- Detailed design of the monitoring system
- Installation assistance
- FEM modeling, model updating and continuous structural diagnostics with automatic alerts
- Continuous monitoring of the state of the stays
- Monitoring of the evolution over time of the response of the footbridge deck
- Early detection of the first signs of cable damage
- Determination of expected dynamic thresholds of the cables corresponding to adequate levels of safety of the structure
- Planning of targeted maintenance interventions.
DESCRIPTION OF THE STRUCTURE AND STRUCTURAL MONITORING SYSTEM
The pedestrian bridge has a steel structure consisting of two parts separated by a structural joint: a cable-stayed part and a statically independent supported part.
The planimetric layout of the structure has a curved path; the carriageway has a width of about 4 m, while the total dimension of the deck in the transverse direction, including the paneling of the edge beams, is about 6 m. The cable-stayed part has a total length of 262 m, the deck geometry is defined by a circular arc with a radius of about 630 m and is composed of edge beams with an asymmetric "I" section, HEA section transverse and diagonal members, and a mixed deck made of corrugated sheet metal and concrete with a total height of 10 cm. In addition, there are steel sheet cladding elements in triangular shape corresponding to the edge beams. The piers on which the cable-stayed part rests are tubular steel profiles, assembled in the form of 'N' and 'V'. Finally, the cable-stayed structure is supported by cables from a metallic arch, 62 m high, 55 m wide and inclined relative to the vertical plane by 25°, making the cables support the arch itself. The transverse section, in equilateral triangle shape, is made of welded steel sheet and stiffened by longitudinal ribs. The suspended portion of the walkway is supported by 38 steel cables, of which 34 are anchored to the arch and 4 anchor the deck to the ground. There is also a pre-tensioning system consisting of a curved cable that runs longitudinally along the entire suspended portion of the walkway. The cable is made up of 3 steel cables with a cross-sectional diameter of 60 mm. Two tuned mass dissipative devices are present at the intrados of the deck, and damping devices, of the stockbridge type, are installed on the cables to suppress wind-induced vibrations (TMD dampers).
The monitoring system, consisting of triaxial accelerometers installed on the deck and cables, has been designed in number and positioning to best capture the dynamic response.
DIAGNOSTICS IN A NUTSHELL
The complex geometry of the pedestrian bridge required a non-linear FEM modeling approach, aimed at simulating in detail the reference dynamic response of the structure, obtained through a dynamic model updating process carried out with respect to signal analyses both in the time and frequency domains. In addition to the analysis of the average and peak vibration levels of the deck and cables, comfort analyses were carried out for pedestrians against vertical and lateral actions, as well as dynamic identification through Operational Modal Analysis (OMA) techniques.
By modeling appropriate reference damage scenarios, dynamic thresholds corresponding to adequate levels of safety of the structure were determined for the continuous monitoring of the state of the cables and the evolution over time of the deck response of the pedestrian bridge. The diagnostics support the early detection of the first signs of cable damage for the planning of targeted preventive maintenance interventions.