Bridge Structural Resistance Verification Tool
This expert tool is intended either for road authorities in order to validate, or not, a request for the passage of an exceptional transport, or for transport operators in order to carry out a study at the request of a road authority. (The characteristics of the bridge must be obtained from the road authority)
While this tool is particularly well suited to French structures (taking into account the various construction regulations from 1927 to 1971 for bridge calculations), it can also be used for any simple structure in Europe, provided that their admissible resistant capacities are known (bending moment, shear force). Once the span has been entered, it will then be possible to use the calculation of the forces generated by the passage and to compare them.
Eurocode structures cannot be calculated with this tool (a dedicated calculator will be developed on this site); however, for Eurocode bridges, capacity reserves are generally very significant, and the calculation is often less critical than for a bridge built in 1940.
Principle of the Crossing Assessment
The tool makes it possible to verify whether a specific exceptional convoy can cross an engineering structure (bridge) by comparing the forces it generates with the resistance capacities defined by historical French regulations.
1. The “Worst-Case Scenario” Principle (Strength of Materials)
-
The software simulates the passage of the convoy over the entire length of the bridge (calculation step of 5 cm).
-
The Convoy: Each axle is modelled as a point load.
-
The Simulation: The program virtually moves the convoy centimetre by centimetre. At each position, it calculates the support reactions and internal stresses.
-
Retained results: Only the absolute maximum values encountered during the passage are retained: the maximum bending moment (risk of failure by bending) and the maximum shear force (risk of failure at the support).
2. Structure Capacities
-
The resistance of the bridge is not a fixed value; it is calculated according to the regulation in force at the time of construction (1927, 1940, 1960 or 1971).
-
Distributed Loads: A compact crowd or a traffic jam of standard trucks is simulated over the entire trafficable surface.
-
Point Loads: The passage of the regulatory standard trucks (Bc or Bt systems) is simulated; these represent the maximum “normal” load envisaged at the design stage.
-
Dynamic Amplification: For older regulations, a “shock” coefficient is applied, increasing the loads to account for vibrations and bouncing of moving vehicles.
3. Calculation Assumptions
For the calculation to be valid, the following assumptions are made:
-
Isostatic Beam: The structure is considered as a single span resting on two supports.
-
Transverse Distribution: Loads are assumed to be distributed homogeneously over the width of the carriageway (via the fess coefficient or the lane width).
-
Ageing: The condition of the structure is taken into account by a reduction coefficient (e.g. 0.80 if the bridge is degraded), directly reducing its resistant capacity.
4. Model Limitations
It is important to note that this calculation is a first-level verification:
-
Complex Structures: This model does not apply to arch bridges, suspension bridges or continuous beam structures (multi-span) without adaptation.
-
Local Effects: The calculation checks the main load-bearing structure (the beams), but does not verify the local resistance of the deck slab (the “hourdis”) under a very heavy isolated wheel.
-
Trajectory: The convoy is assumed to travel along the axis or in an optimal manner. An off-centre passage (too close to the edge) may generate torsional effects that are not taken into account here.
Verdict Conclusion
The displayed utilisation rate is the ratio between the convoy force and the best capacity of the bridge (the maximum between the distributed load and the regulatory point load).
Less than 100%: The convoy generates less force than what the bridge was designed for. Passage is authorised.
More than 100%: The convoy overstresses the structure relative to its original design. Passage is refused or requires restrictive measures (reduced speed, axial circulation, or a study by a specialised engineering consultancy).
DISCLAIMER AND LIMITATION OF LIABILITY
Indicative use: The assessment reports are generated automatically for the purpose of preliminary technical information. They do not in any case constitute an execution-level assessment or an opinion from a specialised engineering consultancy.
Exclusion of liability: The software author, the website publisher and the developers disclaim any responsibility in the event of direct or indirect damage (material, bodily or financial) resulting from the use of these results.
The end user is solely responsible for the use of the data produced by this tool