PSI - Issue 64

Petr Tej et al. / Procedia Structural Integrity 64 (2024) 1089–1094 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

1091

3

2.2. Design of reconstruction and repair of the three 70-metre spans of parabolic arches It is well known that fatigue stresses calculated using fatigue load models from codes, are significantly higher than effective stresses in the structure. This is explained by the rather pronounced conservatism inherent in load models imposed by codes. Fatigue loading using UIC71 and Line Class C3 Load Models were applied by both SUDOP and EPFL. The calculated fatigue stress ranges were similar, which indicates that both models applied for structural analysis are similar. The calculated maximum stress ranges in fatigue relevant members (i.e. bottom chord and tensile diagonals of the lattice girder, cross girder, floor beam) were in the range of 45 to 55 MPa. These stress values are close but lower than the fatigue endurance limit of riveted steel details. Precise determination of fatigue stresses is of utmost importance before any more or less sophisticated method of fatigue damage analysis is conducted. This is because the fatigue duration (number of fatigue cycles) depends on the fatigue stress following a power function (with the power of 5). Consequently, direct in-situ measurement of fatigue relevant stresses is necessary to consolidate fatigue safety verifications and comparison with calculations using fatigue load models from codes. Load testing and monitoring campaign was conducted from May 11, 2017 to May 28, 2017. Strain values using strain gauges have been recorded on fatigue relevant elements of the riveted steel structure and translated into stress values. The stress histories of operating trains have been monitored during 7 days including mostly passenger trains but also single freight trains. Measured stress ranges have been deduced by means of the Rainflow Method to obtain spectra of stress ranges. The two vehicles used in single and tandem composition for static and dynamic load testing had axle loads of 193kN (axle spacing of 2’000mm) and 188kN (axle spacing of 2’400) (Brühwiler, 2015) . The refurbished Vy š ehrad Railway Bridge design has been developed in accordance with the basis defined in REP 001 to: • Remedy the observed defects from the inspection, the ULS strength deficiencies and insufficient remaining fatigue life. • Respond to the modifications. • Minimise the ongoing maintenance requirements whilst maximising the retained heritage aspects of the historic railway bridge. The technical solution for the refurbishment is summarised and depicted within the drawings (Fig. 2a, b)

Fig. 2. (a) Indicative drainage detail repair for end nodes with defects in verticals.; (b) Indicative drainage repair detail for internal nodes with defects at ends of diagonals.

By mass, 15% of the structure requires some structural repair or improvement. Expressed in tonnage terms, the 1,773-tonne structure can be revitalised by the repair or replacement of approximately 261 tonnes of steelwork. The repair strategy is to use a minimum grade replacement S355 J0/J2 steel to EN 10025 for all repair components with like-for-life members with the same overall member and section geometry of the existing truss. The strength required is therefore achieved through the increase in the material grade and avoids major changes to the truss geometry. For the reinstated connections, using rivets is preferable from a heritage perspective and is shown on the drawing in areas visible to the public. Rivets are more costly and will require a careful planning of the installation sequence, as well as a detailing of the splice to account for the tools used by the contractor.