Cable stayed bridge over the River Labe at
- Design and construction of a
longitudinally prestressed extradosed bridge
- Detailed 3D modelling to
analyse live load effects on the structure
- Good correlation obtained with
static and dynamic load tests
Engineers Ltd. used LUSAS Bridge to assist with its design of a slim,
cable stayed bridge on behalf of the Roads and Motorways Directorate
of the Czech Republic. The
a number of original structural elements and technologies, and
provides a modern, light, and aesthetically pleasing solution to
crossing the River Labe. The
bridge is the first cable-stayed bridge in the Czech Republic with
two planes of stays and low pylons, characteristic of an extradosed type of cable
Located to the
north-east of Nymburk in the Czech Republic, and situated in the
flat plain of the Labe lowlands, the bridge carries the I/38 road
over the River Labe as part of a by-pass scheme built to alleviate
traffic congestion from the historical centre of the city. Due
to the requirements of the Labe Basin Authority, a main span of
together with a very shallow structural depth for the bridge
superstructure was required. As a result, a so-called
"extradosed“ main bridge structure with low pylons was
developed, representing a transition between the traditional
cable-stayed bridge and a bridge with external prestressing tendons.
cross-sections of approach bridge, central composite section
and at pylons
complete bridge crossing has a continuous superstructure 530m long with expansion joints
located only at the abutments. The main concrete bridge
superstructure consists of a 132m span over the River Labe and two
adjacent 41m spans that are directly connected to the approach
spans.The concrete deck sections of the main span are of a symmetrical
double-girder shape of variable depth and width, and are supported by sets of 3 parallel grouped stays anchored to the 16m high pylons.
middle section of the main span was designed as a relatively
steel-concrete drop-in structure. This 52m
span comprises two main steel box girders that are tied by steel I
section cross beams at
centres. The thickness of the lower and upper flanges and webs of
the main steel girders vary in accordance with the magnitude
of the internal forces. After being delivered to site by barges the box girders
were lifted into place and welded to 700mm long steel members that
were cast into the concrete structure and tied to it using longitudinal prestressing anchors fixed to the end plates. Shear
studs tie a 245mm thick reinforced concrete slab to the steel
steel girders from barge
The 16m high, heavily reinforced concrete
pylons are topped with hollow steel plated box chambers for anchoring the cable stays. The anchor
plates are one of the most highly stressed parts of the
structure and were fabricated from 150mm thick steel plate.
Welded into the front face of each anchor plate are six,
377mm diameter, 16mm thick steel tubes through which the
stays were passed and then anchored. The bottom flange of
the chamber is formed from 50mm thick steel plate with
stiffeners to provide a uniform distribution of the forces
to the concrete section. The side walls of the box are of
40mm thick plate with 50mm thick vertical stiffeners at the
anchor plate locations. Steel studs, welded uniformly to the
sides and top of the box chamber, bond
the steel box to the self-compacting concrete that was subsequently
600mm square manhole cover in the top of the
pylon provides maintenance access.
Embedded steelwork ready to
receive steel girders
Steel plated pylon box assembly
beams and rocking struts
At the pylon locations the bridge deck has
massive cross beams which
help to distribute the loading from the longitudinal girders and
pylons to the bridge bearings. Prestressed anchor cross beams are
also used where the cable stays are anchored to the
Piers, located where the back hangers of the bridge are anchored, are designed
as rocking struts in order to be able to resist both tensile
and compressive forces and to allow for expansion of the
structure. The rocking struts are made of 610mm external
diameter seamless steel tubes. At both ends of the strut an accurate four-shear pin joint is formed. The
pin joint anchor plates are attached to the bridge deck and
elements of the bridge substructure using prestressing bars.
Rocking struts beneath back
cable hangar anchorage beams
Modelling in LUSAS
A detailed 3D model of the complete
bridge structure including the approach viaducts was created in
LUSAS. Solid hexahedral elements modelled the concrete deck and
pylons. Thick shell elements modelled the steel members of drop-in
span and pylon anchorage boxes. A separate 3D solid element model of
a pylon box assembly was also created to investigate the localised
stresses in this highly stressed part of the structure.
Views of LUSAS
model showing steel topped pylons and drop-in section
Eigenvalue analysis obtained the
first 15 mode shapes and gave a good indication of the potential
response of the structure.
A static analysis investigated the effect
of live loads in the transverse direction, and also investigated the
effects of any eccentric position of live load on the longitudinal
forces induced in the deck and cable stays. Because deck
displacement due to
off-centre vehicle loading was of interest to Pontex a number of
displacement plots were produced showing displacements caused by a
variety of applied loads and load combinations.
of the bridge both static and dynamic load tests were
carried out showing very good correlation with the LUSAS predicted
results, effectively verifying the modelling approach used.
bridge opened to traffic in May 2007. Pontex Consulting
Engineers Ltd., believe that because
of its location, and by the introduction and use of a number of original
structural elements and technologies, the bridge will help contribute to
the further development and use of modern light cable-stayed
structures in the region and, in turn, become one of the most outstanding bridge
structures in the Czech Republic.
"By using LUSAS
on this project we obtained an accurate assessment of the deck
displacements caused by the static and dead loads. The easy-to-use modelling capabilities
and the re-use of previously defined load patterns helped enormously
Engineer, Pontex Consulting Engineers Ltd.
involved in this project:
Client: Roads and Motorways Directorate of the Czech Republic –
Designer: PONTEX Consulting Engineers Ltd.
Main Contractor: Joint Venture SMP CZ, a.s. + Metrostav, a.s., D.4 + PSVS,
the main bridge: SMP CZ, a.s.
- Contractor for the approach bridges: Metrostav, a.s., D.4, together with Sub-contractor JHP mosty, s.r.o.
- Subcontractor for the steel
work: MCE Slaný, s.r.o.
study was created with reference to a technical paper
presented by Milan Kalny of PONTEX Consulting Engineers Ltd.
at the IABSE Symposium on ‘Improving
Infrastructure Bringing People Closer Worldwide’, Weimar,
Germany, 17-21 September 2007.
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