The Bohemian city of Hradec Králové, which lies between the Elbe and Adler rivers, provides a collage-like mixture of historical buildings from various periods of history. Medieval houses and counter-reformation Baroque styles can be found, together with Postmodernist and contemporary structures.
Erecting a new structure against this background calls for a high degree of sensitivity, respect and discipline. These were some of the issues that architectural firm baum & baroš were faced with when they were commissioned to design a pedestrian and cycle bridge to link the historic town centre and its university campus. The bridge would fall within the protected environmental zone of Jirásek Park so all aspects of the design had to be carefully considered.
In addition to technical and functional issues, aspects of production, installation, economics, maintenance, aesthetics and long-term acceptance by the public also played a role in the multi-disciplinary planning for the bridge. This led to very close collaboration between the structural design team from Kosch–Führer–Jürges and the architects from baum & baroš. After careful consideration, it was decided to create a simple, modular steel structure fulfilling the following criteria:
• minimise cost through the selection of a simple, statically defined system
• reduce on-site operations to a minimum
• pre-fabrication of all constructional elements and selection of their dimensions with consideration being given to hot dip galvanizing of the steel
• minimise maintenance costs
• minimise repair costs by using bolted connections
• rapid installation with limited use of expensive lifting gear and ancillary structures
• sustainability to be a guiding principal throughout the project
The designers rejected an asymmetrical suspension type solution, which would be the usual choice in such cases, due to the size of the load-bearing mast that would be required and the visual impact caused within the Park.
The final design solution incorporates a truss with an understressed structure, derived from a Polonceau girder, with the upper beam forming the deck which is divided into two articulated sections. A tensioned cable in the form of a five-sided polygon creates the bottom chord of the truss. The transfer of loads is aided by the incorporation of three compressively stressed elements between the deck structure and the tensioned chord.
Rigidity was guaranteed in the horizontal plane by spacer bars and diagonal bracing. To enhance the lightweight construction and to reduce maintenance costs, a transparent and permeable structure made from 2.25 x 0.75m close-meshed galvanized grid plates was chosen for the surface of the deck. No vibration damping was required due to the inbuilt dynamic of the design.
When the project was completed, a simple, transparent and comprehensible structure was revealed. It has succeeded in not only creating a new link from the town centre to the university campus but also successfully integrating with its surroundings. The silver grey sheen of galvanizing will over time turn to a mottled grey that will naturally fade into the landscape of Jirásek Park.
Architect: baum & baroš Architekten
Image: baum & baroš Architekten