InBridge4EU is organized into 7 Work Packages (WP), where WP1 to WP5 focus on technical aspects, WP6 addresses normative recommendations, and WP7 is dedicated to coordination.
With respect to WP1, the rolling stock database and the identification of critical train parameters for bridge dynamic response have been completed, with car length (D) generally the most important, especially for longer spans, while bogie wheelbase (dBA) and bogie spacing (dBS) are more relevant for shorter bridges. Combinations of these distances also influence the response depending on bridge span (Deliverable D1.1). In the present reporting period, the limitations of spectral methods and strategies for improvement were identified (Milestones MS3 and MS4), and the structure and criteria for defining the new Dynamic Train Categories were established (MS5).
Regarding WP2, simplified models for over 500 bridges in the project database and the tools for dynamic analysis to identify potentially critical structures have been completed (MS8). Preliminary recommendations for parametric studies indicate that bridges most likely to experience critical dynamic responses under real train actions are those with low mass, low fundamental frequency, single-track decks, and simply supported spans, while portal frame bridges show lower responses. These characteristics define realistic worst-case combinations of bridge parameters for further parametric analyses (MS9). Future work will use more complex numerical models to assess bridges that did not meet the dynamic criteria with simplified models.
In WP3, coupled train–track–bridge interaction analyses showed that the 98th-percentile dynamic factor φ″, derived from 1000 track recordings per parameter combination, correlates with the standard deviation of vertical track irregularities in wavelength D1 and follows trends in EN 1991-2 (MS11). Additionally, preliminary revised formulas for φ′ developed during 2025, which account for moving-load effects and track load distribution, showed some exceedances, mainly for simply supported bridges with low natural frequency.
WP4 was the first work package to close with the submission of Deliverable D4.1 presenting a revision of the damping curves in EN 1991-2. Recommendations proposed that existing curves remain valid for filler-beam and steel bridges, prestressed concrete be merged with reinforced concrete, portal frame bridges form a new high-damping category, and steel–concrete composite bridges be separated from steel bridges. These updates reduce conservatism, improve accuracy, and support evidence-based revisions to EN 1991-2, with future work focusing on higher modes and refined criteria for composite bridges.
WP5 deliverables were submitted in the present reporting period, completing the research within this work package. For ballastless track bridges, studies showed that vertical deck acceleration was poorly correlated with derailment risk or passenger comfort, while track quality had a much greater influence on train safety (Deliverable D5.2) suggesting that the EN 1990 limit of 5 m/s² was likely over-conservative, though dynamic assessment remains important for other structural limits. For ballasted bridges, lateral failure modes, such as buckling, proved more critical than vertical settlement, with lateral resistance decreasing at all acceleration levels and high-frequency vibrations up to 100 Hz significantly affecting stability. Based on shaking table tests and discrete element models, it was recommended to consider high-frequency vibrations up to 100 Hz, maintain the 3.5 m/s² acceleration limit, and ensure that any relaxation of limits is supported by measurements, inspections, and careful verification (Deliverable D5.1).
The recommendations proposed so far, along with those expected in 2026, will be incorporated into the final deliverable D6.1 of WP6.
Finally, regarding WP7, the midterm report (Deliverable D7.3) has been submitted, presenting all technical results and dissemination indicators for project follow-up. The midterm event was held online in March 2025, allowing InBridge4EU members and the advisory board to share results with external experts, followed by the 4th Regular Technical Meeting in Madrid in September, where the latest 2025 results were presented.
