We are all familiar with the bollards and barriers that are erected in front of buildings and have probably asked ourselves whether they provide sufficient protection in the event of a terrorist attack.
In the meantime, public places such as pedestrian zones, Christmas markets and fairs are protected by heavy concrete blocks, which are intended to prevent incidents such as the terrorist attack on the Berlin Christmas market in December 2016.
Is there a comparable protection to bollards and fences?
The question is easy to answer.
What does a single concrete stopper weigh? Depending on the size, from 0.5 – 2 tons. However, this is very little compared to a vehicle of the same mass, which collides with a single concrete stopper at 80 km/h. Simple considerations about the conservation of momentum from school physics and the basics of static and sliding friction are sufficient.
Even concrete blocks sliding around at high speed have a considerable destructive potential. Not to mention the shrapnel effect of the concrete debris.
Since city planners might be overburdened with these approaches: When playing billiard or curling, physics becomes quite obvious.
Concrete stoppers are therefore more about psychological protection that raises the assassin’s inhibition threshold and calms pedestrians.
Only the floor anchoring creates crucial advantages, in order to absorb and redirect the energies of a car or even a truck.
For our customer, the Perimeter Protection Group, formerly Elkosta, we investigate such or similar tasks. Further information can be found at www.perimeterprotection.net
Whether lattice fences, gates, bollards or so-called wedge barriers, experiments are very complex as well as costly and time-consuming.
One problem often remains: structural engineers cannot reasonably evaluate the dynamics with static approaches and work instead with replacement forces and adjustment factors that are arbitrarily selectable.
Let’s take a look at the following video to see the test experiments on wedge barriers in the USA and, analogously, a simulation from 2008
Video 1: Crash test wedge barrier
Video 2: Simulation crash test wedge barrier
I can tell you, the simulation is a lot cheaper and faster than the physical test and is accurate enough to confirm or disprove the strength.
Since we reproduce physics with sufficient accuracy, we do not have to invent correction factors and I am sure that the approval of the mathematical evidence of FEM by the verifying authorities will no longer be a question at some point.
After all, the automotive industry has shown that it is possible to identify and optimize weak points in advance using simulation. The final evidence is often the test experiment. But there is a difference whether only a few tests are necessary that are usually passed, or the component that is currently failing has to be identified by means of the test.
Even if you don’t have to protect any buildings, you might have similar topics where we can also help you to save time, money and nerves.
I look forward to your comments and questions.
Please feel free to make an appointment without obligation.
I or one of my colleagues will be happy to call you.
Your Stefan Merkle