Cycle and pedestrian bridge in Perino e Coli (PC)
The bridge was calculated using an application for three-dimensional frames.
The structure consists of two 3-hinged arches made of gluelam timber, placed side by side and braced by means of timber struts and steel diagonals, supporting, by means of steel rods, a deck made of gluelam timber primary and secundary beams, finished by a larch planking.
While for vertical loads this type of structure does not present particular problems, for horizontal ones, because of the very small available width with respect to the large span, difficulties arise regarding bracings.
In similar projects we had to foresee important bracing elements placed externally to the bridge, or large trusses and bridle in timber due to the considerable internal stresses.
For horizontal forces (wind, dynamic forces), the decking behaves like a truss with a large 65 meters span and a very small height equal to the width of the deck, which is about 2.50 meters, too small for an efficient static behavior.
Deck plan view
In our case, having an old bridge running aside the new one, we had 2 possibilities:
- Connect the new bridge to the old one for horizontal forces.
- Use 2 tubolar columns connected to side bridge's abutements to reduce the horizontal span.
We excluded first solution because of bad state of conservation of the old bridge, choosing the second one and so reducing the span for horizontal loads down to 22 meters, thus drastically reducing the necessary bracing structures.
Next image shows the detail of the inserted tubular bracings to reduce the horizontal span of brace system.
Detail of tubular steel bracings
The structure was pre-assembled over the existing old bridge; the two pairs of semiarchs were connected through the struts and bracings, all the steel plates and protection flashings have been put in place, in order to avoid as much as possible the dangerous works interventions in final assembly:
Here you can see the deck support brackets, already in place:
Subsequently each pair of semiarchs has been lifted by two mobile cranes and positioned in such a way allow the insertion of support hinges into their counteraparts already arranged on the abutments:
Detail of the hinges insertion in place:
The two pairs of semiarchs have therefore been placed, posing on the ends of the ridge hinges, on the river bed:
Later, after moving the cranes into the river bed, the two pairs of semiarchs were lifted, making them rotate around the abutment's hinges, until the central hinges could be assembled together:
Detail of the final connection of top hinges:
In the following image you can see the pair of archs completely assembled on site:
The deck, also pre-assembled in sections, was then hung at the tie rods previously arranged and completed with the bracing crosses and the parapets:
View of the bridge at the end of the assembly:
View of the lower part of the deck with the bracing crosses:
View of the bridge completed with the 2 bracing tubes positioned and fixed to the abutments:
Given the remarkable span and the peculiar characteristics of the bridge, a load test was carried out using pallets of construction material as load, in order to simulate the compact crowd on the deck:
Another view of the pellets used during the load test:
The behavior of the bridge during the load test was perfectly consistent with the theoretical model, with errors of less than 5%.
A funny note : the settling of the joints made sudden, strong noises that frightened more than one people, although absolutely in the norm for this kind of structures.