VibraTec in partnership with Venathec, is organizing 2 Webinars on Rail Network Vibration Impact Studies.
The first webinar (given in French), at 2pm on April 1st, will be an introduction and will present associated issues:
➔ Structure-borne noise and the impact of vibration transfer through the ground
➔ Numerical and experimental approaches to manage these issues
➔ Some concrete cases to illustrate these approaches
The webinar will end with a question and answer time.
The second webinar (given in French), at 2pm on April 8th, will address rules of the trade and feedback:
Current French regulations are not very specific about vibration-related annoyances, but there are reference documents, as well as non-French standards. This second webinar will present them.
Afterwards, we will go into the details of numerical and experimental approaches to manage these problems: tools, processes, etc.
We will finish by analyzing concrete project cases to understand the management approaches and identify the gains they bring.
The webinar will end with a question and answer time.
Preliminary analysis of discomfort and inconvenience generated by vibration-emitting rail transport equipment (rolling stock)
Introduction:
The subject of vibrations produced by certain urban transport systems and transmitted to neighboring buildings is becoming a major concern. In common cases, the effects produced are a sensation of discomfort related to:
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The physical perception of vibrations applied to the human body or to installations in buildings,
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Solid-borne noise re-emitted by the structural elements of buildings.
Vibration levels emitted by a moving railway stock depend on a large number of parameters such as:
- Vibratory excitation applied at the track level, as when rolling stock passes (emission),
- Soil properties in terms of vibration transmissibility (propagation),
- Building sensitivity to vibrations (immission).
For transportation systems using iron/iron rolling surfaces, the excitation levels depend on the following parameters:
- Rail and wheel irregularity levels,
- Track dynamic properties,
- Rolling stock dynamic properties.
It is commonly accepted that the most effective and economically advantageous mitigation measures are anti-vibration track systems.
In order to disseminate the knowledge acquired during more than 30 years of industrial and collaborative projects, VibraTec has created training sessions around vibrations in the railway field (see gray links on this page).
VibraTec is also very active in the scientific community and has written many publications that have been presented during international seminars (see red links on this page).
Standards and reference guides
Current French regulations are not very precise on the subject of vibration-related inconveniences, but there are some reference documents, as well as non-French standards.
- Transit Noise and Vibration Impact Assessment Manual. Rapport de Federal TransitAdministration (FTA) No. 0123 (2018)
- ISO/TS 14837-31:2017. Mechanical Vibration – Ground-borne Noise & Vibration Arising from Rail Systems.
- ISO/TS 14837-32:2016. Mechanical Vibration – Ground-borne Noise & Vibration Arising from Rail Systems.
- Article 28 quater A of the draft mobilities orientation bill of 17 September 2019.
Environmental Code. Article L. 571-10-3 of section 3 of chapter I of title VII of bookV of the French Environmental Code.
MECHANICAL VIBRATION – GROUND-BORNE NOISE AND VIBRATION ARISING FROM RAIL SYSTEMS
Defining indicators
In France, there are currently no regulatory values to evaluate and limit the vibration levels transmitted to buildings during the operation of transportation systems. The situation is the same for structure-borne noise re-emitted inside buildings.
Consequently, a set of target values was defined, aimingto evaluate the following effects:
- Annoyance in buildings due to the tactile perception of vibrations,
- Discomfort in buildings due to the perception of structure-borne sound resulting from building structure vibrations.
Vibration study process
- Step 1: Identification of the areas at stake in terms of vibration (sensitive sites, representative buildings)
- Step 2: Determination of the vibration source
- Step 3: Characterization of the soil’sdynamic properties
- Step 4: Calculation of the vibration and structure-borne noise levels for each identified problem area
- Step 5: Sizing of mitigation solutions to meet project targets
- Step 6: Calculation of the vibration and structure-borne noise impact levels, taking into account the mitigation measures
- Step 7: Drafting the specifications for the mitigation solutions
- Step 8: Verification of the mitigation solutions’effectiveness: laboratory tests and/or on the track after it is manufactured
- Step 9: Diagnosis on the operating network: maintenance assistance, control following a complaint from a resident
Typically, this study process is organized around a numerical approach widely validated by VibraTec on industrial markets and collaborative projects for over 15 years. Field measurements can also enrich the numerical approach.
The study with simulation of future vibrations is carried out using the following 2 levels of approach:
- Use of GroundVib software to determine the excitation source at the platform level and preliminary calculations to identify potential critical points.
- If necessary and depending on the complexity of the situation (tunnel, viaducts, non-homogeneous ground, etc), more detailed simulation with 2.5D or 3D modeling at the level of the identified complex points. These simulations are carried out once the platform structures have been defined, to more precisely estimate the future vibration levels at the critical points.
VibraTec has used and validated these methods in the context of the Grand Paris Express project, for which VibraTec carried out the modelling and calculations to determine the vibration and structure-borne noise levels in the residences above the future metro lines 15, 16 and 17. We are also VibrationAssistant to the Owner on line 18.
Examples of possible modelling:
Based on GroundVib software
The vibration impact of future lines can be modelled using GroundVib simulation software developed by VibraTec in 2000 and validated many times by comparing simulations and measurements in real situations.
This software calculates the force injected to the platform; by making assumptions regarding the ground, it is possible to access the vibration levels at the foot of the building, if necessary inside the buildings, in the form of a third octave spectrum of the vibration velocity in the [10 – 200] Hzrange. The input data for this approach are:
- Rolling stock characteristics: wheel mass, unsprung mass, bogie mass, resilient wheel stiffness and primary suspensions, etc.
- Operating speed – track layout and presence of switches and crossings.
- Track characteristics: rail characteristics, dynamic stiffness of the pads under the rail, slab thickness, dynamic stiffness of the mat for floating slabs.
The characteristics of the soil impedance under the platform and the decay rates measured during the vibration measurement stage.
Implemented digital approach
In addition to this GroundVib centered approach, a 2.5D or 3D simulation is used to model areas on structures for which the sole use of GroundVib could be insufficient.
Based on 3D Finite Element Modelling
The soil layers are modeled with solid finite elements. At the ends of the model, non-reflecting wave conditions are added to simulate an infinite medium (see below).
Example of a finite element model with non-reflecting wave conditions
at its ends – model with 3 soil layers
Based on Finite Element Modeling coupled to boundary elements in 2.5D
MEFISSTO is a BEM2.5D Finite Element Model for soil modeling. In most cases, the soil is represented as a succession of horizontal strata, each with its own characteristics. However, it may turn out that the soil stratifications have a particular geometry. MEFISSTO is able to consider this geometry. This numerical model takes the soil-structure interaction into account. The soil is modeled in boundary finite elements while the structure such as the tunnel is modeled in finite elements (FEM).
MEFISSTO is a tool particularly adapted to linear force sources (Metro type): it is also well-adapted for heavy structures of great thickness such as Metro tunnels.
This software also presents an ease in capturing the geometry of a site using predefined geometric functions (circle, arc of circle, polygon, etc).It makes it possible to verify the convergence of the calculations for different wavenumbers in the tunnel axis via simplified tests, while optimizing the number of calculations to be performed. The parameterization of the last dimension is done independently from the 2D configuration, which simplifies the repetition of calculations, especially those related to source modification. MEFISSTO is also capable of performing vibration level mapping.
Example of a map obtained with MEFISSTO