Numerical simulations for the performance assessment of vehicle security barriers

Terrorist attacks on public spaces employing vehicle ramming as modus operandi have become recurrent in Europe in the last years. The attacks in Nice and Berlin in 2016 or Barcelona and London in 2017 constitute sad demonstrations of the impact such attacks can have - in terms of loss of human lives, physical and psychological injuries, economic losses and longer-term sociological repercussions. These so-called vehicle-as-a-weapon attacks comprise of a speeding vehicle (a car or a truck) that rams into a crowded pedestrian area, like city centres or open-air events.

Vehicle security barriers preventing the entry of vehicles into pedestrian zones can be an effective mitigation measure against vehicle-ramming attacks [1]. They can take various forms like bollards, wedge barriers, beam barriers, concrete Jersey barriers, concrete sitting benches, flower planters or other architectural elements that can be harmonically incorporated with the aesthetics of the surrounding public space.

Examples of vehicle security barriers [1]

To serve as an effective mitigation solution, vehicle security barriers must be carefully manufactured, designed and installed to accomplish various tasks, such as for instance preventing heavy-duty incoming trucks at high velocity from breaking through or narrow vehicles to squeeze in between them and access the protected area. Currently, the performance of barriers against vehicle impact is certified through physical tests using full-scale vehicles. This testing method guarantees that all complex phenomena during the vehicle impact test are taken into account, but due to the high cost only a limited number of impact scenarios is assessed (usually only one).

The harmonisation of vehicle barrier testing standards across the EU will ensure common performance and safety levels [2] and will enhance the single market for security products. Harmonization can be assisted through the use of numerical methods. Numerical simulations are cost-efficient and can be used to assess different impact scenarios (changing the vehicle’s velocity, its type or its angle of impact). Numerical testing methods will also open the way to creativity and the development of innovative protective structures which are integrated to the urban aesthetics and cultural character of the surrounding area. Guidelines for the use of numerical tools can be placed at the disposal of urban authorities and security operators for the assessment of ad-hoc security solutions.   

State-of-the-art numerical techniques have been vastly used in the automotive industry for assessing the crashworthiness of vehicles under different impact scenarios. Numerical testing has allowed for a significant reduction in the costs of experimental campaigns without sacrificing the desired accuracy in the performance of the products under various impact loading scenarios. Similar numerical techniques can be employed to study the behaviour of security barriers under vehicle impact.

Examples of numerical simulations [3]

What is still missing in exploiting the potential of numerical tools in the testing of vehicle barriers are generic harmonized numerical models for various vehicle classes independent from the characteristics of the commercial brand. Such general vehicle models will be made available to the relevant stakeholders for the development of numerical techniques which will serve as a basis for harmonization and eventual standardization.

The first step in this process is to determine the needed level of detail for each vehicle class.

Examples of vehicle classes [4]

To this end, the Joint Research Centre of the European Commission organized a workshop with relevant stakeholders, mainly researchers in the field and representatives from city authorities, initiating the process of defining general vehicle classes and the level of detail for the generic numerical models of vehicles.  The workshop allowed for the collection of considerations and know-how of various stakeholders and set up a forum for collaboration in the field. The participants agreed that there is a need to employ numerical simulations in the evaluation of the performance of the protective measures in hostile vehicle mitigation.

All participants agreed that there is a big need to employ numerical simulations in the evaluation of the performance of the protective measures in hostile vehicle mitigation. Cheap solutions can support local authorities that suffers from significant budget limitations due to the COVID 19 crisis. The availability of generic models might allow much cheaper development costs of barriers. On the technical level the main conclusion was that simplifications of the numerical model can increase the computational efficiency. The simplified models should be validated against more detailed models and physical tests (when possible). Two important aspects that should be considered in the simplification procedure are 1) the simplified model should be able to capture the kinematics of the vehicle (running or rolling over the barrier) and 2) formation of fragments and penetration distance.  It has been agreed that a guideline document for numerical simulations in hostile vehicle mitigation can be very useful for the analyst. Also a better representation of the numerical techniques in the existing certification standards would facilitate their use.

A short survey collecting opinion on the needs of developing generic models for hostile vehicle mitigation is available here. On the basis of these discussions, JRC will propose to create general numerical models respective to the existing vehicle classes.

For more information, please contact JRC-PUBLIC-SPACES@ec.europa.eu

References

1. Karlos V., Larcher M., Solomos G. “Guideline Selecting proper security barrier solutions for public space protection”, JRC Technical Report, JRC113778, 2018
2. Action Plan to support the protection of public spaces, COM(2017) 612, European Commission, 2017.
3. Valsamos G., Larcher M., Casadei F., Karlos V. “A numerical framework to support the certification of barrier testing”, JRC Technical Report, JRC120307, 2020
4. International Organization for Standardization, Vehicle Security Barriers-Part 1: Requirement, Vehicle impact test method and performance rating, IWA 14-1, Vernier, Switzerland, 2013.