratio is
1/10), and by the suspended tied concrete deck. The
bridge carries two tram tracks, four road lanes and
two pedestrian lanes. The steel arch has a multiple
box section at the midspan. The section splits into two
legs close to the supports. The arch footings are fixed
to the concrete deck and to the last massive in situ
cast transversal beam. Due to the extreme load, the
footings are filled with self-compacting concrete. The
main span concrete deck is composed of a thin in situ
cast slab, with a typical thickness of 280 mm. The deck
is stiffened by precast prestressed transversal beams,
which are only 500 mm wide and almost 30 m long,
with a weight of 50 tonnes. They are suspended by
tied network hangers. In the longitudinal direction, the
deck is only stiffened by two arch ties with a composite
cross section. The inclined hangers are in the diameter
range of 76-105 mm. They have a pin and fork
connection at the ends to the tie and to the arch. Each
transversal precast beam is prestressed by two cables
with nine strands. The concrete bridge deck is heavily
prestressed. The transversal prestressing tendons are
composed of four strands (15.7 mm) in flat ducts. The
longitudinal prestressing is rather complex. Six cables
with 37 strands are located in each composite tie. The
slab is prestressed by a number of cables with 7 to 22
strands. The pedestrian stripes are located on the steel
cantilevers, which will be attached to the edge stiffening
concrete beam of the bridge deck.
The side span is a single span completely in situ cast
prestressed concrete structure.
Construction stage analysis and global supervision
analysis
For the understanding of the response of the structure
during the construction process several mathematical
models were compiled. The simplest 2D beam model,
where all the structure parts were modelled by the beam
elements, was primarily used for TDA module analysis
of the construction process, taking into account the
effect of creep and shrinkage. The other models were
rather more complex. In the case of the main 3D model,
it was mainly planar 2D elements that were used; only
for hangers and the temporary truss beam elements
were used. For this model, 11,569 planar elements,
4,719 beam elements with 107 cross sections, 19,089
nodes, 7 materials and 107 load cases were defined.
This model was used for the global static, dynamic,
non-linear (geometric and material non-linearity) and
non-linear stability analysis. The model served also
as the basis for the detailed design of the structure’s
aerodynamic stability. In the calculations of geometric
nonlinearity, a solution was considered according to
the theory of the second order. The nonlinear solution
of suspension elements with an axial tensile force was
made with respect to the tension stiffening theory. All the
results were compared with simplified calculations on
models for which exact analytical solutions are known.
Bridge hangers were modelled as nonlinear beam
elements with sag able to only transmit tensile axial
forces. The main 3D mathematical model of the bridge
structure was also used for the analysis of the dynamic
effects of moving loads.
Software: Scia Engineer
