Built in 1886, the old Comenius bridge over the Elbe in the Czech town of Jaroměř provided a link between the market sqaure and the south bank of the Elbe. Although the bridge design was of no great aesthetic value, the frequently used bridge was sadly missed by residents when it was destroyed by flooding in June 2013.
Designed on a small budget the replacement bridge had to overcome some difficult design hurdles. Heritage preservation demands meant that the original bridge abutments would have to be retained within the new design which also resulted in the slightly skewed alignment having to be kept. Loading restrictions on the abutments meant a light single span solution would be required.
The new bridge, developed by baum & baroš architects, in collaboration with structural engineers from EXCON, features a rigid triangulated truss. The relatively simple structure hides a complex structural design that focuses on a prestressed steel beam which provides spacial rigidity, low weight and lower material cost. The structure is mounted on two elastomer pot bearings, which are fixed at either end of the compression member. Lateral buckling of the structure is prevented by two adjustable rocking piers fitted at the end of each span. This anchoring method enables the axial symmetry of the structure to be maintained, irrespective of the skewed angle of the historic bridge.
The central compression member which doubles as a cable channel, is formed from a 76 cm diameter circular hollow section with a one metre chamber. Both end-spans are designed as two-part spatial structures, for transmitting tensile force into the central compression member. Three longitudinal beams act, in part, to absorb the load, and at the same time, support the grid-form deck.
The tensioning system is formed by three flat parabolae. The lower parabola running in the vertical plane serves to absorb the vertical loads, whilst the two parabolae which extend in oblique planes lend torsional rigidity to the structure. The ends of the tension elements are furnished with opposite threads with a turnbuckle in the middle.
The bridge deck is formed from a network of steel elements that integrate with the filigree steel that forms the balustrades. The deck is primarily intended for cycle and pedestrian traffic, but can also accommodate emergency response and maintenance vehicles up to 3.5 tonnes.
All load bearing and non-load bearing steel components of the bridge are hot dip galvanized. Its metallic surfaces, emphasise the technical and functional appearance of the bridge and will provide long-lasting protection for many decades.