On Friday 13 May 2022, the world's longest suspension footbridge was opened in the area of Kralicky Sneznik Mountains. It was built over a period of about two years and spans the valley between the two mountain ridges Slamnik and Chlum at an altitude of over 1100 m above sea level and is 721 metres long. There were several constraints in terms of the design of the footbridge. It was a real challenge to cross a valley more than 700 metres wide at an altitude of nearly 100 metres. The first challenge was to find the most suitable location for entering and exiting the footbridge with the minimum height difference to make the footbridge comfortably navigable. The next important step was to find the appropriate basic geometry and dimensions of the elements, which were derived from static and dynamic calculations, component manufacturing and assembly options.
The suspension bridge is carried by six main load-bearing ropes with a 30.7m span in the middle of the span, which are anchored to two 11,4 metre high V-shaped pylons, each weighing 54 tonnes. The pylons are hinged and inclined towards the slope and are stabilised against lateral swing by system steel rods. The difference in height between the pylons from the entrance on the Slamenka ridge to the exit on the Chlum ridge is 6 metres.
The main load-bearing ropes are in the shape of a parabola, both in plan projection and in lateral view, thus creating a spatial curve. From the visitor's point of view, the main ropes gradually approach each other from the pylon towards the centre of the span, up to a distance of about 2m. The main ropes are anchored into the pylons, which transfer the tensile forces from the ropes to the rear anchor ropes of the same diameter, anchored into the bedrock. The bridge deck in the side view does not exactly follow the shape of the supporting ropes but gradually moves closer to the main ropes. The bridge deck is designed from 244 segments of 3m long anti-slip gratings with a sloping width of 1.2m and is suspended at an angle of 11°, which enhances the perspective effect of the footbridge passing in the distance. The footbridge is stabilized against excessive sway from wind and dynamic excitation by pedestrians by means of stabilizing ropes. Three arches have been designed to counteract the main ropes, to tighten the footbridge and at the same time mitigate lateral swings. The central stabilizing arch is connected to a tensioning device that provides tensioning of the wind ropes, in which the prestressing decreases due to temperature changes and accidental loads.
The ropes used in the construction are designed from Fully Locked Coil, supplemented with turnbuckles, end caps, fork end caps and pins. A total of 66 ropes of various diameters and lengths are used. Only two companies in Europe can produce this type of special ropes and their production took 8 months.
Three arches have been designed to counteract the main cables, tensioning the footbridge and at the same time mitigating side swings. The central stabilising arch is connected to a post-tensioning device, which provides post-tensioning of the wind ropes, where the pre-tension decreases due to temperature changes and accidental loads.
The lower structure consists of one reinforced concrete footing under the pylon and one reinforced concrete rear block for anchoring the rear main cables. Both concrete blocks are founded on bedrock. The anchorage of the footing to the bedrock is made by 24 micropiles of 64mm diameter and 9m long.
The project of the footbridge was realized as Design & Build by the general contractor TAROS NOVA a.s., which focuses on atypical structures made of wood and steel. The implementation of the technologically demanding construction placed extraordinary demands on the design department, which provided not only the actual design documentation, but also the design of the construction technology. The construction itself was even more challenging due to the difficult climatic and terrain conditions. To ensure that the footbridge works in all conditions, a special tensioning and damping mechanism was developed. The design, assembly and pre-tensioning procedure was fine-tuned several times during the construction process.
Basic data
721m bridge length
95m height above ground
234t weight of steel structure
54t weight of pylons
158t weight of ropes
108t weight of both pylons (54t / each)
Hot-dip galvanizing / surface protection
