Loop Pylon Bridge Prague

The new connection from Karlin to Holesovice over the Moldau in Prague is designed as a unique, simple and elegant figure. It connects both riverbanks with a continous path for pedestrians and bycicles supported by a central loop pylon on Stvanice island. A circulation ramp, designed as a virtual shadow of the loop pylon, allows traffic from and to the island.

All three connections to Karlin, Holesovice and Stvanice are designed to allow complete barrier free access. Every connection is carfully blended into the urban environment, allowing adequate space to access the bridge.
On the Karlin side the bridge connects directly to the bycicle and pedestrian path on top of the flooding dam. The park connection towards Rohanske nabr. ensures the barrier free access to the street level.
Holesovice riverbank is connected directly to the pedestrian lane along Bubenske nabr. The bridge support structure on this side preserves the free passage along the lower riverbank pathway.
The loop pylon, it’s shadow ramp and five anchoring cables create a minimum footprint on Stvanice island and adapt in all requirements to the natural landscape planning for the island.

The cross section of the bridge allows for a 4,5m horizontal clearance for any service or rescue vessel. The vertical clearance is only limited by the cables which allow a minimum of 4m height for the full 4,5m profile. A lighting system along the whole bridge illuminates the floor to ensure a safe and comfortable passage for visitors also during night times. A second lighting system on the outside of the bridge profile illuminates the cables and the pylon.

The bridge’s lower edge is in general 190.1m above the sea level to ensure flooding clearance. Minimum clearance for the lower canal between Karlín and Štvanice is thereby also guaranteed. All structural elements below this clearance are designed to allow flood water to bass by continuously.

The Loop pylon is 50m high and holds the bridge with 17 Y-branched cables. Five V-shaped cables on Stvanice island anchor the bride and the pylon to the ground. Branching columns support the connections to Karlin and Holesovice without interfering with any river traffic.

Structural Design

General – The proposed concept for the new Karlin-Holesovice Bridge is a cable stayed integral bridge with a curved bridge deck and two spans of 100 and 155 meters. There is one central ellipsoid pylon in the middle of the bridge which supports the suspension cables. Bridge deck and pylon stay, which allows for horizontal movement due to thermal expansion of the deck. All load bearing elements are designed as hollow steel profiles with bracing ribs on the inside and are coated for corrosion protection. Bridge deck and pylon are accessible from the inside for maintenance.

Assembly – All structural parts can be prefabricated in larger elements and mounted on site.
The Pylon can be assembled horizontally by welding lifted into the final vertical position. After assembling the cantilevering bridge ends the bridge deck and suspension cables will be assembled step by step from the middle parts towards the ends. The bridge deck connections are designed as bolted connections. All elements can be moved into position by floating vessels, then lifted and bolted to the existing structure.

Ellipsoid Pylon – central element of the bridge construction is the ellipsoid pylon. It is supported by a combined pile raft foundation and ha a maximum height of 50 meters. The cross section is a trapezoidal hollow steel profile with rounded corners and bracing ribs in longitudinal and cross direction on the inside. The cross section varies from 1.5×1.1 meters to 3.0×2.0 meters and allows to be accessed from the inside for maintenance. The suspension cables are connected at the upper part of the ellipsoid – all connection details are located on the inside of the profile, which allows extended maintenance intervals. The pylon can be assembled from segments on the site and lifted onto its position.
Suspension Cables – the cables are designed as weaved steel cables with a synthetic coating for protection. Stainless steel fittings are placed at the point where the cables split in order to support both sides of the bridge deck.

Support-Grid – according to the distribution of suspension cables that support the middle part of the bridge, a grid of compression members is placed at the ends of the bridge deck. The increases the constructive height at the supports and allows for a larger cantilever from the end points. The gird also allows influencing horizontal vibration behavior of the bridge deck.

Deck – the bridge deck is designed as a hollow steel cross section with bracing ribs in longitudinal and cross direction and varying wall thickness of 15 to 25 mm. The whole deck is accessible from the inside via revision openings on the top of the deck. In the middle part of the bridge the deck is supported by suspension cables.
V-Suspension – In the area of the island the bridge deck is directly connected to the ground by V-shaped columns. This is reducing the span of the bridge and serves as support for the suspension cables at asymmetric load cases. In addition, these columns allow to effectively damping the horizontal and vertical vibration behavior of the bridge deck.

Ramp – the bridge is accessible from the island by a ramp with an ellipsoid shape in plan.
The ramp deck is designed as a hollow steel cross section similar to the bridge deck and supported by V-shaped columns. The horizontal softness of the ramp allows the bridge thermal expansion and also is damping horizontal vibrations.
Foundation – There are four major supports of the bridge structure: two rigid supports at the ends of the bridge deck, one rigid support at the base of the ellipsoid pylon and hinged supports at the bottom of the V-shaped columns. All supports are designed as base plates from reinforced concrete in combination with bored piles.
Thermal expansion – as the deck of the bridge is curved in plan, longitudinal expansion due to temperature load lead to a horizontal movement in the middle of the bridge. Due to that, no hinged supports at the ends of the bridge are necessary, which allows reducing details and maintenance of the supports of the bridge significantly. In addition, the bridge can easily be rigidly supported, which allows reducing the overall height of the bridge deck cross section.

Vibrations – The bridge stiffness is designed regarding the vibration frequency limitations for pedestrian bridges. The vertical bridge vibration frequencies are above pedestrian frequency impulse and additionally can be damped by the V-shaped columns in the middle of the bridge.

Project Team:
Melisa Ali
Lukas Galehr
Moritz Heimrath
Quirin Krumbholz

Structural Consultant:
Bollinger+Grohmann