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“Ensuring the safety and efficiency of the infrastructural heritage”

Seismic vulnerability assessment of railway bridges

Location

Emilia Romagna region

Implementation period

august 2020 – march 2021

Amount of service

124.000 EUR

Client

Ferrovie Emilia Romagna s.r.l.

Services provided

Six-year inspection including static and seismic assessment of 20 existing bridges located on the Reggio E. – Ciano d’Enza, Reggio E. – Guastalla, Sassuolo – Reggio E. and Bologna – Portomaggiore lines.

The service included: inspection visits with preparation of inspection sheets according to the Domus system, load tests with rolling stock, investigation plan, verification of the works through FEM models, dynamic seismic verifications. The following were studied: masonry arch bridges, reinforced concrete arch bridges and steel truss bridges built between the 1920s and the ‘90s.

Description

Every vulnerability check in the field requires careful preliminary work:

  • Measurements are made with the aim of confirming – or measuring the geometries from scratch, at the ‘macro’ level (perspective drawings, sections and plans) of each work. Some measurement techniques, such as aerophotogrammetric reconstruction, let see the degree of deterioration and the state of defects of the bridges and to be better prepared on them at the inspection.
  • Behaviour, in terms of seismic response of the specific subsoil can be characterised through geoseismic surveys to determine the expected acceleration and assess any amplification effects due to the rigidity and composition of the land. Georadar enables substructures that can’t be seen from the outside to be measured. In addition, surveys to analyse the structural materials, check the thicknesses of metal plates or the residual section of armatures, the degree of corrosion of metals and, generally, the mechanical features of the construction materials in terms of resistance and rigidity are also set out.
  • Static and dynamic load tests are carried out to determine the vibration frequencies of the deck and its real behaviour under load; for railway bridges, this implies the use of locomotives. These assume proper planning of the test, aimed at deciding where the locomotives and sensors should be positioned, and also enable assessment of the real stress that every element measured is subjected to.
  • The calculation model is calibrated starting from the information received from the load tests and, as a result, further simulations and checks on the deck and substructure can be performed and the real vulnerability checks started.

The vulnerability checks set out implementation on the objective physical parameters model (geometry, mass, rigidity, materials and loads) but also performance parameters, partly defined with the clients and which include the parameters of the work, the safety coefficients of action, the PSI2 coefficient, which determines the mass arising from the variable loads to consider during seismic action, and the safety coefficient of materials.

For bridges, static vulnerability checks also include the dynamic amplification coefficient, which varies according to the speed of the vehicles crossing the bridge, the length of the deck and its first flexural frequency. Often, further surveys are required for existing works with the aim of establishing the maximum speed with which trains can safely travel along the works being checked.

Visual-inspectional surveys

Vulnerability checks are integrated with the visual and inspectional surveys carried out in accordance with the Rete Ferroviaria Italiana (RFI – the company that manages the national railway infrastructure) DOMUS borrowed system, which enables a judgement on the degree of conservation of the works following a codified method. This takes into consideration the master data of the structure with cataloguing by type, the definition of the essential structural elements based on the type of bridge, the list of defects of each specific material and the assessment algorithm of the condition of the works, which enables calculation of the index of defectiveness of the infrastructure. This method categorises defects giving them a definition and inspection method, i.e. agreed indications on how to look for each defect during the inspection, how to assess it and with what tools, at the same time also showing a coefficient of importance of the defect on a scale from 1 to 4. The intensity and extension of each defect is also assessed with the use of special coefficients (K2 and K3).

Assessment cards can be developed using the DOMUS method which show additional useful information for inspections. The report on the checks and test of the bridges is drafted at the end of the surveys and this, starting from the subdivision of the work into subgroups, explains the individual defects found and the relative judgement of the people carrying out the assessment. Lastly, a summary card following the Civil Defence model is compiled. This not only includes more detailed master data, requires a check on the area where the bridge is situated with the possibility of indicating any areas subject to landslides or flooding and the reconstruction of the most dramatic events involving the bridge (e.g. collapses, fires, war events, repairs, etc.).

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